Cave hyena

The cave hyena (Crocuta crocuta spelaea and Crocuta crocuta ultima), also known as the Ice Age spotted hyena, are paleosubspecies of spotted hyena known from Eurasia, which ranged from the Iberian Peninsula to eastern Siberia. It is one of the best known mammals of the Ice Age and is well represented in many European bone caves. It preyed on large mammals (primarily wild horses, steppe bison and woolly rhinoceros), and was responsible for the accumulation of hundreds of large Pleistocene mammal bones in areas including horizontal caves, sinkholes, mud pits, and muddy areas along rivers.

Genetic evidence from the nuclear genome suggests that Eurasian Crocuta populations (including the west Eurasian Crocuta crocuta spelaea and Asian Crocuta crocuta ultima) were highly genetically divergent from African populations (having estimated to have split over 1 million years ago), though the lack of clear separation between mitochondrial genome lineages suggests that the two populations interbred for some time after the initial split. Some authors have suggested that the two subspecies should be raised to species level as Crocuta spelaea and Crocuta ultima.

The cause of the cave hyena's extinction is not fully understood, though it could have been due to a combination of factors, including human activity, diminished quantities of prey animals, and climate change.

Description and paleoecology
The main difference between the spotted hyena and the cave hyena lies in the different length of the bones of the hind and front limbs. In the cave hyena, the humerus and the femur are longer, indicating an adaptation to environments other than those of the spotted hyena. The former was also a heavier and more robust animal: an almost complete specimen, found from the Los Aprendices cave in northern Spain, was estimated to weigh 103 kilograms. As in the spotted hyena, the females were larger than the males. A study of 16 fossil specimens of Pleistocene Crocuta indicated that the cave hyena was subject to Bergmann's rule, becoming larger during glacial periods and smaller during interglacial periods. The same study revealed a progressive increase in carnivorous tooth adaptations during glacial periods, indicating that it was an even more active hunter than today's spotted hyena, a behaviour necessitated by the need to feed on calorie rich fresh meat in a freezing environment. Rock paintings in the Lascaux and Chauvet Caves indicate that the cave hyena had the characteristic patches and mane of the spotted hyena. It has been proposed that it possessed thicker fur than the spotted hyena as an environmental adaptation.

Brain
Intracranial digital casts taken from spotted hyenas and two cave hyena skulls showed that the latter had an encephalic volume of 174–218 cm³, higher than today's spotted hyena which has an average volume of 160 cm³. In cave hyenas, however, the anterior telencephalon occupied only 15.9-16.6% of the total brain volume, in contrast to the spotted hyena, whose anterior telencephalon occupied 24.5%. As previous studies show that there is a correlation between telencephalon development and feeding sociability and flexibility in hyenas, it has been proposed, in light of this finding, that the cave hyena did not demonstrate complex social behaviors or adaptability like the spotted hyena, being instead more similar like brown and striped hyena both known as solitary scavengers.

Diet
The cave hyena's diet differed little from contemporary African spotted hyenas. The most common prey found in Europe are invariably horses, and in the Srbsko Chlum-Komin Cave alone (in the Czech Republic), horse remains make up 51% of the species present. This predilection for equines distinguishes the cave hyena from today’s spotted hyenas, which are known to target smaller antelope (impala, gazelle, wildebeest) as well as opportunistically scavenge carrion. Steppe bison remains are generally rare in hyena burrows, and it has been proposed that, except during glacial periods, these were avoided to lessen competition with cave lions and wolves. However, certain sites, such as the cave of San Teodoro, where bison make up 50% of the remains, indicate that certain populations of hyenas specialized their hunting where mammoths and bears were scarce, whose carcasses were a main source of food in much of Europe. Cervids are rare or absent in the burrows, probably being too fast for hyenas. However, exceptions to this pattern also exist; the site of Fouvent-Saint-Andoche represents a hyena den containing remains of red deer, Irish elk, and reindeer. Cave hyenas extensively engaged in cannibalism.

History of discovery and classification
Although the first full account of the cave hyena was given by Georges Cuvier in 1812, skeletal fragments of the cave hyena have been described in scientific literature since the 18th century, though they were frequently misidentified. The first recorded mention of the cave hyena in literature occurs in Kundmann's 1737 tome Rariora Naturæ et Artis, where the author misidentified a hyena's mandibular ramus as that of a calf. In 1774, Esper erroneously described hyena teeth discovered in Gailenreuth as those of a lion, and in 1784, Collini described a cave hyena skull as that of a seal. The past presence of hyenas in Great Britain was revealed after William Buckland's examination of the contents of Kirkdale Cave, which was discovered to have once been the location of several hyena den sites. Buckland's findings were followed by further discoveries by Clift and Whidbey in Oreston, Plymouth.

In his own 1812 account, Cuvier mentioned a number of European localities where cave hyena remains were found, and considered it a different species from the spotted hyena on account of its superior size. He elaborated his view in his Ossemens Fossiles (1823), noting how the cave hyena's digital extremities were shorter and thicker than those of the spotted hyena. His views were largely accepted throughout the first half of the 19th century, finding support in de Blainville and Richard Owen among others. Further justifications in separating the two animals included differences in the tubercular portion of the lower carnassial. Boyd Dawkins, writing in 1865, was the first to definitely cast doubt over the separation of the spotted and cave hyena, stating that the aforementioned tooth characteristics were consistent with mere individual variation. Writing again in 1877, he further stated after comparing the two animals' skulls that there are no characters of specific value.

Analysis of the mitochondrial genomes of Eurasian Crocuta specimens shows no clear separation from African lineages. However, analysis of full nuclear genomes suggests that African and Eurasian Crocuta populations were largely separate, having estimated to have diverged from each other around 2.5 million years ago, closely corresponding to the age of the earliest Crocuta specimens in Eurasia, which are around 2 million years old from China. The nuclear genome results also suggested that the European and Asian populations (the latter often assigned to the separate subspecies C. crocuta ultima) were distinct from each other, but were more closely related to each other overall than to African Crocuta populations. Analysis of the nuclear genome suggests that there had been interbreeding between these populations for some time after the split, which likely explains the discordance between the nuclear and mitochondrial genome results, with the mitochondrial genomes of African and European Crocuta more closely related to each other than to Asian Crocuta, suggesting gene flow between the two groups after the split between the Asian and European populations.

Distribution
Crocuta was formerly widely distributed across northern Eurasia during the Middle-Late Pleistocene, with C. c. ultima at times ranging as far southeast as Thailand and Laos in Southeast Asia.

Interactions
Kills partially processed by Neanderthals and then by cave hyenas indicate that hyenas would occasionally steal Neanderthal kills; and cave hyenas and Neanderthals competed for cave sites. Many caves show alternating occupations by hyenas and Neanderthals. The presence of large hyena populations in the Russian Far East may have delayed the human colonisation of North America. There is fossil evidence of humans in Middle Pleistocene Europe butchering and presumably consuming hyenas.

In rock art
The cave hyena is depicted in a few examples of Upper Palaeolithic rock art in France. A painting from the Chauvet Cave depicts a hyena outlined and represented in profile, with two legs, with its head and front part with well distinguishable spotted coloration pattern. Because of the specimen's steeped profile, it is thought that the painting was originally meant to represent a cave bear, but was modified as a hyena. In Lascaux, a red and black rock painting of a hyena is present in the part of the cave known as the Diverticule axial, and is depicted in profile, with four limbs, showing an animal with a steep back. The body and the long neck have spots, including the flanks. An image on a cave in Ariège shows an incompletely outlined and deeply engraved figure, representing a part of an elongated neck, smoothly passing into part of the animal's forelimb on the proximal side. Its head is in profile, with a possibly re-engraved muzzle. The ear is typical of the spotted hyena, as it is rounded. An image in the Le Gabillou Cave in Dordogne shows a deeply engraved zoomorphic figure with a head in frontal view and an elongated neck with part of the forelimb in profile. It has large round eyes and short, rounded ears which are set far from each other. It has a broad, line-like mouth that evokes a smile. Though originally thought to represent a composite or zoomorphic hybrid, it is probable it is a spotted hyena based on its broad muzzle and long neck. The relative scarcity of hyena depictions in Paleolithic rock art has been theorised to be due to the animal's lower rank in the animal worship hierarchy; the cave hyena's appearance was likely unappealing to Ice Age hunters, and it was not sought after as prey. Also, it was not a serious rival like the cave lion or bear, and it lacked the impressiveness of the mammoth or woolly rhino.

Extinction
The youngest known specimens of cave hyenas in Europe date to around 31,000 years ago, while the youngest specimens in East Asia date to around 20,000 years ago. Potential causal factors for extinction include decreasing temperatures, competition with other carnivores, including humans for food and living space, and decreased prey abundance. Evidence suggests that climate change alone cannot account for the cave hyena's extinction in Europe and that other factors, such as human activity and decreasing prey abundance, are necessary to explain it.