The skull evolution of oviraptorosaurian dinosaurs: the role of niche partitioning in diversification

Abstract

Oviraptorosaurs are bird‐like theropod dinosaurs that thrived in the final pre‐extinction ecosystems during the latest Cretaceous, and the beaked, toothless skulls of derived species are regarded as some of the most peculiar among dinosaurs. Their aberrant morphologies are hypothesized to have been caused by rapid evolution triggered by an ecological/biological driver, but little is known about how their skull shapes and functional abilities diversified. Here, we use quantitative techniques to study oviraptorosaur skull form and mandibular function. We demonstrate that the snout is particularly variable, that mandibular form and upper/lower beak form are significantly correlated with phylogeny, and that there is a strong and significant correlation between mandibular function and mandible/lower beak shape, suggesting a form–function association. The form–function relationship and phylogenetic signals, along with a moderate allometric signal in lower beak form, indicate that similar mechanisms governed beak shape in oviraptorosaurs and extant birds. The two derived oviraptorosaur clades, oviraptorids and caenagnathids, are significantly separated in morphospace and functional space, indicating that they partitioned niches. Oviraptorids coexisting in the same ecosystem are also widely spread in morphological and functional space, suggesting that they finely partitioned feeding niches, whereas caenagnathids exhibit extreme disparity in beak size. The diversity of skull form and function was likely key to the diversification and evolutionary success of oviraptorosaurs in the latest Cretaceous.

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 coexistence scenario and the lack of positive evidence for two morphotypes, “ Nomingia gobiensis” is best regarded as junior subjective synonym of Elmisaurus rarus .…”

“…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].…”

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

“…However, the potential role of the forelimb in niche partitioning has not been previously recognized. Differences in forelimb morphology between caenagnathids and oviraptorids in the Nemegt Basin [33,47,115] may be the result of broader dietary differences already recognized on the basis of the mandibles [110]. Forelimb adaptability could also have contributed to the coexistence of citipatines and heyuannines in the same areas, as the skulls and mandibles of these taxa occupy similar morphospaces [110].…”

Caenagnathids of the Dinosaur Park Formation (Campanian) of Alberta, Canada: anatomy, osteohistology, taxonomy, and evolution

“…Thus, current evidence suggests that all three caenagnathid taxa coexisted in the DPF, rather than constituting an anagenic lineage or a series of sequential forms replaced in association with faunal turnover. Considering the apparently highly specialized niche that oviraptorosaurs occupied relative to other theropods Ma et al 2020), some evidence of resource partitioning might be expected where species richness is relatively high, as is the case in the DPF. The variation in adult body sizes between each taxon may have facilitated the use of different resources later in life, and may have contributed to feeding height stratification , although this is untestable with currently known material and it is unclear what proportion of the caenagnathid diet comprised plant material.…”