A New Large Hyainailourine from the Bartonian of Europe and Its Bearings on the Evolution and Ecology of Massive Hyaenodonts (Mammalia)

<div><p>We describe a new large-sized species of hypercarnivorous hyainailourine–<i>Kerberos langebadreae</i> gen. & sp. nov.–from the Bartonian (MP16) locality of Montespieu (Tarn, France). These specimens consist of a skull, two hemimandibles and several hind limb elements (fibula, astragalus, calcaneum, metatarsals, and phalanges). Size estimates suggest <i>K</i>. <i>langebadreae</i> may have weighed up to 140 kg, revealing this species as the largest carnivorous mammal in Europe at that time. Besides its very large size, <i>K</i>. <i>langebadreae</i> possesses an interesting combination of primitive and derived features. The distinctive skull morphology of <i>K</i>. <i>langebadreae</i> reflects a powerful bite force. The postcranial elements, which are rarely associated with hyainailourine specimens, indicate an animal capable of a plantigrade stance and adapted for terrestrial locomotion. We performed the first phylogenetic analysis of hyainailourines to determine the systematic position of <i>K</i>. <i>langebadreae</i> and to understand the evolution of the group that includes other massive carnivores. The analysis demonstrates that <i>Hemipsalodon</i>, a North American taxon, is a hyainailourine and is closely related to European <i>Paroxyaena</i>. Based on this analysis we hypothesize the biogeographic history of the Hyainailourinae. The group appeared in Africa with a first migration to Europe during the Bartonian that likely included the ancestors of <i>Kerberos</i>, <i>Paroxyaena</i> and <i>Hemipsalodon</i>, which further dispersed into North America at this time. We propose that the hyainailourines dispersed into Europe also during the Priabonian. These migrants have no ecological equivalent in Europe during these intervals and likely did not conflict with the endemic hyaenodont proviverrines. The discovery of <i>K</i>. <i>langebadreae</i> shows that large body size appears early in the evolution of hyainailourines. Surprisingly, the late Miocene <i>Hyainailouros</i> shares a more recent common ancestor with small-bodied hyainailourines (below 15 kg). Finally, our study supports a close relationship between the Hyainailourinae and Apterodontinae and we propose the new clade: Hyainailouridae.</p>