Abstract
Proterosuchidae are the most taxonomically diverse archosauromorph reptiles sampled in the immediate aftermath of the Permo-Triassic mass extinction and represent the earliest radiation of Archosauriformes (archosaurs and closely related species). Proterosuchids are potentially represented by approximately 15 nominal species collected from South Africa, China, Russia, Australia and India, but the taxonomic content of the group is currently in a state of flux because of the poor anatomic and systematic information available for several of its putative members. Here, the putative proterosuchid Tasmaniosaurus triassicus from the Lower Triassic of Hobart, Tasmania (Australia), is redescribed. The holotype and currently only known specimen includes cranial and postcranial remains and the revision of this material sheds new light on the anatomy of the animal, including new data on the cranial endocast. Several bones are re-identified or reinterpreted, contrasting with the descriptions of previous authors. The new information provided here shows that Tasmaniosaurus closely resembles the South African proterosuchid Proterosuchus, but it differed in the presence of, for example, a slightly downturned premaxilla, a shorter anterior process of maxilla, and a diamond-shaped anterior end of interclavicle. Previous claims for the presence of gut contents in the holotype of Tasmaniosaurus are considered ambiguous. The description of the cranial endocast of Tasmaniosaurus provides for the first time information about the anatomy of this region in proterosuchids. The cranial endocast preserves possibly part of the vomero-nasal ( = Jacobson’s) system laterally to the olfactory bulbs. Previous claims of the absence of the vomero-nasal organs in archosaurs, which is suggested by the extant phylogenetic bracket, are questioned because its absence in both clades of extant archosaurs seems to be directly related with the independent acquisition of a non-ground living mode of life.
Highlights
Archosauromorpha is a major group within diapsid reptiles that includes living birds and crocodilians, as well as all extinct species more closely related to these living groups than to lepidosaurs [1]
It is not until the aftermath of the Permo-Triassic mass extinction that the archosauromorph fossil record documents the presence of morphologically diverse and taxonomically abundant groups, including members of Rhynchosauria, Prolacertiformes, Proterosuchidae and Archosauria [10,11,12,13,14,15,16]
The new information gathered from this re-examination provides novel data on the anatomy of the species, including severeal re-interpretations (Table 1), that will contribute to future clarifications of the taxonomy and systematics of Proterosuchidae and other early Archosauriformes
Summary
Archosauromorpha is a major group within diapsid reptiles that includes living birds and crocodilians, as well as all extinct species more closely related to these living groups than to lepidosaurs (lizards, snakes and Sphenodon) [1]. The oldest known archosauromorphs are from Upper Permian rocks of Europe [2,3,4], Russia [5,6,7] and Tanzania [8] It is not until the aftermath of the Permo-Triassic mass extinction One of the putative proterosuchid species that deserves restudy is Tasmaniosaurus triassicus from the Lower Triassic of Tasmania, Australia. This species is known from a single partial skeleton, including cranial and postcranial remains that were originally described by Camp & Banks [19]. The new information gathered from this re-examination provides novel data on the anatomy of the species, including severeal re-interpretations (Table 1), that will contribute to future clarifications of the taxonomy and systematics of Proterosuchidae and other early Archosauriformes
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