N. Jb. Geol. Paläont. Mh. 2004 (2) 87-94 Stuttgart, Februar 2004

Triassic limulids from Madagascar - missing links in the distribution of Mesozoic Limulacea

. Norbert Hauschke, Halle (Saale), Volker Wilde, Frankfurt am Main, and Carsten Brauckmann, Clausthal-Zellerfeld

With 3 figures

HAUSCHKE, N., WILDE, V. & BRAUCKMANN, C. (2004): Triassic limulids from Mada­gascar - missing links in the distribution of Mesozoic Limulacea. - N. Jb. Geol. Paläont. Mh., 2004: 87- 94; Stuttgart.

Abstract: Two specimens of a Lower Triassic limulacean from the Ankitokazo Basin, Madagascar, are described and tentatively determined as cf. Limulitella sp. This is the second record of the group from the Mesozoic of Gondwana outside of Australia. As such, the specimens discussed are of particular importance in bridging the remaining gap in knowledge of limulid distribution in Gondwana during the Mesozoic.

Zusammenfassung: Zwei Fundstücke einer bisher nicht näher bestimmbaren unter­triassischen Art der Limulacea aus dem Ankitokazo-Becken von Madagaskar werden vorgestellt. Sie werden vorbehaltlich als cf. Limulitella sp. bestimmt. Es ist dies der zweite Nachweis dieser Gruppe aus mesozoischen Schichten in Gondwana außerhalb Australiens. Die entsprechenden Funde sind von besonderer Bedeutung, da sie die weiter bestehende große Überlieferungslücke mesozoischer Limulacea in weiten Teilen von Gondwana überbrücken.

Introduction

The Xiphosura are an ancient subclass of the Arthropoda, which attained considerable diversity during Palaeozoic times. Subsequent to the Permian perioc\, they have been restricted to the superfamily Limulacea ("limulids") of the sub order Limulina (BERG STRÖM 1975; ANDERS ON & SELDEN 1997).

0028-3630/04/2004-0087 $ 2.00 ©.2004 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart

88 N. Hauschke et al.

The fossil record of Palaeozoic and Mesozoic limulids shows a widespread distribution in the present Northern Hemisphere. With the exception of possible traces from the Permo-Carboniferous of South Africa (ANDERS ON 1975), the only Southern Hemisphere records (Fig. 1) come from Australia (Permian: EWINGTON et al. 1989; Triassic: RIEK 1955, 1968; PICKETT 1984; Cretaceous: RIEK & GILL 1971). But, a further record from the Lower Creta­ceous of Lebanon (WOODWARD 1879) is also situated on a fragment of Gondwana. Therefore, any palaeogeographic studies on the distribution of limulids must include Gondwana. Following on from the work ofHAUSCHKE & WILDE (1991), their absence in the Palaeozoic and Mesozoic of many parts of Gondwana would be better interpreted as a lack of information, rather than definite absence from suitable habitats. This viewpoint is strongly supported by the discovery of the new specimens from the Triassic of Madagascar, which form the subject ofthis paper.

The Lower Triassic of Madagascar is famous for the fossil-bearing concretionary nodules it contains (BESAIRIE 1971: 27ft). In particular, the well-preserved fish fossils are sold on a commercial basis and are relatively common. Recently, the Institut für Geologie und Paläontologie, TU Claus­thaI, Germany, acquired a single specimen of a limulid from the locality "Ankitokazo, Madagascar" by purchase (specimen no. TUCP Ch 5, "Claus­thai specimen"). A second specimen from Madagascar was purchased by the Museo di Storia Naturale at Milan, Italy (Specimen No. I 11170 a, b; "Milan specimen"). The Milan specimen is not accompanied by exact information of the collection locality.

Preservation

Both fossils are preserved within siderite concretions. The "Clausthai specimen" is preserved as an internal mould in dorsal aspect only. It is almost complete, only lacking the distal end of the telson. The prosoma, opisthosoma and telson remained articulated. The right-hand side of the anterior margin of the prosoma is broken, revealing a section of the doublure, whilst the corresponding area on the left-hand side is obscured by sediment. The entire surface of the fossil is roughly corroded and densely encrusted by smalI, spirally enrolled Spirorbis-like worm tubes. Conse­quently, this obscures the finer morphological details of the fossil, only allowing the gross morphology such as overall outline, prosomal and opisthosomal axis, cardiac lobe and the course of the ophthalmic ridges to be distinguished.

The "Milan specimen" is less well-preserved but occurs as both internal and external moulds. Again, the main tagmata of the fossil are still arti­culated, but the marginal parts of the prosoma and the majority of the telson

Triassie limulids fram Madagascar 89

A

Fig. 1. Geographical distribution of fossil Limulacea in Gondwana (maps modified from HAUSCHKE & WILDE 1991). - A. Records for Permo-Carboniferous to Triassie times, plotted on a reconstruction for the Permian. B. Record for early Cretaceous time -+ Permocarboniferous possible traces of limulids, South Africa; T late Permian, Tasmania; ... Lower Triassie, Madagascar; • Middle Triassie, Australia; • Lower Cretaceous, Lebanon and Australia.

are absent as they were not incorporated within the concretion. Just as in the "Clausthai specimen", the surface is strongly corroded and encrusted by Spirorbis-like worm tubes.

The encrusting epibiota may have some palaeoecological value. Following ANDERS ON (pers. comm.), there are only a few examples ofsolitary Spirorbis on xiphosuran fossils known. Commonly, the digging and burrowing behaviour coupled with the moulting of the exoskeleton of xiphosurans prevents corrosion or encrustation ofthe shell. Thus it may be that

(1) the carcasses (or exuviae) had a long residence time on the sediment surface after death but before burial and subsequent siderite concretion formation. This would have allowed for colonization of the exoskeletons by Spirorbis, or

90 N. Hauschke et al.

(2) the individuals were relatively old aged and had not moulted prior to death,or (3) the animals did not burrow like other xiphosurans.

Description

Clausthal speeimen: The prosoma is semieireular in outline, laterally eontinued into broad-triangular genal angles. A more or less straight hinge line forms the posterior margin of the inter-ophthalmie region between the genal angles. Due to the style of preservation, it ean not be determined whether the ophthalmie ridges originally met anteriorly. On both of the ophthalmie ridges there are bulges approximately one half of the median length ofthe prosoma, indieating the likely position ofthe eompound eyes. A eardiae lobe ean clearly be distinguished in the middle of the inter-oph­thalmie region. With the exeeption of minor parts of the doublure at the lateral margins, features of the ventral side of the earapaee are missing.

The opisthosoma is rounded-trapezoidal in outline, with a eentral part delimited laterally by areuate ridges diverging anteriorly. Due to pre­servation, the lateral margin of the earapace is obseured, and there is no evidenee of any spines. A rhaehis is well developed in eontinuation with the eardiae lobe. In the posterior and middle part of this rhaehis a median keel is clearly indieated. The forward eontinuation on the anterior part of the rhaehis and on the eardiae lobe is unclear. The axial furrows laterally enclosing the rhaehis run more or less parallel to eaeh other. They bear pits, some of them possibly eorresponding to apodemata. Po steriorly, the opisthosoma is poorly preserved, but the lateral parts apparently eontinue into blunt spines, enclosing the proximal portion of the telson. The telson itself was triangular in eross-seetion and is ineompletely preserved. .

Measurements (mm): totallength = 85; length ofprosoma = 31; length of opistho­soma = 34; length of telson = 20; total breadth of prosoma = 70; breadth of opistho­soma (ant.) 40.

Milan speeimen: The prosoma shows no details exeept for the posterior margin of one of the genal angles. Even the hinge line between prosoma and opisthosoma is obseured by the unusual preservational state. The same is true for most of the opisthosoma, only reeognizable by its eharaeteristic shape. The only detail of the margin whieh ean be distinguished is one of the postero-Iateral spines. The telson is triangular in eross-seetion. A faint median elevation on prosoma and opisthosoma on one of the halves may indieate the position of the eardiae lobe and rhaehis. Within the opisthosomal region of the same half three pairs of remarkable struetures are represented

Triassie limulids tram Madagascar 91

Figs. 2-3. cf. Limulitella sp.; Lower Triassic, Madagascar. 2. "Clausthai specirnen", no. TUCP Ch 5; locality: Ankitokazo, internal rnould; total length = 80 rnm. 3A-B. "Milan specirnen", no. I 11170 a-b, without exact information on the locality; totallength = 63 rnrn. A. Internal rnould. B. External rnould. - Scale bar = 10 mm.

92 N. Hauschke et al.

by succeeding depressions close to both of the lateral margins. They are characterized by a fine pattern of narrow grooves curving inwards. Their position and arrangement suggest that they may represent the remains of the respiratory book gill lamellae.

Measurements (mm): preserved length = 63, estimated length of prosoma = 27; estimated length of opisthosoma = 29; further exact measurements impossible.

Systematics

Class Order Superfamily

Family Genus

Merostomata DANA, 1852 Xiphosurida LATREILLE, 1802 Limulacea ZITTEL, 1885 (nom. trans!. RAYMOND, 1944, ex Limulidae ZITTEL, 1885) ?Paleolimulidae RAYMOND, 1944 ?Limulitella ST0RMER, 1952

cf. Limulitella sp. Figs.2-3

Discussion: Overall shape and an exoskeleton consisting of prosoma, opisthosoma and telson still in articulation characterize both specimens as limulids. Any further systematic assignment is restricted due to the poor state of preservation. Most distinctive is the prosoma which is laterally con­tinuous into broad genal angles forming an acute angle with the antero­lateral margin of the completely fused opisthosoma. Such a transition between the prosoma and opisthosoma is most commonly encountered in the Limulitella-type situation sensu HAUSCHKE & WILDE (1987: Fig. 1) and may suggest affinities of the fossils from Madagascar to the genus Limulitella ST0RMER, 1952. This is further supported by a comparatively broad lateral margin of the opisthosoma (GALL 1971). However, adefinite comparison with the genus is impossible prior to arevision of the type species of Limulitella bronni (see SCHIMPER 1853).

Palaeobiogeographic implications

The distribution of fossil and modern Limulacea was most recently summa­rized by HAUSCHKE & WILDE (1987, 1991), and the possible relationship between size of specimens and their occurrence in marine versus non-marine strata were discussed. The new limulids from Madagascar do not contribute to the current discussion, as there is no detailed information available on the exact locality.

Triassie Iimulids fram Madagascar 93

Most of the known fossil limulids from the present northem hemisphere have been described from Europe, with few additional records from North America, Siberia, and Lebanon. This is an indication not only for their presence in Gondwana, but also fot a more or less worldwide distribution during Mesozoic times. The specimens from the Lower Triassie of Mada­gascar are especially important in bridging the still existing gap within Gondwana.

Acknowledgments

We are grateful to the Museo Civieo di Storia Naturale di Milano for providing the Milan speeimen, to Dipl.-Geol. TORSTEN WAPPLER and Dr. ELKE GRÖNlNG (Clausthal-Zellerfeld, Germany) for preparing the figures, and in partieular to Dr. LYALL 1. ANDERSON (NMS, Edinburgh, Seotland) for various he1pful suggestions, eritieal reading and improving the manuscript. Dr. O. APPERT, Werthenstein (CH), kindly provided information on the geology ofthe fossil-bearing strata.

References

ANDERSON, A. M. (1975): Limulid trackways in the Late Palaeozoic Ecca sediments and their paleoenvironmental signifieanee. - South African I Sei., 71: 249-251.

ANoERSON, L. 1. & SELDEN, P. A. (1997): Opisthosomal fusion and phylogeny of Palaeozoic Xiphosura. - Lethaia, 30: 19-31.

BERGSTRÖM, I (1975): Functional morphology and evolution of xiphosurids. -Fossils and Strata, 4: 291-305.

BESAIRJE, H. (1971): Geologie de Madagascar. 1. Les terrains s6dimentaires. - 463 pp.; Tananarive.

EWINGTON, D. L., CLARKE, M. I & BANKS, M. R. (1989): A late Permian fossil horseshoe crab (Paleolimulus: Xiphosura) from Poatina, Great Western Tiers, Tasmania. - Pap. Proc. Roy. Soc. Tasmania, 123: 127-l31.

GALL, I-C. (1971): Faunes et paysages du gres a Voltzia du nord des Vosges. Essai paleoecologique sur le Buntsandstein superieur. - Mem. Servo Carte Geol. Alsace Lorraine, 34: 318 pp.

HAUSCHKE, N. & WILDE, V. (1987): Paleolimulus fuchsbergensis n. sp. (Xiphosura, Merostomata) aus der oberen Trias von Nordwestdeutschland, mit einer Übersicht zur Systematik und Verbreitung rezenter Limuliden. - Paläont. Z., 61: 87-108.

HAUSCHKE, N. & WILDE, V. (1991): Zur Verbreitung und Ökologie mesozoischer Limuliden. - N. Ib. Geol. Paläont. Abh., 183: 391-411.

PICKETT, I W. (1984): A new freshwater Iimuloid from the Middle Triassic ofNew South Wales. - Palaeontology, 27: 609-621.

RrEK, E. F. (1955): A new xiphosuran from the Triassic sediments at Brookvale, New South Wales. - Rec. Austral. Mus. 23: 181-282.

RrEK, E. F. (1968): Re-examination of two arthropod species from the Triassic of Brookvale, New South Wales. - Rec. Austral. Mus., 27: 3l3-321.

94 N. Hauschke et al.

RrnK, E. F. & GILL, E. D. (1971): A new xiphosuran genus from Lower Cretaceous freshwater sediments at Koonwarra, Victoria, Australia. - Palaeontology, 14: 206-210.

SCHlMPER, W P. (1853): Paleontologica alsatica ou fragments paleontologiques des differents terrains stratifies qui se rencontrent en Alsace. - Mem. Soc. Mus. Hist. Nat. Strasbourg, 4 (2/3): 1-10.

WOODWARD, H. (1879): Contributions to the knowledge offossil Crustacea. - Quart. J. Geol. Soc. London, 35: 549-555.

Received: February 28, 2003. Accepted by the Stuttgart editor: March 10,2003.

Addresses of the authors:

Dr. NORBERT HAUSCHKE, Martin-Luther-Universität Halle-Wittenberg, Institut für Geologische Wissenschaften und Geiseltalmuseum, Domstraße 5, D-06108 Halle (Saale), PD Dr. VOLKER WILDE, Forschungsinstitut Senckenberg, Sektion Paläo­botanik, Senckenberganlage 25, D-60325 Frankfurt am Main, Prof. Dr. CARSTEN BRAUCKMANN, Institut für Geologie und Paläontologie, TU Clausthal, Leibnizstraße 10, D-38678 Clausthal-Zellerfeld.