Hyainailouros

Hyainailouros ("hyena-cat") is an extinct polyphyletic genus of hyaenodont belonging to the family Hyainailouridae that lived during the Early to Late Miocene from 20.0 to 11.4 million years ago, making it one of the last known hyaenodonts. This genus comprises at least three species spread across Afro-Eurasia. Currently, there’s a debate whether or not Megistotherium was synonymous to Hyainailouros or a separate genus entirely. The genus currently consists of at least 3 species, H. bugtiensis, H. sulzeri, and H. napakensis. H. sulzeri was the type species of and the largest species within the genus, weighing 500 kg (1,100 lb). On the other hand, H. napakensis was believed to have been the smallest weighing 202–271 kg (445–597 lb), three species would’ve been some of the largest known hyaenodonts.

Hyainailouros and other large hyainailourines were thought to have been large, solitary predators that were specialized on hunting probsocideans and rhinoceroses. The extinction of large hyainailourines such as Hyainailouros, may have been due to the decline of large herbivores and competition with social carnivorans, as their larger, more complex brains, would’ve enabled them to steal kills from the solitary hyainailourines like Hyainailouros. However, studies have found that brain sizes have little to no correlation with sociality among carnivorans, with relative sizes of the anterior brain playing a larger role in the gregariousness among carnivorans, in addition to the habitats being unfavorable to pack hunting in Early Miocene Africa.