An egg fossil suggests that dinosaur embryos prepared to hatch like birds
Probably the embryos of some dinosaurs assumed the same position inside the eggs as those of the birds, which are their-today descendants: this is suggested by a very well preserved fossil of oviraptosaur egg - a group of feathered dinosaurs close to birds - which had been found in China in 2000 but has only recently been analyzed. The embryo inside the egg is arranged in a very similar way to that of a chick just before the egg hatches, a position never observed before in the fossils of non-flying dinosaur eggs.
A study carried out by a group of researchers from the University of Birmingham and the University of Geosciences of China and published in the iScience journal explains that, although many fossils of dinosaur eggs or nests have been found in the last century, only in few of them the embryos have been well preserved: in most cases the bones of the embryos are damaged and dislocated. The one found in the rocky layers of Hekou, in the Jiangxi region, however, has not suffered such damage: it is clear that the head of the embryo is in the middle of the hind legs, under the front ones, and the back is curved.
According to the authors of the study, the comparison with other fossils suggests that oviraptosaur embryos had developed the pre-hatching position of modern birds, functional to breaking the egg shell. Bird embryos that do not put themselves in this position are more likely to die during hatching.
The egg is about 17 centimeters long, is about 66 million years old and is thought to have been preserved thanks to a sudden mudslide that buried it. Fion Waisum Ma, one of the researchers who participated in the study, said it is "the best dinosaur embryo ever found in history".
The full article is available here: https://www.cell.com/iscience/fulltext/S2589-0042(21)01487-5
