The phylogenetic relationships of early dinosaurs: a comparative report

Abstract

Surprising new anatomical information has come to light for the early dinosaurs Eoraptor lunensis and Herrerasaurus ischigualastensis. Eoraptor has a mid mandibular jaw joint, and Herrerasaurus has a promaxillary fenestra at the anterior end of the antorbital fossa. Initial cladistic interpretation placed Herrerasaurus outside Dinosauria. Since then, Eoraptor and Herrerasaurus have been placed at the base of Saurischia or within Theropoda in two large-scale quantitative analyses. A comparative approach is taken here to show, first, that character choice is a major factor behind differing results; only half of the character data critical for each interpretation is incorporated into the opposing analysis. In that shared portion of data, furthermore, nearly 40 percent of character state scores vary for identical, or comparable, ingroup taxa. Resolving these conflictive interpretations is clearly where future progress will be made in understanding early dinosaur phylogenesis.

Keywords:

• Dinosauria
• Eoraptor
• Herrerasaurus
• phylogenetic taxonomy
• cladistics

Acknowledgements

I would like to thank C. Abraczinskas for the final drafts of all figures, R. Masek, W. Simpson and R Vodden for detailed preparation of the material of Eoraptor and Herrerasaurus, M. Langer and J. Wilson for helpful comments on the manuscript, and M. Langer and D. Pol for the invitation to participate in this symposium.