A rare nest of baby giant hadrosaurs has been discovered by paleontologists in Mongolia’s Gobi Desert. The area this fossil nest was found in is known as the “Dragon’s Tomb” as it has produced a vast amount of fossils of this giant hadrosaur, Saurolophus angustirostris, since its discovery in 1947. This find is described by Leonard Dewaele of Ghent University and colleagues in PLOS ONE.
Although S. angustirostris is extremely common in these rocks of the Nemegt Formation, this is the first time embryonic remains of this species have been described. Additionally, this nest of 3-4 individuals was found associated with eggshell fragments. It is rare to find eggshells present with an embryonic dinosaurs, but it is very useful because then it allows a specific eggshell type to be associated with a specific species or group of dinosaur.
A variety of clues that indicate these dinosaurs are definitely perinatal specimens. The first clue is the length of the skulls, which are only about 5% the length of the adult S. angustirostris. Also, when magnified the bones appear spongey and lack ossification at specific joints, which indicate these were very young animals at the time of death.
The characteristic head crest of S. anguistirostris isn’t seen in these fossils, but unfused skull bones indicate that this feature had likely not yet appeared at that stage of development. Lead study author Leonard Dewaele explains, “The poorly developed crest in Saurolophus babies provides evidence of ontogenetic crest growth within the Saurolophini tribe.”
This discovery gives a unique look into the growth of this feature over the life span of this enigmatic extinct animal.
Geological evidence around the fossil indicates that this nest was laid along a river bank. They likely died at some point close to birth and were subsequently buried by the migrating river system. All signs indicate these were baby dinosaurs, but it remains impossible to say whether they died before or during birth.