Journal Article•
Clarazia and Hescheleria: A re-investigation of two problematical reptiles from the Middle Triassic of Monte San Giorgio (Switzerland)
About: This article is published in Palaeontographica Abteilung A-palaozoologie-stratigraphie.The article was published on 1987-01-01 and is currently open access. It has received 26 citations till now. The article focuses on the topics: Clarazia.
Citations
More filters
TL;DR: Skull structure, and jaw mechanics in particular, suggest a relatively plesiomorph position of pachypleurosaurs within the Sauropterygia, which is not carried to the degree observed in other sauropterygians.
Abstract: Pachypleurosaur material from the Middle Triassic `Grenzbitumen'-horizon (Anis-Ladin boundary) of Monte San Giorgio, Kanton Tessin, Switzerland, is described as a new genus and species, Serpianosaurus mirigiolensis. A detailed morphological description is followed by a quantitative analysis. The taxon differs from other pachypleurosaurids primarily by its relatively large skull and its straight lower jaw. Rib pachyostosis is absent. In most characters the taxon remains plesiomorphous with respect to other pachypleurosaurs from the Middle Triassic deposits of Monte San Giorgio, which accords well with its early stratigraphic occurrence at that locality. Sexual dimorphism is expressed by the size and shape of the humerus. A cladistic analysis shows the Pachypleurosauridae to constitute the sistergroup of all other Sauropterygia. The Sauropterygia and the Placodontia together form a monophyletic group, the Euryapsida, which is subordinated to the Diapsida and to the Neodiapsida, but which is classifed outside the archosauromorph-lepidosauromorph dichotomy within the Neodiapsida. A concluding paragraph discusses the status of the pachypleurosaurs within the Sauropterygia. Skull structure, and jaw mechanics in particular, suggest a relatively plesiomorph position of pachypleurosaurs within the Sauropterygia. Their adaptation to an aquatic mode of life was not carried to the degree observed in other sauropterygians, and the ability for rapid and deep dives seems to have been limited by middle-ear structure.
104 citations
TL;DR: The distribution of Mesozoic marine reptile clades exhibit a cosmopolitan, or at least pandemic, distribution very early in their evolutionary history, and the acquisition of morphological adaptations to a fully aquatic life, combined to special thermophysiological characteristics, are probably responsible for these animals to become efficient long-distance open-marine cruisers as mentioned in this paper.
102 citations
TL;DR: High-resolution computed tomography and a novel character/taxon matrix are used to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles.
Abstract: Transitional fossils informing the origin of turtles are among the most sought-after discoveries in palaeontology. Despite strong genomic evidence indicating that turtles evolved from within the diapsid radiation (which includes all other living reptiles), evidence of the inferred transformation between an ancestral turtle with an open, diapsid skull to the closed, anapsid condition of modern turtles remains elusive. Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles. Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence. Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution, thus fortifying a 40-million-year extension to the turtle stem and moving the ecological context of its origin back onto land. Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid. This is important because categorizing the skull based on the number of openings in the complex of dermal bone covering the adductor chamber has long held sway in amniote systematics, and still represents a common organizational scheme for teaching the evolutionary history of the group. These discoveries allow us to articulate a detailed and testable hypothesis of fenestral closure along the turtle stem. Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development.
77 citations
Dissertation•
01 Jan 1992
TL;DR: The extinction of reptiles marins coincide avec a phase of regression importante as discussed by the authors, a phase which includes a reorganisation faunique aboutit a la disparition progressive des formes littorales and a mise en place of groupes pelagiques.
Abstract: Un inventaire des reptiles marins connus du trias inferieur jusqu'au paleocene est presente: 46 familles, environ 200 genres et 400 especes ont ete recenses. Cette base de donnees inclut des commentaires sur la systematique, les extensions stratigraphiques et la distribution geographique des taxons. Les reptiles marins regroupent une mosaique de formes comprenant des groupes exclusivement marins (ichthyosaures, nothosaures, placodontes, thalattosaures, hupehsuchiens, plesiosaures, pliosaures) aussi bien que des groupes encore connus actuellement et qui incluent des representants continentaux (crocodiles, lezards, serpents, tortues). Le registre fossile des reptiles marins a ete ponctue par deux extinctions en masse: la transition ladinien-carnien (64% des familles) affecte preferentiellement les formes infeodees au milieu cotier. Cette extinction coincide avec une phase de regression importante. Durant le trias superieur, une reorganisation faunique aboutit a la disparition progressive des formes littorales et a la mise en place de groupes pelagiques. Durant la crise maastrichtien-danien (36% des familles), les formes pelagiques de grande taille, a savoir les mosasaures et les plesiosaures, sont les plus touchees et leur extinction s'inscrirait plutot dans un modele catastrophique que gradualiste. Au contraire, les pliosaures et les tortues protostegides s'eteignent alors qu'ils etaient deja sur le declin. Les survivants sont des groupes littoraux de taille moderee comme les crocodiles, serpents et certaines tortues qui auraient pu trouver refuge en milieu dulcaquicole. Une rupture de la chaine alimentaire tributaire du phytoplancton est proposee comme scenario d'extinction pour les formes pelagiques
64 citations
TL;DR: The anatomy of the thalattosauriform reptile Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio is redescribed in this paper, which supports the biogeographic interpretation of trans-Pacific relationships and a re-invasion of Tethyan areas.
Abstract: The anatomy of the thalattosauriform reptile Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio is redescribed. Important anatomical features are the plesiomorphic braincase, the unique fronto-lacrimal contact, the absence of a previously described thyroid fenestra, and significant intraspecific variation in the carpus. An analysis of thalattosaur ingroup relationships reveals that Endennasaurus and the monophyletic Askeptosaurus and Anshunsaurus are the sister group to all other thalattosaurs, whereas the Monte San Giorgio taxa Clarazia and Hescheleria form the sister clade of Thalattosaurus, and the Chinese Xinpusaurus and the Californian Nectosaurus form a monophyletic group. The analysis supports the biogeographic interpretation of trans-Pacific relationships and a re-invasion of Tethyan areas.
50 citations