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Metaxytherium subapenninum (Bruno, 1839)(Mammalia, Dugongidae), the latest sirenian of theMediterranean BasinSilvia Sorbi a , Daryl P. Domning b , Stefano Claudio Vaiani c & Giovanni Bianucci da Centro Interdipartimentale Museo di Storia Naturale e del Territorio, Università di Pisa, ViaRoma 79, 56011, Calci, Pisa, Italyb Laboratory of Evolutionary Biology, Department of Anatomy, Howard University,Washington, District of Columbia, 20059, U.S.Ac Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, ViaZamboni 67, 40127, Bologna, Italyd Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126, Pisa, Italy

Available online: 03 May 2012

To cite this article: Silvia Sorbi, Daryl P. Domning, Stefano Claudio Vaiani & Giovanni Bianucci (2012): Metaxytheriumsubapenninum (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin, Journal of VertebratePaleontology, 32:3, 686-707

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Journal of Vertebrate Paleontology 32(3):686–707, May 2012© 2012 by the Society of Vertebrate Paleontology

ARTICLE

METAXYTHERIUM SUBAPENNINUM (BRUNO, 1839) (MAMMALIA, DUGONGIDAE),THE LATEST SIRENIAN OF THE MEDITERRANEAN BASIN

SILVIA SORBI,1 DARYL P. DOMNING,*,2 STEFANO CLAUDIO VAIANI,3 and GIOVANNI BIANUCCI4

1Centro Interdipartimentale Museo di Storia Naturale e del Territorio, Universita di Pisa, Via Roma 79, 56011 Calci, Pisa, Italy,silviasorbi@gmail.com;

2Laboratory of Evolutionary Biology, Department of Anatomy, Howard University, Washington, District of Columbia 20059,U.S.A, ddomning@Howard.edu;

3Dipartimento di Scienze della Terra e Geologico-Ambientali, Universita di Bologna, Via Zamboni 67 40127, Bologna, Italy,stefano.vaiani@unibo.it;

4Dipartimento di Scienze della Terra, Universita di Pisa, Via S. Maria 53 56126, Pisa, Italy, bianucci@dst.unipi.it

ABSTRACT—Metaxytherium subapenninum was a halitheriine dugongid distributed along the northwestern coasts of theMediterranean Basin during the early and late Pliocene. It represents the latest sirenian species of the Mediterranean Basin,the latest Metaxytherium species in the world, and also the latest species belonging to the paraphyletic subfamily Halitheriinae.We review M. subapenninum in the light of new discoveries, including its stratigraphic and geographic distribution, osteology,paleoecology, and relationships. M. subapenninum represents a more derived stage of evolution in comparison with the earlierMetaxytherium species. It is characterized in particular by an increase in body size, an increase in tusk size, and a dorsalbroadening of the nasal process of the premaxilla. Its variation in tusk size does not appear to represent sexual dimorphismas in the modern Dugong, but instead progressive intraspecific evolution of larger tusks as a feeding adaptation convergenton that of derived dugongines. It was a relict species limited to the Mediterranean Basin, and responded to long-term climaticcooling by an increase in body size and by an increase in tusk size and rostral reinforcement in order to obtain a more nutritiousdiet richer in rhizomes.

INTRODUCTION

The dugongid sirenian genus Metaxytherium was a general-ist and cosmopolitan halitheriine genus widely distributed dur-ing the Miocene. It has been the object of several recent studies(e.g., Muizon and Domning, 1985; Domning and Thomas, 1987;Domning, 1988; Aranda-Manteca et al., 1994; Domning and Per-vesler, 2001; Carone and Domning, 2007; Bianucci et al., 2008).It is a paraphyletic genus, having given rise to the subfamilyHydrodamalinae in the North Pacific Ocean (Aranda-Mantecaet al., 1994). During the late Miocene it became extinct through-out the world except along the Euro-North African coasts; inthe latest Miocene and during the Pliocene, only the successivechronospecies M. serresii (Gervais, 1847) Deperet, 1895, and M.subapenninum (Bruno, 1839) Fondi and Pacini, 1974, survived,and only in the Mediterranean Basin (Bianucci et al., 2008).

The object of this paper is M. subapenninum, the latestMetaxytherium species in the world and the end member of asequence of Euro-North African chronospecies, as well as thelatest sirenian species of the Mediterranean Basin and the lat-est species included in the subfamily Halitheriinae (which is alsoparaphyletic). Moreover, it is an intriguing species, characterizedby notable increases in body size and tusk size in comparisonwith the earlier Metaxytherium species (Bianucci et al., 2008), andsupposedly by sexual dimorphism. These traits point to possiblechanges in the late Tertiary seagrass communities of the Mediter-ranean that might be detectable in no other way.

Specimens now referred, or which could be referred, to M. sub-apenninum have been collected since the beginning of the nine-

*Corresponding author.

teenth century (see Appendices 1–2 and Fig. 1). The first finddates back to 1828, when a fragmentary skeleton of a sirenian wasfound at Montiglio near Casale Monferrato (Piedmont, Italy).It was subsequently described as Cheirotherium sub-apenninum[sic] by Bruno (1839). This find was followed by the discoveriesof a skull and partial skeleton from Riosto (Emilia Romagna,Italy) and of an incomplete skull from Case il Poggio, Siena(Tuscany, Italy). These specimens were assigned by Capellini(1872) to Felsinotherium forestii and to F. gervaisi, respectively.Capellini took Bruno’s genus Cheirotherium as a synonym ofFelsinotherium. Capellini (1872) cited also a large sirenian ribfound in the Pliocene deposits of Mongardino, near Bologna(Emilia Romagna, Italy).

In 1877 Lawley reported a tusk and two milk molars fromVolterra (Tuscany, Italy) and referred them to Felsinotheriumforestii Capellini, 1872; but these specimens are now lost. Thenext find was the skull from Bra (Piedmont, Italy) described byZigno (1878b) as the new species Felsinotherium gastaldi. Por-tis (1885) cited in his catalogue, besides the remains studied byBruno (1839) and by Zigno (1878b), two other sets of specimensfrom Montiglio and Casale Monferrato (Piedmont, Italy), verte-bral and rib fragments, respectively, with some shark tooth scarsand three caudal vertebrae, but these specimens are now lost.

At the beginning of the 20th century, additional sirenian re-mains were found in Pliocene sediments of Liguria (Italy) andreferred to the genus Felsinotherium by Issel (1910, 1912). Someof these specimens are now lost. In 1954, a skull roof with amaxillary fragment was collected at Nizza Monferrato (Pied-mont, Italy); the skull roof was illustrated by Thomas in hisunpublished thesis (see Domning and Thomas, 1987). In 1974,Fondi and Pacini described a fragmentary skeleton from S.Quirico d’Orcia, Siena (Tuscany, Italy), and concluded that the

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SORBI ET AL.—METAXYTHERIUM SUBAPENNINUM FROM MEDITERRANEAN 687

FIGURE 1. Location of the geographic terms cited in the text and schematic distribution of the Pliocene marine deposits (dark gray) in the TertiaryPiedmont Basin, Ligurian Basin, Pliocene Intra-Apenninic Basin, and Tuscan Basin (from Boni, 1984; Bossio et al., 1993; and Amorosi et al., 2002).

Pliocene genus Felsinotherium Capellini, 1872, is a synonym ofthe Miocene genus Metaxytherium Christol, 1840, and that F.gervaisi Capellini, 1872, is a junior synonym of M. forestii. Thisview was supported by Domning and Thomas (1987), but not byCanocchi (1987), who described a new cranium from Ruffolo,Siena (Tuscany, Italy) and referred it to M. gervaisi, recogniz-ing M. forestii and M. gervaisi as distinct species. The next yearPilleri (1988a) described a right mandibular ramus and severalvertebrae from Nizza Monferrato (Piedmont, Italy) and referredthem to M. subapenninum, recognizing it as the only valid ItalianPliocene species. Finally, Domning’s (1994) phylogenetic analy-sis of the Sirenia put M. subapenninum and its putative ances-tor M. serresii as the sister group of North Pacific hydrodamalinedugongids, but he considered the node spurious, regarding thesetwo Pliocene Metaxytherium species as direct descendants of theEuropean Miocene M. medium and not closely related to hydro-damalines.

M. subapenninum thus stands recorded with confidence onlyfrom Italian deposits belonging to four depositional basins: theTertiary Piedmont Basin, Pliocene Intra-Apenninic Basin, Lig-urian Basin, and Tuscan Basin (Fig. 1). Two other Pliocene speci-mens, recently discovered in Spain and here discussed, could alsobe referred to M. subapenninum: an incomplete cranium fromMazarron (Murcia) under study by Montoya, and a cranium fromPilar de la Horadada (Alicante) described by Sendra et al. (1999).

Moreover, new Pliocene Italian sirenian specimens from theTuscan Basin (Fig. 1)—a humerus from the lower Pliocene sed-

iments of Camigliano, Siena (Sorbi and Vaiani, 2007), and threeundescribed specimens from Campagnatico, Grosseto—are herereferred to M. subapenninum on the basis of their large size aswell as their stratigraphic position.

These recent discoveries, particularly the specimens from theCampagnatico site, give occasion for a review of the species, pro-viding new information about its chronostratigraphic distribu-tion, osteology, and paleoecology, and substantiating the previ-ous conclusion that all the specimens from the Pliocene of Italyrepresent a single species.

Institutional Abbreviations—DSTG, Museo Paleontologicodell’Universita degli Studi di Genova, Dipartimento per loStudio del Territorio e sue Risorse, Genova, Italy; GAMPS,Gruppo Avis Mineralogia e Paleontologia di Scandicci, Firenze,Italy; IGF, Museo di Geologia e Paleontologia dell’Universitadi Firenze, Firenze, Italy; IGPS, Istituto di Geologia e Paleon-tologia dell’Universita di Siena, Siena, Italy; MACPM, Museodell’Asociacion Culturel Paleontologica Murciana, Murcia,Spain; MC, Museo Craveri, Bra, Cuneo, Italy; MCNV, Museode Ciencias Naturales de Valencia, Valencia, Spain; MGGC,Museo di Geologia Giovanni Capellini, Universita di Bologna,Bologna, Italy; MNHN, Museum National d’Histoire Naturelle,Paris, France; MUSNAF, Museo di Storia Naturale, Accademiadei Fisiocritici, Siena, Italy; NHMUK, Natural History Mu-seum, London, England; NHMB, Naturhistorisches Museum,Basel, Switzerland; PU, Museo di Geologia e Paleontologiadell’Universita di Torino, Torino, Italy.

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FIGURE 2. Stratigraphic distribution of Metaxytherium subapenninum. Specimens dated in this work are marked with asterisks. Specimens dated bymicropalaeontological analyses from previous work are marked with circles. Abbreviations: BSB, Bajo Segura Basin (Spain); LB, Ligurian Basin; PIB,Pliocene Intra-Apenninic Basin; TB, Tuscan Basin; TPB, Tertiary Piedmont Basin. Age boundaries of the chronostratigraphic and biostratigraphicunits after Lourens et al. (2004); magnetostratigraphy after Cande and Kent (1995). Calcareous nannofossil zonation after Rio et al. (1990); planktonicforaminiferal zonation after Cita (1975) and Sprovieri (1992).

Other Abbreviations—c., character state as described andnumbered by Domning (1994), Bajpai and Domning (1997),and/or Domning and Aguilera (2008) (e.g., [c. 3(1)] refers to state1 of character 3); c. 93 (contact of lacrimal and premaxilla) isadopted from Sagne (2001).

An important specimen, MC unnum., does not bear a catalognumber; for clarity, it is mostly referred to in the text by the nameof its locality, as the “Bra” specimen.

STRATIGRAPHIC AND ENVIRONMENTALDISTRIBUTION OF METAXYTHERIUM

SUBAPENNINUM

A detailed paleoecological and chronostratigraphic frame-work is crucial to understanding the evolution of the speciesand to establishing the time of its disappearance. The strati-graphic and environmental distribution of M. subapenninumhas been traced through review of previously published dataand new micropaleontological analyses (see Supplementary Dataand Figs. 2 and 3; supplementary materials available online atwww.tandfonline.com/UJVP).

M. subapenninum occurs from the MPl 2 zone of the Zancleanto the Piacenzian part of the MPl 5a zone (Fig. 2), according tothe planktonic foraminiferal zonation of Cita (1975) as emendedby Sprovieri (1992). Specimens attributed to the MPl 5a zonewere collected only within the Tertiary Piedmont Basin. The pos-sible attribution of the specimens from the Ligurian Basin to theMPl 1 zone of the basal Pliocene is not based upon data directlycollected from specimens (Supplementary Data) and should beverified.

Sirenians are well known to be coastal to estuarine species,and this environmental distribution is confirmed for M. subapen-ninum by the foraminiferal assemblages observed in sedimentsassociated with some specimens or in the sedimentary succes-sions in which selected specimens were found (Fig. 3). Most ofthe specimens come from deposits of shoreface environmentwhere the presence of euryhaline foraminifers is consistent withthe proximity of a river mouth. Specimens collected within shelfsediments commonly provide evidence of sediment transportfrom coastal areas, suggesting possible post-mortem transportof these specimens from a nearshore environment to an openmarine area, as previously suggested by Sorbi and Vaiani (2007)for IGF 8743V. Similarly, specimens from the Ligurian Basincome from outer shelf and slope environments characterized bybasinward transport of shallow marine sediments (Giammarinoand Tedeschi, 1983; Violanti, 1987; Negri et al., 1997), indicat-ing a probable transport of the sirenian remains from coastalareas, which is consistent with the fragmentary state of thesespecimens. However, the lack of micropaleontological data fromsediments associated with these Metaxytherium hampers a soundpaleoenvironmental attribution.

SYSTEMATIC PALEONTOLOGY

Class MAMMALIA Linnaeus, 1758Order SIRENIA Illiger, 1811

Family DUGONGIDAE Gray, 1821Subfamily HALITHERIINAE (Carus, 1868) Abel, 1913

METAXYTHERIUM Christol, 1840

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FIGURE 3. Depositional environments in which the specimens of Metaxytherium subapenninum have been found. Specimens with palaeoenviron-mental attribution defined in this work are marked with asterisks. Specimens with palaeoenvironmental attribution defined by micropalaeontologicalor sedimentological analyses from previous work are marked with circles. Specimens NHMB T.J. 458 and MACPM unnum. are not included becausedata on their depositional environments are not available. For codes of the depositional basins see Figure 2.

METAXYTHERIUM SUBAPENNINUM (Bruno, 1839) Fondiand Pacini, 1974

(Figs. 4–11; Tables 1–4; Figs. 4S–11S)

Cheirotherium sub-apenninum [sic] Bruno, 1839:160, pls. 1–2(original description).

Cheirotherium Brocchii Blainville, 1844:121 (lapsus for C. sub-apenninum; junior synonym).

Manatus Brocchii (Blainville) Blainville, 1844:121 (new combina-tion).

Met[axytherium]. Brocchii (Blainville) Laurillard, 1846:171 (newcombination).

Halitherium Brocchii (Blainville) Gervais, 1847:221 (new combi-nation).

Halianassa Brocchii (Blainville) Bronn, 1848:562 (new combina-tion).

Halitherium subapenninum (Bruno) Kaup, 1855:11 (new combi-nation and emended spelling).

Felsinotherium Forestii Capellini, 1872:617, pls. 1–4; pl. 5, figs.1–7, 9, 11, 13; pls. 6–7 (junior synonym).

Felsinotherium Gervaisi Capellini, 1872:634, pl. 5, figs. 8, 10, 12,14; pl. 8 (junior synonym).

Felsinotherium Forestii (Capellini): Lawley, 1877:341–342.

Felsinotherium subapenninum (Bruno) Zigno, 1878a:70 (newcombination).

Felsinotherium Gastaldi Zigno, 1878b:941, pls. 1–6 (junior syn-onym).

Felsinotherium sabalpinum [sic] Anonymous, 1911, ZoologicalRecord, Mammalia 47:63 (lapsus for F. subapenninum, wronglyattributed to Issel, 1910).

Felsinotherium subappenninum [sic] (Bruno): Issel,1912:119–125, pls. 1–2 (lapsus).

Metaxytherium forestii (Capellini) Fondi and Pacini, 1974:37–43,pls. 43–46 (new combination).

Metaxytherium subappenninum [sic] (Bruno) Fondi and Pacini,1974:45 (new combination).

Metaxytherium gervaisi (Capellini) Fondi and Pacini, 1974:45(new combination).

Metaxytherium gastaldi (Zigno) Fondi and Pacini, 1974:45 (newcombination).

Metaxitherium [sic] gervaisi (Capellini): Canocchi, 1987:498 (lap-sus).

Metaxytherium subapenninum (Bruno): Pilleri, 1988a:57, figs.1–4, pls. 1–22 (emended spelling).

Holotype—PU 13889–13890, partial skull and skeleton.Type Locality—Colline di Montiglio, Valle Tanaro, Piedmont,

Italy.Formation—Sabbie di Asti Formation.Age—Upper part of the Zanclean–lowermost part of the Pia-

cenzian (3.81–3.57 Ma).Referred Specimens—See Appendices 1–2.Range—Pliocene from the lower part of the Zan-

clean to the upper part of the Piacenzian, northwesterncoasts of the Mediterranean Basin (Italy and probablySpain).

Emended Diagnosis and Species Definition—Differs fromsome or all other species of Metaxytherium by having: large bodysize (4–5 m); nasal process of premaxilla dorsally broadened; in-fraorbital foramen very large [c. 13(2)]; nasal incisure at posteriorend of mesorostral fossa absent [c. 37(0)]; supracondylar fossaof exoccipital reduced and located dorsomedial to condyle, orlost [c. 67(3)]; palatines not extending anteriorly beyond poste-rior edge of zygomatic-orbital bridge [c. 99(1)]; tusks large [c.140(2)]. M. subapenninum differs from M. serresii, its presumedimmediate ancestor, in having dorsally broadened nasal processof premaxilla, very large infraorbital foramen [c. 13(2)], and largetusks [c. 140(2)]. M. subapenninum is provisionally defined as theterminal chronospecies (possibly spanning up to 2.7 Ma) of theEuro-North African Metaxytherium lineage, until such time asbetter evidence shows that evolution in tusk morphology withinthis species justifies recognition of its latest members as a distinctchronospecies (“M. gastaldi”).

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FIGURE 4. Metaxytherium subapenninum(GAMPS 62M). Associated ribs, vertebrae,sternum, and chevron bone in depositional po-sition. Scale bar equals 50 cm.

DESCRIPTION

Body Size

The recently discovered partial skeleton (GAMPS 62M; Fig.4) of an adult individual (evidently a young adult, given its open-

FIGURE 5. Composite restorations of skull of Metaxytherium subapen-ninum, based mainly on the Bra specimen. A, lateral view; B, ven-tral view; C, dorsal view (vomer omitted). Abbreviations: AS, alisphe-noid; BO, basioccipital; BS, basisphenoid; E, ethmoturbinal; EO, ex-occipitals; FR, frontal; J, jugal; L, lacrimal; MX, maxilla; PA, parietal;PAL, palatine; PM, premaxilla; PS, presphenoid; SO, supraoccipital; SQ,squamosal. Scale bar equals 5 cm.

rooted tusk; see Table 3) provides a minimum estimate of M. sub-apenninum body size. GAMPS 62M is about 2 m long from themid-thorax to the proximal caudal vertebrae; therefore the in-dividual should have been about 4 m long. This is corroboratedby Sarko et al. (2010:table 4), who estimated the body length of

FIGURE 6. Composite restorations of skull of Metaxytherium subapen-ninum, based mainly on the Bra specimen. A, anterior view; B, posteriorview. For abbreviations see Figure 5. Scale bar equals 5 cm.

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FIGURE 7. Parietal-supraoccipital skull roof of Metaxytherium sub-apenninum (GAMPS 62M) in dorsal view. Scale bar equals 5 cm.

FIGURE 8. Composite restorations of mandible of Metaxytherium sub-apenninum, based mainly on MGGC 9106. A, lateral view; B, dorsal view.Scale bar equals 5 cm.

FIGURE 9. Upper incisor tusks of Metaxytherium subapenninum. A,cast of the Bra specimen; B, IGPS 218; C, DSTG 2537; D, PU 13889/8;E, GAMPS 62M. Scale bar equals 3 cm.

M. subapenninum by extrapolation from data on Recent Dugongdugon and Trichechus manatus latirostris. Depending on which ofthe latter was used for comparison, which of three cranial dimen-sions was used, and which of two M. subapenninum skulls (IGF12100 [a cast of the Bra specimen] or IGF 13747), the 10 meanpredictive values obtained for body length ranged from 361 to593 cm, with six of these values lying between 412 and 494 cm.Thus it seems likely that this species grew to between 4 and 5 min length.

Skull

Diagrams and measurements of the skull are given in Figures5 and 6 and Table 1. Besides the original publications, Pilleri(1988a:figs. 1–4, pls. 1–22) provides a collection of photographsand drawings of the complete skulls and many of the otherspecimens. Several of the skulls are also illustrated by Canocchi(1987), and in Figures 4S–11S in Supplementary Data.

Premaxilla—The rostrum is enlarged relative to the cranium[c. 3(1)]; it has a dorsal keel about 10–15 mm thick anteriorlythat broadens posteriorly into a posteromedially concave or flateminence; the posterior end of the rostrum forms a boss in lat-eral view [c. 10(1)]. The lateral edges are flaring anteriorly andoverhanging ventrolaterally; the sides of the symphysis are con-vex where swollen by the tusk alveoli, which extend, dependingon the specimen, from about half to the entire length of the sym-physis [c. 140(1 or 2, scored as 2)] (see the tusk descriptions be-low). The symphysis is not entirely fused. The nasopalatine canalis elliptical, dorsoventrally flattened. The incisive foramen widensand shallows forward; its anterior end is undefined. The openingof the premaxillary canal lies posteroventral to the tusk alveoli.The masticating surface is trapezoidal in outline; the palatal sur-face is rugose, not deeply concave; its right and left halves forma wide angle of about 150◦. The nasal process is longer than halfthe length of the symphysis [c. 7(0)], and contacts the frontal [c.9(1)], nasal, and probably lacrimal (c. 93(1?); as noted above, thischaracter is adopted from Sagne, 2001), and ventrally lies in agroove formed by the maxilla. The premaxilla tapers at the pos-terior end, having lengthy overlap with frontal and nasal [c. 6(0)],but it is dorsally broadened (Fig. 5C), tending toward the broad-ened and thickened condition of c. 6(1). The mesorostral fossais long, reaching beyond the orbit [c. 8(1)]; its anterior end is

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FIGURE 10. Occlusal views of cheek teeth of Metaxytherium subapenninum. A, upper molar, left M3, IGPS 216. B, lower molar, right m2 (holo-type), PU 13889/6. Abbreviations: ac, anterior cingular cusps; end, entoconid; hld, hypoconulid; hy, hypocone; hyd, hypoconid; mcl, metaconule; me,metacone; med, metaconid; pa, paracone; pc, posterior cingular cusp; plc, posterolingual cusp; prd, protoconid; pr-prl, protocone-protoconule; end,entoconid. Scale bar equals 3 cm.

rounded and constricted by a bulge on medial side of premax-illa. The rostral deflection varies from 57◦ in MGGC 9106 to 63◦

in IGF 13747.Nasal—The nasals are set in sockets in anterior margins of

frontals, and separated in midline by processes of frontals [c.31(1)]. Their dorsal exposure is irregularly elliptical in shape, witha convex medial border and an anterolateral depression for thenasal process of premaxilla.

Lacrimal—The lacrimal is not well preserved, but judging fromthe Bra specimen it appears to be about 4 cm or more long asin most other Metaxytherium, and apparently contacts the pre-maxilla [c. 93(1?)]. (This would be in agreement with M. serresii,where the lacrimal is likewise large [5.4 cm long], prominent indorsal view, and contacts premaxilla; Pilleri, 1988b:pl. 1, figs. b, c;Carone and Domning, 2007.) There is no nasolacrimal canal [c.91(1)]. The lacrimal abuts dorsally against supraorbital processof frontal, is sutured medially to maxilla, and anteroventrally fitsin socket on dorsal surface of jugal. The jugal overlaps its lateralside.

Frontal—The supraorbital process is well developed, about 2cm thick dorsoventrally with a small posterolateral corner [c.36(1)], although MUSNAF 4960 has an anomalous posterolateralextension of the corner (Capellini, 1872:pl. 8). The process is flat-tened in a horizontal plane, with a dorsal surface inclined gentlyventrolaterad [c. 43(0)], and is not divided on its lateral margin[c. 44(0)]. The lateral crests are in continuity with the temporalcrests of parietal, and not significantly overhanging. The thin lam-ina orbitalis of frontal forms the medial wall of the temporal fossa[c. 38(0)]. Its falciform anterior edge does not quite reach as farforward as the posterolateral corner of the supraorbital process,and it forms the lateral wall of a large hollow, open anteriorly,whose posterior and medial walls are not well preserved; theyseem, however, to be formed by the ethmoid. The internasal pro-cess is incomplete in all the specimens, but it appears to be dor-sally flat in midline and without a nasal incisure extending poste-rior to the supraorbital process [c. 37(0)]. The medial portion ofthe frontal roof is more or less convex [c. 42(0)], with a medianboss and two low crests diverging anteriorly. The anterior end ofthe frontoparietal suture lies 1–5 cm posterior to the nasals ex-

cept in NHMB T.J.458 (Domning and Thomas, 1987:22, fig. 10;cited in the legend as NMB T.J. 458), where it reaches the pos-terior end of the nasals. The interfrontal suture is indistinct in allspecimens.

Parietal—The cranial vault is more or less trapezoidal in coro-nal section anteriorly, and about 2–3 cm thick in the anterior mid-line (Fig. 7). The posterolateral corners of the roof are indentedby the squamosals. The parietals are fused to the supraoccipitaland to each other in adults. In the juvenile skullcap described andfigured by Issel (1910:205–206, pl. 2, fig. 8), the interparietal su-ture is closed but evident, whereas in MUSNAF 4960 it appearsto be open. The roof is broad, without constriction, nearly flat,

FIGURE 11. Metaxytherium subapenninum (GAMPS 62M). Detail ofthe skeleton in depositional position (Fig. 4) showing the sternum, ribs,and vertebrae. Scale bar equals 50 cm.

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TABLE 1. Measurements (mm) of crania of Metaxytherium subapenninum.

Dimension MC unnum. MGGC 9106 IGF 13747DSTG2523/7

NHMB TJ458 PU 13889/1∗

MUSNAF4960

MACPMunnum.

GAMPS62M

AB 535 >525 508 >320ab 61 55 52 53AH 229 >210 184 223eBI >218 >245 370CC’ 296 250 237 255cc’ 192 203e 206de 185 144e 155F 179 218 221 >128 200eLFr >68 130 118e >93e 105 92e 98eFF’ 201 170 200 >143 181ff’ 147 120 145GG’ 74 72 60 62e 81 92e 70 60gg’ 60 68 63 60eHI <220 170 175 146ehi 52 60e 42JJ’ 73 63 88e 74KL 123 145e 105 130MM’ 123 96 98 102eno 69 55 70 53 56OP 173 165 150e 125OT 220 210 190eP 85 75 82 79e 81 93e 91Wpmax 115 106 103 114e 94 100e 96 92pq >74 >95 >61 94QR 69 60 65 58rr’ 91 87 86 95ST 126 140e 118ss’ 261 201 233T 21 17 19 20 17tt’ 78 70 86 77eUV 180 161 153 157WX 77 61 58 51yy’ 95 65 123eYZ 192 182 157eHSo 100 70 67 68e 74 57e 66WSo 130 105 98 110e 122 106e 101W/H So 1.3 1.5 1.4 1.6 1.6 1.5RD (◦) 61e◦ 57◦ 63◦P/So (◦) 95◦ 127◦ 97◦ 124◦e 119◦ 95◦ 114◦ 120◦TTC A A A A A A A A A

∗Measurements taken on the cast MNHN A.C. 2290. Abbreviations: AB, condylobasal length; ab, height of jugal below orbit; AH, length of premaxil-lary symphysis; BI, rear of occipital condyles to anterior end of interfrontal suture; CC’, zygomatic breadth; cc’, breadth across exoccipitals; de, top ofsupraoccipital to ventral sides of occipital condyles; F, length of frontals, level of tips of supraorbital processes to frontoparietal suture; LFr, length offrontals in midline; FF’, breadth across supraorbital processes; ff’, breadth across occipital condyles; GG’, breadth of cranium at frontoparietal suture;gg’, width of foramen magnum; HI, length of mesorostral fossa; hi, height of foramen magnum; JJ’, width of mesorostral fossa; KL, maximum heightof rostrum; MM’, posterior breadth of rostral masticating surface; no, anteroposterior length of zygomatic-orbital bridge of maxilla; OP, length ofzygomatic process of squamosal; OT, anterior tip of zygomatic process to rear edge of squamosal below mastoid foramen; P, length of parietals, fron-toparietal suture to rear of external occipital protuberance; Wpmax, maximum width of parietals below level of roof; pq, length of row of tooth alveoli;QR, anteroposterior length of root of zygomatic process of squamosal; rr’, maximum width between labial edges of left and right alveoli; ST, lengthof cranial portion of squamosal; ss’, breadth across sigmoid ridges of squamosals; T, dorsoventral thickness of zygomatic-orbital bridge; tt’, anteriorbreadth of rostral masticating surface; UV, height of posterior part of cranial portion of squamosal; WX, dorsoventral breadth of zygomatic process;yy’, maximum width between pterygoid processes; YZ, length of jugal; HSo, height of supraoccipital; WSo, width of supraoccipital; W/H So, ratio ofwidth to height of supraoccipital; RD (◦), deflection of masticating surface of rostrum from occlusal plane (degrees); P/So (◦), parietal-supraoccipitalangle (degrees); TTC, type of temporal crests; e, estimated measurements.

trapezoidal, without a sagittal crest [c. 51(1)]. The temporal crestsare in all cases lyriform, low, with a maximum height of 5 mm,confined to lateral edges (Type A of Domning, 1988). The inter-nal occipital protuberance is distinct, but not pointed; the trans-verse sulcus is shallow without distinct lateral pits; the bony falxcerebri is low, but reaches the frontoparietal suture. An emissaryforamen is absent, but a small median bump just in front of theexternal occipital protuberance is usually present.

Supraoccipital—The supraoccipital is hexagonal in outlinewith rounded dorsolateral corners. It forms with the after partof the parietals an angle ranging from 95◦ in PU 13889/1 to 127◦

in MGGC 9106. The external occipital protuberance rises abovethe plane of the parietal roof. The median ridge below it is dis-

tinct, moderately to well developed especially in its central part;long, reaching the ventral border of the supraoccipital; and in theBra specimen it is slightly asymmetric, shifted to the right side.The nuchal crest is low, rounded, and indistinct at its lateral endnear the squamosal. The areas of insertion for the semispinaliscapitis muscles (conspicuous in Fig. 7) are flattish, oval, rugose,and face posterodorsad, extending more than halfway to ventralend of supraoccipital. The lower part of supraoccipital is slightlyconcave in midline and convex laterally. The lateral borders arethick and rounded, sloping outward at bottom, without overhang-ing upper corners. The suture with the exooccipitals is M-shapedwith a wide central angle of about 125–130◦. A median notch be-tween the exoccipital facets is absent in the elderly specimens

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TABLE 2. Measurements (mm) of mandibles of Metaxytherium sub-apenninum.

Dimension IGPS 213 MGGC 9106MUSNAF4960

PU MR-P172

AB 415e 360 320AG 250 260 210eAP 105 130 110AQ 233 60 177eAS 130e 150 105eBG 165e 155 144BQ 174e 160 162eCD 270e >252DF 200 205 135DK 216eDL 210 165EF 160 62EU 105 150 110GH 109 120 105GP 116 130 99IJ 170e 140MN 50 74MO 109 86 95RR’ 42×2e 97 89SQ 189e 140 146eTU 106 >90 >70 93VV’ 75 91WW’ 70 60XX’ 160MD (◦) 57◦ 55◦ 61◦

Abbreviations: AB, total length; AG, anterior tip to front of ascending ra-mus; AP, anterior tip to rear of mental foramen; AQ, anterior tip to frontof mandibular foramen; AS, length of symphysis; BG, posterior extremityto front of ascending ramus; BQ, posterior extremity to front of mandibu-lar foramen; CD, height at coronoid process; DF, distance between ante-rior and posterior ventral extremities; DK, height at mandibular notch;DL, height at condyle; EF, height at deflection point of horizontal ramus;EU, deflection point to rear of alveolar row; GH, minimum anteropos-terior breadth of ascending ramus; GP, front of ascending ramus to rearof mental foramen; IJ, maximum anteroposterior breadth of dorsal partof ascending ramus; MN, top of ventral curvature of horizontal ramus toline connecting ventral extremities; MO, minimum dorsoventral breadthof horizontal ramus; RR’, maximum breadth of masticating surface; SQ,rear of symphysis to front of mandibular foramen; TU, length of alveolarrow; VV’, maximum width between labial edges of left and right alve-oli; WW’, minimum width between angles; XX’, minimum width betweencondyles; MD (◦), deflection of symphyseal surface from occlusal plane(degrees); e, estimated measurements.

MC unnum. (Bra) and IGF 13747, but seems to be present in theyounger specimen MGGC 9106. The ratio of width to height ofsupraoccipital varies from 1.3 to 1.6.

Exoccipitals—The exoccipitals are not fused to the supraoccip-ital or to each other. They join in a suture above the oval foramenmagnum in the elderly specimens (Bra and IGF 13747), but theyseem to be separated in the midline with a dorsally peakedforamen magnum in the younger specimen MGGC 9106, and areprobably united in midline but with a dorsally peaked foramenmagnum in the juvenile skullcap described and figured by Issel(1910:205–206). (By this count, three out of four specimensshow the primitive condition of conjoined exoccipitals [c. 66(0)];however, because all other Metaxytherium are scored as 66(1),scoring M. subapenninum as 66(0) would imply a noncongruentreversal. This is avoided by scoring it as 66(1) using the methodof Domning (1994:177–178, 184): because the lower limit of the95% confidence interval for a frequency of occurrence of 3 ina sample of 4 is only 0.194, we cannot be 95% certain of whichstate characterized a majority of the original population.) Thedorsolateral border is about 2–2.5 cm thick, and has a smoothlyrounded posterior edge, posteriorly slightly overhanging but notflangelike [c. 70(0)], forming a rugose surface at the level of the

top of supracondylar fossa. The fossa is shallow, located dorso-medial to condyle, or (in the Bra specimen) lost [c. 67(3)]. Thearc of the condylar articular surface subtends an angle rangingfrom 94◦ to 120◦. The condyloid (hypoglossal) foramen is single.The condyle is oval, extending slightly below the level of thetip of the paroccipital process. The paroccipital process is short,with rugose posterior surface and a posteroventrally curvedflange.

Basioccipital—Fused with exoccipitals and basisphenoid inadults. It bears the ventromedial ends of the condylar articularsurfaces and the greater part of the occipitosphenoidal eminence;the latter bears a pair of convex rugosities for the longus capitismuscles, separated in midline by a longitudinal sulcus with a me-dian crest. The posterior slope is steeper than the anterior.

Basisphenoid—The sella turcica is shallow and the tuberculumsellae is nearly flat. Otherwise does not differ from that of otherdugongids.

Presphenoid—Fused with the surrounding bones. The or-bitosphenoidal crest is present and well developed, overhangingthe chiasmatic grooves.

Orbitosphenoid—The optic foramen lies at the level of thedorsal side of the sphenorbital foramen. The bony wall lateralto the optic foramen does not bear a distinct pointed process.

Alisphenoid—The posterolateral side of the pterygoid processis sculptured (slightly concave dorsally and convex and rugoseventrally) and laterally inclined. A slight convexity continues theforward edge of the zygomatic root anteriorly. An alisphenoidcanal is absent [c. 101(1)]. The foramen ovale is opened to forma notch [c. 103(1)].

Pterygoid—Fused with the surrounding bones; forms the pos-teromedial part of the pterygoid process. The pterygoid fossa isbroad and well developed, extending above the level of the roofof the internal nares [c. 102(1)]. The ventral tips of the alisphe-noid and pterygoid enclose the end of the palatine in a slot be-tween them anteromedially. The ventral tip of the pterygoid pro-cess is enlarged, convex, and rugose.

Palatine—The palatine forms the anteromedial side and (to-gether with alisphenoid) the smooth and rounded anterolateralextremity of the pterygoid process. The palate is thin, less than 1cm thick at the level of M2 [c. 16(0)]. The anterior limits of thepalatines are not clearly distinguishable. The median sutural con-tact between palatines extends forward from the level of M3 toprobably just behind the posterior edge of the zygomatic-orbitalbridge [c. 99(1)]. The posterior border is incised [c. 97(1)].

Maxilla—The alveolar portion of maxilla is heavy and massive;its dorsal side bears a vertical plate that helps to form the wall ofthe temporal fossa and probably contacts the lamina orbitalis offrontal. The edges of palatal surface are lyriform; the surface nar-rows forward of molars, becomes narrowest forward of anterioredge of zygomatic-orbital bridge, then widens at posterior endof rostral masticating surface. The palatal gutter is narrow anddeep with rounded edges. The palatal and rostral surfaces meetin a smooth but tight curve. The part of palate between toothrowand strongly deflected portion of rostrum is downturned about25◦–30◦ from the occlusal plane. The zygomatic-orbital bridge ismediolaterally wide and anteroposteriorly long, slightly concaveon ventral side, and elevated more than 1 cm above alveolar mar-gin [c. 11(1)]. The bridge is slightly posteroventrally sloping; theanterior edge is thinner than the posterior. The posterior openingof maxillo-premaxillary canal is very large. The infraorbital fora-men is consistently very large in the available specimens (at leastone diameter of each foramen >30 mm in adult) [c. 13(2)], notobstructed [c. 20(0)], subtriangular in shape with apex roundedand located dorsally.

Squamosal—The squamosal indents the posterolateral cornersof the parietal roof and extends to the temporal crests [c. 76(1)].The posterior edge along mastoid foramen is rounded. Theprominent sigmoid ridge extends from dorsal end of mastoid

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696 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 32, NO. 3, 2012

TABLE 4. Measurements (mm) of upper cheek teeth of Metaxytherium subapenninum.

IGF 13747 IGF 13747 MC unnum. MC unnum. MACPM unnum. MACPM unnum. IGPS 216 IGPS 217Dimension Left Right Left Right Left Right Left Right

DP4 L (13e) (12e)DP4 W (15e) (14e)DP4 S 8 8DP5 L 18.9 (19e)DP5 AW 18.1 (18e)DP5 PW 17.8DP5 S 5 6M1 L 29e (28e) 20.5 20.3M1 AW 19e (20e) 18.7 18.5M1 PW 17e 15.3 15.6M1 S 9 9 5 7 4 4M2 L 27e 27e 23.3 23e 24.8 25.0M2 AW 21e 21e 22.3 22.7 18.9 18.8M2 PW 19e 19e 19.9 20.3 17.8 18.0M2 S 5 5 5 5 3 3M3 L 30e 30e 29.8 27e 27.8 31.8 30.9M3 AW 24e 24e 22.6 23.3 19.8 21.8 22.0M3 PW 23e 23e 18.2 18.9 16.1 17.7M3 S 5 5 5 5 1 3 3

Abbreviations: AW, anterior width; L, length; PW, posterior width. S, state of teeth and alveoli, modified from Marsh, 1980 (see Appendix 3); W,overall width; e, estimated measurements. Measurements in parentheses were taken from alveoli.

foramen to ventral end of posttympanic process, forming a stronglaterad-projecting flange with its posteroventral edge broad andrugose. The surface of cranial portion dorsal to zygomatic root isnot inflated or bulging. The postglenoid process and postarticularfossa are distinct and well developed. The temporal condyleis irregularly oval. The processus retroversus is moderatelyinflected, not projected below line of suture with jugal [c.77(1)]; its posterior end is smooth, without dorsal and ventralprotuberances. A posttympanic process is present [c. 73(1)]. Theexternal auditory meatus is nearly rounded [c. 82(1)], and lessthan 1 cm long mediolaterally [c. 75(1)]. The zygomatic process isroughly lozenge-shaped in lateral view, broader posteriorly thananteriorly; its medial side is relatively flat or concave, slightlyinclined inward dorsally; its posterodorsal edge is convex laterad;its anterior tip is prolonged, and reaches level of the posteriorextremity of supraorbital process.

Jugal—The ventral-most point lies ventral to orbit [c. 85(2)].The ventral tip is thickened and the border behind it is thickenedand roughened. The preorbital process is relatively flat and thin[c. 88(0)], but with a longitudinal crest on the anterolateral bor-der; its contact with the premaxilla is uncertain [c. 87(?)]. Theventral margin of orbit is not significantly overhanging [c. 90(0)].The zygomatic process is nearly horizontal, tapered in outline,longer than diameter of orbit [c. 89(0)]; its lateral side is flat, itsmedial side is concave. A postorbital process in front of tip ofsquamosal is absent.

Periotic—The periotic sits in a closely fitting socket insquamosal. The lateral surfaces are nearly smooth; the pars mas-toidea and the tegmen tympani (pars temporalis) are separatedby a narrow groove slightly covered by the overhanging bordersof the pars mastoidea and the tegmen tympani. The pars mas-toidea bears a slightly raised, rugose triangular area (processusfonticulus) on the lateral surface that fits into the mastoid fora-men. The endolymphatic foramen is narrow and slitlike. The cav-ity above aquaeductus vestibuli is elongated laterad over medialshelf of tegmen tympani. The medial extremity of pars petrosais rounded in outline; the dorsal side is more or less flat or withvariable low convexities. The ventral end of the promontory isblunt. The fossa for origin of the stapedius muscle is present anddistinct.

Tympanic—As illustrated by Capellini (1872:pl. 5, figs. 11–14),the distal border is ‘V’-shaped, rounded in outline with a blunt

tip. The posterior edge is sinuous. The anterior edge is moreor less straight. The external side is smooth and slightly sinu-ous. The internal side is convex. The proximal border is moreor less concave. The posterior branch forms an angle of about110◦ and is proximally expanded into a broad, nearly flat surfacethat contacts the pars mastoidea; along its proximolateral edge aridge and the sulcus tympanicus for the tympanic membrane arepresent. The anterior branch is short, with a rounded tip incisedby a longitudinal groove.

Malleus—The area of orbicular apophysis on posterior end isconvex. The processus muscularis is massive, swollen, and ellip-tical in outline. A sharp horizontal ridge extends forward on lat-eral side from dorsal end of manubrium. The external edge ofmanubrium is convex. The articulation with the incus is consti-tuted by two facets: the anterior one is larger and flat, the poste-rior is smaller and saddle-shaped. The angle between the incudalfacets is about 70◦.

Incus—As in other Metaxytherium, the anterolateral edge ofcrus breve is very slightly convex in outline; the crus longum(processus lenticularis) is more developed, cylindrical, and curvessharply inward. The ventral side is irregular, with small tuberclesand the articular surface for the malleus.

Mandible—The mandible is incompletely preserved (Fig. 8,Table 2). The condyle is elliptical, overhanging; its dorsal surfaceis slightly concave in the center. The mandibular notch is deep.The posteromedial edge of condylar process is thin and sharp.The edge of angle is thickened. A processus angularis superioris absent and the posterior border of the mandible has a broadlyconvex outline beginning well below the condyle [c. 125(2)]. Theinternal and external pterygoid fossae are large. The coronoidprocess is well developed, but incomplete in all the specimens,lacking its tip. The anterior border extends far anterior to thebase, especially in IGPS 213, but this character may have beenaccentuated by deformation [c. 126(1)].

The horizontal ramus is dorsoventrally broad [c. 128(1)], withventral border strongly concave [c. 122(3)], and not tangent to theangle [c. 129(1)]. Usually a small rounded protuberance is presenton the lateral surface of the horizontal ramus below m1, and inIGPS 213 another protuberance is also present below and behindthe mental foramen.

The mental foramen lies at the level of deflection of dorsaledge of ramus. It is very large, with an anterior groove. It is

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single; but in PU MR-P 172 and in PU 13889/2, a very small fora-men is present behind the main foramen, at the level of the firstmolar alveolus [c. 123(0 or 1, scored as 1)]. The anterodorsal mar-gin of the mental foramen is formed by a sharp ridge. The deflec-tion of masticating surface varies from 55◦ to 61◦. The mandibu-lar foramen opens below the m3 alveolus. The mandibular dentalcapsule is exposed posteroventrally [c. 127(1)]. The masticatingsurface is heart-shaped, notched posteriorly and narrowed ante-riorly, and rugose (although the vestigial alveoli are not distin-guishable); the lateral edges are convex and overhanging. Thesymphysis is broad; its posteroventral side is slightly concave andthe anteroventral side is narrow and concave anteroposteriorly.The symphyseal suture is never completely fused.

Dentition—The lifetime dental formula is presumed to be I1/0, C 0/0, DP 3/3, M 3/3, as in other Metaxytherium [c. 139(0); c.143(1); c. 144(2); c. 150(0); c. 155(1); c. 157(2)]. In old age, the an-terior molars may be lost, as we can observe in IGF 13747, whichpreserves only the last two molars, heavily worn, and the Braspecimen, which preserves the left M1–M3 and the right M2–M3,heavily worn.

Except in the elderly Bra specimen (see below), the tusks (Fig.9, Table 3) are not strongly curved, and are suboval or subellip-tical in cross-section [c. 141(0)], with a small, subconical crownthat is entirely covered by crenulated enamel 1 mm thick or less[c. 136(0)] and is distinct from the root [c. 137(0)]. Where open,the pulp cavity is oval in cross-section. They range from 22 × 23mm to 35 × 54 mm in diameters of crown, with 20–70 mm oftheir length erupted beyond tip of premaxilla; the tusk alveolusin adults extends about half (possibly the case in IGF 13747) or(normally) more than half the length of the symphysis [c. 140(1 or2, scored as 2)]. M. subapenninum tusks show wide intraspecificvariability; therefore, we present observations on all the tuskspreserved (see also Fig. 9).

The holotype preserves the distal portions of left and right in-complete, isolated, unworn tusks (PU 13889/8–9; Fig. 9D). Thetip is narrow and rounded. The pulp cavity is open. They belongclearly to an immature individual.

DSTG 2537 (Fig. 9C) is an isolated tusk, with the unworn distalportion of the enamel crown preserved. The tip is narrow androunded. The pulp cavity is open. This tusk appears to belong toa relatively young individual.

MGGC 9106 preserves only the left tusk fixed in the alveolus,broken apically. On the left side the premaxilla is broken and thealveolus is visible, extending the entire length of the symphysis;the medial surface of the alveolus is incised by transverse lines,which could be interpreted as the marks of the external growthlayers of the tusks, as are found also in some tusks of Dugongdugon (e.g., Marsh, 1980:188, fig. 9B). The tusk curves slightlyforward and upward. About 20 mm of the enamel crown pro-trudes from the bone. MGGC 9106 is interpreted as a subadultindividual, based on its incomplete fusion of the basioccipital-basisphenoid suture (see Capellini, 1872:pl. 3).

IGPS 218 preserves a distal portion of the left tusk enclosed ina worn premaxillary fragment (Fig. 9B). The exact length of theprotruded portion is not determinable. The tip has an ellipticalwear surface on the lateral side.

The IGF 13747 cranium preserves its tusks fixed in the alveoli.They appear to extend about half the length of the symphysis [c.140(1?)]. The tusks curve forward, and are unworn except for avery small apical area on the lateral side.

GAMPS 62M includes an isolated right tusk about 141 mmlong (Fig. 9E). The root is about 74 mm long, mediolaterally com-pressed, slightly flattened on lateral side, and open. The enamelcrown is 67 mm long, with just the tip worn. The greatest diame-ters (22 × 27 mm) are recorded at the base of the crown. A bandof cementum, about 10 mm wide, covers the root near the base ofthe crown. Transverse lines, like those observed in MGGC 9106,are present. This tusk resembles those of Metaxytherium

serresii, but is larger (cf. Carone and Domning, 2007:table 5).

The Bra adult cranium (cast, IGF 12100) preserves only theright tusk embedded in its alveolus. This description of the tuskis based on a cast kept in PU (Fig. 9A). In contrast to the imma-ture specimens described above, this tusk is mediolaterally com-pressed, about 200 mm long, 35.2 × 54.8 mm wide, and slightlyflattened on medial side; its cross-section is thick and slightly sig-moidal. The root is closed. The crown curves anteriorly from theaxis of the root, with a nearly triangular wear surface on thelateral side of the apex. The entire crown seems to be coveredby cementum and the enamel is visible only on the medial sideand appears as a dark, thin, and shiny layer. The enamel may infact be present only on the medial side, thereby making the tuskself-sharpening as in derived dugongines (Domning and Beatty,2007).

The molars of M. subapenninum (Table 4) are large and welldeveloped, with several small accessory cusps. The molar enamelis smooth, generally more than 1 mm thick.

DP3 is not preserved. DP4 is heavily worn in the availablespecimens, and submolariform, being slightly more elongate thanfully molariform teeth and narrower anteriorly than posteriorly.DP5 is heavily worn and fully molariform.

M1 is heavily worn; only the presence of two transverse rowsof cusps is discernible. M2 is moderately to heavily worn; only thetwo transverse rows of cusps are distinguishable. It differs fromM1 primarily in its larger size. M3 is generally larger overall andnarrower posteriorly than M2, and three-rooted like the otherupper cheek teeth.

The following description is based on the best-preserved M3,IGPS 216 (Fig. 10A; see also Fondi and Pacini, 1974:pl. 43, fig.5, where the legends of figs. 5–6 are incorrect: they identify theright molar as the left, and vice versa). The precingulum consistsof four separate cuspules. The anterior cingular valley or basin isopen lingually, but blocked labially by the larger labial cuspule.A crevice on lingual side marks juncture between precingulumand protocone. The protocone is large, transversely developed,and connected to the protoconule. The paracone is long, antero-posteriorly developed. The transverse valley is open but centrallyconstricted by metaconule. The metacone is long and arched. Thehypocone is globose. The posterior cingular valley or basin isclosed, containing one small spur. The postcingulum consists ofan isolated lingual cuspule and a smooth crest attached to meta-cone.

The dp3 and dp4 are not preserved; dp5 and m1 are heavilyworn, rectangular, fully molariform, and two-rooted.

The m2 is moderately to heavily worn in adults. It differs fromm1 primarily in its larger size. It is a rectangular tooth, withtwo transverse anteriorly convex lophids, a usually ‘Y’-shapedhypoconulid, and two anteroposteriorly compressed roots.

The following description is based on the best-preserved, un-worn, isolated m2, PU 13889/5–6 (Fig. 10B). The protolophidhas a slightly crenulated anterior surface. Its summit is not ‘G’-shaped, but a shallow anterior basin and a high protoconid spuron the lingual side are present. The transverse valley is blockedby contact of the protoconid spur and the crista obliqua. The hy-polophid comprises two major cusps medially inclined, plus threeaccessory cusps internal to them; the medial of these lies anteriorto the hypolophid and forms the crista obliqua. The hypoconulidconsists of four cuspules plus an anterior median spur. The smallposterior basin is blocked by the contact of the anterior medianspur and the sharp median ridge extending back from the centerof the hypolophid. This median ridge does not bend labiad, so itdoes not form a distinctly ‘Y’-shaped hypoconulid.

The m3 is moderately worn to unworn in adults. It resemblesm2 except that the posterior root is enlarged and triangular incross-section, and the hypoconulid is usually slightly longer, mak-ing the crown more elongate.

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The following description is based on the best-preserved, notentirely erupted, slightly worn m3, IGPS 213. The protolophidhas a smooth anterior surface; its summit is not ‘G’-shaped. Thetransverse valley is blocked by contact of the protoconid spur andthe crista obliqua. The hypolophid comprises two major cuspsplus two accessory cusps internal to them; the larger of these liesanterolingual to the hypolophid and forms the crista obliqua. Thehypoconulid is not ‘Y’-shaped, but is formed only by two roundedspurs, which, with the hypolophid cusps, enclose a relatively largeposterior basin.

Hyoid Apparatus—The whole hyoid apparatus is not pre-served in any specimen; only a fused stylohyoid-epihyoid-keratohyoid is known (MGGC 9106; called “grandi corna delloioide” by Capellini, 1872:pl. 7, fig. 5). The bone is about 123 mmlong, 30 mm wide proximally, and 32 mm distally. The two su-ture lines are partially discernible at about 48 mm and at about90 mm from the proximal end. The bone is mediolaterally flat-tened, convex, and expanded at the distal end, and rugosities forcartilage attachments are present at both ends. A shallow fossa atthe proximal end and a longitudinal protuberance about 50 mmlong on the medial side may be areas of origin of stylopharyngeusand hyopharyngeus muscles.

Postcranial Skeleton

Vertebrae—The complete column is not preserved in any spec-imen. The holotype (PU 13889–13890) includes several fragmen-tary thoracic vertebrae associated with left ribs encompassed inthe matrix (some of these are now missing; see Bruno, 1839, forillustration of the complete specimen). PU MR-P 172 preservesfive thoracics, possibly three lumbars, at least six caudals, andten other vertebral fragments encompassed in the matrix (Pil-leri, 1988a:52–56, fig. 4, pls. 18–22; pl. 19, fig. h, probably rep-resents a caudal rather than a lumbar). MGGC 9106 preservesthe complete cervical series (atlas and axis isolated, and cervicals3–7 in anatomic connection and partially encompassed in the ma-trix), the first and second thoracics, three other fragmentary tho-racics, the centrum of a lumbar, the sacral, and four incompletecaudals (Capellini, 1872:pl. 6, figs. 8–9). The Fornaci specimenpreserves an incomplete atlas (IGPS 220) and some indetermi-nate vertebral fragments (IGPS 221). The DSTG collection pre-serves an incomplete atlas and axis and some indeterminate ver-tebral fragments. GAMPS 62M preserves 16 vertebrae nearly inanatomic connection and partially encompassed in the matrix: thefour posterior-most thoracics, the three lumbars (Fig. 11), the sin-gle sacral, and the eight anterior-most caudals (Fig. 4). GAMPS64M preserves just three isolated thoracics.

Three atlantes are preserved (MGGC 9106, Capellini, 1872:pl.6, figs. 1–2; IGPS 220, Fondi and Pacini, 1974:pl. 44, figs. 3a, b;DSTG 2534/Ge-IV-G 153, Issel, 1910:pl. 3, figs. 1–2), but are in-complete. The lower arch is complete only in MGGC 9106; ithas a well-developed and slightly concave articular surface forthe odontoid process, and it has an irregular ventral surface witha low protuberance. The upper arch is complete only in DSTG2534/Ge-IV-G 153: it does not have any articular surface for axis;it bears a prominent dorsal keel and a lower ventral keel. MGGC9106 preserves just an incomplete upper arch in which the ventralkeel seems to be absent. The transverse processes are knoblike,irregular, slightly posterodorsally directed in IGPS 220, and pos-teriorly directed in DSTG 2534/Ge-IV-G 153 and MGGC 9106.The passage above anterior condyle for first cervical nerve isclosed on both sides. The anterior condyles are concave, with dor-solateral edge thin and flaring. The posterior condyles are almostflat, with ventrolateral edge slightly overhanging. The vertebrar-terial canal is not demarcated.

Only one complete axis (MGGC 9106, Capellini, 1872:pl. 6,figs. 3–4; Pilleri, 1988a:pl. 10, figs. c, d) and an incomplete neu-ral arch of another (DSTG 2533/Ge-IV-G 152, Issel, 1910:pl. 2,

fig. 10) are preserved. The odontoid process is well developedwith an oval, irregularly rugose tip that is longer than high. Thevertebrarterial canal is not demarcated. The anterior condylesare worn and incomplete; they seem to be irregularly oval andconvex. The arms of the neural arch are flattened. The neuralspine is massive, rounded, and anteriorly directed, without an ar-ticular facet for the atlas; it bears a mid-dorsal convex keel de-scending anteriorly and a low longitudinal protuberance on eitherside.

Cervicals 3–7 are preserved and nearly complete in MGGC9106 (see Capellini, 1872:pl. 6, figs. 5, 6).

The thoracic centra are relatively spongy, with thin sievelikeepiphyses. A low dorsal depression on the posterior vertebraemakes the centra more-or-less heart-shaped, whereas the dorsaldepression is absent on the anterior vertebrae. The centra arerectangular in sagittal section. A ventral keel is present on theposterior vertebrae. Neural arches and spines are wholly of com-pact bone. The neural spines are slightly inclined backward in allthe vertebrae and slightly constricted anteroposteriorly at theirbases. The anterior edges are thin and sharp; the posterior edgesare thicker with lateral and median ridges. The summit of eachspine is relatively flat. The transverse processes are small androunded.

The lumbar neural arches are like those of posterior thoracics.The centra are irregularly oval in anteroposterior view, withoutdorsal depression, but with a shallow ventral one. The trans-verse processes are incomplete, but dorsoventrally flattened, andslightly ventrally inclined. The summits of neural spines becomeprogressively less triangular posterad.

MGGC 9106 (Capellini, 1872:pl. 6, fig. 7) and GAMPS 62Mpreserve the sacral vertebra. It is characterized by having the dis-tal end of the transverse process thickened ventrally to 50 mm,and more downturned than those of lumbars. The centrum ishexagonal. The ventral side of the centrum has a shallow longitu-dinal groove.

The caudal vertebrae are generally similar to those of otherdugongids. The anterior caudals have paired demifacets forchevrons on ventral sides. The neural arches are small, and dimin-ish in size posteriorly. The neural spines bear an anterior protu-berance and diminish in size posteriorly. The transverse processesare flat and relatively long in anterior caudals, shorter and thickerand posteriorly inclined in posterior ones.

Only MGGC 9106 (Capellini, 1872:33, pl. 7, fig. 4) and GAMPS62M preserve chevron bones. GAMPS 62M includes a completeanterior chevron, 134 mm long, ‘Y’-shaped, fused in midline. Thebranches are 85 mm long, and join at angle of 32◦; articular facetsrugose, wide, not separated by a notch; proximal end 49 mm longanteroposteriorly.

Ribs—A complete series is not preserved in any specimen.The ribs are almost wholly made up of compact bone except forsome cancellous bone in heads and distal ends, and their shaftsare subcylindrical or elliptic in cross-section. The holotype (PU13889–13890) and the GAMPS specimens preserve several ribsand rib fragments associated with vertebrae and encompassed inthe matrix; IGPS 222, MGGC 9106, and the DSTG collectionpreserve several rib fragments; MUSNAF 4962 preserves a ribfragment; and the Bra specimen preserves a right anterior rib as-sociated with the cranium.

The rib of the Bra specimen (Zigno, 1878b:pl. 6) is completeand well preserved and merits a detailed description: it is a rightanterior rib 640 mm long, with a maximum diameter at aboutmidshaft of 140 mm; the capitulum juts upwards prominentlyabove level of neck and is about 60 mm distant from the tuber-culum; the tuberculum is rounded and convex; the curvature atangle is quite strong; the flange for an iliocostalis tendon on thedorsal side is 5 mm high at about 70 mm from tip of tuberculum;the distal end tapers slightly to oval rugose termination for carti-lage attachment.

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Sternum—Issel (1910:pl. 3, figs. 4–5) referred to Felsinotheriuman incomplete sternum, of which only a fragment of themanubrium, 135 mm long, is now preserved (DSTG 2529/Ge-IV-G 148). This consists of the spatulate anterior process, withlow ventral keel and thin but incomplete lateral border; its poste-rior extremity is broader with a pair of irregularly concave lateralsurfaces that indicate the costal cartilage attachments. The sec-ond fragment, now missing, represented the incomplete xiphis-ternum, 170 mm long, with a lateral pair of costal cartilage attach-ments. Fortunately, the specimen recently discovered (GAMPS62M) preserves a nearly complete sternum (Figs. 4, 11). The boneis about 410 mm long overall; manubrium and xiphisternum ap-pear to be fused. The anterior process is tapering and the ventralmedian keel is pronounced and more developed posteriorly onthe xiphisternum. The posterior process is thicker and narrower.The costal cartilage attachments are not clearly discernible dueto the state of conservation of the bone.

Scapula—Only a left scapula (MGGC 9106; Capellini, 1872:pl.7, figs. 1–3) and a fragment of a right scapula (IGPS 223)are known. MGGC 9106 does not differ from those of otherMetaxytherium: the supraspinous fossa is broad; the anterior edgeis slightly convex in outline; the spine is high, long, and al-most straight, with the distal part overhanging posteriorly; theacromion is small and protrudes laterally and posteriorly; theneck is narrow; the coracoid process is incomplete, but appearsto be prominent; the glenoid fossa is deep and oval.

Humerus—Just two isolated humeri that could be referredto M. subapenninum have been discovered: a nearly completeright humerus, of which only the distal portion is now pre-served (DSTG 2519/Ge-IV-G 13), referred by Issel (1912) tothe genus Felsinotherium; and a large left humerus damaged byerosion (IGF 8743V), referred by Sorbi and Vaiani (2007) toMetaxytherium cf. subapenninum. On the whole, the bones re-semble those of other Metaxytherium (for detailed descriptionssee Issel, 1912, and Sorbi and Vaiani, 2007).

Radius and Ulna—Only an incomplete radius-ulna, belong-ing to a subadult individual, is preserved (IGPS 224; Fondi andPacini, 1974:pl. 46, fig. 1). These bones resemble those of otherMetaxytherium, and are proximally and distally fused to eachother with torsion. The fusion involves the proximal ends andproximal and distal portions of the shafts; the distal epiphyses arenot preserved. The interosseous space is about 60 mm long. Thereis considerable torsion between radius and ulna: proximally ulnalies slightly medial to long axis of radius, distally it lies slightlylateral to same. The radius is straight; the ulna is slightly curved.The proximal end of radius is rounded with a well-developedradial tuberosity; the articular surface is incomplete, canted tomatch the oblique trochlea of humerus. The medial side adjacentto coronoid process of ulna has a rugose concavity for insertionof the biceps brachii muscle. The lateral sides of distal ends beardistinct grooves for extensor tendons. The distal surfaces of shaftspresent rough surfaces for cartilaginous attachment of distal epi-physes, which are reportedly missing (but see below).

Manus—The only elements preserved are two metacarpals(GAMPS 62M) and a bone identified as an isolated scaphoid (i.e.,part of an unfused scaphoid-lunar-centrale) by Fondi and Pacini(1974:pl. 46, fig. 2) (IGPS 225). However, this bone should bere-examined to rule out the possibility of its being an epiphysis,perhaps of the radius.

Issel (1910:pl. 3, fig. 7) referred to Felsinotherium an isolatedphalanx, but this bone is now missing.

Innominate—Issel (1910:pl. 3, fig. 6) referred to Felsinotheriuma fragment of a left ischium, but this bone is now missing.

SPECIMENS FROM OUTSIDE ITALY

We call attention here to Spanish specimens, chiefly two cra-nia, that could be referred to M. subapenninum. These come

from the Pliocene deposits of SE Spain (Fig. 1), specifically fromMazarron (Murcia) and Pilar de la Horadada (Alicante) (Sendraet al., 1999), plus a possible occurrence in Mallorca (Canigueral,1952). The stratigraphy and age of these deposits is discussed inSupplementary Data and summarized here.

Mazarron lies on the southern margin of the Bajo Segura Basin(Soria et al., 2008). The sirenian cranium (MACPM unnum.) ispresently under study by Montoya. It comes from lower Pliocenemarls possibly assigned to the M Pl 2–M Pl 4a zones, so itschronostratigraphic position is consistent with those of Italianspecimens of M. subapenninum. One of us (Sorbi) personally ex-amined it: the cranium lacks the posterior portion, but is well pre-served; it belongs to a young individual and does not differ in anycharacters from the Italian M. subapenninum specimens.

Pilar de la Horadada lies on the northern margin of the BajoSegura Basin (Caracuel et al., 2004; Soria et al., 2008). The sire-nian specimen was collected in sediment with an age constrainedbetween the base of Zone MPl 3 (4.52 Ma; age after Lourens etal., 2004) and the top of the Mammal Neogene (MN) 14 zone (4.2Ma; age after Agustı et al., 2001). This cranium was referred toMetaxytherium serresii by Sendra et al. (1999). These authors didnot offer an anatomic description of the specimen and made thespecific assignment just on the basis of the measurements; how-ever, its stratigraphic position falls within the range of M. sub-apenninum and some measurements appear to be bigger thanthose of M. serresii specimens (Sendra et al., 1999:table 1). Thespecimen needs a more detailed description in order to establishits specific attribution.

Finally, an isolated tusk from deposits at Son Morello, Mal-lorca, said to be Miocene in age, was described in detail, illus-trated, and identified as a “male Metaxytherium” by Canigueral(1952:387). It was 20 cm long, with diameters of 4 × 2 cm in themiddle of its length, a small, subconical enamel crown, and anopen root. Its present whereabouts are unknown. Isolated mo-lars are also reported from that and other Mallorcan localities. APliocene rather than Miocene age would seem to be indicated, be-cause the only species of Metaxytherium with a tusk of that size isM. subapenninum; but this needs to be confirmed by stratigraphicstudies.

COMPARISONS AND PHYLOGENETICRELATIONSHIPS

We continue the traditional and most common usage (e.g.,Gill, 1872; Abel, 1928; Simpson, 1945; Domning, 1978, 1994,1996) in assigning Metaxytherium to the subfamily Halitheri-inae (or its objective equivalents), now understood to be para-phyletic. Metaxytherium is clearly in evolutionary continuity withthe most morphologically conservative dugongids dating backto the Eocene and Oligocene (e.g., Eotheroides, Eosiren, andHalitherium), which include its structural (and likely actual) an-cestors. Over the 45 million years of their history, these and sim-ilar genera display few changes in cranial and postcranial ar-chitecture or in tooth structure, in contrast to the well-definedand much more altered clades Dugonginae and Hydrodamalinae,which evidently descended from halitheriines (Domning, 1994).Further, nearly 200 years of collecting and taxonomic work onEuro-North African Metaxytherium (the only common Neogenesirenians in that region) have winnowed the nominal taxa intofour Miocene and Pliocene species with (a) no clear evidenceof overlap in geochronological ranges; (b) an absence of autapo-morphies except in the latest species (M. subapenninum); (c) noindication of ghost lineages or cladogenesis (except for one pos-sible short-lived peripheral isolate, M. petersi Abel, 1904; Domn-ing and Pervesler, unpubl. data); and (d) no evidence of Neo-gene immigration from outside the region. The parsimoniousinterpretation is that these four are chronospecies of a single

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FIGURE 12. A, cladogram of species of Metaxytherium, Dusisiren, and Hydrodamalis, after Domning (1994), updated and modified by preliminaryresults of new analysis by Domning and Velez-Juarbe (2012). Character-state transformations discussed in the text are plotted on the tree. B, phylogenyof Euro-North African species of Metaxytherium, interpreted as a lineage of successive chronospecies; approximate geochronological ranges indicatedby bars. Based in part on Bianucci et al. (2008).

lineage (Fig. 12B; Domning and Thomas, 1987; Bianucci et al.,2008).

Domning and Thomas (1987) and Canocchi (1987) agreed thatMetaxytherium serresii and M. subapenninum (Canocchi’s “M.forestii”) represent stages in this chronocline (Fig. 12B). How-ever, Canocchi (1987) recognized M. gervaisi (Capellini, 1872)as a valid species intermediate between these two in chronos-tratigraphic age and in morphology. We see no advantage indoing this. Canocchi’s specimen (IGF 13747) and the holotypeof M. gervaisi (MUSNAF 4960, 4962) are little if at all olderthan the holotypes of M. subapenninum (PU 13889-90) and M.forestii (MGGC 9106) (Fig. 2, Appendix 1), and no clear mor-phological distinction is apparent: Canocchi (1987:500) herselfsays of M. gervaisi, “The main difference from the skulls of M.forestii lies in size and in the somewhat lesser development ofmuscular attachments.” Further, she says that “altogether [M.forestii] differs from M. gervaisi much less than the latter dif-fers from M. serresi [sic]” (Canocchi, 1987:508). Therefore werecognize only a single Metaxytherium species in the Pliocene ofItaly.

It could also be argued, however, that the terminal evolution-ary stage of the Euro-North African Metaxytherium, representedby the distinctively large-tusked specimen from Bra, should berecognized as a distinct chronospecies (resurrecting for it Zigno’s1878 name M. gastaldi, which was based on that specimen).This would be appropriate, if larger samples in the future ruleout sexual dimorphism in this lineage (see below), and givefurther support to a distinction between the earlier populationshere included in M. subapenninum (i.e., with conical, non-self-sharpening tusks) and later ones with the morphology of the Braspecimen. Given only the present meager sample, however, andthe fact that the Bra specimen differs from other M. subapen-ninum in no respect other than the tusk, we provisionally retainall these specimens in a single chronospecies, within which tusk

morphology appears to have changed over time, as discussedbelow.

Relationships amongst Miocene Metaxytherium species arestill unclear, but at least M. medium (Desmarest, 1822) Hooijer,1952 (middle Miocene, Europe), M. crataegense (Simpson, 1932)Aranda-Manteca, Domning, and Barnes, 1994 (middle Miocene,West Atlantic, Caribbean, and East Pacific), and M. floridanumHay, 1922 (late middle Miocene, Florida), are closely similar andcould almost represent a single, small-tusked species with a widegeographical and stratigraphic distribution. We do not think thiswas the case, but it does not appear entirely unreasonable inthe light of the wide distribution of the living dugong (Dugongdugon), which lives in the Indian Ocean and southwestern PacificOcean from southern Africa and the Red Sea to the Ryukyu Is-lands and New Caledonia. In any case, the similarity among thesefar-flung middle Miocene nominal species indicates their close re-lationship (Fig. 12A).

Much more distinctive are M. serresii and M. subapenninum,which are endemic to the Mediterranean Basin. They differ fromthe other Metaxytherium species in having a supracondylar fossaof exoccipital reduced and located dorsomedial to condyle [c.67(3)], palatines not extended anteriorly beyond posterior edgeof zygomatic-orbital bridge [c. 99(1)], and tusks moderate to largein size (c. 140(1) in M. serresii and 140(2) in M. subapenninum).

M. subapenninum, the last and most derived Metaxytheriumspecies, differs from M. serresii in several ways besides their re-markable difference in body size (which mostly reflects ecophe-notypic dwarfing in M. serresii; Bianucci et al., 2008). M. subapen-ninum displays a very large infraorbital foramen [c. 13(2)] and, inparticular, an increase in rostral and tusk size [c. 140(2)], with adorsal enlargement of the nasal process of the premaxilla. Theconsistently large diameter of the infraorbital foramen exceedswhat is observed in most other Metaxytherium spp. (though it isrivaled by some M. floridanum), but it seems not to be simply an

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SORBI ET AL.—METAXYTHERIUM SUBAPENNINUM FROM MEDITERRANEAN 701

artifact of large body size because it does not occur in the evenlarger-bodied Hydrodamalis spp. It appears elsewhere among theSirenia only in certain dugongines.

Domning’s (1994) phylogenetic analysis of the Sirenia in-dicated a sister-group relationship between the North PacificHydrodamalinae and Pliocene Mediterranean Metaxytherium,based on c. 67(3) (reduction of supracondylar fossa) and c. 99(1)(reduction of palatines). However, he considered this node spu-rious, and regarded the two Pliocene Metaxytherium species asdirect descendants of the European Miocene M. medium andnot closely related to hydrodamalines. Because the hydrodama-line Dusisiren jordani (Kellogg, 1925) Domning, 1978, and itsstructural ancestor Metaxytherium arctodites are middle MioceneNorth Pacific species, whereas M. serresii and M. subapenninumare Pliocene Mediterranean species, it is more parsimonious toconsider the similarities between these two clades as conver-gences.

This interpretation is supported by preliminary results of a newanalysis by Domning and Velez-Juarbe (2012), in which the spu-rious node 27 of Domning (1994) is collapsed (Fig. 12A). Thisresults from two changes in the analysis: (a) inclusion of M. arc-todites, in which character states 67(3) and 99(1) are both ab-sent (Aranda-Manteca et al., 1994), as they are in early andmiddle Miocene European and western Atlantic Metaxytherium;and (b) correction of the scoring of D. jordani from 99(1) to99(0) (Domning and Barnes, unpubl. data; its state in D. de-wana Takahashi, Domning, and Saito, 1986, is uncertain). Thesechanges show that c. 67(3) and 99(1) were independently derivedat later stages of evolution in the two clades (Fig. 12A). Thuswe have found no synapomorphy that unites M. serresii, M. sub-apenninum, M. arctodites, and hydrodamalines to the exclusionof other species, and no reason to doubt the earlier conclusionthat the former two species are direct descendants of M. mediumthat underwent tusk enlargement, whereas the hydrodamalineslost the tusks completely.

DISCUSSION AND CONCLUSIONS

Functional Morphology

To explain the adaptations of M. subapenninum, we have toconsider the overall evolution of the genus. Metaxytherium wasa cosmopolitan halitheriine genus with a wide geographical andtemporal distribution. During the Miocene, Metaxytherium livedalong the coasts of the Mediterranean and Paratethyan region(Domning and Thomas, 1987; Domning and Pervesler, 2001;Bianucci et al., 2003; Carone and Domning, 2007), northeast-ern Atlantic (Cottreau, 1928; Hooijer, 1977; Estevens 2003a,b),western Atlantic and Caribbean (Domning, 1988; Toledo andDomning, 1991; Aranda-Manteca et al., 1994), southeastern Pa-cific (Muizon and Domning, 1985), and northeastern Pacific re-gions (Aranda-Manteca et al., 1994). During the late Miocene,Metaxytherium underwent a drastic reduction of range and ap-parently became extinct throughout the world except along theEuro-North African coasts; and by the end of the Miocene andthe Pliocene, it survived only in the Mediterranean Basin with thespecies M. serresii (uppermost Tortonian–lower Zanclean) andM. subapenninum (middle Zanclean–Piacenzian) (see Bianucciet al., 2008). Therefore M. subapenninum is a relict species witha much reduced range.

On the whole, the Euro-North African Metaxytherium speciesshow a slight and gradual increase in body size during theMiocene (Bianucci et al., 2008), abruptly interrupted by the peri-Messinian dwarfing of M. serresii, but resuming and culminatingin the Pliocene with the rapid increase in size observed in M. sub-apenninum (for possible causes of the dwarfism in M. serresii, seeBianucci et al., 2008 and Clementz et al., 2009.) This overall in-crease in size can be plausibly ascribed to the general climaticcooling throughout the later Neogene.

As for feeding adaptations, early and middle MioceneMetaxytherium species have simple, small tusks. These tusks ex-tend less than half the length of the premaxillary symphysis inthe Miocene species M. krahuletzi Deperet, 1895, M. medium, M.floridanum, M. crataegense, and M. arctodites. M. petersi, from themiddle Miocene of the Vienna Basin, does not preserve any traceof tusk alveoli in the available specimens; if tusks were presentthey were at least as small as in other early and middle MioceneMetaxytherium species. These species also have rather stronglydownturned rostra, and a primitively long, narrow nasal processof the premaxilla. On the basis of these and other cranial fea-tures, Metaxytherium is regarded as a generalized bottom-feeder,a consumer of seagrass blades and of the rhizomes of smaller sea-grass species (Domning, 2001; Domning and Beatty, 2007). Iso-topic data (Clementz et al., 2009) corroborate and emphasize thegeneralist-feeder role of this genus. Dietary flexibility could haverepresented the key to its success, allowing Metaxytherium pop-ulations to adapt to the food resources present in their variedhabitats.

But in M. serresii (late Tortonian–early Zanclean), we observean increase in tusk size, followed by the still greater increaserecorded in its putative descendant M. subapenninum. The tusksof M. serresii extend about half the length of the premaxillarysymphysis, and in M. subapenninum generally more than half thelength of the symphysis (see also Bianucci et al., 2008). They alsoseem (in the Bra specimen) to have become more flattened andself-sharpening.

The transformation from a simple, conical tusk to a blade-like,self-sharpening tusk would be a simple one developmentally. Be-cause the crown is worn away by use while the tusk continuesto grow at its open root, all that is necessary is for depositionof thin enamel to continue along the medial edge of the crownwhile ceasing on the rest of its periphery. Once the original con-ical crown is worn away, only the medial surface of the growingtusk has enamel, which forms a resistant edge kept sharp by con-tinued wear. Any flattening of the original subcylindrical formwould make the tusk more blade-like. This condition can be ob-served in Dugong dugon, which has just such a medial layer ofthin enamel producing a self-sharpening edge, as quoted belowfrom Marsh (1980).

Moreover, in M. subapenninum, the increase in tusk sizeaccompanies a change in the nasal process of the premaxillathat is convergent with the more derived genera of dugonginesand could be correlated with changes in feeding behavior. Indugongids generally, including most Metaxytherium, the nasalprocess is primitively long, thin, and tapering at the posteriorend, having a long overlap with the frontal and/or nasal [c. 6(0)].In the Oligo-Miocene Indian dugongines Bharatisiren Bajpai andDomning, 1997, and Kutchisiren Bajpai, Domning, Das, Velez-Juarbe, and Mishra, 2010, it becomes thickened at the posteriorend, but it preserves a long overlap with the frontal [c. 6(1)].In still more derived dugongines including Dioplotherium Cope,1883, Corystosiren Domning, 1990, Rytiodus Lartet, 1866, andDomningia Thewissen and Bajpai, 2009, it becomes broadenedand bulbous at the posterior end, having a more or less verticaljoint surface in contact with the frontal and/or nasal [c. 6(2)]. InM. subapenninum, it becomes dorsally broadened but not thick-ened, and it preserves a long overlap with the frontal—a condi-tion intermediate between c. 6(0) and 6(1). This appears to be anincipient adaptation to support a compressive stress field alongthe dorsal side of the skull, due to more forceful downward andbackward movement of the rostrum and enlarged tusks duringfeeding (cf. Domning and Beatty, 2007:fig. 3).

Sexual Dimorphism?

M. subapenninum tusks show wide intraspecific variability, andit has been suggested, by analogy with the living Dugong, that

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this reflects sexual dimorphism (Abel, 1904:11, 163–164; Canoc-chi, 1987). This is not inherently implausible, because such dimor-phism occurs widely among mammals.

For example, in extant mammals such as pigs (Suidae), chevro-tains (Tragulidae), musk deer (Moschidae), muntjacs (Munti-acus and Megamuntiacus), walruses (Odobenus), and Africanelephants (Loxodonta), the females have smaller, more slen-der upper tusks than the males; in Asiatic elephants (Elephas)the female tusk is usually absent; and in narwhals (Monodon)the female tusks (as in Dugong) usually do not erupt (Nowak,1999). The extinct American mastodon (Mammut) resembledLoxodonta in this regard (Smith and Fisher, 2011), and the ex-tinct walrus-like dolphin Odobenocetops likewise had dimorphicupper tusks (larger in presumed males; Muizon and Domning,2002).

As for lower tusks, Rhinoceros and most other living and ex-tinct rhinocerotids (Dinerstein, 1991; Mihlbachler, 2005, 2007),living (Dalebout et al., 2008) and extinct (Lambert et al., 2010)beaked whales, Babyrousa (MacKinnon, 1981), and probablythe extinct Pseudoceratinae (Webb, 2008) have lower tusk-liketeeth that are enlarged and used as weapons in adult males,but are smaller or absent in females. However, in the extinctrhino Aphelops, “[w]ear patterns on the tusks suggest that somemales utilized the tusks for non-social purposes such as feed-ing” (Mihlbachler, 2005:517). Elephant and walrus tusks can as-sist in feeding also (for walruses in contrast to Odobenocetops,see Muizon et al., 2002); but in other mammals, enlarged tusksof males seem to be purely or mainly for social purposes—as inDugong dugon.

Hence it would not be surprising if a Metaxytherium speciesalso evolved sexually dimorphic tusks. Evolution of dimorphismcould indicate a change in behavior, with competition for fe-males and space in a habitat with unfavorable climatic and/or ge-ographic conditions (such as developed in the Pliocene Mediter-ranean; see below).

A possible example of sexual dimorphism is provided by twoold adult M. subapenninum which differ morphologically onlyin their tusks: IGF 13747 (described by Canocchi, 1987, as aspecimen of “Metaxytherium gervaisi”) and the Bra specimen(described by Zigno, 1878b, as the holotype of “FelsinotheriumGastaldi”). They are both considered old individuals becausetheir basioccipital-basisphenoid sutures are fused, their exoccip-itals meet in the midline, and their posterior molars are heav-ily worn. IGF 13747 has relatively small enamelled tusks (23× 27 mm in diameters) fixed in the alveoli with only 58 mmprotruded, elliptical in cross-section, and unworn except for avery small apical portion on the lateral side. On the contrary,the Bra specimen has a large tusk (35 × 54 mm in diameters),about 200 mm long with about 70 mm protruded, and medio-laterally compressed. This tusk has a closed root and a crownwith a nearly triangular flat wear surface on the lateral side ofthe apex, and the crown is almost completely covered by ce-mentum, as in old dugongs. Enamel may be confined to the me-dial side, giving the tusk a self-sharpening cutting edge. Thesetwo could be interpreted respectively as female and male adults,with a development of tusks analogous to that observed in liv-ing dugongs. Abel (1904:163–164) also proposed the subadultMGGC 9106 (holotype of “Felsinotherium Forestii” Capellini,1872), with a tusk 31 × 42 mm in diameter and protruding morethan 20 mm, as a female, in contrast to the supposed male fromBra.

However, we have also to consider the chronostratigraphic po-sitions of the specimens (Fig. 2): the small-tusked IGF 13747 isdated to 4.12–3.57 Ma and the large-tusked Bra specimen is datedto 3.19–2.59 Ma. On this basis, one could argue for an alternativescenario of gradual evolutionary increase in tusk size in M. sub-apenninum, the earlier specimens showing smaller tusks than thelater ones. MGGC 9106 might represent an intermediate condi-

tion: it is dated to 3.81–3.57 Ma, and the enamel crown of its tuskis larger and more flattened than in IGF 13747. This could be in-terpreted as either a subadult male of a dimorphic species, or aspecimen at an intermediate evolutionary stage of a monomor-phic lineage in which the tusks of both sexes were increasing pro-gressively in size. Before trying to decide between these alterna-tives, we should examine more closely the conditions in the mod-ern species.

Tusk Dimorphism in Dugong dugon—D. dugon has a pair oftiny deciduous incisors and a pair of permanent, ever-growing in-cisors enlarged as tusks; and it is sexually dimorphic in tusk de-velopment. Marsh (1980:186–187, 191–192) describes this dimor-phism as follows: “The growth of the tusks is similar in both sexesuntil about 10 [years of age]”; the tusks then grow “posteriorlythrough the premaxilla, and . . . a hole appears in the lateral sideof the premaxilla at the root of the tusk. . .” In the female, the tusk“continues to grow posteriorly through the premaxilla. The in-crease in length of the tusk is accompanied by a corresponding in-crease in the length of the alveolus. . ., which continues to extendup the premaxilla, the hole in the premaxilla marking the baseof the alveolus. . .. [In old females the tusks can be] erupted andworn, presumably because they [reach] the base of the premax-illa and [can] not grow posteriorly any farther. . . . In the male, thetusks erupt after [about 12 years, and] the length of the tusk alve-olus remains relatively constant thereafter and never reaches thebase of the premaxilla. The premaxillary bones are much thickerthan in the female and the hole in each premaxilla at the baseof each tusk usually disappears around the time that the tuskserupt.” The tip of the tusk is constituted by “postnatal dentine. . . deposited in a prolonged series of coaxial cone-shaped incre-ments” covered by “a layer of enamel up to about 330 µm thick.The enamel becomes thinner on the sides of the tusk and disap-pears altogether after [a few years] except on the ventromesialside, where a layer of enamel about 330 µm thick continues be-neath the cementum to the base of the tusk in both males and fe-males. . . . Cementum covers almost the entire surface of the tuskof older animals but is absent from the tip of the tooth in younganimals. . . . The anterior erupted end of the tusk wears quickly onthe lateral surface into a chisel shape. . ., the cutting edge of whichis reinforced by [an] enamel layer below the cementum. . ..”

Tusks are not essential equipment for feeding in D. dugon,because they are unerupted in almost all females and in youngmales; and males with erupted tusks do not appear to consumemore rhizomes than females without erupted tusks (rather, theyuse the tusks mainly for social purposes like fighting and mating).The wear on the tusks seems to be caused by passing through thesubstrate during normal feeding bouts, with occasional episodesof vigorous cutting of rhizomes by anterior and posterior move-ments of the tusks in the substrate (Domning and Beatty, 2007).Although the intrinsic structure, growth mechanism, and wearpattern of the tusks as described by Marsh (1980) are typicalof sirenian tusks, the sexual dimorphism in their development isnot matched in any fossil sirenian (except possibly M. subapen-ninum), and the apparent non-use of the modern dugong’s tusksin feeding cannot be taken as representative of its extinct rela-tives (Domning and Beatty, 2007).

Evaluation of Hypotheses—In comparison with moderndugong tusks, therefore, the existing sample of M. subapenninumincludes both the ‘female’ morphotype (primitive, with subcon-ical enameled tusks) and the ‘male’ morphotype (derived, withmore flattened, chisel-like tusks, perhaps enameled on only themedial side). Testing for sexual dimorphism requires considera-tion of at least five hypotheses. Unfortunately, too few specimensof M. subapenninum have been collected to permit testing bystatistical analysis. Moreover, these belong to different chronos-tratigraphic levels and to different age classes (juvenile, subadult,adult, old adult; Fig. 2, Table 3, Appendix 1). Studies on sire-nian tusks are additionally complicated because only one tusked

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sirenian is extant (Dugong dugon), and it belongs to a differ-ent subfamily, in which it is morphologically and perhaps behav-iorally aberrant (Domning and Beatty, 2007). But some provi-sional conclusions can be drawn.

Hypothesis 1 (individual variation)—There was no real dimor-phism; the two morphotypes are merely extremes of a continuousspectrum.

Prediction: Both morphotypes, along with intermediate forms,should be present in early as well as late stratigraphic horizons.

Data: The ‘male’ morphotype occurs only in the latest horizon,where the ‘female’ morphotype has not been found. MGGC 9106questionably represents an intermediate condition.

Conclusion: Not supported by present data.Hypothesis 2 (static sexual dimorphism)—Dimorphism is

present and sexual; the entire species was dimorphic throughoutits existence, this dimorphism having evolved in an earlier species(i.e., M. serresii).

Prediction: Both morphotypes should be present in approxi-mately equal proportions in early as well as late stratigraphichorizons (♂♀ → ♂♀).

Data: The earliest horizons contain only the ‘female’ morpho-type; the ‘male’ morphotype occurs only in the latest one: theBra specimen alone, out of the five individuals in which eruptedtusks are preserved (four from Italy plus MACPM unnum. fromSpain), exhibits the derived ‘male’ morphology, and it is one ofthe two latest specimens known (Fig. 2, Appendix 1). Moreover,no examples of the ‘female’ morphotype are known from a com-parably young horizon, so there is no proof of dimorphism evenat that time. M. serresii also shows no evidence of dimorphism,except in one doubtful case (Carone and Domning, 2007:72, 74,90).

Conclusion: Not supported by present data.Hypothesis 3 (evolving sexual dimorphism)—The species be-

came sexually dimorphic during the course of its existence.Prediction: Earlier horizons should contain only the ‘female’

morphotype; later ones should contain both morphotypes in ap-proximately equal proportions (♀ → ♂♀).

Data: The earlier horizons do seem to contain only the ‘female’morphotype, but the latest one has produced only one tuskedspecimen, which is ‘male.’

Conclusion: Possible, but better sampling is required, espe-cially of the latest horizon where only the ‘male’ morphotype hasso far been found.

Hypothesis 4 (evolving monomorphism)—There was nevertrue dimorphism; the entire species gradually evolved from the‘female’ to the ‘male’ morphotype (probably as an adaptation pri-marily for feeding rather than social interaction).

Prediction: The earliest horizons should contain only (or pre-dominantly) the ‘female’ morphotype; the latest ones should con-tain only (or predominantly) the ‘male’ morphotype, with indi-vidual variation possibly evident, at least at intermediate stages(♀ → ♂).

Data: The only example of the ‘male’ morphotype is theBra specimen, which is one of the latest (Fig. 2). MGGC 9106questionably represents an intermediate condition. The enlargednasal process of the premaxilla is also consistent with this hypoth-esis: all the M. subapenninum specimens in which the premaxillais preserved, including the supposed female IGF 13747 and es-pecially the Spanish skull MACPM unnum., show a broadenednasal process, suggesting a similarly forceful use of the tusks in allthe specimens. None of the earlier Metaxytherium species, includ-ing M. serresii, have a similarly broadened process. Moreover, noM. subapenninum, or other tusked fossil sirenians, show a largehole in the side of the premaxilla at the root of the tusk, which is,on the contrary, present in adult female and in subadult D. dugonand indicates that the tusk was not erupted or (potentially) in use(Marsh, 1980:191, quoted above).

Conclusion: Consistent with the available data, but the existingsample is inadequate for certitude.

Hypothesis 5 (degenerating monomorphism)—The ‘male’morphotype was originally evolved in an earlier species for feed-ing (cf. Hypothesis 4), but later fell into disuse for this purpose,and a previously secondary function (social, with sex-role dif-ferentiation) became primary. The species then became sexuallydimorphic (Dugong dugon is a possible example; Domning andBeatty, 2007).

Prediction: The ‘male’ morphotype should predominate in ear-lier horizons; later ones should contain both morphotypes in ap-proximately equal proportions (♂ → ♂♀).

Data: The ‘male’ morphotype has been found only in the latesthorizon. No M. subapenninum skull has the tusks unerupted asdo female D. dugon; those of putative female M. subapenninum(both the old adult IGF 13747 and the subadult MGGC 9106) arefully erupted and hence available for use in feeding. Hence wecan infer that adult M. subapenninum of both sexes had eruptedtusks and used them vigorously for something (such as foragingon seagrass rhizomes; Domning and Beatty, 2007; Bianucci et al.,2008).

Conclusion: Falsified in the present case.Thus the most likely hypotheses are 3 and 4, with the available

evidence tending to support 4. We conclude that, at this time,the hypothesis of sexual dimorphism in M. subapenninum lacksadequate foundation.

Paleoecology

Use of the tusks in M. subapenninum, therefore, was mostlikely for feeding. Probably the tusks gradually increased in sizewithin the entire species to become more effective at harvest-ing rhizomes. This shift toward a diet richer in rhizomes (themost nutritious parts of seagrasses) could reasonably be dueto progressive climatic cooling (lower temperatures require amore nutrient-rich diet). Interestingly, recent isotopic analyses(Clementz et al., 2009) indicated for M. subapenninum a dietrelatively specialized in seagrasses and a mixture of freshwaterto marine habitats; but they did not evidence for this speciesa clear change in diet or habitat in comparison with MioceneMetaxytherium species.

This adaptive scenario also suggests an explanation for the in-crease in tusk size that began with peri-Messinian Metaxytherium.Although the Miocene Mediterranean seagrass flora was likelymore diverse than today’s, both Posidonia sp. and Cymodoceanodosa were presumably present (along with smaller seagrasses),because they are both reported from the Eocene of the ParisBasin (den Hartog, 1970; Phillips and Menez, 1988). Today, thedominant Mediterranean seagrass in terms of biomass, Posido-nia oceanica, is a climax species having ‘large’ rhizomes in thesense of Domning (2001) (i.e., up to 1 cm in diameter). How-ever, it is very sensitive to changes in salinity or temperature.This was probably also true in the Miocene, because seagrassesand their ecology appear to have taken on their modern formseven earlier (Domning, 1981, 2001). Consequently, P. oceanicashould have been among the first seagrasses to succumb to thedisruptions of the Messinian Salinity Crisis (MSC). It would pre-sumably have yielded its dominance to smaller seagrasses suchas Cymodocea nodosa, a eurybiontic ‘pioneer’ species with rhi-zomes of ‘medium’ size (about 2–3 mm), and Zostera marina,also very eurybiontic, with rhizomes 2–5 mm in diameter. Zosteranoltii is a still smaller and also euryhaline Mediterranean species(den Hartog, 1970; Phillips and Menez, 1988).

Small-tusked Metaxytherium (such as M. medium) are hypoth-esized to have fed on small and medium-sized rhizomes (notas large as Posidonia), as well as leaves of seagrasses of allsizes (Domning, 2001). If the onset of the MSC eliminated the

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dominant Posidonia, leaving more eurybiontic species such as C.nodosa to provide the bulk of a reduced total biomass, then thesirenians may have had to shift to a diet richer in rhizomes, es-pecially the newly dominant medium-sized ones. The predictedresult (following the model of Domning, 2001) would be an in-crease in tusk size to the ‘medium’ dimensions observed in M.serresii.

Following the MSC, Posidonia recolonized the Mediterraneanand re-established its dominance. Leaves of seagrasses referredto P. oceanica are found above the Messinian gypsum bed of thePiedmont Basin (Sturani, 1976:18, fig. 5c), and a well-preservedP. oceanica community has been found in the late Pliocene ofRhodes (Moisette et al., 2007). This recolonization might haveled the sirenians to adapt to eating Posidonia rhizomes, ratherthan returning to their less challenging mid-Miocene diet ofsmaller species, because by then the climate had cooled furtherand the larger rhizomes might have provided a greater energyyield. Also, P. oceanica displays a comparatively more stable ar-chitectural complexity throughout the year, whereas the Cymod-ocea nodosa–Zostera noltii species complex is characterized bymarked seasonal changes of the main structural variables (e.g.,shoot density): the leaf canopy of C. nodosa and Z. noltii iswell developed during the warmer months but decreases or com-pletely disappears at the onset of the colder season (den Hartog,1970; Marba et al., 1996). Hence Cymodocea would have beenless available during precisely the most stressful season for thesirenians, giving them still more reason to adapt to eating Posi-donia—by evolving still larger tusks, as observed in M. subapen-ninum.

In summary, M. subapenninum was the last and most de-rived Metaxytherium species, and the last sirenian native to theMediterranean. It was a relict species limited to the Mediter-ranean Basin, and responded to long-term climatic cooling by anincrease in body size and, evidently, by increase in size and cut-ting ability of the tusks and reinforcement of the nasal processof the premaxilla (convergently with derived dugongines), in or-der to obtain a more nutritious diet richer in seagrass rhizomes.Specifically, these would have been the large, tough rhizomes ofthe climax species Posidonia oceanica, the existence of which inthe Pliocene Mediterranean is attested by good fossil evidence(Sturani, 1976; Moisette et al., 2007).

The evolutionary history of M. subapenninum can be con-trasted with that of the contemporary hydrodamaline sirenians inthe North Pacific (see Domning, 1978). Whereas the hydrodama-line lineage survived into historic times, adapting to eat algae incold waters, M. subapenninum does not appear to have been ableto change greatly its seagrass diet, as is reflected in isotopic analy-ses (Clementz et al., 2009; Clementz and Sewall, 2011). It becameextinct during the late Piacenzian, most probably during the ac-celeration of climatic cooling recorded by Ravelo et al. (2004)after 3 Ma.

The sirenian extinction would have had repercussions on theentire marine ecology of the Mediterranean, in that the absenceof large herbivores capable of disrupting the rhizome mats of theclimax seagrass Posidonia oceanica would have allowed diverseMediterranean seagrass communities to proceed to the less di-verse, less productive climax stage of plant succession. (The otherlarge marine herbivore present, the green turtle Chelonia my-das, includes seagrasses in its diet but does not disturb the rhi-zomes, and also consumes large amounts of algae.) As a result,the Mediterranean seagrass communities of today are in an ‘ab-normal’ condition with the dominance of P. oceanica, their bio-diversity is presumably depauperate, and (in the relative absenceof herbivory) their energy pathways are predominantly detritus-based—much as in the present-day Caribbean (Domning,2001).

ACKNOWLEDGMENTS

We thank M. C. Bonci (DSTG), E. Cioppi (IGF), R. Fondi(IGPS), F. Bernal (MACPM), E. Molinaro (MC), C. Sarti(MGGC), C. Sagne (MNHN), C. Lefevre (MNHN), P. Tassy(MNHN), F. Farsi (MUSNAF), A. Ziems (NHMB), J. Hooker(NHM), A. Currant (NHM), and D. Ormezzano (PU) for al-lowing access to specimens under their care. We thank P. Mon-toya (MCNV) and L. Hayek (Smithsonian Institution) for usefulcommunications. Special thanks are due to S. Casati and to theentire GAMPS team for their important discoveries. J. Velez-Juarbe assisted with phylogenetic analysis and illustrations. B.Beatty, M. Voss, and editor J. Geisler improved the manuscriptwith their thorough and helpful critiques. Domning’s travel to ex-amine specimens was supported by National Science Foundationgrant DEB-8020265.

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Submitted March 31, 2011; revisions received November 23, 2011;accepted January 13, 2012.Handling editor: Jonathan Geisler.

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APPENDIX 1. List of specimens referred to Metaxytherium subapenninum. Chronological attributions from Figure 2. Growth stages(Abbreviations: J, juvenile: basioccipital-basisphenoid suture unfused and M2 unerupted; SA, subadult: suture unfused and M2 erupted; A, adult:suture fused and M2 erupted; OA, old adult: suture fused and molars heavily worn) scored following Marsh (1980). Tusk condition scoring modifiedfrom Marsh (1980; see Appendix 3).

Specimens and references Site Basin MaGrowth

stageTusk

condition

MC unnum.: cranium, tusk, rib (Zigno,1878)

Bra, Cuneo, Italy Tertiary Piedmont Basin 3.19–2.59 OA 4C

PU MR-P 172: mandible fragment, molars,vertebrae (Pilleri, 1988a)

Nizza Monferrato, Asti, Italy Tertiary Piedmont Basin 3.19–2.59 A —

NHMB T.J. 458: skull roof, maxillaryfragment (Domning and Thomas, 1987)

Nizza Monferrato, Asti, Italy Tertiary Piedmont Basin A —

MGGC 9106: cranium, mandible, molars,tusks, atlas, axis, vertebrae, chevron,scapula, hyoid fragment, ribs (Capellini,1872)

Riosto, Bologna, Italy Pliocene Intra-ApenninicBasin

3.81–3.57 SA 3

MGGC unnum.: rib (Capellini, 1872) Mongardino, Bologna, Italy Pliocene Intra-ApenninicBasin

3.81–3.57 — —

PU 13889–90 (holotype): skullcap (castMNHN A.C.2290), mandible fragment,molars, tusks, ribs and vertebrae (Bruno,1839)

Montiglio, Casale Monferrato, Asti,Italy

Tertiary Piedmont Basin 3.81–3.57 J 2O

IGPS 213–226: mandible, auditoryfragment, atlas, vertebral and ribfragments, scapula, radius-ulna, bonefragments (Fondi and Pacini, 1974)

Fornaci, S. Quirico d’Orcia, Siena,Italy

Tuscan Basin 3.81–3.57 SA 3

MSNAF 4960, 4962: incomplete cranium,incomplete mandible, rib fragment(Capellini, 1872)

Case il Poggio, Val di Pugna, Siena,Italy

Tuscan Basin 4.12–3.84 A —

IGF 13747: cranium, molars, tusks(Canocchi, 1987)

Ruffolo, Val di Pugna, Siena, Italy Tuscan Basin 4.12–3.57 OA 2

DSTG 2518–2534: fragments of cranium,mandible, ribs, vertebrae, sternum, atlas,axis, humerus (Issel, 1910, 1912)

De Ferrari square, Genoa, Italy Ligurian Basin 5.33–3.81 — —

DSTG 2535–2537: tusk (Issel, 1910) Fornaci, Savona, Italy Ligurian Basin 5.33–3.81 A? 2ODSTG 2538: rib fragment (Issel, 1910) Rio Torsero, Savona, Italy Ligurian Basin 5.33–3.81 — —IGF 8743V: humerus (Sorbi and Vaiani,

2007)Camigliano, Siena, Italy Tuscan Basin 5.08–4.52 A —

GAMPS 62M: incomplete skeleton Cava la Castellina, Campagnatico,Grosseto, Italy

Tuscan Basin 5.08–4.52 A 2O

GAMPS 63M: bone fragments Cava la Castellina, Campagnatico,Grosseto, Italy

Tuscan Basin 5.08–4.52 — —

GAMPS 64M: ribs and vertebrae Cava la Castellina, Campagnatico,Grosseto, Italy

Tuscan Basin 5.08–4.52 — —

APPENDIX 2. List of lost specimens possibly referable to Metaxytherium subapenninum.

Specimens and references Site Basin

Rib fragments (Issel, 1910) Fornaci, Savona, Italy Ligurian BasinFour molars (Issel, 1910) Borzoli, Genoa, Italy Ligurian BasinVertebral and rib fragments with some shark tooth scars

(Portis, 1885)Montiglio, Casale Monferrato, Asti, Italy Tertiary Piedmont Basin

Three caudal vertebrae (Portis, 1885) Casale Monferrato, Asti, Italy Tertiary Piedmont Basin

APPENDIX 3. States of teeth and alveoli (modified from Marsh, 1980).

Tusk in the alveolus Tusk isolated Pulp cavity of tusk

1 Unerupted O Open2 Erupted and unworn 2 Unworn T Tapered At The Base3 Erupted and slightly worn 3 Slightly worn C Closed4 Erupted and worn 4 Worn5 Absent, alveolus emptyCheek tooth in the alveolus Cheek tooth isolated Pulp cavity of cheek tooth

1 Unerupted or partly erupted O Open2 Erupted and unworn 2 Unworn T Tapered at the base3 Cusps worn 3 Cusps worn C Closed4 Lophs worn 4 Lophs worn5 Entire crown worn 5 Entire crown worn6 Broken (stump only in alveolus)7 Absent, alveolus empty8 Absent, alveolus partly filled with spongy bone9 Absent, alveolus not visible

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