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Arizonasaurus and its implications for archosaur divergence.

Sterling J Nesbitt1

  • 1University of California Museum of Paleontology, 1101 Valley Life Science Building, Berkeley, CA 94720-4780, USA. snesbitt@uclink.berkeley.edu

Proceedings. Biological Sciences
|December 12, 2003
PubMed
Summary
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The discovery of Arizonasaurus babbitti in the Moenkopi Formation reveals new insights into Middle Triassic archosaurs. This finding suggests an earlier divergence of birds and crocodiles and aids in correlating Triassic faunas globally.

Area of Science:

  • Paleontology
  • Vertebrate Paleontology
  • Mesozoic Ecosystems

Background:

  • The Moenkopi Formation contains fragmentary remains of Middle Triassic archosaurs, including rauisuchians and poposaurs.
  • Previous understanding of these archosaurs was limited due to the scarcity and isolation of fossil evidence.

Purpose of the Study:

  • To identify and characterize archosaurian fossils from the Moenkopi Formation.
  • To determine the phylogenetic relationships of Middle Triassic archosaurs, specifically ctenosauriscids and poposaurids.
  • To establish the biostratigraphic significance of the Moenkopi Formation fauna for Triassic correlations.

Main Methods:

  • Analysis of a recently discovered, relatively complete skeleton of Arizonasaurus babbitti.
  • Comparative anatomical study of Arizonasaurus with other known archosaur taxa.

Related Experiment Videos

  • Examination of isolated archosaurian remains (centra, pelvic girdle elements, skull fragments) from the Moenkopi Formation.

    • Main Results:

    • The skeleton of Arizonasaurus babbitti represents a single taxon responsible for most previously described Moenkopi archosaur remains.
    • Arizonasaurus is identified as a ctenosauriscid, a poorly known group of Middle Triassic archosaurs.
    • Evidence suggests ctenosauriscids are closely related to, or are, poposaurs, and that both groups are derived rauisuchians.

    Conclusions:

    • The presence of Arizonasaurus (a poposaurid) in the early Middle Triassic indicates the divergence of birds and crocodiles occurred earlier than previously estimated.
    • Middle Triassic ctenosauriscids provide a basis for correlating Triassic faunas across Europe, Asia, North America, and Africa.
    • The Moenkopi Formation fauna represents a crucial transitional assemblage between Early and Late Triassic ecosystems.