Elbow-joint morphology in the North American 'cheetah-like' cat Miracinonyx trumani

Abstract

The North American cheetah-like cat Miracinonyx trumani is an extinct species that roamed the Pleistocene prairies 13 000 years ago. Although M. trumani is more closely related to the cougar (Puma concolor) than to the living cheetah (Acinonyx jubatus), it is believed that both A. jubatus and M. trumani possess a highly specialized skeleton for fast-running, including limbs adapted for speed at the expense of restricting the ability of prey grappling. However, forelimb dexterity of M. trumani has not been yet investigated. Here, we quantify the 3D-shape of the humerus distal epiphysis as a proxy for elbow-joint morphology in a sample of living cats to determine whether the extinct M. trumani was specialized to kill open-country prey using predatory behaviour based on fast running across the prairies and steppe terrains of the North American Pleistocene. We show that M. trumani had an elbow morphology intermediate to that of P. concolor and A. jubatus, suggesting that M. trumani had a less specialized pursuit predatory behaviour than A. jubatus. We propose that M. trumani probably deployed a unique predatory behaviour without modern analogues. Our results bring into question the degree of ecomorphological convergence between M. trumani and its Old World vicar A. jubatus.

Keywords: Miracinonyx trumani; convergence; elbow joint; predatory behaviour; pronghorn.

Figure 1.

Analysis of the elbow joint in M. trumani and other felids. (a) Landmarks digitized to capture the three-dimensional shape of the elbow joint. The elbow of M. trumani (mirrored) as an example. From top to bottom: anterior, posterior and inferior (distal) views. (b) Bivariate graph depicted from the first two eigenvectors obtained from PCA; (c) shape changes accounted for by the first two eigenvectors. (d) Bivariate graph depicted from the first two eigenvectors obtained from PCA for the restricted sample of M. trumani, P. concolor and A. jubatus, where ‘c’ is the centroid. The convex hulls are defined according to the results obtained from K-means analysis—i.e. K-means analysis classified M. trumani with Puma and not with Acinonyx. Ccar, Caracal caracal; Lser, Leptailurus serval; Lwie, Leopardus wideii; Nneb, Neofelis nebulosa; Pleo, Panthera leo; Ponc, Panthera onca; Pviv, Prionailurus viverrinus. Silhouettes are not to scale.

Figure 2.

Elbow joint topological deviations in M. trumani, A. jubatus and P. concolor illustrated with the distal end of the right humerus. (a) Topological superimposition analysis of the three models showing differences between their elbows. (b) Topological deviations analysis between the elbows of M. trumani (reference) compared to that of A. jubatus and P. concolor (targets) separately. Warm colours are positive deviations of the target elbow and cold colours are negative deviations of the target. Green colours represent similar topologies between the target and the reference model. Distance units in mm.