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

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 latestage 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.

Hadrosauroid eggs and embryos from the Upper Cretaceous (Maastrichtian) of Jiangxi Province, China

“…Indeed, the preserved theropod assemblage of the Nanxiong Group, including alioramine tyrannosaurids and oviraptorosaurs [ 22 , 23 ], agrees well with the dinosaur assemblage of the Nemegt Formation in Mongolia, which itself is often considered Maastrichtian in age [ 24 ]. For these reasons, and in keeping with the recent literature (e.g., [ 25 , 26 ]), we accept a probable Maastrichtian age for the Hekou Formation.…”

Phylogenetic Diversity of Ossification Patterns in the Avian Vertebral Column: A Review and New Data from the Domestic Pigeon and Two Species of Grebes

“…The same situation is also present with non-avian theropods. The embryos are known for several clades of maniraptorans closely related to birds, such as therizinosauroids [ 51 ], oviraptorosaurs (e.g., [ 15 , 52 , 53 , 54 ]) and troodontids [ 55 ]. However, the exact ossification sequence of the vertebral column cannot be deduced because the known specimens are not complete enough or represent near-hatching stages when the vertebrae (at least most of them) are already ossified.…”

First titanosaur dinosaur nesting site from the Late Cretaceous of Brazil

“…Like bone tissue, the dinosaur eggshell tissue is a bioceramic with phylogenetic information and provides multiple functions to the embryo 23 , 57 , 58 . There are at least four ways to determine the taxonomy of a fossil egg: (1) with an embryo inside 13 , 16 , 21 , 22 , 59 – 61 ; (2) adults with eggs inside 62 ; (3) adults brooding eggs 63 , 64 and (4) by phylogenetic inferences from the egg and its shell 23 , 50 , 60 . In most egg and eggshell fossil cases should be approached from this last perspective.…”