| Homotherium | |
|---|---|
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| Skeleton ofH. serum from Friesenhahn cave,Texas Science & Natural History Museum,University of Texas at Austin,Austin, Texas. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Suborder: | Feliformia |
| Family: | Felidae |
| Subfamily: | †Machairodontinae |
| Tribe: | †Homotherini |
| Genus: | †Homotherium Fabrini, 1890 |
| Type species | |
| Homotherium latidens Owen, 1846 | |
| Other species | |
For others, see text | |
| Synonyms | |
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Homotherium is anextinctgenus ofscimitar-toothed cat belonging to the extinct subfamilyMachairodontinae that inhabited North America, Eurasia, and Africa, as well as possibly South America during thePliocene andPleistocene epochs from around 4 million to 12,000 years ago.[1][2] It was one of the last surviving members of the subfamily alongside the more famous sabertoothSmilodon, to which it was not particularly closely related. It was a large cat, comparable in size to alion, functioning as anapex 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 aH. latidens cub of Late Pleistocene age found in Siberia having a plain dark brown coat colour. In comparison toSmilodon, the canines ofHomotherium were shorter, though still longer than those of living cats, and it is suggested to have had a different ecology fromSmilodon as apursuit predator adapted to running down large prey, such asequines,bison and juvenilemammoths in open habitats, withHomotherium also proposed to have likely engaged in cooperative hunting.
The first fossils ofHomotherium were scientifically described in 1846 byRichard Owen as the speciesMachairodus latidens,[3] based on Pleistocene aged canine teeth found inKent’s Cavern inDevon, southwestern England by the ReverendJohn MacEnery in 1826.[4] The nameHomotherium (Greek:ὁμός (homos, 'same') andθηρίον (therion, 'beast')) was proposed by Emilio Fabrini in 1890 during a review of machairodont material from the Late Pliocene-Early Pleistocene ofTuscany, Italy, without further explanation, for a new subgenus ofMachairodus, whose main distinguishing feature was the presence of a largediastema (gap) between the two lower (inferior) premolars. He further described two species in this new subgenus:Machairodus (Meganthereon) crenatidens andMachairodus (Meganthereon) nestianus, both from Tuscan remains.[5] The genus name itself was rarely used in the scientific literature until the late 1940s.[6] In 1918, the speciesHomotherium moravicum was described by Josef Woldřich based on remains found in what is now the Czech Republic.[7] In 1936,Teilhard de Chardin described the new speciesHomotherium ultimus based on fossils from the Middle Pleistocene-agedZhoukoudian cave complex near Beijing in northern China.[8] Remains from the late Early Pleistocene-early Middle Pleistocene ofJava in Indonesia have also been attributed to this species (asHomotherium ultimum).[9] In 1972, a speciesHomotherium davitashvili (also spelleddavitasvilii[6]) was described based on fragmentary material found at the late Pliocene Kvabebi locality in Georgia.[10][6] Other material from Odessa in Ukraine was tentatively assigned to this species in 2004.[11] In 1986, the speciesHomotherium darvasicum was described by Scharif Scharapov based on material from Kuruksay,Tajikistan.[12] In 1989, another speciesHomotherium tielhardipiveteaui was named by Scharapov based on fossils also found in Tajikistan.[13] In 1996,Homotherium hengduanshanense was described based on fossils from theHengduan Mountains of southwestern China.[14] Indeterminate remains ofHomotherium have been reported from theSiwalik Hills of the northern Indian subcontinent, of Early - early Middle Pleistocene age.[15]
In a 1954 publication, Jean Viret proposed thatHomotherium crenatidens was the applicable species name for much of theHomotherium material in the Late Pliocene-Early Pleistocene of Europe. While Ficcarelli in 1979 regardedH. crenatidens andH. 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.[6]
A 2014 review recognised only one species ofHomotherium in Eurasia during the Late Pliocene-Pleistocene,Homotherium latidens. Other namedHomotherium species from this time period, includingH. crenatidens, were found not to be distinct. Across time and space, the remains ofH. 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 massetericfossa of the mandible appearing in Middle and Late PleistoceneH. latidens, but not earlier ones), with the morphological variation of the entire span ofHomotherium 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 theOdesa Catacombs in Ukraine) was tenatively considered to belong to a separate species.[6] Some authors have continued to recogniseHomotherium crenatidens as a valid, pan-Eurasian species chronologically earlier thanH. latidens (with these authors suggesting thatH. crenatidens spans the Late Pliocene-Early Pleistocene, whileH. latidens spans the Middle-Late Pleistocene).[16]
In 1947/48,Camille Arambourg described the speciesHomotherium ethiopicum from remains found in the Omo locality in Ethiopia.[17] This publication helped popularise the genusHomotherium, which was little used prior.[6] This species has been later regarded as anomen dubium, with the type specimen, a lower jaw, possibly actually belonging toDinofelis (another machairodontine) instead.[18]
In 1972 the speciesHomotherium problematicum (originallyMegantereon problematicus) was named based on fragmentary material from theMakapansgat locality in South Africa, of late Pliocene-Early Pleistocene age.[19][20]Homotherium hadarensis was described in 1988, based on remains found in the Pliocene agedHadar Formation of the Afar region of Ethiopia.[21] In 2015, further material from the Hadar Formation was tentatively referred toH. hadarensis.[18] A third species,Homotherium africanum (originallyMachairodus africanus), has also been included based on remains found in Aïn Brimba, in Tunisia, North Africa,[22][23][24] dating to the early-middle Pliocene.[25] In 1990, Alan Turner challenged the validity ofH. problematicum andH. hadarensis, and later authors have generally refrained from referring AfricanHomotherium fossils to any specific species due to their largely fragmentary nature.[6] In 2021, indeterminate remains ofHomotherium were reported from the Tobène locality ofSenegal in West Africa, dating to the Early Pliocene.[26] Indeterminate remains ofHomotherium have also been reported from the Ahl al Oughlam locality in Morocco, dating to the Late Pliocene.[25]
In 1905, Merriam described a new speciesMachaerodus ischyrus.[27] Subsequently, in 1918, Merriam reassigned it to a new genusIschyrosmilus along with the new speciesIschyrosmilus idahoensis.[28] The genusDinobastis was originally named byCope in 1893, with the type speciesDinobastis serus.[29] In 1965, the speciesIschyrosmilus johnstoni was described. In the same paper, it was noted that a comparative study of bothIschyrosmilus andHomotherium might conclude them as synonyms.[30]
In 1966, Churcher namedDinobastis a junior synonym ofHomotherium, and recombinedD. serus asHomotherium serum.[31] In 1970, a new speciesIschyrosmilus crusafonti was described from the early Pleistocene of Nebraska.[32] In 1988, after some debate, the genusIschyrosmilus was declared a junior synonym ofHomotherium and all four species were reassigned to that genus asH. ischyrus,H. idahoensis, andH. johnstoni. The same paper also proposed keepingDinobastis serus separate fromHomotherium.[33] Up to five species have been recognised from North America:H. idahoensis,H. crusafonti,H. ischyrus,H. johnstoni, andH. serum,[34] while other authors suggest that there are only two species, with olderBlancan (Pliocene-Early Pleistocene) specimens assigned to the speciesH. ischyrus, while the younger ones (mostly Late Pleistocene in age) are assigned to the speciesH. serum.H. serum is morphologically similar to the EurasianH. latidens, which may suggest that they share a close common origin, withH. serum possibly originating from a migration ofH. latidens into North America rather than from earlier North AmericanHomotherium.[6] Some authors have consideredH. serum to be ajunior synonym ofH. latidens.[35]
In 2005, a new speciesHomotherium venezuelensis was described based on fossils from the Pleistocene of Venezuela.[36] In 2022 and 2023, Jiangzuo et al. proposed thatHomotherium venezuelensis be reassigned to the genusXenosmilus (a genus originally described for Early Pleistocene aged fossils found in Florida)[37][38] which was endorsed by another group of authors in 2024.[39] The 2022 and 2023 studies found thatXenosmilus was nested withinHomotherium as traditionally defined, makingHomotherium without including the species inXenosmilusparaphyletic.[37][38]
The lineage ofHomotherium is estimated (based onmitochondrial DNA sequences) to have diverged from that ofSmilodon about 18 million years ago.[40]Homotherium has been suggested to have originated from African species of the genusAmphimachairodus.[26]Homotherium first appeared during the EarlyPliocene, about 4 million years ago, with its oldest remains being from theOdesa catacombs in Ukraine, andKoobi Fora in Kenya, which are close in age, making the origin location of the genus uncertain. The genus arrived in North America during the late Pliocene (~3.6-2.6 million years ago).[6] Remains either attributed toHomotherium orXenosmilus are known from Venezuela in northern South America, of an uncertain Early-Middle Pleistocene age.[41] On the African continent, the genus disappeared about 1.5 million years ago, during the Early Pleistocene.[42] Across northern and southern China,Homotherium is thought to have gone extinct sometime during the Middle Pleistocene.[43] The latest records ofHomotherium in Europe date to the late Middle Pleistocene, around 300-200,000 years ago,[44] with the exception of a single lower jaw bone from theNorth Sea which dates to around 28-30,000 years ago.[45] It has been suggested that this may represent a Late Pleistocene dispersal from North America, rather than a continuous undocumented occupation of the region.[40] In 2024, a mummy of aHomotherium latidens cub was reported from the Upper Pleistocene from theBadyarikha River,Yakutia in northeasternSiberia, dating to 35,471–37,019 yearsBefore Present, marking the first recorded presence of the species in the Late Pleistocene of Asia.[46] The youngest well dated remains ofHomotherium serum date to around 12,715–12,655 years Before Present, found in southernAlberta, Canada, at the very end of the Late Pleistocene.[47]Homotherium serum became extinct as part of theend-Pleistocene extinction event of most large mammals across the Americas.[48]
Homotherium reached a length of around 1.5–2 m (4 ft 11 in – 6 ft 7 in), a height of 0.9–1.1 m (2 ft 11 in – 3 ft 7 in) at the shoulder and a maximum weight of around 200 kg (440 lb), comparable in size to a livinglion ortiger.[49]Homotherium probably exhibited size-basedsexual dimorphism, with males suggested to be larger than females.[50] Compared toSmilodon, the legs were proportionally longer, and the forelimbs were less powerfully built, being narrow and intermediate in form between those ofcheetahs andlions. The neck was relatively long and thick with a high degree of flexibility, while the back was relatively short. The tail was very short. The claws were small and semi-retractable, thedewclaw being large, with the second phalanges being less asymmetrical than those of lions, giving the feet a dog-like posture. The part of the humerus closest to the foot was narrow, with theolecranon fossa being strongly vertical. The hindfeet were held in a raiseddigitigrade posture.Homotherium likely walked with a posture intermediate between that of living big cats andhyenas, similar to that ofcanids.[51]
In comparison to its likely ancestorAmphimachairodus, the upperincisors display stronger serration, are larger and more arched, the upper secondpremolar (P2) is always absent, and the upper and lower third premolars (P3 and p3) are smaller, and the morphology of the upper fourth premolar (P4) displays differences.[37] Compared to livingpantherine big cats such as tigers and lions,Homotherium has a more elongate and narrower skull with a more elevated snout region, with the top of the skull (dorsal region) having a more straight outline with a highsagittal crest.[52]Homotherium had shorter uppercanine teeth than members of the machairodont tribeSmilodontini such asSmilodon orMegantereon, but these were still longer than those of extant cats.[51] Its large upper canine saber teeth are broad, distinctly flattened and coarselyserrated.[53] The large upper canines ofHomotherium were likely hidden by the lips and gum tissues of the upper and lower jaws when the mouth was closed, similar to extant cats and unlike the larger upper canines ofSmilodon. This hypothesis is further supported by comparable space between the canines and mandible at full closure of the jaws to modern cats; whileSmilodon has significantly more space in this respect, likely for soft tissue to fit between the canine and mandible.[54] The incisors are enlarged relative to those of modern big cats,[52] and arranged in an arc at the front of the jaws, similar to hyenas and canines.[51] The joining region between the two halves of the lower jaw (mandibular symphysis) is angular and high, with thecoronoid process of the mandible being relatively short.[52]
Preserved soft tissue of a three-week old cub of aH. latidens found in Siberia in 2020 and described in 2024 indicates that the coat color for juveniles of this species was a black or dark brown color with pale paws and chin. The fur on the corner of the mouth region and back of the neck were longer than on the forelimbs of the mummy. Additionally, the cub had wide, rounded paws, which lacked a carpal pad, and its fur was dense: adaptations to traversing snowy terrain effectively, showcasing these features developed at a young age.[46]
Homotherium is suggested to have been adapted to the hunting of large prey.[51] The reduced claws, relatively slender and long limbs, and sloping back all appear to be adaptations for moderate speed endurance running in open habitats.[55][51] The running-adapted morphology of its forelimbs suggests that they were less useful than those ofSmilodon or many living big cats in grasping and restraining prey, and that the enlarged incisor teeth at the front of the jaws served an important role in prey restraint, like in hyenas and canids.[51]
It has been suggested thatHomotherium killed prey by slashing bites to the throat inflicted by its canines.[56] Like other sabertooth cats,Homotherium is widely thought to have used a "canine shear bite" technique, where, once the prey was immobilized and the jaws opened around the throat of the prey, the neck muscles ofHomotherium were used to force the skull and the saber canine teeth downwards (more specifically via a downward rotation of the skull) to puncture the throat of prey.[50][57][58] These throat bites would likely have caused massive blood loss resulting in rapid death.[50][59] The elongate and strong neck likely allowed fine control enabling the head to be precisely located, orientated and held in position for the bite.[50][58] However, some recent authors have suggested that its style of prey restraint was probably different to that ofSmilodon (which had more powerful forelimbs which helped to better restrain prey) with a killing technique more similar in some aspects to theclamp-and-hold technique used by living big cats like lions, with the saber teeth ofHomotherium better able to resist sideways directed forces induced by struggling prey without fracturing than those ofSmilodon.[56] Dental microwear analysis of specimens ofH. serum from North America suggests thatHomotherium regularly consumed tough-fleshed prey, but only engaged in defleshing and did not engage in bone crunching/crushing, similar to cheetahs but unlike living lions and hyenas.[53]
It has been speculated based on its adaptation to open habitats and high levels of competition from other carnivores, thatHomotherium probably relied on group hunting, which would make it easier to take down prey to compensate for their relatively weak forelimbs, increase the size of prey able to be taken, enable distraction strategies to be employed, as well as to be better able to defend kills againstkleptoparasitism by other carnivores.[51]
Analysis of the genome of aHomotherium specimen found in permafrost in Yukon suggests thatHomotherium experienced positive selection for genes related to respiration and the circulatory system, which may have been adaptations for endurance running. Positive selection for genes related to vision indicates that sight probably played an important role in hunting, suggesting thatHomotherium was adiurnal (day active) hunter. Selection for genes related to cognition were tentatively suggested by researchers to possibly support the social hunting hypothesis.[60]
Isotopic analysis ofH. latidens from the Venta Micena locality in southeast Spain dating to the Early Pleistocene, around 1.6 million years ago, suggests that at this localityH. latidens was theapex predator and hunted large prey in open habitats, with the equineEquus altidens andbison likely forming a substantial portion of its diet. Juveniles of the mammothMammuthus meridionalis may also have formed a significant proportion (up to 10%) of their diet. It may have also occasionally taken other prey, such as juveniles of the large hippoHippopotamus antiquus.[61][62] At Venta Micena,Homotheriumniche partitioned with the sabertoothMegantereon (a close relative ofSmilodon) and the "European jaguar"Panthera gombaszoegensis, which hunted somewhat smaller prey in forested habitats.[62] In Early Pleistocene Europe, the giant hyenaPachycrocuta brevirostris (the largest hyena ever), is likely to have presented a significant threat to stealH. latidens kills.[63]
Analysis of specimens from Punta Lucero in northern Spain, dating to the early Middle Pleistocene (600-400,000 years ago), suggests thatH. latidens at this locality exclusively consumed large (from 45 kilograms (99 lb) to over 1,000 kilograms (2,200 lb)) prey, likely includingaurochs, bison,red deer, and/or the giant deerPraemegaceros, and heavily overlapped in diet with the coexisting "European jaguar"Panthera gombaszoegensis.[64]
In the late Early Pleistocene- early Pleistocene of Java[9] and Early-Middle Pleistocene of China,[43]Homotherium lived alongside tigers (Panthera tigris), who may have competed withHomotherium.[9]
At the Friesenhahn Cave site in Texas, which dates to theLate Pleistocene (likely around 20-17,000 years ago, during theLast Glacial Maximum[53]), the remains of almost 400 juvenile (on average around 2 years old[53])Columbian mammoths were discovered along with numerousHomotherium serum skeletons of all ages, from elderly specimens to cubs.[65] The sloped back and powerful lumbar section ofHomotherium's vertebrae suggest that these animals could have been capable of pulling formidable loads; further, broken upper canines - a common injury in fossils of other machairodonts such asMachairodus andSmilodon that would have resulted from struggling with their prey - is not seen inHomotherium, perhaps because their social groups would completely restrain prey items before any of the cats attempted to kill the target with their saber teeth, or because the canines were less frail due to being covered. Moreover, the bones of the young mammoths found in Friesenhahn Cave show distinctive marks matching the incisors ofHomotherium, 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 thatHomotherium would disarticulate their kill to transport it to a safe area such as a hidden lair or den and prevent competitors such asdire wolves andAmerican lions from usurping the carcass,[66] with the meatiest parts of the juvenile mammoths like limbs being preferentially transported to the cave.[53] Isotopic analysis ofH. serum dental remains at Friesenhahn Cave have confirmed that at this locality it predominantly fed on mammoths along with otherC4grazers, like bison and horses in open habitats, as well as possibly C4browsers like the camelCamelops.[53]
Isotopic analysis ofH. serum specimens from Eastern Beringia (now Alaska and Yukon) suggests that in this region the species was not a specialised mammoth predator, and consumed a variety of large prey, likely including bison,muskox, horse andreindeer, as well as also probablywoolly mammoths.[67]
Homotherium has a long history of co-occurrence with archaic humans across Afro-Eurasia, ranging fromAustralopithecus in the Pliocene of Africa, toHomo erectus in Zhoukoudian cave in the Early-Middle Pleistocene of China andHomo heidelbergensis in the Middle Pleistocene of Europe. The seeming extinction ofHomotherium latidens in Europe during the Middle Pleistocene may have been the result of competition withHomo heidelbergensis (in combination with the lionPanthera fossilis).[55]
Isotopic analysis of the canine teeth ofH. latidens found inKent's Cavern indicated that they were isotopically distinct from other animal remains found in the cave. This, along with the absence of any other non-tooth remains ofHomotherium in the cave, has led authors to suggest that the teeth (including canines as well as incisors) were deliberately transported into the cave by humans during the Palaeolithic from further afield (possibly from mainland Europe), perhaps as a kind of trade good. The teeth are suggested to have experienced considerable weathering prior to being taken into Kent's Cavern,[68] and it is unclear whether these teeth were taken from the remains of then-relatively recently deadHomotherium or subfossil remains of long-deadHomotherium individuals.[4] Human transport may also explain the presence of aHomotherium canine found in Late Pleistocene layers of Robin Hood's cave in theCreswell Crags ofDerbyshire, central England.[4][6]
A now lostUpper Palaeolithic figurine found inIsturitz cave in southwest France has been suggested by some authors to representHomotherium, but other authors have argued that it more likely represents acave lion based on its anatomical proportions and the much greater abundance of cave lion remains compared to those ofHomotherium in Late Pleistocene Europe.[52]
At the end of the Late Pleistocene in North America,Homotherium serum co-existed withPalaeoindians, the first humans to inhabit the Americas. The effect of human hunting of large herbivores whichH. serum relied upon may have been a contributory factor in its extinction along with other large carnivores in North America.[48]
| Homotherini |  | |
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| Metailurini | ||
| Smilodontini | ||
| Incertae sedis: | ||
Authority control databases: National |
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