A large bird from the Early Cretaceous of China: new information on the skull of enantiornithines

ABSTRACT

We describe the anatomy and bone histology of an enantiornithine specimen from the Early Cretaceous Jehol Group of northeastern China. CNUVB-0903 is larger than most Early Cretaceous enantiornithine birds and also different from all other named taxa. Thus, we erect the new species Zhouornis hani for the new specimen. CNUVB-0903 preserves a suite of new morphologies for the clade. Noteworthy are those of the braincase and occipital region of the skull, which was previously poorly known for enantiornithines. The morphology and placement of the large basipterygoid processes and the well-developed basisphenoid recess—comparable in morphology to those of non-avian dinosaurs—highlights the evolutionary conservatism of the enantiornithine skull. The histological characterization of CNUVB-0903 indicates that it was not yet a full-grown individual at the time of death. This, combined with the comparatively large size of the skeleton, supports previous evidence indicating that early in their history, enantiornithines were able to achieve relatively large sizes.

ACKNOWLEDGMENTS

We are grateful to M. Walsh and D. Trankina for fossil preparation and casting, and to S. Abramowicz for preparing the illustrations. J. Siegel provided assistance with the X-ray imaging and C. Gao provided the measurements for Rapaxavis pani. We also thank F. Zhang and J. Li for access to the specimens under their care, and to G. Dyke, J. O’Connor, and T. Worthy for reviewing the original manuscript. This work was supported by grants from the National Natural Science Foundation of China (30870263, 31071877) and support from C. and L. Cooper.

Handling editor: Trevor Worthy