New choristoderes (Reptilia: Diapsida) from the Upper Cretaceous and Palaeocene, Alberta and Saskatchewan, Canada, and phylogenetic relationships of Choristodera

Authors

  • KEQIN GAO,

    Corresponding author
    1. Department of Vertebrate Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, U.S.A.; Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G2E9 Canada
      *E-mail: kgao@amnh.org
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  • RICHARD C. FOX

    1. Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9 Canada
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*E-mail: kgao@amnh.org

Abstract

New choristoderan fossils from the Late Cretaceous and Palaeocene of Alberta and Saskatchewan, Canada, are described: incomplete maxillae and dentaries from the Upper Cretaceous Oldman Formation, Alberta, extend the range of the primitive Cteniogenys from the Jurassic in the North American Western Interior; an incomplete dentary from the Palaeocene Ravenscrag Formation, Saskatchewan, comprises the first occurrence of the crocodile-like Simoedosaurus in Canada and the earliest record of the genus; well-preserved skulls and mandibles from the Oldman and Horseshoe Canyon formations, Alberta, document a new species of Champsosaurus and clarify the status of previously known species of the genus. New information about Asian choristoderes supports a Tchoiria-(Ikechosaurus + Simoedosaurus) relationship, contrary to previous work. Choristoderes share no convincing synapomorphies with either Lepidosauromorpha or Archosauromorpha, but occupy a more basal position within Diapsida, possibly as a sister-taxon with Neodiapsida (Younginiformes + Sauria).

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