History and naming
Gobicyon was described by Edwin Harris Colbert in 1939, on the basis of the anterior part of a mandible (AMNH FM2659) discovered in the Inner Mongolian Tunggur Formation, who considered it to be a relative of borophagine canids such as Aelurodon and Tomarctus . [2] A mandible from Serbia, described in 1959, was originally assigned to the type species, G. macrognathus, before being moved to Haplocynoides as new species H. serbiae by Ginsburg in 1999. [3] However, later authors note the similarity between this species and G. macrognathus, and have pointed out that Ginsburg incorrectly described the defining characteristic of his new species, and therefore assign it to Gobicyon. [1] Furthermore, the species G. zhegalloi was described by Gabunia in 1981 on the basis of a mandibular fragment found in northwestern Mongolia.
A more detailed review of the genus, including the description of two new species, was published in 2019. This study was based on the discovery of various remains across China, most notably from the Zhang'enbao Formation of Ningxia, during the preceding decades. [1]
Description
Gobicyon was a large amphicyonid, with G. serbiae having been estimated at 109kg [4] and the remains from Laogou at 162kg. [5] It should however be noted, that Gobicyon is only known from cranial and dental remains, which may lead to an overestimation of their mass, as some amphicyonids possess disproportionately large heads in comparison to their body size. [6]
The characteristic traits of Gobicyon are a short snout, deep mandibular ramus, an extremely broad and robust symphysis, giving it a hyaena-like appearance, and large premolars. A platform is formed by the dorsal face of the symphysis, similar to the condition seen in the African wild dog. This enhancement is correlated with the ability to better handle large prey. While the Zx/Zy values obtained for G. macrognathus are smaller than those of the temnocyonines, they still showcase their ability to resist the torsional stresses caused by struggling prey during the canine bite, as in large felids. An angular "chin" can be seen from the side, similar to that seen in some ursids and hyaenas. The lower incisors are well-developed, with the lateral ones being larger than the central ones. The canine is large and robust. The first lower premolar is very small and has almost disappeared, whereas the other premolars are large and high, with distinct accessory cusps. A trenchant blade, most developed on p4 and least developed on p2, is formed by an upgrowth from the swollen cingulum. The talonid of the first molar consists of a well-developed hypoconid and entoconid. The second lower molar is elongated. The first upper incisor is small, while the second, and especially third, are large and have strong lateral keels. The upper premolars resemble the lower ones, as the first one is small, and the second and third one also possess distinct accessory cusps. The third upper molar is lost in all species except for the most primitive one, G. yei. Indeed, a trend towards reduced upper posterior molars and a contemporaneous strengthening of P4 and M1 can be observed, indicating that the crushing function of its dentition moved forward to the premolars and first molar over the course of its evolution. A similar trend can be seen in hyaenas, which possess similar adaptions towards bone-crushing. The dental forma of Gobicyon macrognathus is 
. [2] [1]
No postcranial remains that can be definitely assigned to Gobicyon are known. However, deductions about its body shape can be made based on comparisons with its relatives. Other haplocyonines, such as Haplocyonoides suevicus possess elongated metapodials. Due to this, some foot bones from the Halamagai Formation have been tentatively assigned to Gobicyon, which support the presence of cursorial adaptions in this genus. [7]
Classification and evolution
The closest relative of Gobicyon is Aktaucyon from Kazakhstan. Both genera possess enlarged premolars, a centrally located M1 protocone and a uniformly developed M1 lingual cingulum. Aktaucyon also has a large M2 and a large and anteriorly located protocone, which are very similar to those of G. yei, suggesting that these features are derived for haplocyonines, but primitive for Gobicyon. Due to their close relationship, Kordikova et al. erected the tribe Aktaucyonini for the two genera. [8] However, they considered it to be part of the Daphoeninae, which is endemic to North America, and lacks their enlarged premolars, making their assignment to this subfamily unlikely. They do share numerous features with the Temnocyoninae, which may be the sister group of the haplocyonines, who evolved similar adaptions convergently. But as this subfamily is also restricted to North America, died out several million years prior to the appearance of Gobicyon, and lacks several features the genus shares with other haplocyonines, most notably the strongly anterobuccally turned p2, but also the large M2 found in G. yei and less derived haplocyonines alike, referral of Aktaucyonini to this subfamily is ruled out. Within the Haplocyoninae, Gobicyon is an aberrant taxon, showing pronounced differences to all other genera, except for Aktaucyon, by the pronounced cusps on its central premolars, the weaker angle between the P4 paracone and metacone and the reduction of metaconid and entoconid on its nearly sagittally symmetrical first two lower molars. It does, however, possess more similarities with Haplocyonopsis than with Haplocyon and Haplocyonoides. The considerable differences between the Aktaucyonini and other members of the subfamily suggest that they represent an early diverging branch, instead of being derived from one of the other genera. [1]
Below is a cladogram showcasing the phylogenetic relationships of Gobicyon, taken from Jiangzuo et al., 2021: [1]
Species
G. acutus
It is both the most derived and youngest member of the genus, being found near in the Hujialiang Formation at Yadang, Gansu in association with a Kubanochoerus skeleton, suggesting that it lived near the boundary of the Middle to Late Miocene. [9] The protocone of its p4 is rather small, and the posterior molars are greatly reduced, whereas the premolars are robust and distinct posterolingual convexities are developed on P2 and P3. This clearly showcases the forward movement of the dentitions crushing function during the evolution of Gobicyon. This is further supported by the fact that G. acutus possesses an enlarged paracone on its first upper molar. The two skulls found at Yadang are of different size and robustness, indicating sexual dimorphism. [2]
G. macrognathus
This is both the type and most completely known species of Gobicyon. Its fossils have been found in the Tunggur Formation of Inner Mongolia, more specifically the Wolf Camp, which belongs to the Morgen Fauna of the middle Formation, and correlates to early MN7/8. [7] It is also known from Gujiabei, Shataigou and Beigoudonggou, which belong to the lower/middle subfaunas of Zhang'enbao Formation and correlate to MN5/6, and the Laogou Fauna of the Hujialiang Formation, [10] which is slightly younger than the Dingjia'ergou fauna. [11] Distinct characteristics of this species include the "waist" of its M1, which is located just lingual to the buccal cusp, and the lack of an expanded inner lobe. Uniquely among Gobicyon its p3, p4 and P4 bear distinct anterior accessory cuspids. The posterior cingulid cuspid of the fourth lower molar is subdivided as in the African wild dog. [1]
G. serbiae
This poorly known species is the only European member of the genus, and is known from a mandible discovered at Prebreza in Serbia (MN 6) and a mandibular fragment from the locality Tairum Nor, which corresponds to European MN6, and is part of the Tunggur Formation. G. serbiae is very similar to G. macrognathus, and differs from that species by the lack of anterior accessory cusps on p3 and p4, and by the lower margin of the enamel on its p4 and m1, which are nearly straight. It is proposed that this species is considered valid until more material is described. [1]
G. yei
This species is known from a single rostrum discovered in the Zhang'enbao Formation of Tongxin, Ningxia. The Dingjia'ergou fauna to which it belongs corresponds to the European MN5-6. It is a primitive member of the genus, and still possesses a button-like M3, as well as a large M2, which is only slightly smaller than its M1. Its P4 has a distinct buccal concavity and a large, anteriorily protruding protocone. These two characteristics are also found in Haplocyon and Haplocyonoides, and represent a primitive character of the subfamily. [1]
G. zhegalloi
This is the largest species of the genus, and also the most poorly known, and is differentiated from the others by its proportionally larger m2 and p4. Its m1 is also aberrant, as the metaconid nearly in line with the protoconid and the hypoconid, whereas it completely disappeared in G. serbiae and G. macrognathus, and is least reduced in most other hypercarnivorous Caniformia. This may have helped it to crack bone. A similar characteristic is seen in the bears Arctodus and Arctotherium . It is known from Hingis-Nor of north-western Mongolia, which dates to the late early Miocene or early middle Miocene, corresponding to European MN4-MN5, the Halamagai Formation of Xinjiang, which corresponds to MN5, and the locality Beigoudonggou of the Zhang'enbao Formation. [1] [7]
Palaeoenvironment
The Halamagai Formation, where Gobicyon zhegalloi was discovered, preserves a diverse assemblage of amphicyonids, which also includes the large Amphicyon ulungurensis and several species of the genus Cynelos . [7] Pollen data indicate that the environment was a rather arid prairie and dominated by grasses and Artemisia , with only scattered trees. [12] This is furthermore supported by the presence of the earliest known grazing gomphothere, and the isotope analysis of the giraffid Discokeryx , which suggest it was an open-land grazer. [13] Several smaller taxons known from the formation are also associated with arid and open habitats, most notably the ground squirrel Atlantoxerus [14] and the ochotonid Alloptox . [15] However, other mammals are more indicative of a humid environment, with patches of forests. [16] These include Amphicyon and Cynelos, [7] bats, browsing proboscideans, [16] the beaver Steneofiber , [17] the cervid Stephanocemas, the moschid Micromeryx [18] and, most notably, the primate Pliopithecus . Especially the latter genus indicates the presence of at least local humid environments in an otherwise drier region, and a more diverse terrain than often assumed. [18] [19] Other genera found at the site include the mustelid Tungurictis , [20] the small hyaenid Protictitherium , a nimravid, the browsing horse Anchitherium , the anthracothere Elomeryx [21] and the lagomerycid Stephanocemas . [22]
The slightly younger Moergen fauna of the Tunggur Formation also shows a mix of small animals adapted to an arid habitat, such as Atlantoxerus, the hedgehog Mioechinus , various ochotonids, cricetids and jerboas, and large, browsing mammals which suggest a more forested habitat. The presence of the beaver Anchitheriomys , cyprinid fish and bivalves furthermore showcases the presence of notable amounts of water, while marls suggest that small, alkaline ponds were present during periods of drought. All this indicated that the Tunggur Formation was deposited in a mixed environment of forests and open grasslands, with shallow rivers meandering through the landscape. Other large predators of this locality include the sabertoothed-cat Metailurus and the barbourofelid Albanosmilus , [23] the possibly hyaenid Percrocuta and the wolf-sized Amphicyon tairumensis. The herbivore assemblage includes a large variety of deer, the suids Listriodon and Kubanochoerus, the proboscidean Platybelodon , the bovid Turoceros , the equid Anchitherium, two species of rhinoceros and Chalicotherium . [24]
Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene, spread to Europe by the late Eocene, and further spread to Asia and Africa by the early Miocene. They had largely disappeared worldwide by the late Miocene, with the latest recorded species at the end of the Miocene in Africa. They were among the first carnivorans to evolve large body size. Amphicyonids are colloquially referred to as "bear-dogs".
Amphicyon is an extinct genus of large carnivorans belonging to the family Amphicyonidae, subfamily Amphicyoninae, from the Miocene epoch. Members of this family received their vernacular name for possessing bear-like and dog-like features. They ranged over North America, Europe, Asia, and Africa.
Gomphotherium is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. It is the most diverse genus of gompothere, with over a dozen valid species. The genus is probably paraphyletic.
Lufengpithecus is an extinct genus of ape, known from the Late Miocene of East Asia. It is known from thousands of dental remains and a few skulls and probably weighed about 50 kg (110 lb). It contains three species: L. lufengensis, L. hudienensis and L. keiyuanensis. Lufengpithecus lufengensis is from the Late Miocene found in China, named after the Lufeng site and dated around 6.2 Ma. Lufengpithecus is either thought to be the sister group to Ponginae, or the sister to the clade containing Ponginae and Homininae.
Miomachairodus is an extinct genus of large machairodontine containing only a single species, Miomachairodus pseudailuroides. It is mainly known from Middle Miocene-age fossils in Turkey and persisted until the early Late Miocene (Vallesian). Fossils of this machairodont have been found in the Vallesian-age Bahe Formation in Shaanxi, China, and Yeni Eskihisar in Anatolia. This Turkish site is of Miocene age and is well known for its pollen studies.
Agnotherium is a genus of large sized carnivoran mammals, belonging to the Amphicyonidae, which has been found in Western Europe, and possibly China and Northern Africa, and lived during the Late Miocene epoch. Despite only being known from fragmentary remains, the genus notable for hypercarnivorous adaptions, which have been said to represent the "apex" among its family.
Ysengrinia is an extinct genus of carnivoran in the family Amphicyonidae, that lived during the Late Oligocene to Early Miocene. Fossil remains have been discovered in Western Europe, the United States and possibly China. The European species are among the earliest known members of the Thaumastocyoninae, a group of aberrant amphicyonids showcasing hypercarnivorous adations, but are only known from fragmentary remains. The American species is much better preserved and shows a robust, black-bear sized predator. These fossils play an important role in our understanding of the biotic interchange between Eurasia and North America during the earliest Miocene. However, more recent research suggests that the genus might be polyphyletic, and that several of its species should be excluded from Ysengrinia.
Galerix kostakii is a fossil erinaceid mammal from the early Miocene of Greece. It is known from the site of Karydia, assigned to the biostratigraphical zone MN 4; similar fossils have been found at an approximately contemporary Czech site and a slightly younger Greek site. With characters like the presence of a hypocone on the upper third premolar, the presence of a connection between the protocone and metaconule cusps on the second upper molar in only a few specimens, this species is intermediate between the slightly older Galerix symeonidisi and the slightly younger Parasorex pristinus. It may form part of the lineage leading from the genus Galerix to the younger genus Parasorex.
Indraloris is a fossil primate from the Miocene of India and Pakistan in the family Sivaladapidae. Two species are now recognized: I. himalayensis from Haritalyangar, India and I. kamlialensis from the Pothohar Plateau, Pakistan. Other material from the Potwar Plateau may represent an additional, unnamed species. Body mass estimates range from about 2 kg (4.4 lb) for the smaller I. kamlialensis to over 4 kg (8.8 lb) for the larger I. himalayensis.
Sivaladapis is a genus of adapiform primate that lived in Asia during the middle Miocene.
Magericyon is an extinct genus of Amphicyonid ("bear-dog") that lived during the Miocene 10-9 Ma in what is now Spain.
Sivaelurus is a fossil genus of felid containing only a single species, S. chinjiensis, which was described based on a partial right maxilla collected from the Chinji Formation in the Lower Siwaliks. The species was originally described by Guy Ellcock Pilgrim as Pseudaelurus chinjiensis in 1910, who later erected a new genus, Sivaelurus, for it in 1913.
Ammitocyon is a genus of large sized carnivoran mammals, belonging to the Amphicyonidae, that lived during the Late Miocene in what is now Spain. It is notable for its extreme adaptations towards hypercarnivory, its extremely robust skeleton, and was one of the last surviving members of its family.
Thaumastocyoninae is an extinct subfamily of amphicyonids, large terrestrial carnivores, which inhabited what is now Europe during the Miocene epoch. The subfamily was erected by Hürzeler (1940), and is defined by the complete suppression of m1 metaconid, reduction of the premolars, except the p4, which is reinforced, and the oblique abrasion of the teeth, and the possession of hypercarnivorous tendencies. Thaumastocyonines are poorly known, with only about 65 dental specimens, most of those isolated teeth, being known as of 2020, although more complete remains have recently been discovered.
Diamantofelis is an extinct genus of felids that lived in what is now Namibia during the Early Miocene. It contains a single species, Diamantofelis ferox.
Aurorarctos is an extinct North American genus of bears. It contains a single species, Aurorarctos tirawa, which lived in the Middle Miocene. Its fossils were discovered in the Valentine formation and Myers Farm of Nebraska, and represent the earliest known member of the Ursinae, showcasing that basal members of this subfamily were small, but already showed adaptions towards increasing herbivory as well as an arboreal lifestyle The genus name combines the Latin words aurora (dawn) and Greek arctos (bear); the specific epithet references the creator god Tirawa in Pawnee mythology.
Myacyon is an extinct genus of large sized carnivoran mammals, belonging to the family Amphicyonidae, that lived in Africa during the Miocene epoch. Due to the limited scope and fragmentary nature of the severely damaged holotype, as well as the illustrations in its descriptions, which have been called inadequate, usage of this genus poses serious issues. However, it is notable for being one of the last surviving members of its family and its adaptions to hypercarnivory. Its relationships to other amphicyonids are obscure, and it is not closely related to Bonisicyon, the other late surviving African genus, although it has been proposed that it descends from a species of Cynelos or Namibiocyon.
Bonisicyon is an extinct genus of carnivoran mammals, belonging to the family Amphicyonidae. It is the last-surviving member of its family, living in East Africa during the end of the Miocene epoch. Known only from a damaged mandible and isolated teeth from the Nawata Formation, and possibly also the Lukeino Formation, its closer taxonomic affinities are unclear. It is notable for both its small size, and its unique dentition.
Namibiocyon is an extinct genus of carnivoran mammals, belonging to the family Amphicyonidae, that lived in Namibia during the Early Miocene epoch. Before the erection of this taxon in 2022, the type and only species, N. ginsburgi, had been assigned to a variety of other genera. It is notable for its adaptions toward hypercarnivory.
Peignecyon is an extinct genus of large carnivorans belonging to the family Amphicyonidae. It belongs to the subfamily Thaumastocyoninae, which is characterized by their adaptions towards hypercarnivory. Whereas most other thaumastocyonines are often only known from fragmentary remains and isolated teeth, Peignecyon is known from a variety of well-preserved remains. It contains a single species, P. felinoides from the Early Miocene of the Czech Republic.
