Homotherium Latidens

''Homotherium'', also known as the scimitar-toothed cat or scimitar cat, is an extinct genus of machairodontine saber-toothed predator, often termed scimitar-toothed cats, that inhabited North America, South America, Eurasia, and Africa during the Pliocene and Pleistocene epochs (4 mya – 12,000 years ago), existing for approximately .

It became extinct in Africa some 1.5 million years ago. The most recent Eurasian remains, recovered from what is now the North Sea, have been dated to around 28,000 years BP. In South America it is only known from a few remains in the northern region ( Venezuela), from the mid-Pleistocene.

Taxonomy and distribution

The name ''Homotherium'' ( Greek: (, 'same') and (, 'beast')) was proposed by Emilio Fabrini (1890), without further explanation, for a new subgenus of ''Machairodus'', whose main distinguishing feature was the presence of a large diastema between the two inferior premolars.

The lineage of ''Homotherium'' is estimated (based on mitochondrial DNA sequences) to have diverged from that of '' Smilodon'' about 18 million years ago. ''Homotherium'' probably derived from '' Machairodus'' and appeared for the first time at the Miocene– Pliocene border, about 4 to 5 million years ago. During the Pleistocene it occurred in vast parts of Eurasia, North America and until the middle Pleistocene (about 1.5 million years ago) even in Africa. A fossil of ''H. crenatidens'' was inadvertently dredged from the bed of the North Sea, which was a flat, low-lying extent of marshy tundra laced with rivers during the last glacial period. It was thought that ''H. latidens'' had gone extinct relatively early, nearly 300,000 years ago, but a rogue specimen of ''H. latidens'' was found in the North Sea of Europe, dated to be from 28,000 years ago. There has also been a discovery of 1.8-million-year-old fossils in Venezuela, indicating that scimitar-toothed cats were able to invade South America along with '' Smilodon'' during the Great American Interchange. These remains form the holotype of ''Homotherium venezuelensis''. How long they lasted in South America is not yet evident. ''Homotherium'' survived in Eurasia until about 28,000 years ago.

Several Eurasian species have been recognized based mainly on differences in the size and shape of the upper canines and body size: ''H. latidens'', ''H. nestianus'', ''H. sainzelli'', ''H. crenatidens'', ''H. nihowanensis'', and ''H. ultimum''. However, given the range of sizes found in extant large cats, it is likely that they represent a single species, ''Homotherium latidens''.

Two species described from early Pleistocene Africa, ''H. ethiopicum'' and ''H. hadarensis—''also hardly differ from the Eurasian forms. On the African continent the genus disappeared about 1.5 million years ago. In North America a very similar species, ''H. serum'', occurred from the late Pliocene until the late Pleistocene. However, both morphological and genetic data suggest that all late Pleistocene ''Homotherium'' individuals worldwide should probably be regarded as members of ''H. latidens''. Remains have been found at various sites between Alaska and Texas. In the southern parts of its range the American ''Homotherium'' co-existed with ''Smilodon''; in the northern parts it was the only species of saber-toothed cat. The American ''Homotherium'' was originally described by the name ''Dinobastis''.

Despite ''Homotherium''s vast range and the large quantity of fossil remains from Eurasia, Africa and North America, complete skeletons of this cat are relatively rare. One of the most famous sites of ''Homotherium'' remains is Friesenhahn cave in Texas, where 30 ''Homotherium'' skeletons were found, along with hundreds of juvenile mammoths and several dire wolves.

The genus ''Dinobastis'' was originally named by Cope (1893). Its type is ''Dinobastis serus''. It was synonymized subjectively with ''Smilodon'' by Matthew (1910) and later with ''Homotherium'' by Churcher (1966), Schultz ''et al.'' (1970), Waldrop (1974), Kurtén and Anderson (1980), Churcher (1984) and and Carpenter (1988).

Description

''Homotherium'' reached at the shoulder and weighed an estimated and was therefore about the size of a male African lion. Compared to more familiar machairodonts, like ''Smilodon'' or '' Megantereon'', ''Homotherium'' had comparatively shorter upper canines, but these flat, serrated teeth were still longer than those of any living cat. ''Homotheriums incisors and lower canines formed a powerful puncturing and gripping device. The skull was longer than in ''Smilodon'', and it possessed a well-developed sagittal crest, where muscles were attached to power the lower jaw. The lower jaw had downwards-flared flanges to protect the upper canines. Its large canine teeth were crenulated and designed for slashing rather than purely stabbing. However, a 2018 study by Figueirido and colleagues found that ''Homotherium'' possessed a bite adapted to clamp and hold while inflicting damage with its canines, similar to a lion's, due to the larger amounts of trabecular bone present in the skulls of the genus. This is unlike the canine shear-bite of ''Smilodon'', which it has been compared to, and this difference in killing bites provides evidence for distinct ecological adaptations.

The large upper canines of ''Homotherium'' were likely hidden by the upper lips and gum tissues of the lower lips jaw similar to extant cats, unlike the larger upper canines of ''Smilodon''.

The unusually large, square nasal opening, similar to that of the cheetah (''Acinonyx jubatus''), may have allowed faster oxygen intake, which would have facilitated strenuous cursorial activity and cooling of the brain following such behaviour. The visual cortex in ''Homotheriums brain was large and complex, also alike that of the modern cheetah, implying that it relied heavily on vision during the hunt.

Diet and habitats

The decline of ''Homotherium'' could be a result of the disappearance of large herbivorous mammals like mammoths in America at the end of the Pleistocene. In North America fossil remains of ''Homotherium'' are less abundant than those of its contemporary ''Smilodon''. For the most part it probably inhabited higher latitudes and altitudes and therefore was likely to be well adapted to the colder conditions of the mammoth steppe environment. The reduced claws, relatively slender limbs, and sloping back all appear to be adaptations for endurance running in open habitats.

Genomic analysis supports the hypothesis that ''Homotherium'' was social and well-adapted to life as a pursuit predator. Genes revealing high genetic diversity indicate the genus was far more common than previously assumed due to the preservation bias of the fossil record. The study also revealed that this genus of machairodont was most likely diurnal, and would have mainly hunted in daylight.

African ''Homotherium'' species seem to have hunted early Pleistocene species of '' Deinotherium'', likely preferring to target the more vulnerable adolescents or calves in a herd. Due to their saber-teeth, an attack on such thick-skinned prey would have likely been significantly easier and less time-consuming compared to a similar hunt on modern elephants by lions.

At the well known Friesenhahn Cave site in Texas, the remains of almost 400 juvenile mammoths were discovered along with numerous ''Homotherium'' skeletons of all ages, from elderly specimens to cubs. Based on this fossil site, ''Homotherium'' was likely a social predator that would have been specialized in hunting young mammoths and that subsequently dragged the kills into secluded caves to eat in relative peace. ''Homotherium'' also seemed to have retained the excellent nocturnal vision typical of most cats, and hunting at night in the arctic regions where many ''Homotherium'' have been found would have been a prime hunting method. The sloped back and powerful lumbar section of ''Homotherium''s vertebrae suggest a bear-like build, and thus that these animals could have been capable of pulling formidable loads; further, broken upper canines - a common injury in fossils of other machairodonts such as ''Machairodus'' and ''Smilodon'' that would have resulted from struggling with their prey - is not seen in ''Homotherium'', perhaps because their social groups would completely restrain prey items before any of the cats attempted to kill the target with their saber teeth. Moreover, the bones of the young mammoths found in Friesenhahn Cave show distinctive marks matching the incisors of ''Homotherium'', indicating that they could efficiently process most of the meat on a carcass and that the mammoths had been deposited in the caves by the cats themselves and not by scavengers. Examination of the bones also indicates that the carcasses of these juvenile mammoths were dismembered after being killed by the cats before being dragged away, suggesting that ''Homotherium'' would disarticulate their kill to transport it to a safe area such as a hidden lair or den and prevent competitors such as dire wolves and American lions from usurping the carcass.

See also

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References

External links

The saber-toothed cat of the North Sea
2008, accessed 10/28/2019



Saber-toothed cat jaw

South America gets two more sabercats

{{Taxonbar, from=Q132606

Homotherini
Pliocene carnivorans
Pleistocene carnivorans
Pleistocene extinctions
Cenozoic mammals of Africa
Cenozoic mammals of Asia
Cenozoic mammals of Europe
Cenozoic mammals of North America
Holarctic fauna
Prehistoric carnivoran genera
Zanclean first appearances
Fossil taxa described in 1890
Pleistocene mammals of North America
Pleistocene mammals of Africa
Saber-toothed cats