Morphometric analysis of the teeth and taxonomy of the enigmatic theropod Richardoestesia from the Upper Cretaceous of Uzbekistan

ABSTRACT

Richardoestesia is an enigmatic theropod dinosaur originally described on the basis of a pair of dentaries (holotype of R. gilmorei Currie et al., 1990) and isolated distinctive teeth, which are abundant in the Upper Cretaceous of North America. Richardoestesia asiatica (Nesov, 1995) is represented by numerous isolated teeth from the Upper Cretaceous Khodzhakul, Bissekty, and Aitym formations of Uzbekistan. Richardoestesia asiatica shows the typical features of the genus, including small mesial and distal denticles (on average 28.4 and 34.5 denticles per 5 mm, respectively), rectangular or knob-like denticles, and an apically convex distal margin of the tooth crown. The sample of R. asiatica has a large proportion of straight teeth (morphotype A) and includes several types of recurved teeth related to their position in the jaws (morphotypes B–E). This species differs from R. gilmorei in the presence of straight teeth and fully serrated mesial carinae. Richardoestesia asiatica cannot be distinguished from R. isosceles Sankey, 2001, which we consider a nomen dubium due, in part, to the imperfect nature of its holotype. Discriminant function analysis (DFA) of dental measurements found no distinction between the samples from Khodzhakul and Bissekty formations. In DFA including North American samples, the morphospace of R. asiatica completely overlaps that of the sample from the Lance Formation (Maastrichtian) of Wyoming and only partly overlaps with that of the sample from the Milk River Formation (Santonian) of Alberta.

ACKNOWLEDGMENTS

We thank C. Hendricks and an anonymous reviewer for their constructive comments. Field work in Uzbekistan was facilitated by, and conducted in cooperation with, the Zoological Institute of the National Academy of Sciences of Uzbekistan, particularly D. A. Azimov and Y. A. Chikin. For their efforts in the field, scientific expertise, and camaraderie, we thank A. V. Abramov, J. D. Archibald, G. O. Cherepanov, I. G. Danilov, S. Dominguez, N. Morris, C. M. Redman, A. S. Resvyi, C. Skrabec, P. P. Skutschas, E. V. Syromyatnikova, and D. J. Ward. The field work in 1997–2006 was funded by the National Science Foundation (EAR-9804771 and EAR-0207004 to J. D. Archibald and H.D.S.), the National Geographic Society (5901-97 and 6281-98 to J. D. Archibald and H.D.S.), and the Navoi Mining and Metallurgy Combinat. The laboratory research by A.A. received support from the Russian Scientific Fund (19-14-00020). The work was performed as part of the Russian Government Program of Competitive Growth of Kazan Federal University.

ORCID

Alexander Averianov http://orcid.org/0000-0001-5948-0799

Hans-Dieter Sues http://orcid.org/0000-0002-9911-7254