Spotted Hyena - Taxonomy, Origins and Evolution

Taxonomy, Origins and Evolution

Unlike the striped hyena, for which a number of subspecies were proposed in light of its extensive modern range, the spotted hyena is a genuinely variable species, both temporally and spatially. Its range once encompassed almost all of Africa and Eurasia, and displayed a large degree of morphological geographic variation, which lead to an equally extensive set of specific and subspecific epithets. It was gradually realised that all of this variation could be applied to individual differences in a single subspecies. In 1939, biologist L. Harrison Matthews demonstrated through comparisons between a large selection of spotted hyena skulls from Tanzania that all the variation seen in the then recognised subspecies could also be found in a single population, with the only set of characters standing out being pelage (which is subject to a high degree of individual variation) and size (which is subject to Bergmann's Rule). When fossils are taken into consideration, the species displayed even greater variation than it does in modern times, and a number of these named fossil species have since been classed as synonymous with Crocuta crocuta, with firm evidence of there being more than one species within the genus Crocuta still lacking.

Both Björn Kurtén and Camille Arambourg promoted an Asiatic origin for the species; Kurtén focussed his arguments on the Plio-Pleistocene taxon Crocuta sivalensis from the Siwaliks, a view defended by Arambourg, who nonetheless allowed the possibility of an Indo-Ethiopian origin. This stance was contested by Ficarelli and Torre, who referred to evidence of the spotted hyena's presence from African deposists dating from the early Pleistocene, a similar age to the Asian C. sivalensis. Studies on the phylogeographic distribution of mtDNA haplotypes indicates three migration events from Africa to Eurasia, though neither the topology of the phylogenetic tree or the fossil record exclude the possibility of an Asian origin. The earliest migration of spotted hyenas from Africa to Eurasia began less than 3.5 million years ago, most probably from the area where the first spotted hyena fossils were discovered, reaching East Asia and most likely also Pakistan. The second migration of spotted hyenas occurred less than 1.3–1.5 million years ago and resulted in the first arrival of hyenas in Europe and a separation of African spotted hyenas in a southern and a northern population. The third spotted hyena migration took place after 0.36 million years ago, starting from the northern African population and reaching both Europe and Asia. Unlike other African carnivores, with the exception of the leopard, there is no evidence to suggest that spotted hyenas underwent a genetic bottleneck during the Pleistocene.

The ancestors of the genus Crocuta diverged from Hyaena (the genus of striped and brown hyenas) 10 million years ago. The ancestors of the spotted hyena probably developed social behaviours in response to increased pressure from other predators on carcasses, which forced them to operate in teams. At one point in their evolution, spotted hyenas developed sharp carnassials behind their crushing premolars; this rendered waiting for their prey to die no longer a necessity, as is the case for brown and striped hyenas, and thus became pack hunters as well as scavengers. They began forming increasingly larger territories, necessitated by the fact that their prey was often migratory, and long chases in a small territory would have caused them to encroach into another clan's land. It has been theorised that female dominance in spotted hyena clans could be an adaptation in order to successfully compete with males on kills, and thus ensure that enough milk is produced for their cubs. Another theory is that it is an adaptation to the length of time it takes for cubs to develop their massive skulls and jaws, thus necessitating greater attention and dominating behaviours from females. Its appearance in Europe and China during the Cromerian period coincided with the decline and eventual extinction of Pachycrocuta brevirostris, the giant short-faced hyena. As there is no evidence of environmental change being responsible, it is likely that the giant short-faced hyena became extinct due to competition with the spotted hyena.