Amphicyon

In a note dated back to May 16, 1836, French geologist Alexandre Leymerie wrote a letter in April that he requested from French palaeontologist Édouard Lartet, which provided details of his exploits in palaeontological sites in the French department of Gers, in particular the commune Sansan. Lartet described his finds of fossil taxons that he found within the sites, including "Mastodonte" (species assigned to it were later reclassified to another mammutid Zygolophodon and the gomphothere Gomphotherium), "Dinotherium" (its species eventually reclassified as either Deinotherium or Prodeinotherium), "Rhinoceros" (reclassified as an aceratherine rhinocerotid Hoploaceratherium), and "Palaeotherium" (the referred equid species now known as belonging to an anchitherine Anchitherium). He also recalled finding fossil "deer" species of which he said that the largest ones were the size of extant deer in France while the smallest ones were the size of small antelope. The palaeontologist noted that the "peaceful ruminants" coexisted with a "formidable" large carnivore he provisionally named Amphicyon based on two half-jaws and bones that he sent to a museum. He described it as having unilobed incisors and compressed canines similar to raccoons but also a carnivorous molar and its first two tubercles conforming those to dogs. Lartet then stated that the genus's most distinct trait was the existence of a third tubercle at the upper jaw, which was not known in any other carnivore. The genus name may come from Ancient Greek ἀμφί (amphí), meaning "both", and κύων (kúon), meaning "dog", but Lartet did not define the genus's etymology. Despite the initial status of the genus name Amphicyon as nonpermanent, French anatomist Henri Marie Ducrotay de Blainville, a peer who Lartet had regularly discussed his fossil findings with, had sketched mammal skeletons and fossils in 1841, where he recognized the 2 species "Amphicyon major" and "Amphicyon? minor." In 1851, Lartet reviewed the fossil carnivoran genera from Sansan. Among them were Amphicyon, in which it was reconfirmed as a carnivorous mammal the size of extant bears that was discovered in Sansan in 1835. He recalled that its single-lobed incisors and its canines of serrated ridges are similar to the raccoon while the molars were similar to that of a dog. He confirmed the fossil specimens along with the third tubercle in the upper jaw (of which he said that it only exists in the extant bat-eared fox (then known as "Canis megalotis")) as belonging to the species Amphicyon major. The palaeontologist described it as also having an anatomy of plantigrade locomotion similar to extant bears with few differences in form. Blainville was mentioned as speculating that it must have had a long and very strong tail. The species "Amphicyon minor" was reclassified as a separate genus Hemicyon, which he described as a carnivore larger than a European wolf that was closer in form to a dog than Amphicyon and had dentition similar to mustelids. He also described a newer genus Pseudocyon, which he misidentified as being digitigrade and described as being smaller than Amphicyon and coming closest to canids based on its dentition and bones. All three genera, Lartet said, had canines that retained finely serrated edges, implying that they were some of the top coexisting predators of the Miocene in modern-day France. ==Species==

European species • Amphicyon astrei :The oldest known species of the genus, A. astrei is known from the Early Miocene sites Gardouch and Paulhiac in France, which date to MN1 (or "Mammal Neogene 1" as part of the Mammal Neogene zones). The species was originally described by Kuss in 1962, however, he also noted that its features do not completely match any known genus, and later moved it to the genus Pseudocyon, as subspecies of P. sansanienis, and considered it to be ancestral to P. s. intermedius (which has since then been moved to the separate genus Crassidia). Ginsburg and Antunes later reassigned it to Amphicyon, which was followed by other authors, and suggested that it was ancestral to later species of the genus. Unlike later members of the genus, it did not possess enlarged posterior molars. It first appeared in MN4 and lasted until at least MN6. Amphicyonid remains from La Grive Saint-Alban, dating back to MN7/8, have also been assigned to this species. The taxonomic status of this species is controversial, with Kuss and several other authors considering this taxon to be a subspecies or synonym of A. major. Later authors however suggest that the two species are distinct, with A. eppelsheimensis possibly being the last representative of the A. major lineage. Notably, the p4 is more strongly reduced than in A. major, and it is also slightly larger. Viranta followed his arguments for the distinction of this species, but did not consider Hubacyon to be a valid genus. The highest point of its hypoconid is located more posterior than in other members of this genus, and a line drawn from the posterolingual corner to the posterobuccal corner possesses a greater angle on the buccal side, due to the extended posterobuccal corner. Both of these features are similar to those seen in thaumastocyonines. Its type locality Mannersdorf, in Austria, is of uncertain age, but the presence of hipparionine horses shows that it is no older than MN9. Viranta also tentatively assigns molars from Kohfidisch, previously referred to cf. A. giganteus, to this species. As this locality dates to MN11, this would make it one of the youngest members of the family. However, the terrestrial assemblage of the sandpit generally points towards an Early Pannonian (Vallesian) age, as which is in agreement with Kretzoi's original description. This species is potentially hypercarnivorous, and only known from a single, fragmentary tooth, which is smaller, more slender and gracile than that of A. gutmanni, as well as considerably more brachydont. • Amphicyon giganteus :A. giganteus was originally described by Schinz in 1825, and in 1965 Kuss erected the genus Megamphicyon for this species, based on differences in its dentition and size between it and A. major. Others, however, reject the reclassification in favour of the older classification A. giganteus. A. giganteus was a widespread European species that lived during the late Burdigalian to late Seravallian, corresponding to the MN4-MN7/8. Most remains were found in Western Europe, although the youngest known record of the species is from Turkey, possibly suggesting the species survived in Anatolia after it had already gone extinct in Europe. Fossils from this species are also known from Bosnia and Herzegovina as well as the locality Arrisdrift in Namibia. It has also been referred to fossil specimens from Moghra in Egypt, but the referral of these fossils remains controversial. It has furthermore been reported from levels 5 to 6 of Pakistans lower Vihowa Formation. The age of these remains is between 19 and 18.5 Ma, with a molar from the base of the Potwar Plateau sequence extending its range in the Siwaliks to 17.9 Ma. An even younger fossil possibly referable to this species is a large humerus known from the base of the Manchar formation. Its holotype is a maxilla, previously referred to A. astrei, possesses a parastyle and a more posteriorly located protocone. Both these localities date to MN4, although there is a possible report from La Retama, which dates to MN5, but the remains from there are as of yet undescribed. Differences in dentition, most notably the reduction of its premolars, led Viranta to erect the separate genus Euroamphicyon for this species. : Asian species • Amphicyon ulungurensis :A. ulungurensis is known from the early Langhian in the Halamagai Formation, near the Ulungur River from which it derives its name. Due to the lack of observation on the characteristics of the upper molars, there is neither evidence for including it nor for excluding it from the genus, in which it is placed mostly on the basis of its very large size. • Amphicyon zhanxiangi :The only Asian amphicyonid which definitely belongs to the genus Amphicyon, A. zhanxiangi was described in 2018 based on a maxillary fragment from the Zhang'enbao Formation in Ningxia, China. The Yinziling subfauna to which it belongs dates to the late Shanwangian, roughly corresponding to MN5. A. zhanxiangi is medium-sized, comparable to A. major, and closely related to A. giganteus. • Amphicyon lydekkeri :A. lydekkeri is known from the Dhok Pathan horizon in Pakistan and was described by Pilgrim in 1910, who later attributed it to its own genus, Arctamphicyon. However, Pilgrim identified the holotype as first m1 and then as M1, despite it actually being a M2, making the diagnosis invalid. It has furthermore been argued that the differences between "Arctamphicyon" and Amphicyon are negligible, with the former being a junior synonym of the latter. It was described by Pilgrim in 1932. He noted that the tooth is very similar to that of A. shahbazi, although A. cooperi lacks an external cingulum, and that it may actually belong to that species. Later authors referred a fragmentary mandible from Chinji, isolated teeth from the Chinji and the Nagri zones, and the Dang Valley, to this species. The exact age of the Chinji specimens cannot be defined, as the fossil-bearing localities in this region stretch from ca. 15 to 9 Ma, although the correlation of the Dang Valley fauna suggests that they're of late middle Miocene age, whereas the Nagri fauna dates to the Vallesian. It has been suggested that none of the Siwalik species truly belong to Amphicyon, although others suggests that A. palaeindicus should be referred to this genus. In a 2025 review of Siwalik carnivorans, it is argued that most remains previously referred to A. pithecophilus should actually be referred to this species, alongside a number of isolated remains, expanding the timespan during which A. palaeindicus existed from ca. 18 to 11 Ma. The various fossils indicate a notable size variation within this species, though the range of its dimensions is broadly similar to A. major. It is a wolf-sized predator, considerably smaller than A. major. North American species • Amphicyon galushai :A. galushai represents the first occurrence of Amphicyon in North America, approximately 18.8–17.5 Mya during the early Hemingfordian. Described by Robert M. Hunt Jr. in 2003, it is mostly known from fossils found in the Runningwater Formation of western Nebraska and includes a complete adult skull, a partial juvenile skull, 3 mandibles and teeth and postcranial elemenents representing least 15 individuals. There is an additional skull fragment from the Troublesome Formation of Colorado. A. galushai is considered ancestral to the late Hemingfordian species, Amphicyon frendens. A. frendens specimens have since been found at sites in Harney and Malheur Counties, Oregon. It was considerably bigger than the earlier A. galushai, and possessed a larger M2. • Amphicyon ingens :This huge species lived during the early to middle Barstovian, 15.8–14.0 Mya. It was originally described by W. Matthew in 1924 from specimens found in the Olcott Formation, Sioux County, Nebraska. Two years later White described another species, A. longiramus, named for its exaggeratedly long skull, from the same locality, which he believed was disti nct due to its larger size, among other factors. Since then, others have noted that the supposed difference between these two species is likely to be a result of sexual dimorphism. Olsen therefore referred to A. longiramus as the valid name for this taxon, an assignment that was acknowledged by Heizmann and Kordikova as well as the Florida Museum of Natural History. Beyond its type locality, it is furthermore known from the lower part of the Calvert Formation at the Pollack Farm Site in Delaware as well as the Garvin Gulley and the Brenham Local Fauna from Texas, possibly indicating that it was widely distributed across eastern North America during the Hemingfordian. ==Description==

, Amphicyon giganteus and Crocuta crocuta''|300x300px Amphicyon was a large to very large predator, although the various species differ considerably in size, ranging from moderately sized species such as A. astrei to the huge A. ingens, which was one of the biggest carnivorans of all time. The estimated weight of male A. major is 212 kg, while females are smaller, at only 122 kg, indicating significant sexual dimorphism. The shoulder height of a young female, which has been estimated to have weighed 125 kg, has been reconstructed as 65 cm. As the largest Old World species of the genus, A. giganteus was considerably larger, with females weighing 157 kg and males 317 kg, although they may have grown even greater sizes. The mass of several other European species has been estimated craniodental measurements, which generally falls into the range of estimations derived from postcranial remains, although it may slightly overestimate their weight. A. astrei is the smallest species, estimated at 112 kg, while A. laugnacensis and A. lactorensis were somewhat larger, at ~130 kg and 132 kg, respectively. A. olisiponensis is estimated at 147 kg and A. carnutense as 182 kg, while A. eppelsheimensis and A. gutmanni are among the biggest members of the genus, with estimated weights of 225 and 246 kg. Its skeleton showcases a variety of features resembling canids, ursids and felids. Amphicyon possessed a powerful skull, with a long snout and high sagittal crests. The canines are robust, and the posterior molars are enlarged, whereas the anterior premolars are reduced. Its neck is wide, similar to that of a bear. Its postcranial skeleton is stout and robust, with massive, powerful limbs, and mobile shoulder joints as well as flexible wrists. The upper limb bones are comparatively long in comparison to the lower ones, and it did not possess any adaption towards cursoriality. Its posture was more similar to plantigrade taxa such as ursids than to digitgrade ones like felids, and their claws were not retractable. Amphicyon also had a rather flexible back, and a heavy tail, which has been estimated to have possessed as many as 28 caudal vertebrae, and may have been as long as the rest of the spine. ==Palaeobiology==

Diet and predatory behaviour The diet of Amphicyon has proven difficult to reconstruct, as its dentition possesses both crushing and shearing functions. It has been proposed, on the basis of dental wear patterns and morphology, that European species of this genus were bone-crushing mesocarnivores. Another dental microwear analysis also supports an omnivorous diet for A. giganteus, whose dentition possesses a high number of large pits and several small pits, and notes that it clearly differs from bone-crushing taxa such as hyaenas. As both its anterior premolars and posterior molars are reduced, A. olisiponensis may have been more hypercarnivorous than other European species. Other bitemarks referred to the species A. olisiponensis were found on a metapodial belonging to the large anthracothere Brachyodus onoideus. Bite traces on various mammalian long bones from the Early Miocene of Czechia have also been attributed to Amphicyon. As patterned bones have no immediate benefit for feeding, they likely represent evidence of active predation. Sexual dimorphism Strong sexual dimorphism is present in a variety of species, known from both Europe and North America, with the males being considerably larger than the females. Although this size difference is present in many amphicyonids, it is more strongly developed in Amphicyon than in Cynelos lemanensis. The males furthermore possess slightly longer and more robust snouts, larger canines and immense sagittal crests. Comparison with other strongly sexually dimorphic carnivorans suggests that Amphicyon was polygynous, with territorial males competing with each other for females during the mating season. This may have contributed to the size increase observed within the genus. Another ichnotaxon associated with Amphicyon is Platykopus maxima from the Hungarian Early Miocene locality Ipolytarnóc. The footprints were attributed to A. major on the basis of their size and short phalanges. ==Fossil distribution==

Fossil remains of Amphicyon are most common in Western and Central Europe, where they were discovered in various countries, including France, Germany, Spain and Hungary, but were also found in Bosnia-Herzegovina and Turkey. A. astrei is the oldest known species, and may have been the ancestor of the later members of the genus, and is known from the earliest Miocene of France. It has been suggested that there were at least three dispersal events from European Amphicyon into Eastern Asia, with the first one being the ancestors of the North American species, the second one dating to the Early Miocene or earliest Middle Miocene, leading to A. zhanxiangi, and the last one, that of the A. ulungurensis lineage, which occurred slightly later. There was generally no closer affinity between the Chinese amphicyonids and those of the Indian Subcontinent during the middle Miocene. A very large humerus from the Manchar formation indicates that a gigantic species was present in the Siwaliks during the early parts of the Middle Miocene. South East Asian reports include a large incisor from the Aquitanian (~23-21 Ma) of Vietnam, and a species from the Lower Irrawaddy Formation of Myanmar, which is likely closely related to Arctamphicyon. Scarce dental remains have furthermore been reported from the Saudi Arabian Dam Formation, which dates to ca 17-15 Ma, in 1982. These remains show morphological differences to A. major, and several of the species to which it had been compared, mostly because of their similar, small size, including A. bohemicus, A. styriacus and A. steinheimensis (which also shares the apomorphic features present in the Arabian taxon), have since been moved to other genera. The only definitive African remains of Amphicyon are from Arrisdrift in Namibia, which has variously been dated to 17.5 Ma or 16 Ma, and belong to the species A. giganteus. Others tentatively refer this taxon to the genus Myacyon. The migration of Amphicyon from Eurasia to North America was part of a trans-Beringian faunal exchange between the two continents during the Early Miocene. The oldest North American member of the genus is A. galushai, which first appeared between 18.8 and 18.2 Ma. It likely gave rise to the larger A. frendens, which itself was ancestral to the huge A. ingens, which was also the last North American member of the genus, disappearing around 14.2 Ma. This lineage was probably endemic to North America, and is mostly known from the Great Plains, although remains of A. ingens were also discovered in California and New Mexico. ==References==