ARE TROCHLEAE THE KEY TO UNRAVELING THE RIDDLE OF KANSAS' "MAXIMUM CAT?"

True cats first appeared in North America in the Late Miocene, but their early evolutionary history on the continent remains shrouded in mystery. Three felid genera are currently recognized from the North American Miocene: the bobcat-sized Pseudaelurus, the saber-toothed Machairodus, and the enigmatic endemic Nimravides. However, an enormous humerus excavated in 1890 was assigned to the new species "Felis maxima" and provided the first indication that exceptionally large cats were present early in the group's history in North America; the species is now a nomen nudum, but similar specimens have since been uncovered throughout the Great Plains and the Intermountain West. Do these specimens represent normal body size variation within a currently recognized taxon or sexual dimorphism within a species, or do they indicate the presence of an as-yet unnamed cat? Determining the answer to this question has proven difficult, in large part because the relevant fossils are almost entirely postcrania, which are much less diagnostic than cranial and dental remains. It has been suggested that humeral trochleae may be valuable tools for assigning big cat postcrania to either the Pantherinae or the Machairodontinae, as a medially elongated and deflected trochlea was thought to be characteristic of saber-toothed cats. However, more recent work has suggested that trochlea morphology may be shaped by function more than by phylogeny, negating its value as a diagnostic tool. We tested the diagnostic utility of felid trochleae by incorporating data from extinct felids and other feliform carnivores into an existing data set of trochlea shape in extant felids. Our data support the hypothesis that trochlea shape is driven primarily by forearm function and therefore cannot be used to identify postcrania in the absence of craniodental remains. This leaves the identity of “Felis maxima” a mystery, though the size and distribution of these remains suggest that they can most likely be attributed to large specimens of Nimravides.