Scimitar cat

''Homotherium'' is an extinct genus of scimitar-toothed cat belonging to the extinct subfamily Machairodontinae that inhabited North America, Eurasia, and Africa, as well as possibly South America during the Pliocene epochs from around 4 million to 12,000 years ago. It was one of the last surviving members of the subfamily alongside the more famous sabertooth ''Smilodon'', to which it was not particularly closely related. It was a large cat, comparable in size to a lion, functioning as an apex predator in the ecosystems it inhabited. It had an elongate neck and relatively elongate legs, a relatively short back and a very short tail, with the mummy of a ''H. latidens'' cub of Late Pleistocene age found in Siberia having a plain dark brown coat colour. In comparison to ''Smilodon'', the canines of ''Homotherium'' were shorter, though still longer than those of living cats, and it is suggested to have had a different ecology from ''Smilodon'' as a pursuit predator adapted to running down large prey, such as equines, bison and juvenile mammoths in open habitats, with ''Homotherium'' also proposed to have likely engaged in cooperative hunting.

Research history and taxonomy

Eurasia

The first fossils of ''Homotherium'' were scientifically described in 1846 by Richard Owen as the species ''Machairodus latidens,'' based on Pleistocene aged canine teeth found in Kent’s Cavern in Devon, southwestern England by the Reverend John MacEnery in 1826. The name ''Homotherium'' (Greek: (, 'same') and (, 'beast')) was proposed by Emilio Fabrini in 1890 during a review of machairodont material from the Late Pliocene-Early Pleistocene of Tuscany, Italy, without further explanation, for a new subgenus of ''Machairodus'', whose main distinguishing feature was the presence of a large diastema (gap) between the two lower (inferior) premolars. He further described two species in this new subgenus: ''Machairodus (Meganthereon) crenatidens'' and ''Machairodus (Meganthereon) nestianus,'' both from Tuscan remains. The genus name itself was rarely used in the scientific literature until the late 1940s. In 1918, the species ''Homotherium moravicum'' was described by Josef Woldřich based on remains found in what is now the Czech Republic. In 1936, Teilhard de Chardin described the new species ''Homotherium ultimus'' based on fossils from the Middle Pleistocene-aged Zhoukoudian cave complex near Beijing in northern China. Remains from the late Early Pleistocene-early Middle Pleistocene of Java in Indonesia have also been attributed to this species (as ''Homotherium ultimum''). In 1972, a species ''Homotherium davitashvili'' (also spelled ''davitasvilii'') was described based on fragmentary material found at the late Pliocene Kvabebi locality in Georgia. Other material from Odessa in Ukraine was tentatively assigned to this species in 2004. In 1986, the species ''Homotherium darvasicum'' was described by Scharif Scharapov based on material from Kuruksay, Tajikistan. In 1989, another species ''Homotherium tielhardipiveteaui'' was named by Scharapov based on fossils also found in Tajikistan. In 1996, ''Homotherium hengduanshanense'' was described based on fossils from the Hengduan Mountains of southwestern China. Indeterminate remains of ''Homotherium'' have been reported from the Siwalik Hills of the northern Indian subcontinent, of Early - early Middle Pleistocene age.'

In a 1954 publication, Jean Viret proposed that ''Homotherium crenatidens'' was the applicable species name for much of the ''Homotherium'' material in the Late Pliocene-Early Pleistocene of Europe. While Ficcarelli in 1979 regarded ''H. crenatidens'' and ''H. latidens'' as distinct species, this was disputed by Alan Turner in a 1999 publication, who considered that the proposed morphological differences separating the two species were invalid and the two species were not distinct.

A 2014 review recognised only one species of ''Homotherium'' in Eurasia during the Late Pliocene-Pleistocene, ''Homotherium latidens.'' Other named ''Homotherium'' species from this time period, including ''H. crenatidens'', were found not to be distinct. Across time and space, the remains of ''H. latidens'' display considerable morphological variability, though there does not appear to be any clear pattern in this variation temporally or geographically (with the exception of the presence of "pocketing" of the margin of the masseteric fossa of the mandible appearing in Middle and Late Pleistocene ''H. latidens'', but not earlier ones), with the morphological variation of the entire span of ''Homotherium'' in Eurasia from the Late Pliocene to the Late Pleistocene being similar to the variation found at the large sample for individuals from the Incarcal locality from the Early Pleistocene of Spain, supporting a single valid species. Some older material from the Pliocene of Eastern Europe (such as that from the Odesa Catacombs in Ukraine) was tenatively considered to belong to a separate species. Some authors have continued to recognise ''Homotherium crenatidens'' as a valid, pan-Eurasian species chronologically earlier than ''H. latidens'' (with these authors suggesting that ''H. crenatidens'' spans the Late Pliocene-Early Pleistocene, while ''H. latidens'' spans the Middle-Late Pleistocene).

Africa

In 1947/48, Camille Arambourg described the species ''Homotherium ethiopicum'' from remains found in the Omo locality in Ethiopia. This publication helped popularise the genus ''Homotherium'', which was little used prior. This species has been later regarded as a ''nomen dubium'', with the type specimen, a lower jaw, possibly actually belonging to '' Dinofelis'' (another machairodontine) instead.

In 1972 the species ''Homotherium problematicum'' (originally ''Megantereon problematicus'') was named based on fragmentary material from the Makapansgat locality in South Africa, of late Pliocene-Early Pleistocene age. ''Homotherium hadarensis'' was described in 1988, based on remains found in the Pliocene aged Hadar Formation of the Afar region of Ethiopia. In 2015, further material from the Hadar Formation was tentatively referred to ''H. hadarensis''. A third species, ''Homotherium africanum'' (originally ''Machairodus africanus''), has also been included based on remains found in Aïn Brimba, in Tunisia, North Africa, dating to the early-middle Pliocene. In 1990, Alan Turner challenged the validity of ''H. problematicum'' and ''H. hadarensis'', and later authors have generally refrained from referring African ''Homotherium'' fossils to any specific species due to their largely fragmentary nature. In 2021, indeterminate remains of ''Homotherium'' were reported from the Tobène locality of Senegal in West Africa, dating to the Early Pliocene. Indeterminate remains of ''Homotherium'' have also been reported from the Ahl al Oughlam locality in Morocco, dating to the Late Pliocene.

Americas

In 1905, Merriam described a new species ''Machaerodus ischyrus''. Subsequently, in 1918, Merriam reassigned it to a new genus ''Ischyrosmilus'' along with the new species ''Ischyrosmilus idahoensis''. The genus ''Dinobastis'' was originally named by Cope in 1893, with the type species ''Dinobastis serus''. In 1965, the species ''Ischyrosmilus johnstoni'' was described. In the same paper, it was noted that a comparative study of both ''Ischyrosmilus'' and ''Homotherium'' might conclude them as synonyms.

In 1966, Churcher deemed ''Dinobastis'' as a junior synonym of ''Homotherium'', and recombined ''D. serus'' as ''Homotherium serum.'' In 1970, a new species ''Ischyrosmilus crusafonti'' was described from the early Pleistocene of Nebraska. In 1988, after some debate, the genus ''Ischyrosmilus'' was declared a junior synonym of ''Homotherium'' and all four species were reassigned to that genus as ''H. ischyrus'', ''H. idahoensis'', and ''H. johnstoni''. The same paper also proposed keeping ''Dinobastis serus'' separate from ''Homotherium''. Up to five species have been recognised from North America: ''H. idahoensis'', ''H. crusafonti'', ''H. ischyrus'', ''H. johnstoni'', and ''H. serum,'' while other authors suggest that there are only two species, with older Blancan