Osteology and reassessment of Dineobellator notohesperus, a southern eudromaeosaur (Theropoda: Dromaeosauridae: Eudromaeosauria) from the latest Cretaceous of New Mexico

Abstract

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the end of the Cretaceous Period. The recently described Dineobellator notohesperus, consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, is the only diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southwestern United States. Reinterpreted and newly described material include several caudal vertebrae, portions of the right radius and pubis, and an additional ungual, tentatively inferred to be from manual digit III. Unique features, particularly those of the humerus, unguals, and caudal vertebrae, distinguish D. notohesperus from other known dromaeosaurids. This material indicates different physical attributes among dromaeosaurids, such as use of the forearms, strength in the hands and feet, and mobility of the tail. Several bones in the holotype exhibit abnormal growth and are inferred to be pathologic features resulting from an injury or disease. Similar lengths of the humerus imply Dineobellator and Deinonychus were of similar size, at least regarding length and/or height, although the more gracile nature of the humerus implies Dineobellator was a more lightly built predator. A new phylogenetic analysis recovers D. notohesperus as a dromaeosaurid outside other previously known and named clades. Theropod composition of the Naashoibito Member theropod fauna is like those found in the more northern Late Cretaceous North American ecosystems. Differences in tooth morphologies among recovered theropod teeth from the Naashoibito Member also implies D. notohesperus was not the only dromaeosaurid present in its environment.

Introduction to Dinosaurs: New Ideas from Old Bones papers honoring Peter Dodson

“…The Cretaceous Dineobellator notohesperus of New Mexico is the only diagnostic dromaeosaurid from the latest Cretaceous of all the southwestern United States. Jasinski and others reinterpret as well as describe new material attributable to this taxon (Jasinski et al, 2023). Morphological differences between Dineobellator and other dromaeosaurids shed new light on total morphological variation within Dromaeosauridae as well as imply possible behavioral differences (Jasinski et al, 2023).…”

“…Morphological differences between Dineobellator and other dromaeosaurids shed new light on total morphological variation within Dromaeosauridae as well as imply possible behavioral differences (Jasinski et al, 2023). And with the discovery of additional southern specimens, they suggest that a southern North American eudromaeosaur clade will eventually be found (Jasinski et al, 2023).…”