"Group nesting traces" where multiple nest fossils are found in the same place have been reported all over the world.Collective nesting is a common behavior in current seabirds, but if parents do not protect their nests, the risk of eggs being attacked by foreign enemies increases.Previous studies have shown that, unlike birds, many groups of dinosaurs did not incubate, and the behavior of dinosaur parents during mass nesting was unknown.

　This research team, consisting of Japan, Mongolia, South Korea, and Canada, is a group nesting trace of theropod dinosaurs thought to be Therizinosauria from the Late Cretaceous stratum called the Jabrant Formation in the eastern part of the Mongolian Gobi Desert in 2011. I found.Furthermore, excavation surveys were repeated until 2018, and a total of 15 nest fossils were confirmed.

　Nest fossils were all found in the same strata, and the contents of the egg fossils contained common deposits, suggesting that these nests were created during the same breeding season.In addition, evidence of egg hatching was found in 15 out of 9 nests, and a high nesting success rate of 60% was estimated.Since the success rate of nesting is similar to that of the current crocodiles and birds that protect the nest, it is highly likely that the parents of Therizinosauria also protected the nest.

　Now that it is almost certain that birds have evolved from a sect of theropod dinosaurs, research is focused on exploring how bird-specific behaviors have been acquired.The discovery reveals that the current population conservation behavior of birds can be traced back to non-incubating dinosaurs.

　By accumulating such research, it is expected that it will be possible to clarify how ecology and behavior have evolved from dinosaurs to birds.

Paper information:[Geology] Exceptional preservation of a Late Cretaceous dinosaur nesting site from Mongolia reveals colonial nesting behavior in a non-avian theropod