A SMALL ALVAREZSAURID CAUDAL VERTEBRA FROM THE HELL CREEK FORMATION (UPPER CRETACEOUS) OF MONTANA SHED LIGHT ABOUT THE DIVERSITY AND DISTRIBUTION OF PARVICORSORINAE IN NORTH AMERICA

JORGE GUSTAVO MESO

Revista del Museo Argentino de Ciencias Naturales

Latindex

Año: 2024

Alvarezsauridae is a bizarre clade of middle to small-sized maniraptoran theropods that diversified from the Lower Cretaceous to the Upper Cretaceous. This family includes the Parvicursorinae subclade, whose geographical distribution is limited to Laurasia, with a record of numerous species coming mainly from the Late Cretaceous beds of Asia. Here, I'm reporting a new small Parvicursorinae proximal caudal vertebra (LACM 153311) from the uppermost Maastrichtian Hell Creek Formation, Montana. This specimen possesses an unequivocal synapomorphy of the Alvarezsauridae clade, namely, the procoelous caudal vertebra. Likewise, also bears several Parvicursorinae features, such as the diameter of the neural canal concerning the height of the centrum, and absence of a subcircular depression on both lateral surfaces, and the development of a small ridge beneath the transverse process at mid-height of the centrum that not present. Body length estimation suggests that this specimen belonged to a roughly 1.47 m long animal, indicating an individual slightly smaller than the only alvarezsaurid known for this formation, Trierarchuncus prairiensis. LACM 153311 indicates that during the Late Cretaceous, the Parvicursorinae was more abundant and diverse than was believed previously in North America.