A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria

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.

A partial oviraptorosaur skeleton suggests low caenagnathid diversity in the Late Cretaceous Nemegt Formation of Mongolia

“…the Dinosaur Park and Horseshoe Canyon Formations), taxa in these ecosystems are highly disparate in morphology and body size [29,33]. Indeed, several studies have suggested that high oviraptorosaur diversity in several ecosystems was the result of morphological niche segregation [14,15,33,58]. Considering the low likelihood of this…”

“…Whereas caenagnathids were the only oviraptorosaurs in North America, both avimimids and oviraptorids coexisted with caenagnathids in the Nemegt Formation. Oviraptorids in particular were highly diverse in the Nemegt Formation [14,15,72] and although they were specialized for different diets [58,73], they may still have competed with caenagnathids for niche space as similarly-sized omnivores. The same may be true of other Late Cretaceous ecosystems in Asia, as several formations like the Bayan Mandahu, Djadokhta, and Nanxiong Formations have high diversities of oviraptorids and other small theropods, but have not yet produced any caenagnathids, despite the clear presence of caenagnathids in Asia by this time [37,[74][75][76][77][78].…”

“…The theropod component of this fauna is particularly well known, in contrast to other parts of the world, where the delicate bones of theropods are rarely preserved [ 8 , 9 ]. From the Nemegt Formation alone, a diverse assemblage of alvarezsaurids [ 10 ], dromaeosaurs [ 11 ], ornithomimids [ 12 , 13 ], oviraptorosaurs [ 14 , 15 ], therizinosaurs [ 16 ], troodontids [ 17 ], and tyrannosaurs [ 18 , 19 ] is known, comprising nearly 250 associated skeletons [ 7 , 20 ]. Whereas tyrannosaurs and ornithomimids form the bulk of the collected specimens, the oviraptorosaurs are the most diverse component of the fauna, known from at least nine genera [ 14 , 15 ].…”

“…From the Nemegt Formation alone, a diverse assemblage of alvarezsaurids [ 10 ], dromaeosaurs [ 11 ], ornithomimids [ 12 , 13 ], oviraptorosaurs [ 14 , 15 ], therizinosaurs [ 16 ], troodontids [ 17 ], and tyrannosaurs [ 18 , 19 ] is known, comprising nearly 250 associated skeletons [ 7 , 20 ]. Whereas tyrannosaurs and ornithomimids form the bulk of the collected specimens, the oviraptorosaurs are the most diverse component of the fauna, known from at least nine genera [ 14 , 15 ]. Unlike elsewhere [ 21 ], these genera represent each of the three Late Cretaceous families of oviraptorosaurs: avimimids, caenagnathids, and oviraptorids.…”

“…Funston et al [ 14 ] discussed this issue, noting that specimens not currently incorporated into phylogenies showed that each of the characters uniting Nomingia gobiensis with oviraptorids were also present in caenagnathids. Indeed, an updated phylogeny including these specimens recovers Nomingia gobiensis as a deeply-nested caenagnathid [ 15 , 33 ].…”