New choristoderes (Reptilia : Diapsida) from the upper Cretaceous and Palaeocene, Alberta and Saskatchewan, Canada, and phylogenetic relationships ofChoristodera
Kq. Gao et Rc. Fox , New choristoderes (Reptilia : Diapsida) from the upper Cretaceous and Palaeocene, Alberta and Saskatchewan, Canada, and phylogenetic relationships ofChoristodera, ZOOL J LINN, 124(4), 1998, pp. 303-353
New choristoderan fossils from the Late Cretaceous and Palaeocene of Albert
a and Saskatchewan, Canada, are described: incomplete maxillae and dentarie
s from the Upper Cretaceous Oldman Formation, Alberta, extend the range of
the primitive Cteniogenys from the Jurassic in the North American Western I
nterior; an incomplete dentary from the Palaeocene Ravenscrag Formation, Sa
skatchewan, comprises the first occurrence of the crocodile-like Simoedosau
rus in Canada and the earliest record of the genus; well-preserved skulls a
nd mandibles from the Oldman and Horseshoe Canyon formations, Alberta, docu
ment a new species of Champsosaurus and clarify the status of previously kn
own species of the genus. New information about Asian choristoderes support
s a Tchoiria-(Ikechosaurus + Simodeosaurus) relationship, contrary to previ
ous work. Choristoderes share no convincing synapomorphies with either Lepi
dosauromorpha or Archosauromorpha, but occupy a more basal position within
Diapsida, possibly as a sister-taxon with Neodiapsida (Younginiformes + Sau
ria). (C) 1998 The Linnean Society of London.