A new hypothesis of dinosaur relationships and early dinosaur evolution.
For 130 years, dinosaurs have been divided into two distinct clades-Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.|Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK.
Matthew G
MG
Baron
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
David B
DB
Norman
Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK.
Paul M
PM
Barrett
D000818:Animals; D001842:Bone and Bones / Q000033:anatomy & histology; D060435:Carnivory; D002965:Classification; D025061:Dinosaurs / Q000033:anatomy & histology / Q000145:classification* / Q000502:physiology; D049810:Genetic Speciation; D008954:Models, Biological; D010802:Phylogeny