Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America¹

Tyrannosaurids were the apex predators of Late Cretaceous Laurasia and their status as dominant carnivores has garnered considerable interest since discovery, both in popular scientific realms. As a result, they are well studied much is known anatomy, diversity, growth, evolution. In contrast, little earliest stages tyrannosaurid development. Tyrannosaurid eggs embryos remain elusive, juvenile specimens — although rare. Perinatal bones teeth from Campanian–Maastrichtian western North America provide first window into this critical period life tyrannosaurid. An embryonic dentary (cf. Daspletosaurus) Two Medicine Formation Montana, measuring just 3 cm long, already exhibits distinctive tyrannosaurine characters like “chin” deep Meckelian groove, reveals tooth When considered together with remarkably large ungual Horseshoe Canyon Alberta, minimum hatchling size tyrannosaurids can be roughly estimated. A perinatal premaxillary likely pertains to Albertosaurus sarcophagus it shows small denticles on carinae. This that hallmark distinguish other theropods present early raises questions about ontogenetic variability serrations teeth. Sedimentary taphonomic similarities sites produced clues nesting habits may help refine prospecting search image continued quest discover baby tyrannosaurids.