Dnia 15 maja 2021 07:02 Ben Creisler <bcreisler@gmail.com> napisaÅ(a):
The paper is now out in final form with a free pdf:Free pdf:Shundong Bi, Romain Amiot, Claire Peyre de FabrÃgues, Michael Pittman, Matthew C.Lamanna, Yilun Yu, Congyu Yu, Tzuruei Yang, Shukang Zhang, Qi Zhao & Xing Xu (2021)An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaurs.Science Bulletin 66(9): 947-954***Also, it is the cover story for the May issue:An oviraptorid atop an embryo-bearing egg clutch sheds light on the theropod reproductive biologyIn recent years, several specimens of adult oviraptorid dinosaurs have been found atop nests of their eggs, but no embryos have ever been found inside those eggs. Bi et al. describe the first non-avialan dinosaur fossil sitting on a nest of embryo-bearing eggs, helping to resolve controversies associated with the brooding hypothesis for oviraptorosaurs. The specimen was recovered from the Upper Cretaceous Nanxiong Formation, some 70 million years old, in Ganzhou City in southern Chinaâs Jiangxi Province. The fossil consists of an incomplete skeleton of a large, presumably adult oviraptorid crouched in a bird-like brooding posture over a clutch of at least 24 eggs. The paired eggs were arranged in three superposed rings and are 21.5 cm in length and 8.5 cm in width across their equatorial regions. Seven of these eggs preserve bones or partial skeletons of unhatched oviraptorid embryos inside. The embryos in the nest are at different developmental stages, suggesting that oviraptorid eggs in the same nest hatched asynchronously. The discovery of asynchronous hatching in oviraptorosaurs is interesting given its late appearance even among crown birds. Apparently, this feature evolved independently in oviraptorids and some extant birds, reinforcing previous hypotheses that the evolution of modern avialan reproductive biology was not an incremental, linear process. The cover illustration depicts the nesting oviraptorid as it may have appeared in life. Though the coloration of the adult is conjectural, other recent research suggests that oviraptorid eggs may have originally been blue-green in color. Artwork by Chuang Zhao (see the article by Shundong Bi et al. on page 947).High resolution cover image:==Ben CreislerA new paper:[NOTE: This paper should be free from the Chinese journal website after it is officially published.]====Shundong Bi, Romain Amiot, Claire Peyre de FabrÃgues, Michael Pittman, Matthew C.Lamanna, Yilun Yu, Congyu Yu, Tzuruei Yang, Shukang Zhang, Qi Zhao & Xing Xu (2020)An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaursScience Bulletin (advance online publication)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.