IGM 100 972

IGM 100/972 and IGM 100/974 are the fossilized skulls of two juvenile troodontid dinosaurs.

Mark Norell and colleagues described IGM 100/972 and IGM 100/974 in 1994. The two specimens were found in a nest of oviraptorid eggs in the Late Cretaceous "Flaming Cliffs" of the Djadokhta Formation of Mongolia. The nest is quite certainly that of an oviraptorosaur, since an oviraptorid embryo is still preserved inside one of the eggs. The two partial troodontid skulls were first described by Norell et al.. (1994) as dromaeosaurids, but reassigned after further study. The troodontids were either hatchlings or embryos, and fragments of eggshell are adhered to them, although these seem to be oviraptorid eggshell. The presence of tiny troodontids in an oviraptorid nest is an enigma. Hypotheses explaining how they ended up in an oviraptorid nest include that they were the prey of the adult oviraptorid, that they were there to prey on oviraptorid hatchlings, or that some troodontids may have been nest parasites.