A unique feeding strategy of the extinct marine mammalKolponomos: convergence on sabretooths and sea otters

Abstract

Mammalian molluscivores feed mainly by shell-crushing or suction-feeding. The extinct marine arctoid, Kolponomos, has been interpreted as an otter-like shell-crusher based on similar dentitions. However, neither the masticatory biomechanics of the shell-crushing adaptation nor the way Kolponomos may have captured hard-shelled prey have been tested. Based on mandibular symphyseal morphology shared by Kolponomos and sabre-toothed carnivores, we hypothesize a sabretooth-like mechanism for Kolponomos prey-capture, whereby the mandible functioned as an anchor. Torque generated from jaw closure and head flexion was used to dislodge prey by prying, with prey then crushed using cheek teeth. We test this hypothesized feeding sequence using phylogenetically informed biomechanical simulations and shape analyses, and find a strongly supported, shared high mandibular stiffness in simulated prey-capture bites and mandibular shape in Kolponomos and the sabre-toothed cat Smilodon. These two distantly related taxa converged on using mandibles to anchor cranial torqueing forces when prying substratebound prey in the former and sabre-driving forces during prey-killing in the latter. Simulated prey-crushing bites indicate that Kolponomos and sea otters exhibit alternative structural stiffness-bite efficiency combinations in mandibular biomechanical adaptation for shell-crushing. This unique feeding system of Kolponomos exemplifies a mosaic of form-function convergence relative to other Carnivora.

A biomechanical approach to understand the ecomorphological relationship between primate mandibles and diet

“…Molar Biting) although they are not characteristic of the strength of the jaw and, as a consequence, not used in our interpretation. These results are consistent with previous research on armadillos 29 , 41 , marine mammals 59 , Artiodactyla and Perissodactyla 27 and Carnivora 60 . The latter studies used FEA to test mandibular stiffness in relation to diet and feeding classification and yielded significant relationships.…”

The coastal North Pacific: Origins and history of a dominant marine biota

“…It is likely that the Desmostylia and the sea otter entered from the Asian side, whereas pinnipeds, Kolponomos and Salmonidae almost certainly entered the North Pacific from North America. All these groups became important consumers, either herbivores (Desmostylia), predators targeting molluscs and other invertebrates ( Kolponomos and Enhydra ; see Tseng, Grohé, & Flynn, ), or fish eaters (pinnipeds, Oncorhynchus and some populations of Enhydra ). Desmostylians are probably the earliest temperate‐zone herbivorous mammals anywhere in the marine world, and as such have significantly affected algal evolution (see above).…”

Comparative biogeography: innovations and the rise to dominance of the North Pacific biota

“…Another North Pacific innovation with large ripple effects was the in situ evolution of durophagy, defined as the predation of hard-shelled animals by means of breakage or other extractive techniques. The most important durophages in the North Pacific are large mammals, beginning with Kolponomos in the Late Oligocene [6] and followed successively by walruses (Odobenidae) and the extinct sea-lion genus Gomphotaria [7,8] during the Late Miocene, and the sea otter Enhydra during the Pliocene [9,10]. In each of these lineages, durophagy is a derived condition evolving from more raptorial modes of predation on more active prey.…”