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The segnosaurian dinosaurs: relics of the prosauropod–ornithischian transition?

1984; Taylor & Francis; Volume: 4; Issue: 4 Linguagem: Inglês

10.1080/02724634.1984.10012026

1937-2809

Gregory S. Paul,

Evolution and Paleontology Studies

ABSTRACT Segnosaurus Perle, 1979, and Erlikosaurus Barsbold & Perle, 1980, are recently described dinosaurs of unusual form from the Late Cretaceous of Mongolia. Both taxa are medium-sized herbivores with small skulls, beaks, spatulate teeth, retroverted pubes, and broad four-digit hindfeet. Barsbold and Perle consider them to be theropods. However, the feet of segnosaurs are much less derived than are the bird-like feet of theropods. Further, the segnosaurs do not show any distinctive theropod-like characters that justify their assignment to this group. They appear, instead, to be derived prosauropods with a number of early ornithischian adaptations. Notable among these ornithischian-like adaptations are their beaked jaws with cheeks. A cladistic comparison of the segnosaurs with thecodonts and early dinosaurs of the Triassic suggests that, despite their late appearance, the segnosaurs are phylogenetic intermediates between herbivorous prosauropods and early ornithischians. As such the segnosaurs strengthen the hypothesis of dinosaur monophyly. Segnosaurs cannot be placed in the theropods, but traditional schemes of dinosaur classification do not recognize the possibility of dinosaur monophyly. Here the segnosaurs are considered to represent a clade between the prosauropods and ornithischians.