TAPHONOMIC ANAI,YSIS OF TAPIRUS A R V E R N E N S I S REMAINS

FROM THE LOWER VAIJDARNO (TUSCANY, CENTR/ IJ ITAIJY)

MARCO RUSTIONI, PAUL MAZZA

Rustoni, M., Mazza, P., 2001. Taphonomic analysis of Tapirus arvernensis remains from the Lower Valdarno (Tuscany, Central Italy). [L'anatyse taphonomique des restes de Tapirus arvernensis du Valdarno inf~rieur (Toscane, Italie centrale)]. Geobios 34 (4), 469-474. Villeurbanne, le 30.09.2001.

Manuscrit d~pos6 le 25.08.2000; accept5 d~finitivement le 08.01.2001.

ABSTRACT - The present investigation describes the taphonomic evidence that can be observed on the remains of two Tapirus arvernensis individuals, a prime-aged adult and a juvenile, recovered at Casenuove (Empoli), in the Lower Valdarno marine Pliocene sediments. The spatial arrangement of the bones on the fossiliferous surface sug- gests the action of one or two currents, and seems to agree with the tentative reconstruction of the shoreline at the Early-Mid-Pliocene transition. Reference to the biology and ethology of presently living Asian tapirs leads to inter- pret the two individuals as a female, presumably at its first breeding experience, and its cub. © 2001 Editions scien- tifiques et m~dicale Elsevier SAS

KEYWORDS: TAPIRUS ARVERNENSIS, TAPHONOMY, PLIOCENE, LOWER VALDARNO, TUSCANY, ITALY.

R]~SUMt~ - La recherche actuelle est destin~e ~ d~crire les caract~res taphonomiques d~montr~s qui peuvent ~tre observSs sur les restes de deux individus de Tapirus arvernensis, un jeune adulte et un juvSnile, r6cup~r~s fi Casenuove (Empoli), dans les d~p6ts plioc~nes marins inf~rieurs de Valdarno. La disposition et l'orientation des ossements sur la surface fossilif'ere font penser ~ l'action d'un ou deux courants et semb]ent en accord avec l'hypo- th6tique reconstruction de la ligne de rivage ~ la transition Plioc~ne inf~rieur-Plioc~ne moyen. La r~f6rence fi la bio- logie et ~ l'~thologie des tapirs asiatiques actuels m~ne ~ interpreter les deux individus en tant que femelle, vrai- semblablement fi sa premiere experience de reproduction, et son jeune. © 2001 ]~ditions scientifiques et m6dicale Elsevier SAS

MOTS-CL]~S: TAPIRUS ARVERNENSIS, TAPHONOMIE, PLIOCENE, VALDARNO INF]~RIEUR, TOSCANE, ITALIE.

INTRODUCTION

In 1993 some amateurs found and collected an almost complete prime-age adul t skeleton and iso- la ted tee th and bone f ragments of a juvenile of Tapirus arvernensis. The remains were recovered from clastic Pliocene sediments outcropping in the Casenuove clay quarry, about 2 km south of Empoli, in the Lower Valdarno basin. The bone- bear ing sediments are h ighs tand Bittium reticula- rum-bearing silty sands, jus t capping a t ransgressi- ve cycle. In a more detailed view of the section, the Tapirus remains were found embedded in sedi- ments containing scat tered Bittium reticulatum shells and root traces, overlain by an Ostrea bed (Fig. 1). A sparse microfauna was found with the Tapirus bones, represented by large Ammonia bec- cari and Elphidium crispum specimens, and ostra- cods. The absence of brackish water-dwellers is sugges t ive of a del taic i n t e r d i s t r i b u t a r y bay connected with the open sea and passing to a coas- tal subaereal plain with caliche paleosoils and pul- monate gastropods (Dominici et al. 1995). For fur- t he r details on the sequence, the reader should refer to Dominici et al. (1995).

F rom the characters of the sequence one can infer t ha t the skeletal remains were lying at the base of

the regressive cycle whose climax is dated to the Middle Pliocene in Tuscany. I t is therefore presu- mable tha t the tapi r skeleton s traddles the t ransi- t ion from the Ear ly to the Middle Pliocene (Domi- nici et al. 1995).

NOTES ON THE PRESENT-DAY TAPIRS

Presently, the genus Tapirus is represented by four different species, th ree of which live in Centra l and Southern America and one in South-East Asia. The weight of the individuals general ly ranges around 200 and 300 kg and usual ly females exceed males in size (Grzimek 1976).

Soli tary animals, they exclusively live in woodlands with hot and humid cl imate in proximity of rivers, swamps and marshes. The diet especially includes roots, acquatic plants and other tender vegetables.

Due to the i r primit ive anatomical features, ex tan t tapirs can be considered living fossils because thei r main anatomical s t ruc tures were fully developed during the Miocene. The dimensions and some skull t ra i ts are the only noticeable differences. The Asian (T indicus) and Baird (T bairdi) tapirs, the

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FIGURE I - Stratigraphic position of the tapir skeletal remains in the local Pliocene marine sequence (modified from Dominici et al. 1995). Position stratigraphique des restes squelettiques du tapir dans la succession marine du Plioc~ne locale (modifid par Dominici et al. 1995).

lat ter distr ibuted in Central and Southern America, are larger than the other two species (T terrestris and T pinchaque). The skull of T bairdi is characterized by having an ossified nasal sep- turn, while the more common T terrestris has a steep forehead and a well developed sagittal crest (Rustioni 1992a). In the skull of T indicus the occi- pital condyles are projected well beyond the occipi- tal profile, the fronto-parietal structure is steeper than that of other living tapirs and the dorsal pro- file is straight and not inclined forwards as it is in the other species.

In the genus Tapirus, the teeth and the other cha- racters are fairly similar among all the different species. The dentition is complete and the lateral teeth are low crowned. The third upper incisors are more developed than the upper and lower canines. The premolars are molarized. The only advanced feature is the shortening of the nasal bones. The nasal fossae are consequently extended backward which corresponds to the developement of the short and flexible proboscis. The limbs are short and stoc- ky, built with four digits in the manus and three in the pes. The third digit is more developed than the others (Grass~ 1955).

THE GENUS TAPIRUS IN E U R O P E

The genus Tapirus L. appears in Europe during the Middle Miocene. In the Middle and Late Miocene, the genus dispersed widely as testified by its occur- rence in several Western European sites. In the Late Miocene localities of Western Europe, three different species were described: Tapirus priscus, Tapirus antiquus and Tapiriscus pannonicus (GuE- RIN & EISENMANN, 1994). Nevertheless, only the first species mentioned is well known. In fact, T priscus was found in about fifteen European sites and its anatomical characters are very similar to those of

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FIGURE 2 - Italian fossiliferous localities with tapir remains: the site studied in the present paper is reported with number 12 (modified from Rustioni 1992). Les gisements fossili]~res italiens avec des restes de tapir: le site dtudid dans ce travail est dEsigng par le nombre 12 (modifiE par Rustioni 1992a).

Tapirus arvernensis (Gul~RIN • EISENMANN, 1994). The latter appeared and dispersed in Western Europe during the Pliocene as testified by the remains recovered in the fossiliferous sites of Fran- ce, Italy, Germany, The Netherlands and the Slova- kia Republic (Rustioni 1992a, b). The species Tapi- rus arvernensis was established by Croizet and Jobert in 1828 on fragmental mandibles and some isolated teeth of an adult and a juvenile individual recovered from the Pliocene levels of Les Etouaires in France. It was smaller and more slenderly built than the present-day and extinct species (Rustioni 1992a). Nevertheless in its cranial characters, T arvernensis clearly recalls T indicus. For this Rus- tioni (1992a) postulated that the European and Asian lineages are offsprings from a common Miocene stock.

In Northern and Central Italy, 13 Pliocene sites with tapir remains are known (Fig. 2). Tapirus arvernensis definitively disappeared from Europe during the Late Pliocene at the time of the transi- tion from the Faunal Unit Tiversa to the Faunal Unit Montopoli following the Mammal biochronolo- gic scale, about 3 million years ago in time (Azzaroli et al. 1982, 1986).

TAPHONOMIC ANALYSIS AND I N F E R E N C E S

The Lower Valdarno marine Sedimentary sequence yielded Tapirus bones for the first time. The adult specimen is represented by about 55 % of the ske- leton (Fig. 3), while only three definitive upper molar germs, one unworn lower deciduous tooth, DP 2 or DP3, and very few fragments of postcranial bones of the juvenile were preserved. Unfortu- nately, the excavation of a ditch in the proximity of

471

FIGURE 3 - Representat ion (in grey) of the preserved bones of the prime-aged adult (modified from Rustioni 1992a). Reprdsentation (en gris) des os prdservds du jeune adulte (modifid d'apr~s Rustioni 1992a).

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FIGURE 4 - a. Rose diagram of the spatial orientation of the bones, b. Bidimensional arrangement of the bones on the fossiliferous sur- face (modified from Dominici et al. 1995) and their orientation relatively of the reconstruction of the Early-Mid-Pliocene shoreline (Bartolini & Pranzini 1981). a. Rose diagramme de l'orientation spatiale des os. b. Distribution bidimensionelle des ossements sur la sur- face fossili[~re (modifig d'apr~s Dominici et al. 1995).

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FIGURE 5 - 1. Incomplete left maxillary: occlusal view. 2. Incomplete right mandible: lateral view; a, occlusal view. 3. Right radius: dor- sal view. a, left radius: distal end. 4. Complete right femur. 5. Left femur: particular of the distal end. 1. Maxillaire gauche incomplet: vue occlusale. 2. Demi-mandibule droite incomplete: vue latgrale; a, rue occlusale. 3. Radius droit: vue dorsale, a, Radius gauche: extr4- mitg distale. 4. Fdmur droit complet. 5. Fdmur gauche: d~tail de l'extrgmitd distale.

473

the remains entirely destroyed a few parts, or badly damaged others, such as the skull and the man- dibles of the adult, which were found mechanically reworked in the trench. The teeth of the older indi- vidual are slightly worn and the ossification of its bones is not so extensive as is generally observed on fully adult specimens; for this we believe that the skeleton belongs to an adult at the very beginning of its breeding age. Most of its elements, and espe- cially the diaphyses of the long bones, are partly crushed and transversely fractured by the sedi- ment burden. Despite this, the adult postcranial skeleton is fairly well preserved, although tho- roughly disarticulated. The bones were associated within a restricted area of I by 1.7 m and arranged bimodally (Fig. 4a), about half trending NW-SE and the other half NE-SW (Fig. 4b). The limited physi- cal transport suggested by these two aspects was confirmed by the relatively low value (1.15) of Behrensmeyer's (1975) tooth/vertebra ratio and by the presence of many of the bones of the Voorhies Groups I and I&II (Voorhies 1969; Behrensmeyer 1975). The energy of the transporting agent was therefore very low, the bones having been locally re- arranged.

The deltaic interdistributary bay environment, pos- tulated on the basis of the sedimentologic evidence and on the invertebrate content of the embedding deposits, is normally rich in abandoned channels. In these settings channel-fill bone assemblages, formed by accumulations of complete, autochtho- nous and unabraded skeletons, can be encountered (Behrensmeyer 1988). Although the tapir speci- mens form an isolated find, they have exactly the characteristics expected for channel-fill bone clus- ters.

The peculiar setting of the adult skeleton seems to suggest the result of a rolling of the parts of the car- cass due to the back and forth motion of the tide, as well as the action of two weak transverse currents which must have displaced the bones of the rotted tapir carcass, without however being so strong to take away the smaller and lighter parts of the ske- leton. Given the location of the specimens and their orientations with respect to the reconstructed sho- reline at the Early-Mid-Pliocene transition (Barto- lini & Pranzini 1981), one might identify the NW- SE-trending dispersing agent with the sea wave action and the other with contour currents running parallel to the Pliocene shoreline (Fig. 5).

The limb bones of the prime-age adult skeleton are dispersed but the single elements of each limb are mostly close to their original position of articula- tion. The skeleton was presumably entirely dis- membered by the action of decay and sea scaven- gers, responsible for the elimination of the soft tis- sues, and the loosen bones were successively re- arranged by the wave action and sea currents, which gave the skeletal parts their final setting before final burial.

At a closer analysis, most of the adult bones show evidence of load fracturing, although there is the suspect that some of the alterations may likely be due to improper collecting and restoration methods. There is no evidence of vertebrate carnivore activi-

ty on the bone surfaces, nor cracking by subaerial exposure; the dominant weathering stage is 0, although on both radii few slighly marked fissures can be interpreted as an initial stage 1. The teeth are also unaltered (Tab. 1). The porosities of most of the elements, as also the nutrient foramina, are not filled with sediment, a clear indication of the occur- rence of a soft tissue cover at the final inhumation. The very modest weathering detected on the radii may be suggestive of temporaneous exposures of the adult carcass short after death, a reasonable possi- bility in littoral settings, where the specimen layed, given the alternating income of the tides.

The teeth of the juvenile individual are all in the stage of germs, included the deciduous lower pre- molar. Justified by the phylogenetic relationship postulated in the previous section, we applied the same biological features of the Asian living tapir to the fossil representatives in study. We can thus pre- sume that the young individual died before the end of its weaning, and therefore within its first six to eight months of life. Since in Asian tapirs breeding occurs between May and June, the two individuals presumably died between November and February.

The biology and ethology of living Asian tapirs lead us to further considerations. Given the absence of the pelvis, the sex of the adult specimen could not be established. However, since in living tapirs cubs are reared exclusively by the females, which give birth to one or, exceptionally, to two cubs at a time, the co-existence of an adult and of a juvenile may be interpreted as a female and its cub, which pre- sumably died together for some unfortunate cir- cumstance. Moreover, females in the Asian tapir reach their sexual maturi ty at about 3-4 years of age. This can be the approximate age of death of the adult female, as its tooth-wear and stage of bone ossification apparently suggest. We can thus speculate that the carcasses belong to an unexpe- rienced female at its first breeding and to its cub.

Acknowledgements - Many thanks to Prof. Danilo Torre for his help. The authors are deeply indepted to Prof. A. Beherensmeyer and to Prof. Christiane Denys for critically revising the manus- cript and for their invaluable suggestions which contributed considerably to the improvement of the text.

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Bartolini, C., Pranzini, G., 1981. Plio-Quaternary evolution of the Arno basin drainage. Zeitschrift f~ir geomorphologie N.F. 40, 77-91.

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Grzimek, B., 1976. Mammiferi. In: Vita degli animali. Bramante (Eds), 13, 19-72.

Gu~rin, C., Eisenmann, V., 1994. Les tapirs (Mammalia, Perisso- dactyla) du Miocene sup6rieur d'Europe occidentale. Geobios 27 (1), 113-127.

Rustioni, M., 1992a. On Pliocene tapirs from France and Italy. Bollettino della Societ~ paleontologica italiana 31 (3), 269- 294.

Rustioni, M., 1992b. Tapirus arvernensis CROIZET • JOBERT, 1828 del Valdarno superiore con osservazioni sui tapiri pliocenici dell' Europa centro-occidentale. Quaderni di Museo S. natu- rale di Livorno 12, 1-12.

Voohries, M., 1969. Taphonomy and population dynamics of an early Pliocene vertebrate fauna, Knox County, Nebraska. University of Wyoming Contributions to Geology, Sp. pap., 1.

M. RUSTIONI & P, MAZZA Museum of Natural History

Section of Geology and Paleontology University of Florence

Via La Pira, 4 1-50121, Florence