Abstract
Proterochampsids are crocodile-like, probably semi-aquatic, quadrupedal archosauriforms characterized by an elongated and dorsoventrally low skull. The group is endemic from the Middle-Late Triassic of South America. The most recently erected proterochampsid species is “Chanaresuchus ischigualastensis”, based on a single, fairly complete skeleton from the early Late Triassic Ischigualasto Formation of northwestern Argentina. We describe here in detail the non-braincase cranial and postcranial anatomy of this species and revisit its taxonomy and phylogenetic relationships. The phylogenetic analysis recovered ‘Chanaresuchus ischigualastensis’ as part of a trichotomy together with Gualosuchus reigi and Chanaresuchus bonapartei. Accordingly, “Chanaresuchus ischigualastensis” can be potentially more closely related to Gualosuchus reigi, or even Rhadinosuchus gracilis, than to Chanaresuchus bonapartei. In addition, after discussing previously claimed synapomorphies of Chanaresuchus, we could not find unambiguous support for the monophyly of the genus. As a result, we propose here the erection of the new genus Pseudochampsa for ‘Chanaresuchus ischigualastensis’, which results in the new combination Pseudochampsa ischigualastensis. The information provided here about the anatomy and taxonomy of Pseudochampsa ischiguaslastensis will be useful for future quantitative analyses focused on the biogeography and macroevolutionary history of proterochampsids.
Highlights
The Triassic witnessed the origin, radiation and complete extinction of several diapsid clades, including morphological disparate forms such as kuehneosaurids, rhynchosaurs, erythrosuchids, doswelliids, proterochampsids, aetosaurs, and silesaurids among others [1,2,3,4,5,6,7]
A detailed description of the braincase was published by Trotteyn & Haro [10]. In this contribution we redescribe in detail the holotype of ‘Chanaresuchus ischigualastensis’ and include this species for the first time in a quantitative phylogenetic analysis
In order to test the phylogenetic relationships of Pseudochampsa ischigualastensis we included this species in the most recent and comprehensive data matrix focused on proterochampsids published so far, Dilkes & Arcucci [23]
Summary
The Triassic witnessed the origin, radiation and complete extinction of several diapsid clades, including morphological disparate forms such as kuehneosaurids, rhynchosaurs, erythrosuchids, doswelliids, proterochampsids, aetosaurs, and silesaurids among others [1,2,3,4,5,6,7]. These groups achieved generally a global distribution, but proterochampsids are endemic forms of the Middle and Late Triassic of South America [8]. A detailed description of the braincase was published by Trotteyn & Haro [10] In this contribution we redescribe in detail the holotype of ‘Chanaresuchus ischigualastensis’ and include this species for the first time in a quantitative phylogenetic analysis. A more complete knowledge of the anatomy and phylogenetic relationships of Pseudochampsa ischigualastensis will shed light on the evolution of proterochampsids and archosauriforms before the divergence of Archosauria
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