An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures

Lida Xing; Kecheng Niu; Waisum Ma; Darla K Zelenitsky; Tzu-Ruei Yang; Stephen L Brusatte

doi:10.1016/j.isci.2021.103516

An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures

iScience. 2021 Dec 21;25(1):103516. doi: 10.1016/j.isci.2021.103516. eCollection 2022 Jan 21.

Authors

Lida Xing^{1

2

3}, Kecheng Niu³, Waisum Ma⁴, Darla K Zelenitsky⁵, Tzu-Ruei Yang⁶, Stephen L Brusatte⁷

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
² School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
³ Yingliang Stone Nature History Museum, Nan'an 362300, China.
⁴ School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.
⁵ Department of Geoscience, University of Calgary, Calgary, AB, Canada.
⁶ Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
⁷ School of GeoSciences, University of Edinburgh, Edinburgh, UK.

Abstract

Despite the discovery of many dinosaur eggs and nests over the past 100 years, articulated in-ovo embryos are remarkably rare. Here we report an exceptionally preserved, articulated oviraptorid embryo inside an elongatoolithid egg, from the Late Cretaceous Hekou Formation of southern China. The head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo. Comparison to other late-stage oviraptorid embryos suggests that prehatch oviraptorids developed avian-like postures late in incubation, which in modern birds are related to coordinated embryonic movements associated with tucking - a behavior controlled by the central nervous system, critical for hatching success. We propose that such pre-hatching behavior, previously considered unique to birds, may have originated among non-avian theropods, which can be further investigated with additional discoveries of embryo fossils.

Keywords: Biological sciences; Evolutionary biology; Evolutionary processes; Phylogenetics.