Ontogenetic changes in long-bone histology of an ornithomimid theropod dinosaur from the Upper Cretaceous Bissekty Formation of Uzbekistan

Abstract

An ornithomimid theropod dinosaur from the Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan is one of the basal members of Ornithomimidae. Here we present a description of ontogenetic changes in the long-bone histology of this taxon and distinguish four distinct histological stages. Analysis of a growth series of femora demonstrates early histological maturation during ontogeny in the Bissekty ornithomimid, expressed by the progressive formation of Haversian bone, endosteal bone deposition, and changing of composition of primary bone tissue from fibrolamellar complex to parallel-fibered bone with only a small amount of woven bone. The long-bone histology of the Bissekty ornithomimid is similar to that of the basal ornithomimid Archaeornithomimus asiaticus and differs from those of derived ornithomimids in early histological maturation, the absence of laminar and plexiform vascularization of the primary cortex, and the presence of little or no woven bone in medium-sized and large individuals. These differences could reflect size-related evolutionary transformation of the bone histology during the transition from basal to derived ornithomimids. The discovery of apparent medullary bone in a mid-sized femur suggests that the females of the Bissekty ornithomimid were sexually mature at least after attaining 75% of maximum size.

Keywords:

• Bone histology
• Theropoda
• Ornithomimidae
• Cretaceous
• Uzbekistan

Acknowledgements

Fieldwork 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, C. King, N. Morris, C.M. Redman, A.S. Resvyi, C. Skrabec, E.V. Syromyatnikova, and D.J. Ward. We are very grateful to the staff of the “Geomodel” Research Center at the Saint Petersburg State University (Saint Petersburg, Russia), especially Alexander M. Kulkov for his help in using the Leica 2500P microscope and preparing images of the histological sections. The authors thank an anonymous reviewer for providing helpful comments that improved the quality of the manuscript.