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Asilisaurus kongwe, the Oldest Avian-line Archosaur and the Early Diversification of Ornithodira



Nesbitt, S.J., Sidor, C.A., Irmis, R.B., Angielczyk, K.D., Smith, R.M.H.,
and L. A. Tsuji. 2010. Ecologically distinct dinosaurian sister group shows
early diversification of Ornithodira. Nature. doi:10.1038/nature08718

Abstract - 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.

I have a more detailed write-up of this over at

chinleana.blogspot.com

************************************************************************
Bill Parker
Vertebrate Paleontologist
Division of Resource Management
Petrified Forest National Park
P.O. Box 2217
1 Park Road
Petrified Forest, AZ 86028
(928) 524-6228 x262