Abstract
Background
Archosauria and their closest relatives, the non-archosaurian archosauriforms, diversified in the Early and Middle Triassic, soon after the end-Permian extinction. This diversification is poorly documented in most Lower and Middle Triassic rock sequences because fossils of early groups of archosauriforms are relatively rare compared to those of other amniotes. The early Middle Triassic (? late Anisian) Manda beds of southwestern Tanzania form an exception, with early archosaur skeletons being relatively common and preserved as articulated or associated specimens. The Manda archosaur assemblage is exceptionally diverse for the Middle Triassic. However, to date, no non-archosaurian archosauriforms have been reported from these rocks.
Methodology/Principal Findings
Here, we name a new taxon, Asperoris mnyama gen. et sp. nov., from the Manda beds and thoroughly describe the only known specimen. The specimen consists of a well-preserved partial skull including tooth-bearing elements (premaxilla, maxilla), the nasal, partial skull roof, and several incomplete elements. All skull elements are covered in an autapomorphic highly rugose sculpturing. A unique combination of character states indicates that A. mnyama lies just outside Archosauria as a stem archosaur within Archosauriformes, but more precise relationships of A. mnyama relative to other early archosauriform clades (e.g., Erythrosuchidae) cannot be determined currently.
Conclusions/Significance
Asperoris mnyama is the first confirmed non-archosaurian archosauriform from the Manda beds and increases the morphological and taxonomic diversity of early archosauriforms known from the Middle Triassic. The direct association of A. mnyama with species referable to Archosauria demonstrates that non-archosaurian archosauriforms were present during the rise and early diversification of Archosauria. Non-archosaurian archosauriforms and archosaurs co-occur in fossil reptile assemblages across Pangaea from the late Early Triassic to the end of the Late Triassic.
A larger gamut study nests Asperoris as the sister to Vjushkovia. More here:
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Also, I found unossified babies and flamboyant dorsal frills preserved in the empty black background of figure 2 when viewed in Photoshop.
ReplyDeleteSeriously though, the grade of archosauriform Asperoris falls out as is basically the outgroup of Nesbitt's analysis, so any analysis including multiple 'proterosuchids', erythrosuchids and proterochampsians, as well as doswellians, would have been more useful.
I just skimmed the paper so feel free to correct me if I am wrong, but I beieve they do say that they simply plugged the new specimen in the Nesbitt (2011) matrix to test if it would fall out within the crown group Archosauria and that their matrix was unable to provide further resolution. Future analyses focusing on the non-Archosaurian archosauromorphs should be able to tell us more.
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