Simbakubwa

Simbakubwa ("great lion" in Swahili) is an extinct genus of hyaenodonts belonging to the family Hyainailouridae that lived in Kenya during the Early Miocene. It was discovered between 1978 and 1981 near Meswa Bridge in western Kenya, and its remains, consisting of a lower jaw, part of the snout, and some of the smaller limb bones, were originally believed to come from hyena. After re-examination by Matthew Borths and Nancy Stevens, it was named and assigned to the hyaenodont lineage in 2019. One species of Simbakubwa, S. kutokaafrika, has been described.

Body mass estimates for Simbakuba vary considerably based on which method is used, with the smallest being about 280 kg (620 lb), and the largest being 1,308 and 1,554 kg (2,884 and 3,426 lb), which would surpass modern polar bears. Based on body mass alone it is the second-largest known hyainailourid, behind Megistotherium. Due to the fact that the type skull has been heavily restored, not much is known about its shape. As with other hyaenodonts, Simbakubwa's molars bore so-called carnassial blades. These would have sharpened as the animal opened and closed its jaw, forming a perpetual cutting edge. Though little is known of the hindlimb anatomy of Simbakubwa, it appears to have had a semi-digitigrade gait, in which the heel was held off the ground, though not as strongly as in true digitigrades. A similar gait is seen in Hyainailouros, whereas Kerberos is an example of the ancestral plantigrade (with the heel planted on the ground) condition. A semi-digitigrade or digitigrade stance is an efficient means of conserving energy and is often associated with an open environment.

The enormous body size of Simbakubwa may be the result of its lineage evolving to specialise in large prey, such as proboscideans (elephants and their relatives) and rhinoceroses. Its extinction, along with that of other giant hyainailourines, may have been a consequence of this specialisation, as large herbivores tend to breed slowly and even a temporary population decrease would significantly impact a hyainailourine's prey base. Furthermore, as solitary animals, they may have been repelled from carcasses by more social carnivorans, further decreasing the resources available to them.