No compelling evidence for deinocheirids in the Judith River Formation: a comment on Chinzorig et al. (2025)

A pair of large ornithomimosaurian dentaries from the Judith River Formation (upper Campanian) of Montana were recently suggested to belong to Deinocheiridae, based on gross morphological features. If true, a deinocheirid from the Upper Cretaceous of Montana would be remarkable, given that none have been found there or in adjacent, penecontemporaneous deposits before; ornithomimosaurs are otherwise represented only by Ornithomimidae. We reconsider those features of the dentary that purportedly differentiate deinocheirids from ornithomimids and find them to be of limited diagnostic value. The incompleteness of the recently assigned Montanan material further frustrates morphometric analysis. Thus, we argue that it cannot confidently be assigned to Deinocheiridae, the taxonomic constituency of which remains unsettled. The Montana specimen is nevertheless significant, as it represents an aberrantly large ornithomimosaur from the Upper Cretaceous of North America.