First species of Enantiornithes from Sihedang elucidates skeletal development in Early Cretaceous enantiornithines

Abstract

The Sihedang locality of the Lower Cretaceous Yixian Formation is the only recognized ornithuromorph-dominated locality in the Jehol Group of north-eastern China. Here we report on the first enantiornithine from this locality and erect a new taxon Monoenantiornis sihedangia gen. et sp. nov. The holotype and only specimen preserves a rare ontogenetic stage in which the intermedium is ossified but free from the other proximal tarsals and the tibia, consistent with the pattern of ossification that occurs in neornithines. In order to explore the pattern of skeletal development in the enantiornithines, we select several published specimens inferred to represent different ontogenetic stages and document their degree of fusion in five key compound bones and the sterna. This provides a preliminary hypothesis for the sequence in which compound bones form in Early Cretaceous enantiornithines. From this hypothesis, most known specimens can be categorized into four major ontogenetic stages: all the compound bones unfused; synsacrum and pygostyle fused; tarsals fused; tibiotarsus and carpometacarpus formed.

http://zoobank.org/urn:lsid:zoobank.org:pub:347485CA-87E6-4834-BEB5-687B6798644E

Keywords:

• Aves
• Mesozoic
• Enantiornithes
• ontogeny
• skeletal development

Acknowledgements

We thank Dahan Li and Yutong Li (IVPP) for preparing the specimen, Jie Zhang and Wei Gao (IVPP) for taking the photographs, and Shukang Zhang for assistance with the histological preparation. This project was supported by the National Basic Research Program of China 973 Program (2012CB821906) and the National Natural Science Foundation of China (91514302).

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Funding

This project was supported by the National Basic Research Program of China 973 Program (2012CB821906) and the National Natural Science Foundation of China (91514302).