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

Abstract

The Nemegt Formation of the Gobi Desert of Mongolia has produced one of the most abundant and diverse oviraptorosaur records globally. However, the caenagnathid component of this fauna remains poorly known. Two caenagnathid taxa are currently recognized from the Nemegt Formation: Elmisaurus rarus and Nomingia gobiensis. Because these taxa are known from mostly non-overlapping material, there are concerns that they could represent the same animal. A partial, weathered caenagnathid skeleton discovered adjacent to the holotype quarry of Nomingia gobiensis is referable to Elmisaurus rarus, revealing more of the morphology of the cranium, mandible, pectoral girdle, and pubis. Despite metatarsals clearly exhibiting autapomorphies of Elmisaurus rarus, overlapping elements are identical to those of Nomingia gobiensis, and add to a growing body of evidence that these taxa represent a single morphotype. In the absence of any positive evidence for two caenagnathid taxa in the Nemegt Formation, Nomingia gobiensis is best regarded as a junior synonym of Elmisaurus rarus. Low caenagnathid diversity in the Nemegt Formation may reflect broader coexistence patterns with other oviraptorosaur families, particularly oviraptorids. In contrast to North America, competition with the exceptionally diverse oviraptorids may have restricted caenagnathids to marginal roles in Late Cretaceous Asian ecosystems.

A new oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America

“…The astragalus and calcaneum are fused into a single element without a suture ( Fig 2 ), as is seen in Anzu wyliei [ 12 ] but not all other caenagnathids, including Maastrichtian examples (RSM P2600.1) [ 39 , 53 , 62 ]. Surprisingly, the astragalocalcaneum itself appears to be coossified with the end of the tibia ( Fig 3 ), a trait that is so far unknown in caenagnathids, but has been described in Avimimus [ 24 ] and observed in an undescribed partial tibiotarsus, possibly also from a caenagnathid, from the Dinosaur Park Formation of Alberta (TMP 1985.065.0001; GFF pers.…”

“…infernalis exhibits several characters of the metatarsus noted to be diagnostic of the clade Caenagnathidae [ 46 ]. Specifically, the semi-arctometatarsalian relationship of the proximal ends of metatarsals III and IV, the anteroposteriorly flattened metatarsal III, the prominent and deep concavity on the posterior surface of the tarsometatarsus, and the cruciate ridges on the posterior side of metatarsal III are diagnostic of caenagnathids [ 2 , 12 , 41 , 42 , 45 , 53 ]. While the specimen’s incompleteness makes it difficult to place within Caenagnathidae with any great precision, it does share some affinities with Citipes elegans and Elmisaurus rarus in the pronounced development of the cruciate ridges on metatarsal III, the development of a proximal posterior protuberance on metatarsals III and IV, and the fusion of distal tarsal IV to metatarsal IV.…”

“…However, some discrepancies in caenagnathid diversity remain. Differences in species richness between Asia and North America were recently addressed [ 53 ], but differences within North American ecosystems are less clear [ 41 , 44 ]. Whereas caenagnathids were highly diverse in the Campanian [ 37 , 41 , 45 , 47 ], they appear to be less diverse in the Maastrichtian, with Anzu wyliei as the only named taxon [ 12 ].…”

A New Dromaeosaurid (Dinosauria: Coelurosauria) from Khulsan, Central Mongolia

“…These are short compared to the elongate hypapophyses of some oviraptorids, such as Citipati osmolskae (Napoli et al, in prep. ), but similar in size to those of most pennaraptorans, including dromaeosaurids like Shri devi (IGM 100/980) and oviraptorosaurs such as Nomingia gobiensis (possibly a junior synonym of Elmisaurus rarus; see Funston et al, 2021) and Khaan mckennai (Barsbold et al, 2000;Balanoff and Norell, 2012). The transverse processes are poorly preserved but appear to be anteroposteriorly broad at their base, tapering toward their lateral extent.…”