One among many: the enigmatic case of the Miocene mammal, Kolponomos newportensis

Abstract

<p><i>Kolponomos newportensis</i> is an enigmatic Miocene mammal allied to stem Pinnipedimorpha. It has been suggested that <i>Kolponomos</i> fed on hard-shelled benthic marine invertebrates by using its mandible as a wedge to dislodge its prey from the sea bottom by means of strong pull and torque forces. This unique feeding style was thought to originate from a singular case of mosaic convergence in mandible biomechanics between <i>Kolponomos</i> and the sabretoothed cat <i>Smilodon</i>, which complied with similarly strong torque forces when grappling with prey. As such forces must have reflected on the cranium as well, we hypothesize that the convergence between <i>Kolponomos</i> and the sabretoothed cats could have affected its shape. To test this hypothesis, we looked for patterns of morphological convergence in cranial shape between <i>Kolponomos</i> and sabretoothed cats. We found that <i>Kolponomos</i> is not distinctly closer to <i>Smilodon</i> than a number of other pinnipeds. Yet, local areas of shape convergence with Smilodon are observed in the canine area and the posterior part of the cranium, that is where the bite applies and the temporalis muscle is located, respectively. These results indicate that the mosaic convergence present between the mandibles of <i>Kolponomos</i> and <i>Smilodon</i> is partially reflected in the cranium as well.</p>