August 2020
Vol 43-1
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Print ISSN: 0031-0247
Online ISSN: 2274-0333
Frequency: biannual

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Palaeovertebrata Vol 43-1:August 2020

Table of contents


The skull of Tetraceratops insignis (Synapsida, Sphenacodontia)
Frederik Spindler
Keywords: cranium; pelycosaur; Permian; therapsid origins

doi: 10.18563/pv.43.1.e1

    Tetraceratops insignis is known from a single, crushed skull from the Lower Permian of Texas. Its unique proportions and osteological details gained central meaning in the question of the origins of Therapsida since this early synapsid has been determined as the oldest and less derived therapsid. Apart from Tetraceratops, the ‘mammal-like’ Therapsida and their sister, the pelycosaur-grade Sphenacodontidae, are separated by one of the longest ghost lineages in tetrapod fossil record. However, the minor, though well justified critique faced insistent publication regarding the therapsid hypothesis. A carefull re-evaluation of the holotypic skull reveals that therapsid traits cannot be supported, including a rejection of the formerly supposed adductor shelf in the temporal fenestra. Increased understanding of ‘pelycosaur’ character variation underlines a haptodontine-grade or, less likely, sphenacodontid position for Tetraceratops

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New material of “Eurysternidae” (Thalassochelydia, Pan-Cryptodira) from the Kimmeridgian of the Swiss Jura Mountains
Christian Püntener, Jérémy Anquetin and Jean-Paul Billon-Bruyat
Keywords: Eurysternidae; Late Jurassic; morphology; Switzerland; Testudines; Thalassochelydia

doi: 10.18563/pv.43.1.e2

    The region of Porrentruy (Swiss Jura Mountains) is known for its rich and diverse assemblage of Late Jurassic coastal marine turtles (Thalassochelydia). Dominated by the “Plesiochelyidae”, this assemblage also includes representatives of the two other thalassochelydian groups, the “Thalassemydidae” and “Eurysternidae.” In this study, we present new shell-based material from Porrentruy referable to eurysternids. One specimen represents a juvenile individual or a relatively small taxon, and is notably characterized by a well fenestrated plastron exhibiting a wider than long central plastral fontanelle. Two other specimens are much larger and possibly represent the largest eurysternids known to date. The fourth specimen is characterized by a unique plastral morphology otherwise only known in very small juveniles. This is the first time this unique plastral morphology is known to persist in an adult or subadult. The new material described herein represents at least three distinct taxa, all of them probably new. However, we refrain from naming new species based on this incomplete material in order to avoid adding confusion to an already complex taxonomical situation. This study provides new insights into the great diversity of eurysternids during the Late Jurassic. 

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Short Communications

Difficulties with the origin of dinosaurs: a comment on the current debate
Matthew G. Baron
Keywords: dinosaur anatomy; dinosaur evolution; Ornithoscelida; palaeobiogeography; Triassic Period

doi: 10.18563/pv.43.1.e3

    The origin and early evolutionary history of the dinosaurs is a topic that has recently gone through a period of renewed interest and academic debate. For 130 years, one way of classifying the various dinosaur subgroups persisted as the accepted model, with increasing levels of research in the past quarter-century also providing evidence for the hypothesis that dinosaur origination occurred in the Southern Hemisphere, particularly in South America. It is, after all, from within the Late Triassic strata of countries like Argentina and Brazil that we get some of the very best early dinosaur specimens; many of these specimens are the earliest known representatives of some of the major dinosaur subgroups, such as the theropods and sauropodomorphs. However, some recent analyses have brought about a shift in terms of what is currently accepted and what is now disputed regarding the origin of dinosaurs – the Southern Hemisphere origination hypothesis was questioned (although this was based upon observations and not with quantitative analysis techniques), as has the shape of the dinosaur tree. Responses to the new hypothesis were numerous; many further supported a Southern Hemisphere point of origin. Whilst the interrelationships between the major dinosaur clades remains to be resolved, the current data does seem to comprehensively answer the question of where the dinosaurs first originated. However, it is arguable whether the current data that is being used in such palaeobiogeographical analyses is sufficient to provide an answer to the question of where specifically the dinosaur clade first appeared. This short communication urges a degree of caution about the current consensus and what steps may need to be taken to ensure that more meaningful results are produced in the future. 

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The geologically youngest remains of an ornithocheirid pterosaur from the late Cenomanian (Late Cretaceous) of northeastern Mexico with implications on the paleogeography and extinction of Late Cretaceous ornithocheirids
Eberhard D. Frey, Wolfgang Stinnesbeck, David M. Martill, Héctor E. Rivera-Sylva and Héctor Porras Múzquiz
Keywords: Coahuila; Late Cenomanian; north-eastern Mexico; Ornithocheiridae; Pterosauria

doi: 10.18563/pv.43.1.e4

    Ornithocheirid pterosaurs were the largest of the toothed pterodactyloids and had a worldwide distribution, although their fossil record is fragmentary, with the exception of the north-eastern Brazilian Crato and Santana Formations (Aptian, ?Albian, Early Cretaceous). With Istiodactylidae, they were also the only toothed pterosaurs that survived into the Cenomanian (Late Cretaceous), becoming extinct at the end of this period. Here we report on an ornithocheirid metacapus from the Late Cenomanian laminated limestone of north-eastern Mexico discovered about 120 km north-west of Ciudad Acuña, northern Coahuila at the south banks of Rio Bravo. The specimen comprises a fragmentary distal syncarpal, a crushed but complete metacarpal IV, two fragmentary preaxial metacarpals and a possible fragmentary terminal left wing finger phalanx. It represents the geologically youngest known ornithocheirid worldwide. We suggest that ornithocheirid pterosaurs may have become extinct because of massive sea level fluctuations during the mid to late Cretaceous that may have obliterated their breeding sites on coastal plains and low lying islands. 

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