Abstract
Late Cretaceous trends in Asian dinosaur diversity are poorly understood, but recent discoveries have documented a radiation of oviraptorosaur theropods in China and Mongolia. However, little work has addressed the factors that facilitated this diversification. A new oviraptorid from the Late Cretaceous of Mongolia sheds light on the evolution of the forelimb, which appears to have played a role in the radiation of oviraptorosaurs. Surprisingly, the reduced arm has only two functional digits, highlighting a previously unrecognized occurrence of digit loss in theropods. Phylogenetic analysis shows that the onset of this reduction coincides with the radiation of heyuannine oviraptorids, following dispersal from southern China into the Gobi region. This suggests expansion into a new niche in the Gobi region, which relied less on the elongate, grasping forelimbs inherited by oviraptorosaurs. Variation in forelimb length and manus morphology provides another example of niche partitioning in oviraptorosaurs, which may have made possible their incredible diversity in the latest Cretaceous of Asia.
Highlights
Oviraptorosaurs are theropod dinosaurs known from an excellent fossil record spanning much of the Cretaceous of Asia and North America [1]
MPC-D 102/110a,b and MPC-D 102/11 show evidence of rapid growth, but the bone matrix and vasculature of MPC-D 102/12 is more organized, which indicates a slower growth rate [49]. This is especially true towards the periosteal surface of the femur of MPC-D 102/12, which shows a transition to parallel-fibred bone with reduced vascularity and closely spaced growth marks [50]
The presence of five growth marks indicates a minimum age of 5 years, it is likely that this individual was older and its earlier growth marks were obliterated by expansion of the medullary cavity [50,51,52]
Summary
Oviraptorosaurs are theropod dinosaurs known from an excellent fossil record spanning much of the Cretaceous of Asia and North America [1]. Oviraptorosaurs had pennaceous feathers [2,3,12], and most were completely edentulous [1], presumably possessing a keratinous rhamphotheca. They retained two functional oviducts [13], but brooded their eggs like birds [6]. Between the Nanxiong Formation of China and the Nemegt Basin of Mongolia, at least 15 oviraptorid genera are known, of which eight have been described in the last decade [14,15,16] This flurry of discovery has documented one of the last diversifications of non-avian theropods prior to the Cretaceous–Palaeogene (K-Pg) extinction [14,15]
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