Publication Date:
2010-03-06
Description:
The early evolutionary history of Ornithodira (avian-line archosaurs) has hitherto been documented by incomplete (Lagerpeton) or unusually specialized forms (pterosaurs and Silesaurus). Recently, a variety of Silesaurus-like taxa have been reported from the Triassic period of both Gondwana and Laurasia, but their relationships to each other and to dinosaurs remain a subject of debate. Here we report on a new avian-line archosaur from the early Middle Triassic (Anisian) of Tanzania. Phylogenetic analysis places Asilisaurus kongwe gen. et sp. nov. as an avian-line archosaur and a member of the Silesauridae, which is here considered the sister taxon to Dinosauria. Silesaurids were diverse and had a wide distribution by the Late Triassic, with a novel ornithodiran bauplan including leaf-shaped teeth, a beak-like lower jaw, long, gracile limbs, and a quadrupedal stance. Our analysis suggests that the dentition and diet of silesaurids, ornithischians and sauropodomorphs evolved independently from a plesiomorphic carnivorous form. As the oldest avian-line archosaur, Asilisaurus demonstrates the antiquity of both Ornithodira and the dinosaurian lineage. The initial diversification of Archosauria, previously documented by crocodilian-line archosaurs in the Anisian, can now be shown to include a contemporaneous avian-line radiation. The unparalleled taxonomic diversity of the Manda archosaur assemblage indicates that archosaur diversification was well underway by the Middle Triassic or earlier.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Nesbitt, Sterling J -- Sidor, Christian A -- Irmis, Randall B -- Angielczyk, Kenneth D -- Smith, Roger M H -- Tsuji, Linda A -- England -- Nature. 2010 Mar 4;464(7285):95-8. doi: 10.1038/nature08718.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20203608" target="_blank"〉PubMed〈/a〉
Keywords:
Animals
;
Beak/anatomy & histology
;
Biological Evolution
;
Birds/*anatomy & histology/*classification
;
Diet/veterinary
;
Dinosaurs/anatomy & histology/classification
;
Extremities/anatomy & histology
;
*Fossils
;
Geography
;
Jaw/anatomy & histology
;
*Phylogeny
;
Reptiles/*anatomy & histology/*classification
;
*Skeleton
;
Tanzania
;
Tooth/anatomy & histology
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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