Michael W. Maisch

Float, explode or sink: postmortem fate of lung-breathing marine vertebrates

What happens after the death of a marine tetrapod in seawater? Palaeontologists and neontologists have claimed that large lung-breathing marine tetrapods such as ichthyosaurs had a lower density than seawater, implying that their carcasses floated at the surface after death and sank subsequently after leakage of putrefaction gases (or ‘‘carcass explosions’’). Such explosions would thus account for the skeletal disarticulation observed frequently in the fossil record. We examined the taphonomy and sedimentary environment of numerous ichthyosaur skeletons and compared them to living marine tetrapods, principally cetaceans, and measured abdominal pressures in human carcasses. Our data and a review of the literature demonstrate that carcasses sink and do not explode (and spread skeletal elements). We argue that the normally slightly negatively buoyant carcasses of ichthyosaurs would have sunk to the sea floor and risen to the surface only when they remained in shallow water above a certain temperature and at a low scavenging rate. Once surfaced, prolonged floating may have occurred and a carcass have decomposed gradually. Our conclusions are of significance to the understanding of the inclusion of carcasses of lung-breathing vertebrates in marine nutrient recycling. The postmortem fate has essential implications for the interpretation of vertebrate fossil preservation (the existence of complete, disarticulated fossil skeletons is not explained by previous hypotheses), palaeobathymetry, the physiology of modern marine lung-breathing tetrapods and their conservation, and the recovery of human bodies from seawater.

A relict basal tetrapod from Germany: first evidence of a Triassic chroniosuchian outside Russia

Chroniosuchians are basal tetrapods nesting within the paraphyletic anthracosaurs and were so far only well known from the Permian and Triassic of Russia. In this study, we present evidence for their existence in the upper Middle Triassic of Germany, based on diagnostic osteoderms and vertebrae from the Kupferzell and Vellberg localities in southern Germany. The finds are most similar to Synesuchus, a Middle Triassic bystrowianid chroniosuchian from the Northern Ural Pechora region. They demonstrate that by Middle Triassic time, chroniosuchians were much more widespread than previously thought.

A new Middle Jurassic xinjiangchelyid turtle (Testudines; Eucryptodira) from China (Xinjiang, Junggar Basin)

Abstract A new Middle Jurassic xinjiangchelyid turtle from China, Xinjiangchelys chowi sp. nov., is described from the Toutunhe Formation of the southern Junggar Basin, southwest of Urumchi (NW China). The material consists of a nearly complete carapace and the right hypoplastron. It shows important autapomorphies of the family Xinjiangchelyidae and the genus Xinjiangchelys: first neural larger than second, anterior peripherals guttered, posterior peripherals expanded, a reduced first thoracic rib, and lateral pegs of the bridge of the plastron. It is distinguished from all other species of Xinjiangchelys by the following autapomorphies: a first costal rib with free rib end, at least two anterolateral peripheral fontanelles of the carapace, a thin plastron with large lateral fontanelles, and a median hypoplastral suture with strong pegs. These features indicate that X. chowi is the most derived xinjiangchelyid turtle hitherto known. Together with X. tianshanensis, this is the oldest xinjiangchelyid turtle known so far. Therefore, a long ghost lineage must be claimed for the Xinjiangchelyidae.

A new species of Xinpusaurus (Thalattosauria) from the Upper Triassic of China

Abstract A new species of Xinpusaurus Yin in Yin et al., 2000 (Thalattosauria, Thalattosauridae), is described from the Wayao Member of the Falang Formation (Tuvalian, Carnian, Upper Triassic) of Guanling County in Guizhou, southwestern China. It is the third thalattosaur species known from the Guanling faunal assemblage of marine reptiles. The type and only specimen consists of an entire skeleton, including a complete skull. It differs from the type species, X. suni, by its smaller adult size, the larger nasal, the more slender angular and low retroarticular process, the shape of the cervical neural spines, the number of presacral vertebrae, the large size of the scapula, the shape of the radius, the presence of a well ossified carpus, the more slender femur, the smaller hindfin, the presence of a complete row of distal tarsal ossifications, and the proportions of the metatarsals. It is consequently referred to a new species, Xinpusaurus kohi. A new analysis of thalattosaur interrelationships based on 30 cranial and postcranial characters corroborates a sister-group relationship between Xinpusaurus and Nectosaurus from the Carnian of California.

The Liassic ichthyosaurStenopterygius cf.quadriscissus from the lower Toarcian of Dobbertin (northeastern Germany) and some considerations on lower Toarcian marine reptile palaeobiogeography

An incomplete skull of the lower Toarcian ichthyosaurStenopterygius cf.quadriscissus is described from the lower Toarcian of Dobbertin (Mecklenburg, northeastern Germany). It represents both the northeasternmost occurrence of this ichthyosaur genus and the first diagnostic specimen from East Germany. It therefore extends the palaeobiogeographic range ofStenopterygius considerably and demonstrates that this ichthyosaur also inhabited the Germanic Basin east of the Rhenish Massif by Early Jurassic times. A palaeobiogeographical pattern is evident within the genusStenopterygius, with the ubiquitous speciesS. longifrons andS. hauffianus on one hand, andS. megalorhinus andS. quadriscissus on the other hand, which appear not to have ranged northwest of the London-Brabant Massif. It is suggested that, whereas the Rhenish Massif was not an effective barrier for dispersal of ichthyosaurs in Western Europe during early Toarcian times, the London-Brabant Massif played a rather significant role, as is also shown by the fossil record of other marine reptile groups. A provincialism of early Toarcian marine reptiles is suggested for Western Europe, with a northwestern province which contains the British occurrences, an intermediate, Subgermanic province in France and the Benelux countries, and a southeastern province in the Germanic Basin. The British and Germanic provinces are each characterized by a typical assemblage of ichthyosaurs, plesiosaurs, and marine crocodiles, wheres the intermediate Subgermanic region shows an intermingling of faunal elements.KurzfassungEin unvollständiger Schädel des untertoarcischen IchthyosauriersStenopterygius cf.quadriscissus wird von Dobbertin (Mecklenburg, Nordostdeutschland) beschrieben. Es handelt sich um das bisher nordöstlichste Vorkommen der Gattung und das erste diagnostische Exemplar aus Ostdeutschland. Es erweitert die paläobiogeographische Verbreitung vonStenopterygius beachtlich und zeigt, dass diese Ichthyosauriergattung im Unterjura das Germanische Becken auch östlich des Rheinischen Massivs bewohnte. Die paläobiogeographische Verbreitung vonStenopterygius lässt ein deutliches Muster erkennen, mit den weitverbreiteten ArtenS. longifrons undS. hauffianus einerseits undS. megalorhinus undS. quadriscissus andererseits, die anscheinend nordwestlich des London-Brabanter Massivs nicht vorkamen. Es deutet sich an, dass während das Rheinische Massiv für diese Tiere keine effektive paläobiogeographische Barriere darstellte, das London-Brabanter Massiv die Verbreitung der untertoarcischen Ichthyosaurier stark beeinflusste. Dies bestätigen auch Befunde bei anderen Meeresreptilien. Es ist daher ein Provinzialismus bei den untertoarcischen Meeressauriern Westeuropas festzustellen. Klar können eine nordwestliche, britische Provinz (England), eine intermediäre „subgermanische“ Provinz, die Frankreich und den Benelux umfasst, und eine südöstliche Provinz im Germanischen Becken unterschieden werden. Die britischen und germanischen Provinzen weisen jeweils charakteristische exklusive Arten von Ichthyosauriern, Plesiosauriern und Meereskrokodilen auf, während die intermediäre Provinz eine stärkere Durchmischung zeigt.

A New Basal Lystrosaurid Dicynodont from the Upper Permian of South Africa

A new genus and species of late Permian dicynodont, Kwazulusaurus shakai, is described on the basis of a complete skull from the late Permian Dicynodon Assemblage Zone of the South African Beaufort Group. It is an advanced form which shows characters, such as the shape of the snout and the loss of the ectopterygoid, that link it to the early Triassic genus Lystrosaurus. Kwazulusaurus represents the most basal member of the lystrosaurian lineage. The phylogeny of progressive pristerodontian dicynodonts is discussed. It appears possible that the Kannemeyeriiformes and Lystrosauridae do not form a monophylum, as previously assumed. Instead a sister-group relationship between lystrosaurids and dicynodontids plus kannemeyeriiforms is suggested.

The first haramiyoid mammal from Asia

A lower molar of a haramiyoid mammal is described from the Toutunhe Formation of Liuhuanggou near Urumqi in the southern Junggar Basin, Xinjiang, China. It is referred to Eleutherodon sp., otherwise exclusively known from the Upper Bathonian of England. It is the first record of the order Haramiyida from Asia and the first Mesozoic mammal described from the southern Junggar Basin. Apart from the English specimens of Eleutherodon and Staffia from the Upper Jurassic of East Africa, it is the geologically youngest haramiyoid known. It is the first vertebrate taxon from the Toutunhe Formation that is probably not endemic and lends some support to the dating of the Formation as late Middle Jurassic, probably Bathonian.

THE CRANIAL OSTEOLOGY OF THE ICHTHYOSAURLEPTONECTESCF. TENUIROSTRISFROM THE LOWER JURASSIC OF ENGLAND

Abstract For the first time, a three-dimensionally preserved skull of the Lower Jurassic leptonectid ichthyosaur Leptonectes cf. tenuirostris is described. The specimen reveals a wealth of new data on the cranial anatomy of basal leptonectid neoichthyosaurs. The osteology of the skull roof differs fundamentally from other well-known post-Triassic ichthyosaurs and is highly autapomorphic. The structure of the sclerotic ring, which is well preserved in situ, is described and it appears plausible that L. cf. tenuirostris was capable of stereoscopic vision. Inadequate description makes comparison to other leptonectids difficult. It can be demonstrated, however, that L. cf. tenuirostris is most similar to L. tenuirostris among known leptonectids. It is fundamentally different from the Upper Liassic Eurhinosaurus longirostris in the osteology of the skull roof and the size and orientation of the major skull openings, making generic distinction of these two species a necessity. At the moment, no autapomorphies are known of the genus Leptonectes, which therefore must be considered as a metataxon that comprises basal leptonectids from the Lower to Middle Liassic.

Cranial osteology of the sauropterygian Plesiosaurus brachypterygius from the Lower Toarcian of Germany

An osteological re-study of the holotype skull of Plesiosaurus brachypterygius leads to a correction of several inaccuracies and misidentifications of the original description by von Huene and reveals additional facts on the cranial anatomy of this plesiosaur. Comparison with the type species, Plesiosaurus dolichodeirus, from the Lower Lias of England shows considerable differences in many parts of the cranial skeleton, even though the two species are generally so similar that their inclusion in the same genus proposed by von Huene, and agreed with by all subsequent authors, can be supported. Plesiosaurus brachypterygius is provisionally considered as a valid species distinguishable from the contemporaneous Plesiosaurus guilelmiimperatoris by its much shorter limbs, a difference that cannot be explained by ontogenetic variation as proposed by Storrs. Plesiosaurus brachypterygius was probably an ichthyophagous form that occurred rarely in the Posidonienschiefer fauna.

A NEW TRITYLODONTID FROM THE UPPER JURASSIC SHISHUGOU FORMATION OF THE JUNGGAR BASIN (XINJIANG, NW CHINA)

Abstract A new tritylodontid cynodont, Bienotheroides ultimus sp. nov., is described from the Upper Jurassic Shishugou Formation of Jiangjunmiao in the northeastern Junggar Basin of Xinjiang (NW China). The type consists of a partial skeleton, including teeth, a partial skull, and a considerable portion of the postcranium. It is identifiable as Bienotheroides because of the structure of the upper molars and the characteristically deep zygomatic arch. It is distinguished from Bienotheroides zigongensis from the Middle Jurassic of the Junggar Basin particularly by characters of the forelimb, including a humerus that shows little torsion of the proximal and distal ends. Bienotheroides ultimus is the last of the Chinese tritylodontids known so far, and apart from Xenocretosuchus from the Lower Cretaceous of Russia and an unnamed form from the Lower Cretaceous of Japan, it is the last non-mammalian therapsid known in the entire fossil record.