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A new hypothesis of dinosaur relationships and early dinosaur evolution Baron, Norman & Barrett, 2017

*This image is copyright of its original author

Figure 1: Phylogenetic relationships of early dinosaurs.
Time calibrated strict consensus of 94 trees from an analysis with 73 taxa and 457 characters (see Supplementary Information). A, the least inclusive clade that includes Passer domesticus, Triceratops horridus and Diplodocus carnegii—Dinosauria, as newly defined. B, the least inclusive clade that includes P. domesticus and T. horridus—Ornithoscelida, as defined. C, the most inclusive clade that contains D. carnegii, but not T. horridus—Saurischia, as newly defined. For further information on definitions see Table 1. All subdivisions of the time periods (white
and grey bands) are scaled according to their relative lengths with the exception of the Olenekian (Early Triassic), which has been expanded relative to the other subdivisions to better show the resolution within Silesauridae and among other non-dinosaurian dinosauromorphs.

Abstract:
"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."

The old family tree structure. Credit: University of Cambridge

*This image is copyright of its original author

The new family tree structure. Credit: University of Cambridge

*This image is copyright of its original author

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