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| Eoneophron infernalis Atkins-Weltman, Simon, Woodward, Funston & Snively, 2024 Illustration by Zubin Erik Dutta facebook.com/ZDuttaArt |
Abstract
Caenagnathidae is a clade of derived, Late Cretaceous oviraptorosaurian theropods from Asia and North America. Because their remains are rare and often fragmentary, caenagnathid diversity is poorly understood. Anzu wyliei is the only caenagnathid species currently described from the late Maastrichtian Hell Creek Formation of the USA and is also among the largest and most completely preserved North American caenagnathids. Smaller, less complete caenagnathid material has long been known from the Hell Creek Formation, but it is unclear whether these are juvenile representatives of Anzu or if they represent distinct, unnamed taxa. Here, we describe a relatively small caenagnathid hindlimb from the Hell Creek Formation, and conduct osteohistological analysis to assess its maturity. Histological data and morphological differences from Anzu wyliei and other caenagnathids allow us to conclude that this specimen represents a new species of caenagnathid from the Hell Creek Formation, with a smaller adult body size than Anzu. This new taxon is also distinct from other small caenagnathid material previously described from the area, potentially indicating the coexistence of three distinct caenagnathid species in the Hell Creek Formation. These results show that caenagnathid diversity in the Hell Creek ecosystem has been underestimated.
Systematic paleontology
Theropoda Marsh 1878
Oviraptorosauria Barsbold 1976
Caenagnathidae Sternberg 1940
Eoneophron gen. nov.
Eoneophron infernalis sp. nov.
Holotype: CM 96523, partial hindlimb including right femur, right tibia and astragalocalcaneum, a right metatarsal III, and a right metatarsal IV.
Diagnosis: Caenagnathid oviraptorosaur diagnosed by the following combination of traits (autapomorphies are denoted with an asterisk): femoral head directed dorsomedially, rather than perpendicular to the shaft; astragalocalcaneum fused to tibia*, metatarsal III with well-developed posterior cruciate ridges continuous with the distal condyle; distal condyle of metatarsal III transversely wider than anteroposteriorly deep, with medial portion of condyle larger than lateral portion; proximal end of metatarsals III and IV project posteriorly to form proximal protuberance; distal tarsal IV coossified with the proximal end of metatarsal IV at maturity; shaft of metatarsal IV with well-developed oblique longitudinal ridge on anterior surface extending along the distal three-quarters of the shaft*.
Etymology: Genus name derived from the Ancient Greek “eo”–meaning “dawn,” and from the genus name of the Egyptian vulture, Neophron, sometimes referred to as the “pharaoh’s chicken.” The species name derives from Latin for Hell, in reference to the Hell Creek Formation. Together the taxon name equates to “Pharaoh’s dawn chicken from Hell.”
Locality and horizon: Collected from exposures of the upper Maastrichtian Hell Creek Formation, Meade County, South Dakota, United States of America. The specimen was prepared prior to acquisition, but matrix remains adhered to some areas, such as the proximal portion of the tibia and anterodistal region of the femur. These sediments resemble those of typical floodplain deposits such as siltstones with organic material as seen elsewhere in the Hell Creek Formation (KLAW, pers. obs.).
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| Artist’s depiction of Eoneophron infernalis (top left), MOR 752 (bottom left), and Anzu wyliei (right) in the Hell Creek Formation. Illustration by Zubin Erik Dutta. |
Kyle L. Atkins-Weltman, D. Jade Simon, Holly N. Woodward, Gregory F. Funston and Eric Snively. 2024. A New oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America. PLoS ONE. 19(1): e0294901. DOI: 10.1371/journal.pone.0294901