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Homotherium
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Homotherium
Temporal range: Early Pliocene to Late Pleistocene, 4–0.012 Ma[1]
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Skeleton of H. serum from Friesenhahn cave, Texas Science & Natural History Museum, University of Texas at Austin, Austin, Texas.
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Subfamily: †Machairodontinae
Tribe: †Homotherini
Genus: †Homotherium
Fabrini, 1890
Type species
†Homotherium latidens
Owen, 1846
Other species
  • †H. ischyrus (Merriam, 1905)
  • †H. serum (Cope, 1893)
  • †H.? venezuelensis Rincón et al., 2011

For others, see text

Synonyms
  • Dinobastis Cope, 1893
  • Ischyrosmilus Mawby, 1965
  • Hemimachairodus Koenigswald, 1974

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 and Pleistocene epochs from around 4 million to 12,000 years ago.[1][2] A probable descendant of Amphimachairodus, it was one of the last surviving members of Machairodontinae 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 with a body mass of up to 200 kilograms (440 lb), 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 moderate speed endurance pursuit predator adapted to running down large prey, such as antelope, equines, bovines, and juvenile mammoths in open habitats, with Homotherium also proposed to have likely engaged in cooperative hunting.

Once widely distributed over most of the world's continents, the genus saw a protracted decline over the course of the Pleistocene, disappearing from Africa during the Early Pleistocene around 1.5 million years ago, and declining in abundance and distribution in Eurasia during the Middle Pleistocene, though with a handful of records in the Late Pleistocene. In North America, the genus survived until the end of the Late Pleistocene around 12,000 years ago, becoming extinct as part of the end-Pleistocene extinction event along with most other large animals native to the Americas. This followed the arrival of humans into the Americas, who may have caused a decline in populations of large prey on which Homotherium depended.

Research history and taxonomy

[edit]

Eurasia

[edit]

The first fossils of Homotherium were scientifically described in 1846 by Richard Owen as the species Machairodus latidens,[3] based on Pleistocene aged canine teeth found in Kent's Cavern in Devon, southwestern England by the Reverend John MacEnery in 1826.[4] The name Homotherium (Greek: ὁμός (homos, 'same') and θηρίον (therion, '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.[5] The genus name itself was rarely used in the scientific literature until the late 1940s.[6]

In 1918, the species Homotherium moravicum was described by Josef Woldřich based on remains found in what is now the Czech Republic.[7] Homotherium davitashvili (also spelled davitasvilii[6]) was described by Abesalom K. Vekua in 1972 based on fragmentary material found at the late Pliocene Kvabebi locality in Georgia in the southern Caucasus.[8][6] Other material from Odessa in Ukraine was tentatively assigned to this species in 2004.[9] In 1986, the species Homotherium darvasicum was described by Scharif Scharapov based on material from Kuruksay, Tajikistan in Central Asia.[10] In 1989, another species Homotherium tielhardipiveteaui was named by Scharapov based on fossils also found in Tajikistan.[11]

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.[12] Remains from the late Early Pleistocene-early Middle Pleistocene of Java in Indonesia have also been attributed to this species (as Homotherium ultimum),[13] though others have attributed Javan remains of Homotherium to H. latidens. The also Javan Hemimachairodus zwierzyckii, originally named Epimachairodus zwierzyckii by Gustav Heinrich Ralph von Koenigswald in 1934 and placed in the new genus Hemimachairodus by the same author in 1974 (with indeterminate fossils attributed to Hemimachairodus also reported from Tajikistan[14]), is now also regarded as a synonym of Homotherium.[15] In 1996, Homotherium hengduanshanense was described based on fossils of Late Pliocene-Early Pleistocene age from the Hengduan Mountains of Sichuan, southwestern China.[16][17] Indeterminate remains of Homotherium have been reported from the Siwalik Hills of the northern Indian subcontinent, of Early - early Middle Pleistocene age.[18]

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.[6]

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.[6] 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.[17]

Africa

[edit]

In 1947/48, Camille Arambourg described the species Homotherium ethiopicum from remains found in the Omo river valley in southern Ethiopia.[19] This publication helped popularise the genus Homotherium, which was little used prior.[6] 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.[20]

In 1972 the species Homotherium problematicum (originally Megantereon problematicus) was named by G. E. Collings, based on fragmentary material from the Makapansgat locality in northeast South Africa, of late Pliocene-Early Pleistocene age.[21][22] Homotherium hadarensis was described by G. Petter and F.C. Howell in 1988, based on remains found in the Pliocene aged Hadar Formation of the Afar region of northern Ethiopia.[23] In 2015, further material from the Hadar Formation was tentatively referred to H. hadarensis.[20] A third species, Homotherium africanum (originally Machairodus africanus), was named by Arambourg in 1970 based on remains found in Aïn Brimba, in southern Tunisia, North Africa,[24][25][26] dating to the early-middle Pliocene.[27] 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.[6] In 2021, indeterminate remains of Homotherium were reported from the Tobène locality of northwestern Senegal in West Africa, dating to the Early Pliocene.[28] Indeterminate remains of Homotherium have also been reported from the Ahl al Oughlam locality in northern Morocco, dating to the Late Pliocene.[27]

Americas

[edit]

The genus Dinobastis was named by Edward Drinker Cope in 1893, with the type species Dinobastis serus, named in the same publication based on phalanges, a partial femur and several teeth collected from western Oklahoma.[29] In 1905, John Campbell Merriam described a new species of sabertooth cat, Machaerodus ischyrus based on a partial lower jaw found at the foot of the Temblor Range in Kern County, California.[30] Subsequently, in 1918, Merriam reassigned it to a new genus Ischyrosmilus along with the new species Ischyrosmilus idahoensis, based on another lower jaw found in the vicinity of the Snake River in southwestern Idaho.[31] In 1965, the species Ischyrosmilus johnstoni was described by John E. Mawby based on several partial lower jaws, a partial skull and teeth collected from Cita Canyon in Randall County in the Texas panhandle,[32] dating to the Late Pliocene (~3-2.6 million years ago).[33] In the same paper, Mawby noted that a comparative study of both Ischyrosmilus and Homotherium might conclude them as synonyms.[32] Charles Stephen ("Rufus") Churcher argued in 1984 that the remains from Cita Canyon instead represented the Eurasian species Homotherium crenatidens,[34] though Martin et al. 2011 considered them to belong to Homotherium ischyrus.[35]

Skeleton of the South American species "Homotherium" venezuelensis, which recent authors have suggested may be better placed in Xenosmilus

In 1966, Churcher deemed Dinobastis as a junior synonym of Homotherium, and recombined D. serus as Homotherium serum.[36] In 1970, a new species Ischyrosmilus crusafonti was described by Charles Bertrand Schultz and Larry D. Martin based on a partial lower jaw from the Early Pleistocene of Morrill County in western Nebraska.[37] After some debate, the genus Ischyrosmilus was declared a junior synonym of Homotherium and all four species were reassigned to that genus in a 1988 publication by Larry Martin, Charles Bertrand Schultz and Marian Othmer Schultz, as H. ischyrus, H. idahoensis, and H. johnstoni. The same paper also proposed keeping Dinobastis serus separate from Homotherium.[38] Ischyrosmilus and Dinobastis are now generally accepted as synonyms of Homotherium.[33] Up to five species of Homotherium have been recognised from North America: H. idahoensis, H. crusafonti, H. ischyrus, H. johnstoni, and H. serum. Martin et al. 2011 recognised two valid species in the Pliocene of North America, H. crusafonti and H. ischyrus , as well as H. serum in the Late Pleistocene (alongside possibly H. latidens in the Late Pleistocene of Alaska).[35] Other authors suggest that there are only two well-supported North American species, with older Blancan (Pliocene-Early Pleistocene) specimens assigned to the species H. ischyrus, while the younger ones (mostly Late Pleistocene in age) are assigned to the species H. serum. H. serum is morphologically similar to the Eurasian H. latidens (to the degree that H. serum specimens would likely be classified as H. latidens if they were found in Eurasia), which may suggest that they share a close common origin, with H. serum possibly originating from a migration of H. latidens into North America rather than from earlier North American Homotherium.[6] Some authors have considered H. serum to be a junior synonym of H. latidens.[39]

In 2011, a new species Homotherium venezuelensis was described by Ascanio Rincón et al. based on a partially crushed skull along with several partial lower jaws and teeth collected from tar seep deposits of Early to Middle Pleistocene age (around 1-0.5 million years ago) of Monagas in northeastern Venezuela.[40] In 2022 and 2023, Jiangzuo et al. proposed that Homotherium venezuelensis be reassigned to the closely related homotheriin genus Xenosmilus (a genus originally described for Early Pleistocene aged fossils found in Florida)[41][42] which was endorsed by Manzuetti et al. in 2024. Homotheriin remains had previously been reported from South America in the form of a lower jaw from southern Uruguay in 2004, dating to sometime between the Late Pliocene and the Middle Pleistocene, which the original 2004 study and Manzuetti et al. 2024 attributed to cf. Xenosmilus.[43] The 2022 and 2023 studies found that Xenosmilus was nested within Homotherium as traditionally defined (with H. ischyrus more closely related to Xenosmilus than to other Homotherium species), making Homotherium without including the species in Xenosmilus paraphyletic.[41][42]

Description

[edit]
Size comparison of Homotherium latidens compared to a human

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 living lion or tiger.[44] Homotherium probably exhibited size-based sexual dimorphism, with males suggested to be larger than females.[45] Compared to Smilodon, the legs were proportionally longer, and the forelimbs were less powerfully built, being narrow and intermediate in form between those of cheetahs and lions. 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, the dewclaw 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 the olecranon fossa (a depression on the end of the humerus closest to the elbow joint) being strongly vertical. The hindfeet were held in a raised digitigrade posture. Homotherium likely walked with a posture intermediate between that of living big cats and hyenas, similar to that of canids.[46] The calcaneus and metatarsal bones of the hindfoot were relatively short.[47]

Skulls of Homotherium; 1. H. latidens/crenatidens; 2. H. serum; 3. Generalized illustration by Mauricio Anton
Natural mummy of a three-week old H. latidens cub from Yakutia, Russia.
Life restorations of Homotherium
  • Comparison between the skeletons and reconstructions of Smilodon (left) and Homotherium (right)
    Comparison between the skeletons and reconstructions of Smilodon (left) and Homotherium (right)
  • Life restoration of the head and neck of Homotherium latidens
    Life restoration of the head and neck of Homotherium latidens
  • Life restoration of Homotherium latidens
    Life restoration of Homotherium latidens

In comparison to its likely ancestor Amphimachairodus, the upper incisors display stronger serration, are larger and more arched, the upper second premolar (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.[41] The Pliocene-Early Pleistocene North American H. ischyrus differs from the Eurasian H. latidens in having better developed upper and lower third premolars bearing three cuspids/cusps, with their mandibular rami (the upper posterior part of the lower jaw that articlulates with the skull) being in comparison to H. latidens relatively low and elongate.[6]

Compared to living pantherine 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 high sagittal crest.[48] Homotherium had shorter upper canine teeth than members of the machairodont tribe Smilodontini such as Smilodon or Megantereon, but these were still longer than those of extant cats.[46] Its large upper canine saber teeth are broad, distinctly flattened and coarsely serrated.[49] The large upper canines of Homotherium 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 of Smilodon. This hypothesis is further supported by comparable space between the canines and mandible at full closure of the jaws to modern cats; while Smilodon has significantly more space in this respect, likely for soft tissue to fit between the canine and mandible.[50] The incisors are enlarged relative to those of modern big cats,[48] and arranged in an arc at the front of the jaws, similar to hyenas and canines.[46] The joining region between the two halves of the lower jaw (mandibular symphysis) is angular and high, with the coronoid process of the mandible being relatively short.[48]

Preserved soft tissue of a three-week old cub of a H. latidens found in Siberia in 2020 and described in 2024 shows that the coat color for at least the juveniles of this species was a black or dark brown color with pale fur on the paws and chin. The fur on the corners of the mouth and back of the neck were longer than on the forelimbs of the mummy, and the pelage is generally dense all over the body. Additionally, the cub had wide rounded paws lacking a carpal pad. These are thought to be adaptations to living in snowy environments, and the fact that a three-week old had these features indicates that they developed them at a young age.[51] A study on the microstructure of the cub's hair revealed that the medulla (the innermost part of the hair strand) made up only a relatively small part of the total diameter of the hair strands, suggesting that the heat-protective properties of the hair were poor and lacked specific adaptations to cold environments. It is likely that the cub was born in spring and died in summer.[52]

Paleobiology and paleoecology

[edit]

Homotherium is suggested to have been adapted to hunting large prey.[46] The reduced claws, relatively slender and long limbs, and sloping back all appear to be adaptations for the lifestyle of a pursuit predator engaging in moderate-speed endurance running (similar to hyenas, but unlike the short distance high speed sprint running exemplified by the living cheetah) in open habitats.[47][46] The running-adapted morphology of its forelimbs suggests that they were less useful than those of Smilodon 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.[46] While somewhat lacking in power, the forelimbs of Homotherium probably did play some role in restraining prey, likely relying on the large dewclaw to grasp effectively as is the case in cheetahs.[47] Homotherium likely adopted an energy efficient galloping stride when pursuing prey.[47] The short calcaneus or heel bone in the hindfoot indicates that Homotherium was probably a less capable jumper compared to modern pantherine big cats, with the shortened calcaneus and metatarsals likely helping to stabilize the foot, perhaps when restraining prey.[47]

Illustration of Homotherium performing a "canine shear bite" on a prey animal. Artwork by Mauricio Antón.

It has been suggested that Homotherium killed prey by slashing bites to the throat inflicted by its canines,[53] with Homotherium like other sabertooths thought to have been capable of a wider gape than living cats to accommodate enveloping the large canine teeth around its prey.[46] 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 of Homotherium 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.[45][54][55] These throat bites would likely have caused massive blood loss resulting in rapid death.[45][56] The elongate and strong neck likely allowed fine control enabling the head to be precisely located, orientated and held in position for the bite, allowing the canine saberteeth to avoid hitting bone which could damage them.[45][55] However, some recent authors have suggested that its style of prey restraint was probably different to that of Smilodon (which had more powerful forelimbs which helped to better restrain prey) with a killing technique more similar in some aspects to the clamp-and-hold technique used by living big cats like lions, with the saber teeth of Homotherium better able to resist sideways directed forces induced by struggling prey without fracturing than those of Smilodon.[53] Dental microwear analysis of specimens of H. serum from North America suggests that Homotherium 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.[49]

It has been speculated based on its adaptation to open habitats and high levels of competition from other carnivores, that Homotherium 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, and enable distraction strategies to be employed during hunting, as well as to be better able to defend kills against kleptoparasitism (kill stealing) by other carnivores.[46]

Analysis of the genome of a Homotherium specimen found in permafrost in Yukon in northern Canada, suggests that Homotherium 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 that Homotherium was a diurnal (daytime) hunter. Selection for genes related to cognition were tentatively suggested by researchers to possibly support the social hunting hypothesis.[57]

Illustration of Homotherium delivering a killing bite to an equine, along with a diagram of the skull and neck from above, showing muscles involved in positioning head. By Mauricio Antón

Isotope analysis of Homotherium and other animals from the Pliocene of Hadar, Ethiopia, dating to around 3.45–2.95 million years ago, suggests that its prey at this locality were large, on average around 200–300 kilograms (440–660 lb) and primarily consumed C3 plants. Prey animals primarily consisted of (in descending order of importance) antelopes belonging to the genus Tragelaphus, the swine Nyanzachoerus, the bovine Ugandax, the three-toed hipparionine equine Eurygnathohippus, and the antelope Damalborea. Homotherium was overlapping in diet though distinct in niche from that of the contemporary hyena Crocuta venustula.[58]

Isotopic analysis of H. latidens from the Venta Micena locality in southeast Spain dating to the Early Pleistocene, around 1.6 million years ago, suggests that at this locality H. latidens was the apex predator and hunted large prey in open habitats, with the equine Equus altidens and bison likely forming a substantial portion of its diet. Juveniles of the mammoth Mammuthus 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 hippo Hippopotamus antiquus.[59][60] At Venta Micena, Homotherium niche partitioned with the smilodontin sabertooth Megantereon (a close relative of Smilodon) and the "European jaguar" Panthera gombaszoegensis, which hunted somewhat smaller prey in forested habitats.[60] In Early Pleistocene Europe, the giant hyena Pachycrocuta brevirostris is likely to have presented a significant threat capable of stealing H. latidens kills.[61]

Isotope analysis of specimens from Punta Lucero in northern Spain, dating to the early Middle Pleistocene (600-400,000 years ago), suggests that H. latidens at this locality exclusively consumed large (from 45 kilograms (99 lb) to over 1,000 kilograms (2,200 lb)) prey, likely including aurochs, bison, red deer, and/or the giant deer Praemegaceros, and heavily overlapped in diet with the coexisting European jaguar Panthera gombaszoegensis.[62]

In the late Early Pleistocene-early Pleistocene of Java[13] and Early-Middle Pleistocene of China,[63] Homotherium lived alongside the extant tiger, who may have competed with Homotherium.[13]

At the Friesenhahn Cave site in Bexar County, south Texas, which dates to the Late Pleistocene (likely around 20-17,000 years ago, during the Last Glacial Maximum[49]), the remains of almost 400 juvenile (on average around 2 years old[49]) Columbian mammoths were discovered along with numerous Homotherium serum skeletons of all ages, from old adults to cubs.[64] The sloped back and powerful lumbar section of Homotherium's vertebrae suggest that these animals could have been capable of pulling formidable loads; furthermore, 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, 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 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,[65] with the meatiest parts of the juvenile mammoths like limbs being preferentially transported to the cave.[49] Isotopic analysis of H. serum dental remains at Friesenhahn Cave have confirmed that at this locality it predominantly fed on mammoths along with other C4 grazers, like bison and horses in open habitats, as well as possibly C4 browsers like the camel Camelops.[49]

Isotopic analysis of H. 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 and reindeer, as well as probably woolly mammoths.[66]

Palaeopathology

[edit]

A fossil of a palaeopathological H. latidens scapula from Schöningen, Germany reveals that the individual it belonged to suffered from scapular osteoarthritis, as evidenced by a caudal subchondral multilobular cystic lesion found within the mediocaudal glenoid fossa and an osteophyte located on the glenoid fossa's caudal border. The cause of the condition is believed to have been natural aging, physical trauma, or some combination of both of these factors. The slow development of the lesion is indicative of the individual surviving for a considerable length of time after developing the condition, suggesting that this pathology did not hinder the animal's ability to acquire food to any significant degree.[67]

Evolution and extinction

[edit]

The lineage of Homotherium is estimated (based on mitochondrial DNA sequences) to have diverged from that of Smilodon about 18 million years ago.[68] Homotherium has been suggested to have originated from African species of the genus Amphimachairodus.[28] Homotherium first appeared during the Early Pliocene, with its oldest remains being from the Odesa catacombs in Ukraine around 4.2 million years old, Koobi Fora in Kenya, around 4.35–4.1 million years old, and Kanapoi also in Kenya, dating to around 4.2 million years ago.[28] The genus arrived in North America during the Late Pliocene (~3.6-2.6 million years ago).[6] On the African continent, the genus disappeared about 1.5 million years ago, during the Early Pleistocene.[69] Remains either attributed to Homotherium or Xenosmilus are known from Venezuela in northern South America, suggested to date to the late Early - early Middle Pleistocene, around 1-0.5 million years ago.[70]

Eurasian Homotherium began to decline in size during the latest part of the Early Pleistocene, and its body mass decline continued over the Middle Pleistocene, along with becoming increasingly rare in the Eurasian fossil record. This may be due to competition with other predators, such as the very large lion Panthera fossilis that arrived in Europe at the beginning of the Middle Pleistocene, and/or archaic humans.[47][71] Across northern and southern China, Homotherium is thought to have gone extinct sometime during the Middle Pleistocene.[63] The latest well-dated records of Homotherium in Europe date to the late Middle Pleistocene, around 300-200,000 years ago,[71][72] with the exception of a single lower jaw bone from the North Sea which has been radiocarbon dated to around 28-30,000 years ago.[73] It has been suggested that this may represent a Late Pleistocene dispersal from North America, rather than a continuous undocumented occupation of the region.[68] In 2024, a mummy of a Homotherium latidens cub was reported from the Upper Pleistocene from the Badyarikha River, Yakutia in northeastern Siberia, dating to 35,471–37,019 years Before Present, marking the first recorded presence of the species in the Late Pleistocene of Asia.[51]

The youngest well dated remains of Homotherium serum date to around 12,715–12,655 years Before Present, found in southern Alberta, Canada, at the very end of the Late Pleistocene.[74] Homotherium serum became extinct as part of the end-Pleistocene extinction event of most large mammals across the Americas.[75] The extinction of Homotherium, along with fellow sabertooth Smilodon, at the end of the Late Pleistocene in North America has been suggested to be the result of the decline and extinction of the large prey species on which they depended.[76]

Relationship with humans

[edit]

Homotherium has a long history of co-occurrence with archaic humans across Afro-Eurasia, ranging from Australopithecus in the Pliocene of Africa, to Peking Man in Zhoukoudian cave in the Early-Middle Pleistocene of China and Homo heidelbergensis in the Middle Pleistocene of Europe. The decline of Homotherium latidens in Eurasia during the Middle Pleistocene may have been the result of competition with archaic humans, in combination with other factors.[71][47]

Image of a now lost Upper Paleolithic figurine found in Isturitz cave, France, which has been controversially argued by some to depict Homotherium, though others suggest it represents a cave lion (Panthera spelaea)

Isotopic analysis of the canine teeth of H. latidens found in Kent'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 of Homotherium 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,[77] and it is unclear whether these teeth were taken from the remains of then-relatively recently dead Homotherium or subfossil remains of long-dead Homotherium individuals.[4] Human transport may also explain the presence of a Homotherium canine found in Late Pleistocene layers of Robin Hood's cave in the Creswell Crags of Derbyshire, central England.[4][6] Although a felid humerus from the late Middle Pleistocene Schöningen site in Germany was originally claimed to represent Homotherium and to have been used as a tool by Neanderthals,[44] later analysis suggested that the humerus represented that of a lion (Panthera fossilis or Panthera spelaea) that instead had been scavenged by hyenas.[72]

A now-lost Upper Palaeolithic figurine found in Isturitz cave in southwest France has been suggested by some authors to represent Homotherium, but other authors have argued that it more likely represents a cave lion based on its anatomical proportions and the much greater abundance of cave lion remains compared to those of Homotherium in Late Pleistocene Europe.[48]

At the end of the Late Pleistocene in North America, Homotherium serum co-existed with Paleoindians, the first humans to inhabit the Americas. The effect of human hunting of large herbivores which H. serum relied upon may have been a contributory factor in its extinction along with other large carnivores in North America.[75]

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Homotherium

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Homotherium (also known as the scimitar-toothed cat) is an extinct genus of machairodontine saber-toothed cats in the subfamily , characterized by its large body size comparable to that of a modern , serrated saber-like canines, powerful forelimbs, a sloping back, and enlarged optic bulbs adapted for keen vision. These felids were highly successful predators that roamed across , , , and during the Plio-Pleistocene epochs, from approximately 4 million years ago until their extinction at the end of the around 10,000 years ago, making them the saber-toothed cat with the widest geographic distribution. The Homotherium was first described by Fabrini in 1890, with several recognized based on evidence over its history; forms in and belong to the same species, H. latidens. Morphologically distinct from extant felids and other saber-toothed cats like , Homotherium exhibited adaptations for hunting, such as robust limbs suited for long-distance pursuit of prey, and genetic evidence suggests diurnal activity patterns and possibly social behaviors, including cooperative hunting of Pleistocene megafauna like mammoths and . records indicate high morphological variability, with lion-sized adults weighing up to 400 kg, short mandibles, reduced premolars, and large incisors that facilitated a slashing bite for deep wounds rather than bone-crushing. Paleobiological studies reveal that Homotherium diverged from the lineage leading to modern cats around 22.5 million years ago, with no between the groups, and maintained high until its , possibly driven by the decline of large herbivores, changes, and from other predators at the end of the Pleistocene. Notable recent discoveries include a well-preserved mummified juvenile H. latidens from , dated to approximately 36,000 years ago, which provides insights into early growth stages and confirms the genus's presence in northern during the , expanding our understanding of its cold-climate adaptations. Overall, Homotherium represents a pinnacle of felid , embodying specialized traits for open-environment predation that persisted longer than many contemporaries.

Taxonomy and phylogeny

Etymology and nomenclature

The genus Homotherium was established by Italian paleontologist Emilio Fabrini in 1890, derived from the Greek words homo (ὁμός, meaning "same") and therion (θηρίον, meaning "beast"), alluding to the relatively uniform dental morphology compared to other saber-toothed cats. The initial description was based on fossil material from the Valdarno region in , though the genus name was not widely adopted until later in the . The is Homotherium latidens (Owen, 1846), originally classified under latidens by based on an upper canine from Kent's Cavern in . This specimen was unfortunately destroyed during the 1941 bombing of but is documented in Owen's original publication. H. crenatidens Fabrini, 1890, initially proposed as another from Italian deposits, has since been synonymized with H. latidens due to overlapping morphological traits. Taxonomic revisions have consolidated much of the genus's diversity; for instance, H. ultimum Teilhard de Chardin, 1936, from Asian Pleistocene sites including and , was later subsumed under H. latidens based on comparative analyses of cranial and dental features. In 2011, a new species, H. venezuelensis Rincón et al., 2011, was recognized from Pleistocene fossils in northern , representing the first confirmed South American record and highlighting post-Great American Biotic Interchange dispersal. Homotherium is classified within the subfamily (tribe ), distinguished nomenclaturally from the later-diverging Smilodontinae by its earlier stratigraphic occurrence and distinct generic allocations in felid .

Recognized species

The of Homotherium remains contentious, with the number of recognized varying between lumpers who favor a single widespread and splitters who identify multiple based on subtle morphological differences in , size, and limb proportions. The is H. latidens (Owen, 1846), originally described as Machairodus latidens from Kent's Cavern, (). H. crenatidens Fabrini, 1890, from Italian deposits and sometimes associated with earlier Eurasian forms, is now considered a junior synonym of H. latidens due to overlapping traits. H. latidens (Owen, 1846) is the most extensively documented species, ranging from the late Pliocene to late Pleistocene (approximately 4.0 Ma to 28,000 years BP) across , , and parts of , with key fossils from sites like Kent's Cavern in and Dafnero-3 in . It is characterized by laterally compressed upper canines with serrated edges, enlarged and robust incisors, an elongated and narrow upper (P4), and a robust featuring a flattened deltopectoral crest, adaptations suggesting a cursorial hunting style. Early African forms, such as H. ethiopicum and H. hadarensis from the early Pleistocene (approximately 2.0–1.5 Ma), are often considered junior synonyms of H. latidens owing to minimal diagnostic differences in tooth morphology and overall size. In , H. serum Cope, 1895, is recognized as a valid Pleistocene species (approximately 1.8 Ma to 10,000 years BP), primarily from sites in the and , distinguished from H. latidens by nuclear genome analysis revealing a around 300,000 years ago despite morphological similarities; it exhibits slightly larger body size (up to 250 kg) and proportionally longer limbs suited to open habitats, with patterns on the canines showing finer denticles. Ancient evidence initially suggested synonymy between late Pleistocene H. latidens and H. serum, but subsequent full-genome studies confirmed their separation, highlighting low genetic variability within each but clear interspecies differences. The southernmost record is H. venezuelensis Rincón, Prevosti, and Carlini, 2011, from the (approximately 30,000–20,000 years BP) tar pits of El Breal de Orocual in , marking the first confirmed South American occurrence and likely resulting from the Great American Biotic Interchange. This species is diagnosed by a robust but distorted partial and showing broader and thicker lower jaws than northern counterparts, with body size estimates around 200 kg and limb proportions indicating adaptation to forested environments. Several proposed species have been debated or synonymized, including H. ultimum Teilhard de Chardin, 1936, from early to middle Pleistocene sites in and , previously distinguished by larger size and coarser canine serrations but now regarded as a or synonym of H. latidens based on morphological overlap and genetic continuity inferred from Asian samples showing no major divergences. Similarly, taxa like H. nestianum and H. moravicum are often folded into H. latidens due to insufficient distinguishing features beyond minor variations in body size and dental wear patterns.

Evolutionary relationships

Homotherium belongs to the extinct subfamily within the family, which diverged from the lineage leading to modern cats () during the early , approximately 22.1 million years ago. This deep split is supported by genomic analyses showing no gene flow between machairodontines and extant felids for at least the last 16 million years. Within , Homotherium is classified in the tribe Homotheriini and shares close phylogenetic ties with other scimitar-toothed machairodonts, such as Amphimachairodus, based on craniomandibular and dental characters. It is distinguished from the dirk-toothed , a member of the separate tribe , by a substantial divergence estimated at around 20.65 million years ago (95% : 15.25–26.07 Ma), as confirmed by DNA phylogenies from ancient and modern samples. The saber-toothed morphology of Homotherium, characterized by elongated upper canines, represents a convergent evolutionary trait seen in multiple felid lineages, adapting independently to similar predatory niches. Ancient DNA studies provide further insights into Homotherium's late evolution, particularly for the species H. latidens. Mitogenomic analysis of samples from sites reveals minimal between European (, ~28,000 years old) and North American (Yukon Territory, >47,500 years old) populations, with a dated to approximately 145,000 years ago. This low diversity indicates that H. latidens formed a single, widely dispersing species across the Holarctic during this period.

Physical characteristics

Cranial and dental features

The skull of Homotherium exhibits a distinctive morphology adapted for its predatory lifestyle, featuring an elongated and flattened cranial roof that contrasts with the more domed of modern felids. This structure includes large nasal apertures, which are proportionally broader than those in related machairodonts, potentially enhancing and oxygenation during high-intensity pursuits. The braincase is relatively spacious, suggesting cognitive capabilities akin to those of extant large cats despite the specialized saber-tooth anatomy. Dentally, Homotherium is defined by its signature upper canines, which measure up to 10-12 cm in length in adults and adopt a scimitar-like with fine serrations along the mesial and distal edges for efficient tissue penetration. The incisors are enlarged in size and form a pronounced arch compared to modern felids, while the teeth (P4 and m1) show a shearing , with flattened crowns suited for slashing flesh rather than bone-crushing. This dental configuration prioritizes precision wounding over , reflecting the genus's role as a hunter. The mandibular architecture supports these features through a flexible, slender lower that permits an exceptionally wide gape, estimated at up to 120 degrees in biomechanical models, enabling the canines to engage large prey without risking . Recent analysis of a 2024-discovered juvenile of H. latidens from Siberian reveals early ontogenetic development of these traits, with deciduous upper canines formed to the hollow cap stage and an enlarged oral cavity indicating preparation for hypertrophied permanent sabers. In comparison to other saber-toothed felids like , Homotherium's cranium is less robust overall, with a longer rostrum, reduced lower canines, and a more gracile that emphasizes speed and maneuverability over raw power in prey subdual. These differences underscore Homotherium's specialization for open-plains predation, distinct from 's ambush-oriented build.

Postcranial anatomy and adaptations

Homotherium exhibited a slender, elongated body build adapted for endurance rather than ambush predation, contrasting with the more robust and stocky form of its contemporary . Adult individuals typically weighed between 190 and 350 kg, with recent estimates for large specimens suggesting up to 410 kg, and measured 2 to 3 in total length, with a shoulder height of approximately 1.1 , enabling efficient movement across open Pleistocene landscapes. This morphology supported a lifestyle, with the cat's overall frame optimized for sustained pursuit of prey over long distances. The postcranial skeleton featured long, limbs characteristic of felids, with a higher brachial index (radius-to-humerus ratio) indicating adaptations for extended running in open habitats. Forelimbs were robust and powerful, equipped with less-retractable claws for enhanced traction during and subduing large herbivores, while the hindlimbs were relatively slender to facilitate speed and endurance. The sloping back and elongated forelegs relative to hindlegs further contributed to a hyena-like profile, promoting stability and efficiency in prolonged chases rather than short bursts of acceleration. Recent myological reconstructions based on a well-preserved juvenile from Siberian reveal significant in the and musculature, with a notably thicker and more massive compared to modern lions (Panthera leo). These powerful and muscles, part of the brachycephalic complex, likely enabled Homotherium to maintain head position and deliver sustained force during pursuits of megafaunal prey. Sensory adaptations included an enlarged optic bulb and expansive , supported by positive selection on genes related to and development, suggesting enhanced suited to diurnal activity in bright, open environments. Evidence from the same mummified juvenile indicates a uniform coat of short, thick, dark brown fur, approximately 20–30 mm long and denser on the back and neck, providing insulation in cold conditions without distinct spotting or striping patterns.

Fossil record

Discovery history

The first recognized fossils attributable to Homotherium were described by in 1846 as Machairodus latidens, based on an upper canine from Kent's Cavern in ; this was later destroyed during World War II bombings. The genus Homotherium was formally established by Carlo Fabrini in 1890, using mandibular and cranial material from the Early Pleistocene Val d'Arno site in , where serrated, scimitar-like canines distinguished it from other machairodonts. Early 20th-century European discoveries, particularly by paleontologist Miklós Kretzoi, included fragmentary remains from Hungarian and other sites; Kretzoi named provisional taxa like Epimachairodus hungaricus in 1929, which subsequent revisions synonymized under H. latidens. In the , major African discoveries expanded the genus's known distribution, with Robert Broom describing H. capense from the Pleistocene Kromdraai site in based on dental and postcranial fragments, marking the first substantial continental African record. These finds highlighted Homotherium's to open habitats but were often fragmentary, leading to initial misclassifications as Panthera spelaea (cave lion) due to similar size and isolated bones. Later 20th-century work refined identifications, but challenges persisted with incomplete specimens. Key 21st-century milestones include the 2011 description of H. venezuelensis by Aldo Rincon and colleagues from fossils in Venezuela's Formation, representing the southernmost South American record and evidence of Great American Biotic Interchange dynamics. In 2017, a 28,000-year-old mandible dredged from the was analyzed via , confirming genetic continuity between late-surviving European and North American populations of H. latidens and pushing back the estimated extinction in . Recent advances include the 2024 discovery of a mummified H. latidens cub (approximately three weeks old) from Siberian near the Badyarikha River, dated to over 35,000 years ago; CT-scan analysis revealed ontogenetic details like muzzle shape, patterns, and early dental development, previously unknown from soft tissues. studies, such as those from the specimen and a 2020 genomic analysis, have further resolved taxonomic debates by confirming Homotherium's across Holarctic regions and clarifying species boundaries amid fragmentary records.

Geographic distribution and key sites

Homotherium exhibited a broad geographic distribution across multiple continents during the and Pleistocene epochs, with fossil evidence spanning , , and the . In , remains are widespread, ranging from early localities in to late Pleistocene sites in , reflecting the genus's adaptability to diverse environments. Key European sites include Schöningen in , where mandibular and dental fragments of Homotherium latidens were recovered from Middle Pleistocene layers, providing insights into its presence alongside early tools. Additional significant finds come from the Nihewan Basin in , yielding a complete cranium that highlights morphological variation in Asian populations. In , a remarkably preserved juvenile of H. latidens, discovered in along the Badyarikha River, represents one of the northernmost records and confirms late survival in high-latitude habitats. In , Homotherium fossils are documented from early to early contexts, indicating an origin on the continent before dispersal elsewhere. Notable sites include in , where rare dental remains of the genus occur in Upper Laetolil Beds, associated with early hominin footprints and a diverse . Further south, in has yielded carnivoran fossils, including machairodontine elements attributable to Homotherium, from Member 4 deposits that also contain remains. Other African localities, such as Langebaanweg and Tobène in , provide additional cranial and postcranial evidence, underscoring the genus's early diversification in open woodland and grassland ecosystems. The host Pleistocene records of Homotherium, primarily in but extending southward via the Great American Biotic Interchange. In , fossils are abundant from Territory, including a permafrost-preserved used for ancient DNA analysis, demonstrating genetic continuity with Eurasian populations. A fragmentary premaxilla-maxilla from McFaddin Beach, Texas, dated to the Pleistocene, represents a coastal record along the . The genus reached during the interchange, with the earliest evidence from El Breal de Orocual tar pits in , where partial skeletons of the endemic H. venezuelensis were excavated, marking the southernmost expansion around 1.8 million years ago. This migration highlights Homotherium's role in intercontinental faunal exchanges. Beyond these core regions, occurrences in are sporadic, with isolated teeth and bones from fragmentary remains suggesting limited penetration into southern interiors, though they require further verification.

Temporal range

first appeared during the Early , approximately 4–5 million years ago, with the earliest fossils recovered from sites in , such as the in , and contemporaneous African localities like those in . These initial records indicate an origin in or , followed by rapid dispersal. The genus reached its peak abundance and widest distribution from the through the middle Pleistocene, expanding across , via , and persisting in before its regional decline there. This expansion lasted roughly 4 million years, with fossils documenting its presence in diverse ecosystems from open plains to forested regions across both hemispheres. Biostratigraphic correlation of faunal assemblages has been key to establishing these early to mid-range dates, placing Homotherium within the Blancan North American Land Mammal Age (late to early Pleistocene) and equivalent European stages. Homotherium exhibited regional variation in its persistence into the . In , it became extinct by the , around 1.5 million years ago, as evidenced by the absence of fossils in younger deposits. In , the latest confirmed record is a dentary from the , radiocarbon-dated to approximately 28,000 years (yr BP), indicating survival into the Weichselian Glacial. In , particularly , Homotherium persisted post-Last Glacial Maximum (after ~21,000 yr BP), with remains from deposits dated to around 10,000 years ago through stratigraphic association and radiocarbon analysis of associated fauna, confirming its late survival in northern refugia.

Paleobiology

Locomotion and physiology

Homotherium displayed adaptations indicative of running over long distances rather than short bursts of speed, characterized by elongated limbs and a flexible spine that enhanced stride efficiency. Biomechanical analyses of its long bones, modeled as beams, reveal high resistance to bending stresses, supporting sustained locomotion at moderate speeds without the robust build typical of predators. These features, including relatively slender metapodials and elongated zeugopodia, align with those of modern felids like cheetahs, though Homotherium's build suggests greater emphasis on in open habitats. Physiological inferences from genomic data indicate a high aerobic capacity, with genetic variants in genes linked to cardiovascular and respiratory functions enabling prolonged physical exertion. Large nasal passages suggest well-developed turbinates for efficient air warming, humidification, and oxygenation during extended activity, contributing to enhanced endurance. was likely aided by its large body size, which reduced surface-to-volume ratio for heat retention, and a of short, thick, dark brown (20–30 mm long) that provided insulation in varied climates, as preserved in a juvenile specimen. Sensory systems included forward-facing eyes providing for precise during pursuits, comparable to extant big cats. Olfactory capabilities were similarly advanced, with genomic evidence of variants in genes supporting acute scent detection for tracking prey over distances. A remarkably preserved of a juvenile Homotherium latidens, dated to approximately 36,000 years ago (cal ), reveals rapid early limb development, with forelimbs 18–23% longer than those of comparable cubs and wide, rounded paws with subsquare digital pads suited for mobility on . This accelerated growth in postcranial elements underscores adaptations for early and mobility, essential for survival in harsh Pleistocene environments.

Diet and predatory behavior

Homotherium was a hypercarnivorous felid, subsisting primarily on the flesh of large ungulates including horses (Equus sp.), bison (Bison sp.), and juvenile mammoths (Mammuthus columbi). Stable carbon isotope analysis of tooth enamel from North American specimens indicates a diet dominated by C4 grazers (δ¹³C ≈ -3.4 ± 0.6‰), accounting for roughly 62% of intake via mixing models, with the remainder from C3 browsers typical of open grassland ecosystems. This isotopic signature aligns with prey adapted to Pleistocene savannas and steppes, emphasizing Homotherium's role as an apex predator targeting herd animals in expansive habitats. Dental microwear texture analysis reveals high (epLsar 0.0043 ± 0.0020) indicative of tough flesh consumption, such as thick-skinned , alongside low complexity (Asfc 1.740 ± 0.831) showing avoidance of hard foods like . These patterns confirm exclusive soft-tissue feeding without durophagy, though ecological inferences suggest opportunistic scavenging supplemented when available, as no direct evidence exists but microwear permits fleshed carcasses. Predatory behavior centered on pack hunting, supported by genomic signatures of social adaptations in genes like SCTR and NTF3 linked to coordinated interactions, alongside fossil accumulations at sites implying group exploitation of prey. Homotherium likely pursued large prey over long distances to exhaustion, using its build for endurance, then delivering slashing wounds to the throat or flanks with scimitar-shaped canines designed for mediolateral load resistance and bloodletting rather than deep piercing. This contrasts with the dirk-toothed fatalis, which favored ambush stabs, positioning Homotherium as a versatile hunter. Ecologically, Homotherium occupied a niche as a specialist, competing with pack-oriented carnivores like dire wolves (Canis dirus) for megafaunal prey and overlapping with early human scavengers or hunters in and the during the . Its facilitated rapid debilitation of mobile ungulates, minimizing energy expenditure in contested open environments.

Reproduction and growth

The of Homotherium remains poorly understood due to the scarcity of evidence directly pertaining to breeding and early life stages, with inferences primarily drawn from juvenile dentitions and associated remains in den sites. Like modern felids, Homotherium likely gave birth to litters of 2–4 cubs, a size comparable to that of lions (Panthera leo), based on the social structure implied by multiple juvenile individuals found together in sites such as Friesenhahn Cave in . Growth in Homotherium juveniles is documented through dental eruption sequences and rare soft-tissue preservation. Analysis of 13 juvenile dentitions from H. serum at Friesenhahn Cave identifies eight progressive stages of tooth development, starting with the eruption of deciduous incisors and premolars shortly after birth (Stage 1, neonatal) and culminating in the near-complete replacement by permanent teeth around 2 years of age (Stage 8), closely mirroring the timeline in P. leo. A remarkably preserved mummy of a H. latidens cub, dated to approximately 36,000 years ago (cal BP) and recovered from Siberian permafrost, represents an individual about 3 weeks old, as determined by the early eruption stage of its deciduous incisors. This specimen exhibits milk dentition with fully formed deciduous cheek teeth but no permanent canines erupted, alongside early postcranial traits such as elongated limbs indicative of the species' cursorial adaptations. These findings suggest rapid early growth to facilitate integration into social packs, with weaning likely occurring within months to support predatory behaviors. Sexual maturity in Homotherium is estimated to occur at 2–3 years, aligned with the completion of dental replacement and skeletal development observed in the fossil record, enabling participation in group hunting. Lifespan estimates, inferred from growth patterns and comparisons to extant large felids, range from 15–20 years, though direct evidence such as annual bone growth rings has not been documented in Homotherium s. Parental care appears to have been socially mediated, with evidence from den sites like Friesenhahn Cave yielding remains of adults and juveniles of varying ages, suggesting communal rearing within packs to protect and provision young cubs. Genomic analysis of Homotherium supports this, indicating low rates consistent with group-living and cooperative behaviors that would extend to survival.

Evolutionary history

Origins and early diversification

Homotherium evolved from Miocene machairodonts within the tribe Machairodontini, with ancestral forms closely related to the genus Machairodus, a large saber-toothed felid that flourished across during the late Miocene. The lineage's first appearances are traced to late Miocene , around 9–8 million years ago (Ma), exemplified by early transitional taxa in regions like the northeastern . These precursors represent a basal radiation of scimitar-toothed cats, adapting to increasingly open habitats amid regional driven by tectonic uplift. Early diversification of Homotherium occurred during the , marked by the genus's emergence around 5–4 Ma, likely originating in before spreading to and . This expansion facilitated the development of the characteristic scimitar-shaped upper canines, a key innovation for slashing prey in open environments, distinguishing Homotherium from dirk-toothed relatives like . Dispersal to occurred via the during the late (Blancan stage), enabling the genus to occupy vast Holarctic ranges. In , early records from sites like Langebaanweg indicate a southward migration, coinciding with faunal turnover. Key drivers of this radiation included climate shifts, such as the (approximately 5.96–5.33 Ma), which altered Mediterranean connectivity and promoted intercontinental faunal exchanges between and . Genomic analyses from , including a 2021 study on saber-toothed cat phylogenomics, reveal deep basal splits within the clade around 20.65 Ma, with Homotherium's lineage diverging early and maintaining high genetic diversity suggestive of population expansions during the . Transitional forms, such as Amphimachairodus species (e.g., A. hezhengensis), exhibit intermediate morphologies with elongated snouts and robust builds, bridging Machairodus-like ancestors to true Homotherium and underscoring anagenetic evolution toward cursorial predation.

Adaptations over time

Throughout its temporal range from the to the Pleistocene, Homotherium underwent significant morphological evolution, with forms showing increasing specialization for hunting in open environments, though body sizes remained generally comparable to those of modern lions (around 190 kg). Larger individuals, up to approximately 400 kg, are known from late and records, including a notable specimen from southern . In contrast, later Pleistocene species like H. serum in and H. latidens in exhibited enhanced adaptations, including elongated limbs, a high brachial index, and less retractable claws suited for long-distance pursuit. These forms also featured more robust forelimbs and a sloping back, optimizing them for endurance running rather than short bursts of speed. These adaptations were primarily responses to environmental changes, including the expansion of open and habitats during the Pleistocene due to and . Pliocene Homotherium likely inhabited more forested or mixed environments, where shorter limbs and a less specialized build facilitated navigation through denser vegetation. As proliferated, limb elongation—particularly in the distal segments—evolved to enable efficient traversal of vast open plains, paralleling adaptations in other carnivores. Dietary preferences shifted accordingly, from preying on smaller, forest-adapted herbivores to targeting large migratory grazers like equids and bovids in ecosystems, supported by the cat's serrated scimitar-like canines for slashing deep wounds during chases. Ancient DNA analyses indicate strong genetic continuity within Homotherium, with minimal divergence observed among populations despite extensive migrations across continents. A 2017 study of mitochondrial genomes from Alaskan and Spanish specimens confirmed they belonged to the same , H. latidens, with genetic distances suggesting recent and high dispersal capability, likely facilitated by Beringian land bridges. However, local adaptations in body size and limb proportions emerged regionally, as seen in the more H. serum compared to Eurasian forms, reflecting responses to varying prey availability and habitat openness. A 2020 nuclear genome analysis further revealed positive selection on genes involved in mineralization, vision, and metabolism, underpinning these ecological specializations without major lineage divergence. The evolutionary trajectory of Homotherium showed increasing specialization that mirrored broader trends in the Pleistocene, where predators adapted to exploit expanding herds of large grazers in open landscapes. This progression from generalized forms to highly cursorial Pleistocene hunters highlights Homotherium's success in dynamic ecosystems, with inferred social behaviors—supported by evidence of injury care in related machairodonts—enhancing its ability to take down .

Extinction

Timeline and regional patterns

The extinction of Homotherium exhibited a staggered timeline across continents, with the genus disappearing first in during the early Pleistocene. In , the last records date to approximately 1.5 million years ago, after which no further fossils have been identified. In , Homotherium underwent a gradual decline beginning in the middle Pleistocene, becoming increasingly rare. The latest confirmed remains in come from a juvenile mummy discovered in the River basin of , Siberia, radiocarbon dated to 31,808 ± 367 years (calibrated to 35,471–37,019 cal BP), representing the first evidence from the region. In , the most recent well-dated specimen is a dentary from the off the Friesack area in , dated to approximately 28,000 years BP, indicating survival into the late Pleistocene. In the , Homotherium persisted longer, aligning with the broader megafaunal turnover, though records differ between continents. North American populations, primarily H. serum, survived until around 12,000–10,000 radiocarbon years ago, with last appearance dates falling between 13,800 and 11,400 calendar years . In , Homotherium is known only from early Pleistocene fossils in (H. venezuelensis), dated to approximately 1.8 million years ago, indicating an early arrival via the Great American Biotic Interchange, with extinction likely in the early to middle Pleistocene. Overall, this regional pattern reflects a progressive disappearance starting in around 1.5 Ma, followed by rarity in after 400,000–300,000 years ago, and final holdouts in until the terminal Pleistocene.

Proposed causes

The extinction of Homotherium at the end of the Pleistocene has been attributed to a combination of environmental and biotic pressures, with playing a central role through the warming that characterized the Bølling-Allerød interstadial and subsequent cooling around 12,000–11,000 years ago. This climatic shift led to the contraction of open steppe-tundra habitats across and , which were essential for Homotherium's endurance-based . The loss of these vast grasslands reduced the availability of migratory megafaunal prey, such as mammoths (Mammuthus spp.) and horses (Equus spp.), whose populations declined sharply due to and vegetation changes from shrub expansion and forest regrowth. Human expansion into Homotherium's range also contributed, particularly in and the , where temporal overlap with Homo sapiens is evidenced by fossils dated to approximately 28,000 years ago in . A well-preserved dredged from the , identified as H. latidens and radiocarbon-dated to ~28,000 , indicates survival in regions already occupied by modern humans, raising hypotheses of direct for resources or indirect from human overhunting of shared prey species. In the , H. serum persisted until around the time of arrival (~13,000 years ago), suggesting possible exacerbation of prey depletion by early human hunters. Interspecific competition intensified these stresses, as Homotherium faced rivals including invading felids like cave lions () and American lions (P. leo atrox), as well as canids such as dire wolves (Aenocyon dirus) in . During the , habitat compression likely heightened overlap with these more versatile predators, which could exploit smaller or alternative prey as waned; Homotherium's specialization on large, open-country herbivores left it vulnerable to such biotic pressures. Prey depletion was further compounded by human overhunting, creating a feedback loop that disadvantaged Homotherium's pack-hunting ecology. A multi-factorial model best explains Homotherium's demise, integrating climatic loss, prey scarcity, competitive exclusion, and anthropogenic influences as synergistic drivers rather than isolated causes. analyses from a ~42,000-year-old specimen from , , reveal no signs of or low immediately prior to , with heterozygosity levels comparable to extant large felids, indicating that population health was not compromised by genetic bottlenecks in the terminal phases. This supports the view that external ecological disruptions, rather than intrinsic demographic collapse, were decisive.

Human interactions

Evidence of coexistence

Paleontological evidence indicates that Homotherium coexisted temporally with early populations in both and the during the . In , H. latidens overlapped with Neanderthals (Homo neanderthalensis), who inhabited the continent from approximately 400,000 to 40,000 years ago, as well as with early modern s (Homo sapiens) arriving around 45,000 years ago. Although earlier estimates suggested Homotherium's extinction in by the Middle Pleistocene (around 300,000–400,000 years ago), revised dating of fossils extends its survival to at least 28,000 years ago, firmly within the period of presence. In the , H. serum persisted until approximately 12,000 years ago, coinciding with the (dated to about 13,000–12,700 years ago), representing the earliest widespread archaeological evidence of activity in . Archaeological sites provide direct associations between Homotherium remains and artifacts. At Schöningen, (dated to ~300,000 years ago), multiple Homotherium latidens bones, including a showing cut marks and percussion damage from hominin use as a tool for or hammering, were recovered alongside wooden spears and stone implements attributed to early hominins, likely , precursors to Neanderthals. In , fossils from Friesenhahn Cave, Texas (dated to ~13,000–11,000 years ago), overlap temporally with Clovis hunter-gatherers, though no direct artifacts are co-located; the site's megafaunal assemblage suggests shared habitats with groups exploiting similar resources. Additionally, a mummified H. latidens cub from in Siberia's Badyarikha River basin, radiocarbon dated to 31,808 ± 367 years (calibrated to 35,471–37,019 years cal BP), is contemporaneous with Beringian populations who occupied the unglaciated region between and from ~30,000 years ago. A key piece of direct evidence comes from a lower jawbone of Homotherium latidens dredged from the off the in 2000, radiocarbon dated to ~28,000 years ago. analysis confirms its identity and links it genetically to earlier European Homotherium populations, indicating persistence in northern refugia during the and aligning with the timing of modern migrations into . This spatial and temporal overlap implies potential interactions between Homotherium and early s, including the possibility of occasional predation on hominins or competition for large herbivores like and in open landscapes. Such dynamics are inferred from shared site faunas and the cats' adaptations for pursuing animals also targeted by human hunters, though no unambiguous evidence of direct conflict exists.

Depictions in human culture

Possible depictions of Homotherium in are scarce and subject to debate. A key artifact is a 6-inch stone figurine unearthed in 1896 from Isturitz Cave in southwestern , dating to the . Initially described in 1910 as representing a cave lion (Panthera leo spelaea), it was reinterpreted by Vratislav Mazák in 1970 as potentially depicting Homotherium latidens based on features like its short tail, deep facial profile, and lack of prominent canines. However, a 2009 study by Mauricio Antón and colleagues concluded that the figurine's stocky build and other traits align more closely with a cave lion cub, casting doubt on the Homotherium identification while noting no confirmed representations of machairodontine cats exist. In the , Homotherium entered scientific discourse through fossils recovered from Kents Cavern in , first described by in 1846 as Machairodus latidens. These early finds contributed to narratives in that grouped saber-toothed cats with Pleistocene cave , sometimes loosely termed "cave tigers" in popular accounts to evoke their association with deposits. Such misidentifications blurred distinctions between Homotherium and contemporaneous felids like cave lions, shaping initial perceptions of these predators as elusive "tigers." Modern depictions often portray Homotherium as a long-legged, pack-hunting of open Pleistocene landscapes, contrasting with the more ambush-oriented . It features in documentaries such as (2002), which reconstructs it pursuing herds across , and Monsters We Met (2003), emphasizing its endurance-based predation. In animated films like the Ice Age series (starting 2002), saber-toothed cats draw inspiration from machairodontines including Homotherium, though primarily modeled after . The 2024 discovery of a remarkably preserved juvenile Homotherium latidens in Siberian , dated to about 35,000 years ago, has reignited public fascination, with the intact , claws, and providing the first direct glimpse of its appearance and garnering widespread media coverage. As an emblem of Pleistocene , Homotherium symbolizes the raw power of carnivores in , often invoked in discussions of human-prey dynamics during the era of megafaunal extinctions. While specific indigenous Beringian oral traditions referencing Homotherium are not well-documented, broader Native American narratives preserve memories of large Pleistocene predators, underscoring its role in cultural reflections on ancient ecosystems.

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