evolution

Hyenas arose in the Miocene, about 10 million years ago or so, from ancient relatives of the civet in Eurasia. Their success can be directly related to their efficient digestive system - other carnivores of the era could not make use of all parts of the carcass (such as bone) like the hyena.

In ancient times there were more species of hyenas than exist today. The peak of diversity was during the Pleistocene, with 4 genera and 9 species of hyena. 69 different species have been found in the fossil record, of which many have not been named.

The earliest known member of the hyaenidae is Protictitherium Gaillardi, which looked a lot like a civet, had retractable claws, and lived in trees. Several other species of Protictitherium lived during the Miocene after Gallardi. The first known European hyaenid was Plioviverrops Orbignyi, which specialized in insects.

Other hyaenids began evolving after this, getting bigger and changing dentition. Some became running hyenas, some small predators like jackals, and some started down the road to the bone-crushing hyenas of today.

The best known of the jackal-like hyenas was Ictitherium Viverrinum, which lived between 11 million and 6 million years ago. The genera of running hyenas were Chasmaporthetes, Lycyaena, and Hyaenictis. Chasmaporthetes crossed the Bering land bridge to America where it evolved into Chasmaporthetes Ossifragus, becoming North America's only native hyaenid before being brought to extinction by the end of the Ice Age.

The bone-crushing hyaenids included the genera of Belbus, Palinhyaena, Ikelohyaena, and Leecyaena. The teeth on these species got larger and heavier, but little is known about them beyond that because all we have discovered are fragmentary skulls. The most extreme bone-crusher was Adcrocuta Eximia, which lived in Greece, which had an even more powerful jaw than today's spotted hyena.

At the end of the Miocene, these early hyaenids became extinct. The Chasmaporthetes survived longer than most, as did a giant version of the spotted hyena that we call the cave hyena. Two other species evolved, Tongxinictes and Tungurictis, but they didn't last long. Hyaenids became extinct in Europe, only remaining in Africa in the 4 species we know today.

The aardwolf is currently believed to have split off early from the rest of the hyaenid family, but there is nothing that has been discovered that relates to the aardwolf in the fossil record, so he remains a mystery.