Waisum Ma

Abstract A dietary shift from carnivory to insectivore has been proposed to explain the dramatic morphological evolution of alvarezsaurians, particularly the adaptation related to the manual digital reduction and body size miniaturization. However, based solely on morphological shifts, this hypothesis lacked direct dietary evidence to support either carnivory or insectivore.

Highlights • A Late Cretaceous oviraptorid theropod dinosaur embryo is preserved in-ovo • Its head lies ventral to the body, and the back curled along the egg's blunt pole • Its posture is similar to that of a late-stage modern bird embryo • Avian tucking behavior possibly originated among non-avian theropods Summary Despite the discovery of many dinosaur eggs and nests over the past 100 years, articulated in-ovo embryos are remarkably rare.

Highlights • A general trend of jaw strengthening is observed along all theropod lineages • Carnivores and herbivores achieved this via different morphofunctional modifications • Same jaw strengthening trend is also detected in tyrannosaurids ontogenetically • This common trend is linked to functional peramorphosis of bone functional adaptation Summary 1 Nesbitt S.J. Smith N.D. Irmis R.B. Turner A.H. Downs A.