previously been attributed to therizinosaur-grade dinosaurs. The multiple clutches indicate that some therizinosaurids were colonial nesters and the fact that they were found in a single stratigraphic layer suggests that they nested at the site on a single occasion and therefore did not exhibit philopatric behaviour. This nesting site was formally described in 2019 by Kohei Tanaka and colleagues. In this comprehensive description, the amount of egg clutches was corrected to at least 15, noting that the eggs were laid in clutches composed of 3 to 30 eggs and hatched in the same single nesting season. The eggs have an average diameter of with some variations between and . Based on the smooth outer surface, both inner and outer portions, and several irregular-shaped pore canals of these eggs, they were corroborated to pertain to the Dendroolithidae. Approximately the 50% of the nesting area has been eroded, and based on the egg clutches distribution, the nest density can be estimated around 1 nest per 10 m2. This indicates that up to 32 nests were originally present. The habitat that the parents nested in was a semi-arid flood plain and the egg clutches were covered in organic-rich material during incubation as some extant archosaurs do today (crocodiles and megapode birds). In addition, the egg-shell fragments association indicates that many of the clutches hatched before the site was buried by a flood event. Out of a total of 15 clutches, at least 9 successfully hatched, which represents a nesting success rate of at least 60% for the entire site. The prominent nesting site of the Javkhlant Formation indicates that colonial nesting first evolved in non-avian dinosaur species to increase hatching success in ecosystems subject to high nest predation pressure (such as this formation). Lastly, though dendroolithid eggs are also attributed to megalosauroids, and therizinosaurids are not known from the Javkhlant Formation, it overlies the Bayan Shireh Formation, where other dendroolithid eggs and the therizinosaurs Enigmosaurus, Erlikosaurus and Segnosaurus were found. Moreover, the absence of megalosauroids on these formations is notable. Ontogeny At least four developmental embryonic stages were reported from the Nanchao embryos; Kundrát and colleagues classified them from stages A to D depending on the development. Stage A is the earliest of all and is characterized by the poor ossification of bones and the porous structure of the centra in the vertebral column. During stages B and C the bones become slightly