Birdlike growth and mixed-age flocks in avimimids (Theropoda, Oviraptorosauria).

Avimimids were unusual, birdlike oviraptorosaurs from the Late Cretaceous of Asia. Initially enigmatic, new information has ameliorated the understanding of their anatomy, phylogenetic position, and behaviour. A monodominant bonebed from the Nemegt Formation of Mongolia showed that some avimimids were gregarious, but the site is unusual in the apparent absence of juveniles. Here, a second monodominant avimimid bonebed is described from the Iren Dabasu Formation of northern China. Elements recovered include numerous vertebrae and portions of the forelimbs and hindlimbs, representing a minimum of six individuals. Histological sampling of two tibiotarsi from the bonebed reveals rapid growth early in ontogeny followed by unexpectedly early onset of fusion and limited subsequent growth. This indicates that avimimids grew rapidly to adult size, like most extant birds but contrasting other small theropod dinosaurs. The combination of adults and juveniles in the Iren Dabasu bonebed assemblage provides evidence of mixed-age flocking in avimimids and the onset of fusion in young individuals suggests that some of the individuals in the Nemegt Formation bonebed may have been juveniles. Regardless, these individuals were likely functionally analogous to adults, and this probably facilitated mixed-age flocking by reducing ontogenetic niche shift in avimimids.

A dinosaur community composition dataset for the Late Cretaceous Nemegt Basin of Mongolia.

Dinosaur community composition data for eleven fossil localities in the Late Cretaceous Nemegt Basin of Mongolia are compiled from field observations and records in the literature. Counts were generated from skeletons and represent numbers of individuals preserved in each locality. These data were used in the analyses of Funston et al. [1] "Oviraptorosaur anatomy, diversity, and ecology in the Nemegt Basin" in the Nemegt Ecosystems Special Issue of Palaeogeography, Palaeoclimatology, Palaeoecology, where the results are discussed.