Homotherium

Eurasia The first fossils of Homotherium were scientifically described in 1846 by Richard Owen as the species Machairodus latidens, based on Pleistocene aged canine teeth found in Kent's Cavern in Devon, southwestern England by the Reverend John MacEnery in 1826. The name Homotherium (Greek: (, 'same') and (, 'beast')) was proposed by Emilio Fabrini in 1890 during a review of machairodont material from the Late Pliocene-Early Pleistocene of Tuscany, Italy, without further explanation, for a new subgenus of Machairodus, whose main distinguishing feature was the presence of a large diastema (gap) between the two lower (inferior) premolars. He further described two species in this new subgenus: Machairodus (Meganthereon) crenatidens and Machairodus (Meganthereon) nestianus, both from Tuscan remains. The genus name itself was rarely used in the scientific literature until the late 1940s. In 1918, the species Homotherium moravicum was described by Josef Woldřich based on remains found in what is now the Czech Republic. Homotherium davitashvili (also spelled davitasvilii In 1986, the species Homotherium darvasicum was described by Scharif Scharapov based on material from Kuruksay, Tajikistan in Central Asia. In 1989, another species Homotherium tielhardipiveteaui'' was named by Scharapov based on fossils also found in Tajikistan. In 1936, Teilhard de Chardin described the new species Homotherium ultimus based on fossils from the Middle Pleistocene-aged Zhoukoudian cave complex near Beijing in northern China. Remains from the late Early Pleistocene-early Middle Pleistocene of Java in Indonesia have also been attributed to this species (as Homotherium ultimum), 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), is now also regarded as a synonym of Homotherium. In 1996, Homotherium hengduanshanense was described based on fossils of Late Pliocene-Early Pleistocene age from the Hengduan Mountains of Sichuan, southwestern China.'' 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. Africa In 1947/48, Camille Arambourg described the species Homotherium ethiopicum from remains found in the Omo river valley in southern Ethiopia. This publication helped popularise the genus Homotherium, which was little used prior. 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. In 2015, further material from the Hadar Formation was tentatively referred to H. hadarensis. 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, dating to the early-middle Pliocene. In 1990, Alan Turner challenged the validity of H. problematicum and H. hadarensis, and later authors have generally refrained from referring African Homotherium fossils to any specific species due to their largely fragmentary nature. Indeterminate remains of Homotherium have also been reported from the Ahl al Oughlam locality in northern Morocco, dating to the Late Pliocene. 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. 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. 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, In the same paper, Mawby noted that a comparative study of both Ischyrosmilus and Homotherium might conclude them as synonyms. Charles Stephen ("Rufus") Churcher argued in 1984 that the remains from Cita Canyon instead represented the Eurasian species Homotherium crenatidens, though Martin et al. 2011 considered them to belong to Homotherium ischyrus. 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. 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. Ischyrosmilus and Dinobastis are now generally accepted as synonyms of Homotherium. 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. 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. 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) 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. 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. ==Description==

Homotherium reached a length of around , a height of at the shoulder and a maximum weight of around , comparable in size to a living lion or tiger. Homotherium probably exhibited size-based sexual dimorphism, with males suggested to be larger than females. 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. Its large upper canine saber teeth are broad, distinctly flattened and coarsely serrated. The incisors are enlarged relative to those of modern big cats, 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. ==Paleobiology and paleoecology ==

Homotherium is suggested to have been adapted to hunting large prey. 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. These throat bites would likely have caused massive blood loss resulting in rapid death. 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. 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 and primarily consumed 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. 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. In Early Pleistocene Europe, the giant hyena Pachycrocuta brevirostris is likely to have presented a significant threat capable of stealing H. latidens kills. 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 to over ) 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. In the late Early Pleistocene-early Pleistocene of Java Homotherium lived alongside the extant tiger, who may have competed with Homotherium. The sloped back and powerful lumbar section of Homotheriums 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, with the meatiest parts of the juvenile mammoths like limbs being preferentially transported to the cave. 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. Palaeopathology 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. == Evolution and extinction ==

The lineage of Homotherium is estimated (based on mitochondrial DNA sequences) to have diverged from that of Smilodon about 18 million years ago. Homotherium has been suggested to have originated from African species of the genus Amphimachairodus. 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. 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. Across northern and southern China, Homotherium is thought to have gone extinct sometime during the Middle Pleistocene. 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. It has been suggested that this may represent a Late Pleistocene dispersal from North America, rather than a continuous undocumented occupation of the region. Homotherium serum became extinct as part of the end-Pleistocene extinction event of most large mammals across the Americas. == Relationship with humans ==

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. 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. 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. == See also ==