Wednesday, December 30, 2020

[Paleontology • 2020] An Oviraptorid Preserved Atop An Embryo-bearing Egg Clutch sheds light on the Reproductive Biology of Non-avialan Theropod Dinosaurs



 an oviraptorid specimen [LDNHMF2008]
consisting of an adult skeleton preserved atop an embryo-bearing egg clutch. 

Bi, Amiot, Peyre de Fabrègues, ... et Xu, 2020.
 Artwork by Zhao Chuang. english.IVPP.cas.cn

 
Abstract
Recent studies demonstrate that many avialan features evolved incrementally prior to the origin of the group, but the presence of some of these features, such as bird-like brooding behaviours, remains contentious, in non-avialan dinosaurs. Here we report the first non-avialan dinosaur fossil known to preserve an adult skeleton atop an egg clutch that contains embryonic remains. The preserved positional relationship of the adult to the clutch, coupled with the advanced growth stages of the embryos and their high estimated incubation temperatures, provides strong support for the brooding hypothesis. Furthermore, embryos in the clutch are at different developmental stages, suggesting the presence of asynchronous hatching—a derived feature even among crown-group birds—in non-avialan theropods. These findings demonstrate that the evolution of reproductive biology along bird-line archosaurs was a complex rather than a linear and incremental process, and suggest that some aspects of non-avialan theropod reproduction were unique to these dinosaurs.

Keywords: Oviraptorosauria, Cretaceous, Clutch, Brooding, Embryos, Asynchronous hatching


Fig. 1. LDNHMF2008, an oviraptorid specimen consisting of an adult skeleton preserved atop an embryo-bearing egg clutch.
(a) Photograph. (b) Interpretive drawing with bones and gastroliths in white and eggs color-coded by ring (A, red; B, green; C, blue).
(c) Restoration (white indicates bones preserved in the adult skeleton).

Abbreviations: I, digit I; II, digit II; III, digit III; A#, egg in lowermost ring (A); as, astragalus; B#, egg in middle ring (B); C#, egg in uppermost ring (C); cav, caudal vertebra; ch, chevron; cv, cervical vertebra; di, manual digit; dr, dorsal ribs; dv, dorsal vertebra; em, egg known to preserve embryo; fe, femur; fi. fibula; ga, gastralium; gl, gastroliths; h, humerus; il, ilium; is, ischium; mt, metatarsal; O2, egg sampled for oxygen isotope analysis; pb, pubis; pp, pedal phalanges; ra, radius; sl, semilunate carpal; ti, tibia; ul, ulna. Note that C11 and C12 are not paired eggs. The eggs that would have been paired with C11 and C12 are probably not preserved, as is the case for some other eggs and skeletal elements.
 

An attentive oviraptorid theropod dinosaur broods its nest of blue-green eggs while its mate looks on in what is now Jiangxi Province of southern China some 70 million years ago.
 Artwork by Zhao Chuang.


 Shundong Bi, Romain Amiot, Claire Peyre de Fabrègues, Michael Pittman, Matthew C. Lamanna, Yilun Yu, Congyu Yu, Tzuruei Yang, Shukang Zhang, Qi Zhao and Xing Xu. 2020. An Oviraptorid Preserved Atop An Embryo-bearing Egg Clutch sheds light on the Reproductive Biology of Non-avialan Theropod Dinosaurs. Science Bulletin. In Press. DOI: 10.1016/j.scib.2020.12.018

Researchers Announce World’s First Dinosaur Preserved Sitting on Nest of Eggs that Includes Fossilized Babies