New information on the cranial morphology of Avimimus (Theropoda: Oviraptorosauria)

ABSTRACT

The cranial morphology of the oviraptorosaurian Avimimus portentosus is described based on a new specimen, one that includes bones such as the nasal and the jugal, which had not been available or only incompletely preserved previously. The left and right nasals are fused together as in oviraptorids. Morphology of the jugal, which is not fused with the quadratojugal, and the postorbital indicate that the infratemporal fenestra is completely separate from the orbit, not confluent with the latter, as inferred previously. The left and right dentaries are fused together without a trace of suture. Such newly available information indicates that the skull of Avimimus is not as ‘avian’-like as inferred in previous studies. Rather, it shows a mixture of plesiomorphic and derived character states observed in Oviraptorosauria, consistent with an intermediate phylogenetic position of this dinosaur between Early Cretaceous basal oviraptorosaurians and the diverse clade of Caenagnathoidea.

ACKNOWLEDGMENTS

We are grateful to K. Hayashibara (former president of Hayashibara Company Limited, Okayama, Japan) for his continuous financial support to the Japanese-Mongolian Joint Paleontological Expedition since 1993. We also thank the Japanese and Mongolian members of the joint expedition team for their help in the field and laboratories. Olympus, Mitsubishi Motor Company, and Panasonic supported the expedition. T.T. was supported by JSPS Overseas Research Fellowship. Funding for L.M.W. was provided by the U.S. National Science Foundation (IOB-0517257, IOS-1050154, IOS-1456503) and the Ohio University Heritage College of Osteopathic Medicine. We thank R. C. Ridgely and D. L. Dufeau for fruitful discussion. TNT was freely available thanks to the Willi Hennig Society. J. Choiniere, an anonymous reviewer, and editor A. Turner made constructive suggestions that greatly improved the clarity of the manuscript. This paper is Japanese-Mongolian Joint Paleontological Expedition Contribution Number 88.