Volume 25, Issue 1, 21 January 2022, 103516
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An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures rights and content
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A Late Cretaceous oviraptorid theropod dinosaur embryo is preserved in-ovo

Its head lies ventral to the body, and the back curled along the egg's blunt pole

Its posture is similar to that of a late-stage modern bird embryo

Avian tucking behavior possibly originated among non-avian theropods


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.

Subject areas

Biological sciences
Evolutionary biology
Evolutionary processes

Data and code availability

Dataset used in this study has been deposited at Zenodo. DOI is listed in the key resources table.

This paper does not report original code.

Any additional information is available from the lead contact upon request.


These authors contributed equally


Present address: Department of Geology, National Museum of Natural Science, Guanqian Road 1, North District, 404605 Taichung, Taiwan


Lead contact