Hyaenodon

Hyaenodon Temporal range: Middle Eocene to Early Miocene (Bartonian to Burdigalian) 38–17  Ma PreꞒ Ꞓ O S D C P T J K Pg N
Mounted H. sp. skeleton, Science Museum of Minnesota
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	† Hyaenodonta
Superfamily:	† Hyaenodontoidea
Family:	† Hyaenodontidae
Subfamily:	† Hyaenodontinae
Tribe:	† Hyaenodontini Leidy, 1869 [1]
Genus:	† Hyaenodon Laizer & Parieu, 1838
Type species
†Hyaenodon leptorhynchus Laizer and Parieu, 1838
Species
[see classification]
Synonyms [2]
synonyms of genus: Gobipterodon(Lavrov, 1999) [3] Macrohyaenodon(Lavrov & Emry, 1998) Macropterodon(Lavrov, 1999) Megalopterodon(Dashzeveg, 1964) Microhyaenodon(Lavrov, 1999) [3] Neohyaenodon(Thorpe, 1922) Prohyaenodon(Lavrov, 1999) Protohyaenodon(Stock, 1933) Pseudopterodon(Schlosser, 1887) Taxotherium(Blainville, 1841) synonyms of species: H. brachyrhynchus: Canis brachyrhynchus(Blainville, 1841) Hyaenodon brachyrhenchus(Lavrov, 1999) Hyaenodon cuvieri(Pictet, 1853) [4] Hyaenodon leptorhynchus(Dujardin, 1840) [5] Hyaenodon parisiensis(Laurillard, 1845) [6] Hyaenodon vulpinum(Filhol, 1877) Hyaenodon vulpinus(Gervais, 1873) Nasua parisiensis(Blainville, 1841) Pterodon brachyrhynchus(Pomel, 1846) [7] Pterodon cuvieri(Pomel, 1846) Taxotherium parisiense(Blainville, 1841) H. brevirostrus: Hyaenodon brevirostris(Joeckel, 1997) [8] Protohyaenodon brevirostrus(Mellett, 1977) H. chunkhtensis: Microhyaenodon chunkhtensis(Lavrov, 1999) H. crucians: Hyaenodon leptocephalus(Scott, 1888) [9] Hyaenodon minutus(Douglass, 1902) Hyaenodon paucidens(Osborn & Wortman, 1894) [10] Protohyaenodon crucians(Mellett, 1977) Prtohyaenodon crucians(Lavrov, 1999) Pseudopterodon minutus(Douglass, 1902) H. dubius: Hyaenodon aymardi(Filhol, 1882) [11] H. exiguus: Hyaenodon exigus(Lavrov, 1999) Pterodon exiguum(Gervais, 1873) H. filholi: Hyaenodon compressus(Filhol, 1876) Hyaenodon vulpinus(Filhol, 1876) Microhyaenodon filholi(Lavrov, 1999) Pseudopterodon ganodus(Schlosser, 1887) H. gervaisi: Hyaenodon ambiguous Hyaenodon ambiguus(Martin, 1906) H. gigas: Macropterodon zelenovi(Lavrov, 1999) Neohyaenodon gigas(Lavrov, 1999) H. heberti: Hyaenodon arnaudi(Depéret, 1917) [12] H. horridus: Hyaenodon cruentus(Leidy, 1853) Neohyaenodon horridus(Thorpe, 1922) Neohyaenodon semseyi(Kretzoi, 1941) [13] H. incertus: Gobipterodon exploratus(Lavrov, 1999) Hyaenodon exploratus(Polly, 1993) [14] Neohyaenodon incertus(Lavrov, 1999) Pterodon exploratus(Dashzeveg, 1985) H. leptorhynchus: Canis leptorhynchus(Blainville, 1841) Hyaenodon bavaricus(Dehm, 1935) [15] Hyaenodon cayluxi(Filhol, 1876) Hyaenodon martini(Depéret, 1917) Hyaenodon milloquensis(Martin, 1906) Pterodon leptorhynchus(Pomel, 1846) H. macrocephalus: Neohyaenodon macrocephalus(Lavrov, 1999) H. megaloides: Neohyaenodon megaloides(Mellett, 1977) H. microdon: Microhyaenodon microdon(Lavrov, 1999) Protohyaenodon microdon(Mellett, 1977) H. milvinus: Neohyaenodon milvinus(Lavrov, 1999) H. minor: Hyaenodon aimi(Cooper, 1926) [16] Hyaenodon hantonensis(Lydekker, 1884) [17] H. mongoliensis: Epipterodon mongoliensis(Lavrov, 1999) Megalopterodon mongoliensis(Dashzeveg, 1964) Neohyaenodon mongoliensis(Morlo & Nagel, 2006) [18] Pterodon mongoliensis(Van Valen, 1967) [19] H. montanus: Protohyaenodon montanus Neohyaenodon montanus(Mellett, 1977) H. mustelinus: Hyaenodon mustilinius Prohyaenodon mustelinus(Lavrov, 1999) Protohyaenodon mustelinus(Scott, 1894) H. pervagus: Hyaenodon neimongoliensis(Huang & Zhu, 2002) [20] H. pumilus: Microhyaenodon pumilus(Lavrov, 1999) H. raineyi: Microhyaenodon raineyi(Lavrov, 1999) Protohyaenodon raineyi(Gustafson, 1986) H. requieni: Hyaenodon heberti euzetensis(Depéret, 1917) Pterodon requieni(Gervais, 1846) H. venturae: Hyaenodon exiguus(Stock, 1933) Microhyaenodon venturae(Lavrov, 1999) Protohyaenodon exiguus(Stock, 1933) Protohyaenodon venturae(Mellett, 1977) H. vetus: Neohyaenodon vetus(Mellett, 1977) Pterodon californicus(Stock, 1933) H. yuanchuensis: Hyaenodon yuanchüensis(Young, 1937)

Hyaenodon ("hyena-tooth") is an extinct genus of carnivorous placental mammals from the tribe Hyaenodontini, part of the subfamily Hyaenodontinae (which is within the family Hyaenodontidae), that belonged to the now extinct order Hyaenodonta. ^[21] The genus was found lived in Eurasia and North America from the Middle Eocene to the Early Miocene, from 38 to 17 million years ago, existing for 21 million years. ^[22] Hyaenodon first evolved in Asia, ^[23] probably evolving from Propterodon . ^[24]

The genus currently consists of at least 40 species, ^[24] although due sexual dimorphism and intraspecific variation, they were likely fewer species within the genus. ^[23] The species within the genus ranged in size from H. filholi, who weighed 2 kg (4.4 lb), to H. gigas and H. mongoliensis, who were estimated to be similar in size to Hyainailouros . The largest species were likely the apex predators of their time, with fossil records suggesting they could’ve occasionally hunted smaller predators. Several species within the genus were cursorial predators, either being ambushing or pounce-pursuit predators. The canines of the animal mediolaterally compressed much like canids, landing shallow bites on their prey. Unlike canids such as wolves, they were thought to have been solitary predators.

The genus saw a decline during the Late Eocene to Early Oligocene, with only one species, H. weilini, being present in the Miocene. Initially, experts hypothesize their decline and extinction was the result of competition with carnivorans. However, over the recent years, this hypothesis has been questioned. Instead, experts now hypothesize cause of their decline and eventual extinction was the inability to adapt to open environments.

Classification and phylogeny

Taxonomy

Tribe: †Hyaenodontini(Leidy, 1869) Genus: †Hyaenodon(Laizer & Parieu, 1838) †Hyaenodon brachyrhynchus(Blainville, 1841) [25] †Hyaenodon chunkhtensis(Dashzeveg, 1985) [26] †Hyaenodon dubius(Filhol, 1873) [27] †Hyaenodon eminus(Matthew & Granger, 1925) [28] †Hyaenodon exiguus(Gervais, 1873) [29] †Hyaenodon filholi(Schlosser, 1887) [30] †Hyaenodon gervaisi(Martin, 1906) [31] †Hyaenodon heberti(Filhol, 1876) [32] †Hyaenodon leptorhynchus(Laizer & Parieu, 1838) [33] †Hyaenodon lingbaoensis(Li, 2025) [34] †Hyaenodon minor(Lange-Badré, 1979) [35] †Hyaenodon pervagus(Matthew & Granger, 1924) [36] †Hyaenodon pumilus(Lavrov, 2019) [37] †Hyaenodon requieni(Gervais, 1846) [38] †Hyaenodon rossignoli(Lange-Badré, 1979) †Hyaenodon weilini(Wang, 2005) [39] †Hyaenodon yuanchuensis(Young, 1937) [40] Subgenus: †Neohyaenodon(paraphyletic subgenus)(Thorpe, 1922) [41] †Hyaenodon gigas(Dashzeveg, 1985) †Hyaenodon horridus(Leidy, 1853) [42] †Hyaenodon incertus(Dashzeveg, 1985) †Hyaenodon macrocephalus(Lavrov, 1999) [3] †Hyaenodon megaloides(Mellett, 1977) [43] †Hyaenodon milvinus(Lavrov, 1999) [3] †Hyaenodon mongoliensis(Dashzeveg, 1964) [44] †Hyaenodon montanus(Douglass, 1902) [45] †Hyaenodon vetus(Stock, 1933) [46] Subgenus: †Protohyaenodon(paraphyletic subgenus)(Stock, 1933) †Hyaenodon brevirostrus(Macdonald, 1970) [47] †Hyaenodon crucians(Leidy, 1853) †Hyaenodon microdon(Mellett, 1977) †Hyaenodon mustelinus(Scott, 1894) [48] †Hyaenodon raineyi(Gustafson, 1986) [49] †Hyaenodon venturae(Mellett, 1977)

Description

Skull of Hyaenodon horridus

Size

The species within the genus vary in size, with most being small to medium-sized predators, while some were among the largest terrestrial carnivorous mammals of their time. ^[39] Intraspecific dimorphism has also been reported in the genus, although its ecological significance is unclear. H. crucians, from the early Oligocene of North America, was estimated to have weighed around 10–25 kg (22–55 lb). H. microdon and H. mustelinus, from the late Eocene of North America, were even smaller and weighed probably about 5 kg (11 lb). ^[50] H. filholi was the smallest European species and within the genus, weighing 2 kg (4.4 lb). The type species, H. leptorhynchus, was estimated to have weighed 11 kg (24 lb). ^[51]

H. horridus was one of the largest North American species. While m1 regressions suggested it could have weighed 91.8 kg (202 lb), ^[52] regressions based on limb morphology suggest the species was instead a bit smaller, with adults weighing 41.42 kg (91.3 lb) on average and the largest adults wouldn't have exceeded 60 kg (130 lb). ^[50] H. megaloides, the largest North American species, was three times heavier than H. horridus, weighing 30–120 kg (66–265 lb). ^[50] It has been suggested that the size decrease among North American Hyaenodon species may have been the result of competition with nimravids. ^[50] In Europe, the largest species known species was H. geravisi, weighing 50 kg (110 lb). ^[51] The largest species within the genus was H. gigas, followed by H. mongoliensis. ^[53] Both species had a skull length of 60 cm (2.0 ft) and are similar in size to Hyainailouros. ^[54] H. weilini was another very large species, described to be similar in size to H. gigas and H. mongoliensis. ^[39]

Postcranial remains

Postcranial remains have been recovered for Hyaenodon, although the fossil records within Eurasia are rather scarce compared to North America. ^[55] While the neck of the animal was relatively short, the body and tail were long. ^[55] Compared to Hyainailouros, the spine of Hyaenodon was longer and more robust, suggesting it didn't bore its head as low. ^{[56] [57]} Cervical vertebrae of Hyaenodon was more relatively short and resembled that of a felid than a canid. ^[55]

The neural spines were prominent and was posterior projecting Hyaenodon in comparison to carnivorans. Within Hyaenodon, the transverse processes and neural spine of the thoracic vertebrae were larger and more robust than what is seen with carnivorans. The more developed spines would’ve supported a larger head with hypothetical nuchal ligament. ^[55]

The femur of Hyaenodon was found to have been nearly as long as the humerus, which was short and massive, supporting a large, rounded head. Compared to carnivorans, the greater tuberosity has a more irregular shape and faces anteromedially. It would’ve been an insertion site for the infraspinatous muscles, which isn't seen in carnivorans. ^[55] Despite this, the humerus of Hyaenodon was similar to that of wolves and hyenas. Compared to hyenas, it shows an anconeal fossa, a well-developed brachial flange and a similarly elongated trochlea shape. Despite this, the trochela shape of Hyaenodon is more similar in to the red fox. ^[55]

Compared to wolves, the radius and ulna of Hyaenodon are rather short. The anatomy of the radius suggests it lost any possible rotatory capabilities. The shaft of the radius was not as flattened as seen in carnivorans, although within the cross section it was quadratic, with the distal part being heavy. The ulna had a relatively long olecranon, along with a heavy shaft and a deep channel that runs into the radical notch to the styloid process. ^[55]

Paleobiology

Reconstruction of Hyaenodon by Heinrich Harder (around 1920)

Predatory behavior

The canines of Hyaenodon were mediolaterally compressed, similar to canids, this was ideal for slashing bites. This suggests Hyaenodon landed shallow bites on potential prey and likely didn't perform the killing bite seen in felids. ^[55] Hunter-Schreger bands observed in the tooth enamel of H. horridus are zigzag, suggesting that this species was osteophagous, whereas those of H. brevirostris and H. mustelinus transition from undulating at the base of the tooth to zigzag at the tip, indicating that these species were not as well adapted for feeding on bone. ^[58] However, dental microwear patterns suggests that North American Hyaenodon had a diet more similar to lions, suggesting it ate mostly meat with various intakes of bone. On the other hand, European Hyaenodon microwear were more similar to that of spotted hyenas, suggesting bone cracking was likely a major part of their diet. ^[59] The tooth wearing on P4 of H. gigas suggests the primary function of the tooth was for bone-cracking. ^[39] Despite having adaptations towards bone consumption, compared to Hyainailouros , the dentition of Hyaenodon was geared more towards shearing meat and less towards bone crushing. ^[60] A 2024 study found that canine bite mechanic efficiency increased with tooth macrowear in Hyaenodon. ^[61]

Ontogeny

Studies on juvenile Hyaenodon specimens show that the animal had a very unusual system of tooth replacement. Juveniles took about 3–4 years to complete the final stage of eruption, implying a long adolescent phase. In North American forms, the first upper premolar erupts before the first upper molar, while European forms show an earlier eruption of the first upper molar. ^[62]

Locomotion

Life reconstruction of H. horridus

Initially, Hyaenodon was thought to have been a semi-plantigrade walker, however other experts considered it to have been a digitigrade. ^{[55] [56]} Due to the presence of relatively straight ungual phalanges, short phalanges, intermediate long metatarsals, cadually oriented olecranon, with a long olecranon, suggests Hyaenodon was a terrestrial animal. ^[55] A 2003 study found that based on elbow morphology H. horridus was a cursorial predator and was the most cursorially adapted Oligocene carnivore sampled within the study. ^[63] Furthermore, a 2025 study found that based on elbow morphology found that H. crucians and H. horridus were a pounce-pursuit predators. ^[64] Much like H. horridus, H. eminus, H. gigas, and H. pervagus were recovered as a cursorial predators. ^[65] On the other hand, analysis on the bony labyrinth of H. exiguus suggests this species was semi-arboreal. ^[22]

Despite being a cursorial predator, Hyaenodon probably still tended to hunt within short distance. ^{[55] [66]}

Brain anatomy and senses

While it has typically been assumed that Hyaenodon had a very massive skull, but a small brain, this has been called into question. ^[67] Flink and colleagues found that Hyaenodon, had encephalization quotient of 0.36-0.37 and 0.42-0.46, for H. horridus and H. crucians respectively. This similar to basal and some modern carnivorans such as cougars, Hesperocyon gregarius , Hoplophoneus primaevus , and striped hyena and exceeding jaguars, Daphoenus , Hoplophoneus primaevus , and Eusmilus bidentatus . Their discovery found that hyaenodonts had relative brain sizes that overlapped with both extinct and extant carnivorans. ^[68] The endocast of Hyaenodon stands out from other hyaenodontoids as they had relatively high EQ, in addition to relatively gyrencephalic and neocorticalized brains, however the cause of the increase in EQ for the genus is still unknown. ^[67] Despite having neocorticalized brains compared to other hyaenodonts, the neocortex of Hyaenodon was only moderately folded. ^[55]

The olfactory bulbs were found to have been large in Hyaenodon, suggesting smell was the primary method of finding prey. ^[55] However, compared to Neogene carnivorans of similar size, Hyaenodon sense of smell wasn't as acute, which would’ve been disadvantageous in prey detection. ^{[69] [55]}

Social behavior

Due the small size of the neocortex, some experts proposed that Hyaenodon probably didn't hunt in packs. Further evidence to suggest it was a solitary predator was fossil evidence of defecation, as defecating on food was an indication of a solitary predator. ^[55]

Paleoecology

North America

During the early Paleogene, North America consisted of subtropical swampy, densely forested habitats which supported predators such as oxyaenids. However, during the Middle Eocene, these habitats were replaced by more temperate, open forests. ^[70] Because of these environmental changes, hyaenodonts would replace oxyaenids, as well as mesonychians and miacoids. ^[66] Hyaenodon first appeared in North America during the Middle Eocene with the appearance of H. venturae, ^[23] likely the result of immigration from Asia. ^[56]

Reconstruction of H. horridus and Leptomeryx evansi by W. B. Scott (1913)

The most well known species, H. horridus, roamed North America from 36.5 to 31.4 Ma. ^[71] This species was found in the Calf Creek locality of Cypress Hills Formation. ^[72] The herpetofauna present within the locality suggests Calf Creek had a tropical or subtropical climate. ^[73] In this locality, Hyaenodon coexisted with hyaenodonts such as H. microdon and the hyainailourid Hemipsalodon grandis. Carnivorans that were present in this formation were daphoeninae amphicyonids Brachyrhynchocyon dodgei and Daphoneus , nimravids Dinictis and Hoplophoneus , hesperocyonine canid Hesperocyon gregarius , and the subparictid Parictis. ^{[72] [52] [74]} In addition, Hyaenodon also coexisted with the entelodont Archaeotherium . Herbivores present in this locality include the equid Mesohippus , the hyracodontid Hyracodon priscidens , rhinoceroses Subhyracodon occidentalis , Trigonias osborni , and Penetrigonias sagittatus , tapirid Colodon occidentalis , the brontothere Megacerops kuwagatarhinus , and the anthracothere Bothriodon advena. ^[74]

The predators present in Calf Creek likely practiced niche partitioning via different body sizes, with H. horridus focusing on prey that weighed 166 kg (366 lb) and faced little competition from carnivorans. While Hoplophoneus could’ve induced some competition pressure via pack hunting, H. horridus could still hunt prey outside of the most probable range of the carnivoran. On the other hand, H. microdon was thought to have faced intense competition from five contemporary carnivorans. ^[52]

Restoration of Archaeotherium eating roots. Several species of both taxa were contemporary with each other across North America

H. horridus was also found in Brule Formation of South Dakota. ^[75] The paleoenvironment of Brule Formation was believed to have been a woodland grassland and gallery forest, populated in part by hackberry trees ( Celtis ). ^[76] Contemporary predators would've included fellow species H. crucians, the nimravid Hoplophoneus, the amphicyonid Daphoneus, and the entelodont Archaeotherium mortoni. Herbivores present include the early horse Mesohippus, hypertragulid Hypertragulus calcaratus , leptomerycid Leptomeryx evansi , tapirs such as Protapirus simplex and Colodon occidentalis, the camel Poebrotherium wilsoni , anthracotheres Aepinacodon americanus and Heptacodon occidentale , oreodonts Merycoidodon culbertsonii and Miniochoerus affinis . ^[75]

Fossil evidence suggests that H. horridus could've predate on other predators such as Dinictis and juvenile Archaeotherium. ^{[77] [78] [55]} Despite being one of the top predators, it still probably lost its kills to an adult Archaeotherium. ^[55]

Pre-Grand Coupure Europe

Palaeogeography of Europe and Asia during the middle Eocene with possible artiodactyl and perissodactyl dispersal routes.

From the early to middle Eocene, the climate of Europe was warm and humid, hosting tropical to subtropical closed forests. However, from MP17b to the end of the Eocene, the climate started to become more arid, turning forests into wooded savannas. Multiple groups of mammalian predators present on the continent include mesonychians, oxyaenids, hyaenodonts, and carnivoramorphs. The extinction of European mesonychians, oxyaenids, and viverravids were connected to the Early Eocene Climatic Optimum. This likely led to the diversification of hyaenodonts at the Ypresian-Lutetian boundary, resulting in them becoming the dominant group of predators in Europe. ^[79]

During the Bartonian and Priabonian stage, there was major restructuring of the predator guild, which marked the end of endemism. The restructuring was also marked by the appearance of hyaenodontines and hyainailourines, along with amphicyonids. ^[79] Hyaenodon first appears in the fossil records around MP17a of the Bartonian stage of the Eocene marked by the appearance of H. brachyrhynchus, H. minor, and H. requieni. ^[51] Their appearance was likely the result of Hyaenodon migrating into Europe from Asia. ^[79]

Reconstruction of Pterodon dasyuroides , a hyainailourine that was found in Western Europe and coexisted with Hyaenodon requieni. The appearance of hyainailourines, hyaenodontines, and amphyicyonids represented a major restructuring of the carnivore guild

H. requieni was found in La Debruge of France. ^[80] Mammalian predators present in this locality other than H. requieni included the hyainailourine Pterodon dasyuroides and the amphicyonine Cynodictis lacustris . Contemporary herbivores include perissodactyls (palaeotheres), endemic (amphimerycids, Anoplotheriidae, choeropotamids, and xiphodontids) and non-endemic artiodactyls (dichobunides, tapirulids, and anthracotheres). Other mammalian fauna includes primates (adapids and omomyids), rodents (ischyromyids, theridomyids, and glirids), soricomorphs (nyctitheriids), and tribosphenidans (Herpetotheriidae). ^[80]

Grand Coupure

Anoplotherium , an iconic genus of the Western European endemic fauna. It was one of the many endemic artiodactyls that went extinct during the Grand Coupure

The boundary of the Eocene and Oligocene in Europe was marked by the Grand Coupure (MP20-MP21), which saw a transition from subhumid to cooler, semi-arid seasons, resulting in the reduction of forests, swamps, and mangroves. In Western Europe, the boundary is marked by the spread of conifers and temperate woodlands, and even savannas in some areas. The change in European flora suggests marked seasonality and open environments replacing forests. ^{[79] [81]} The massive drop in temperature stemmed from the first major expansion of the Antarctic ice sheets that caused drastic pCO₂ decreases and an estimated drop of ~70 m (230 ft) in sea level. ^[82]

During the Grand Coupure, the extinction rate of western European mammalian lineages increased to 60%. ^[83] The turnover saw the extinction of frugivorous/folivorous families of endemic artiodactyls such as xiphodontids and choeropotamids, ^[84] as well as the extinction of several hyaenodonts including H. requini and the hyainailourines. ^{[85] [86] [79] [87] [88]} The Grande Coupure event also marked a large faunal turnover would mark the arrivals of later anthracotheres, entelodonts, ruminants (Gelocidae, Lophiomerycidae), rhinocerotoids (Rhinocerotidae, Amynodontidae, Eggysodontidae), carnivorans (later Amphicyonidae, Amphicynodontidae, Nimravidae, and Ursidae), eastern Eurasian rodents (Eomyidae, Cricetidae, and Castoridae), and eulipotyphlans (Erinaceidae). ^{[89] [90] [83] [88]} The arrivals of these animals was likely the result of the Turgai Strait receding, establishing a new land connection between Europe and Asia. The faunal turnover also marked the shift in dominance among predators, from hyaenodonts to carnivoraforms. However the transition was gradual as newcomers didn't appear in Europe until MP21, while the endemic hyaenodontoids and carnivoraforms disappeared between MP18-MP20. ^[79]

Post-Grand Coupure Europe

The Rupelian stage corresponds with the peak floral changes that started in the Late Eocene. Despite seeing the extinction of some paleotropical elements and dispersal of deciduous trees, there was still evidence of warm Mediterranean to subtropical paleoenvironments. However, for most of Europe, there were arid conditions with relatively low mean annual temperatures, which is associated with (sub)desert to lightly forested habitats. Two million years after the Grand Coupure, the Bachitherium Dispersal Event saw some of the earliest ruminants in Europe. ^{[79] [91] [59]}

Palaeobiogeography of eastern Eurasian ruminants during the late Eocene-early Oligocene with dispersal routes to western Europe during the Grande Coupure (33.9 Ma) and Bachitherium Dispersal Event (31 Ma).

At the end of the Rupelian (MP24-MP25), saw the extinction of the nimravids, as well as the reduction in diversity among other mammalian groups such as rodents, likely the result of the increased aridity. ^[79] H. geravisi and H. leptorhynchus were found in Séon Saint-André, which was dated to MP26. The carnivorans present in this locality were amphicyonids Cynelos rugosidens and Pseudocyonopsisambiguus. All predators within this locality are believed to have practiced some niche partitioning. H. leptorhynchus is believed to have hunted small artiodactyls such as Bachitherium and Mosaicomeryx . ^[51] However the larger predators would've hunted larger artiodactyls such as Anthracotherium cuvieri and Elomeryx borbonicus and perissodactyls such as Protaceratherium albigense and Ronzotherium romani . H. geravisi and Pseudocyonopsis were believed to competed for the same prey due to being similar in size to one another. Although, it is possible they preferred different environments as Hyaenodon was a cursorial predator and likely preferred open environments compared to amphicyonids, who preferred more closed environments. ^[51]

The end of the Oligocene was marked by increased seasonality, characterized by a dry season and open environments. ^{[79] [92]} However, some experts found closed forests and temperate to subtropical climates still prevailed in Europe, although the humidity wasn't as high as the Priabonian. ^{[93] [79]} The contradictions would suggest that Europe supported mosaic environments during the late stages of the Oligocene. ^[79] Around MP28, the Microbunodon Event saw the ruminants transition from wooded environments to more open environments, which was likely the result of the Late Oligocene Warming and Alpine orogeny. ^{[94] [79]} MP27 to MP29 also saw the appearance of many caniforms such as mustelids and ailurids, and large amphicyonids. The appearance of large amphicyonids, such as Ysengrinia , suggests that Western Europe was a wooded savanna and environments were becoming more open. ^{[79] [51]}

Asia

In East Asia, H. gigas lived from Late Eocene to Early Oligocene. ^{[23] [53]} The species was found within the Khoer-Dzan locality of the Ergilin Dzo Formation. ^[53] Based on the presence of brontotheres and the abundance of low crowned herbivores, it was initially thought that the climate was humid and it was warm, with the environment thought to have been relatively closed. However, the absence of primates and the rarity of crocodyliforms suggests the formation had some open areas and was more arid than contemporary formations across Eurasia. ^[95] Sedimentary analysis of Khoer-Dzan found the presence of root traces which suggests red soils, which is associated with floodplain environments, with no evidence of lacustrine environments. ^[96]

Within this locality, H. gigas coexisted with other predators like hyaenodonts H. eminus, H. incertus, H. mongoliensis, and H. pervagus, nimravids Eofelis and Nimravus intermedius , and entelodonts Brachyhyops trofimovi and Entelodon gobiensis . Contemporary herbivores include the anthracothere Bothriodon , the praetragulid Praetragulus electus , the brontothere Embolotherium andrewsi , the chalicothere Schizotherium avitum , and rhinocerotoids such as the paraceratheriid Urtinotherium parvum and rhinocerotid Ronzotherium orientale. ^[97]

Extinction

From the middle to late Eocene, hyaenodonts experienced a decline in diversity with only one genus, consisting of a few species by the end of the Eocene in North America. ^[98] With H. brevirostrus being the last species in North America, which disappeared in the late Oligocene. ^[99] In Europe, the last species to go extinct, H. exiguus and H. leptorhynchus, were last known in MP30 of the late Oligocene. ^{[51] [100]} The youngest species, H. weilini, lived during the Early Miocene of China, going extinct 17 Ma. ^[39]

The cause of their extinction has been debated by experts. Some experts argued due to the anatomy of the neocortex, Hyaenodon lacked the mental capacity to adjust to the changing environment and prey evolving larger brains. However, this has been contested as the degree of folding doesn't automatically apply to intelligence. ^[55] However, many argued that their extinction was due to competition with carnivorans, such as amphicyonids, hesperocyonines, hemicyonines, and hyenas. ^{[66] [98] [101]} Lang and colleagues theorize that the success of carnivorans compared to hyaenodonts was likely due to the retention of a basal morphotype throughout their evolutionary history. They also suggested that carnivorans possibly played a role in the extinction of hyaenodonts, probably due to the adaptive potential of their carnassials. ^[102]

Friscia and Valkenburgh argued that while "creodonts" didn't limit the evolution of carnivorans in North America, carnivorans may have limited the ecological evolution of creodonts, with the large hypercarnivorous ecomorphs being the "last stand" of the order. ^[98] Serio and colleagues found that North American creodonts had a significant degree of morphological differentiation until the middle Eocene, with disparity among carnivorans increasing around the same time. The authors also argue that carnivoran disparity may have negatively impacted the disparity of creodonts, supporting the hypothesis that carnivorans competitively replaced the hyaenodonts. ^[101]

However, competitive replacement in North America has been questioned by many experts, arguing their extinction correlated with abiotic changes in their environments. ^{[64] [52]} Christison and colleagues found that only small hyaenodont, H. microdon, experienced significant competition with the five contemporary carnivorans. The largest hyaenodonts such as H. horridus and Hemipsalodon , didn't experience little to no competition from carnivorans. This suggests competition with carnivorans couldn't have been the driver of the extinction of North American hyaenodonts in the Late Eocene. Instead, they argued the highly specialized niche of hyaenodonts enhanced their extinction rates. The global cooling of the early Oligocene resulted in the extinction of large browsers such as brontotheres, as ecosystems became drier and more open. Brontotheres were replaced by equids and rhinoceroses, who were better adapted for open environments. But rhinoceroses wouldn't reach large sizes until the Miocene epoch, leaving the gap of accessible large herbivores for the large, hypercarnivorous hyaenodonts. Furthermore, hyaenodonts tend to have relatively short legs, which may have been a disadvantage in open environments and likely played a role in their extinction. ^[52] Castellanos, in their 2025 paper, found that despite hyaenodonts showing adaptations towards cursoriality, because of their short distal limbs, hyaenodonts couldn't exploit open environments as well as amphicyonids, which may have resulted in their extinction and in addition to the low diversity of the clade by the start of the Oligocene. ^[64]

There was also no evidence of Carnivorans competitively displacing hyaenodonts in Europe as hyaenodonts were more diverse than carnivorans up until the Grand Coupure. ^[79] In addition, it was found that Hyaenodon and amphicyonids preferred different environments, with the former presumably hunting in more open environments which would’ve limited competition between the two predators, suggesting climatic changes were responsible for their extinction. ^{[51] [103]} MP30 and MN1 saw an increase in aridity, and was associated with a cooler climate. ^{[104] [105]} It saw the extinction of other groups of animals such as Theridomorpha. ^[104] Despite being recovered as a cursorial predator, European Hyaenodon went extinct because of the expansion of open environments as it reduced the access to resources. ^[51]

References

1. Leidy J. (1869). "On the extinct Mammalia of Dakota and Nebraska: including an account of some allied forms from other localities, together with a synopsis of the mammalian remains of North America." Journal of the Academy of Natural Sciences Philadelphia 7: 1–472.
2. J. Alroy (2002). "Synonymies and reidentifications of North American fossil mammals."
3. A. V. Lavrov (1999.) "Adaptive Radiation of Hyaenodontinae (Creodonta, Hyaenodontidae) of Asia." in 6th Congress of the Theriological Society, Moscow, April 13–16, p. 138 [in Russian].
4. F. J. Pictet (1853.) "Traité de Paléontologie." I (2^e edit.):584 p. + atlas 110 pl.
5. F. Dujardin (1840.) "Note sur une tête fossile Hyaenodon trouvée au bord du Tarn, près de Rabastens." Comptes-Rendus de l'Académie des Sciences de Paris, 10:134-135
6. Ch. Laurillard (1845.) "Hyaenodon." in: d'Orbigny: "Dictionnaire Universel d'Histoire naturelle 1-6": 767-769, Renard, Martinet édit., Paris
7. A. Pomel (1846.) "Note sur le Pterodon, genre voisin des Dasyures dont plusieurs espèces ont été trouvées dans les terrains tertiaires." Bulletin de la Société Géologique de France, 4(2):385-393
8. R. M. Joeckel, H. W. Bond and G. W. Kabalka (1997). "Internal Anatomy of the Snout and Paranasal Sinuses of Hyaenodon (Mammalia, Creodonta)" Journal of Vertebrate Paleontology, Vol. 17, No. 2, pp. 440-446
9. W. B. Scott (1888). "On some new and little know creodonts." Journal of the Academy of Natural Sciences of Philadelphia 9:155-185
10. H. F. Osborn and J. L. Wortman (1894). "Fossil mammals of the Lower Miocene White River beds. Collection of 1892." Bulletin of the American Museum of Natural History 6(7):199-228
11. H. Filhol (1882). "Étude des Mammifères de Ronzon (Haute-Loire)." Ann. Sci. géol., Paris, 12(3):270 p., 25 pl.
12. Depéret C. (1917). "Monographie de la faune de mammiféres fossiles du Ludien inférieur d'Euget-les-Bains (Gard)." Ann. Univ. Lyon (N. S.), Div. 1, 40, 1-288.
13. Kretzoi, M. (1941). "Ausländische Säugetierfossilien der Ungarischen Museen. (1-4)" Földtani Közlöny, vol. 71, nos. 4-6, pp. 1-6
14. P. D. Polly (1993.) "Hyaenodontidae (Creodonta, Mammalia) from the Early Eocene Four Mile Fauna and their biostratigraphic implications." PaleoBios, Vol. 14, No. 4, pp. 1-10
15. R. Dehm (1935). "Über tertiäre Spaltenfüllungen im Fränkischen und Schwäbischen Jura [On Tertiary fissure fillings in the Franconian and Swabian Jura]." Abhandlungen der Bayerischen Akademie der Wissenschaften Mathematisch-naturwissenschaftliche Abteilung, Neue Folge 29:1-86
16. Forster Cooper, C. (1926). "Hyænodon aimi, sp. n., and a note on the occurrence of Anthracotherium minus from the Headon Beds at Hordle." Annals and Magazine of Natural History (9)18(106):370–373
17. R. Lydekker (1884.) "Notes on some fossil Carnivora and Rodentia." Geol. Mag., London, (3)1:442-445, 2 figs.
18. Michael Morlo, Doris Nagel (2006). "New remains of Hyaenodontidae (Creodonta, Mammalia) from the Oligocene of Central Mongolia." Annales de Paléontologie 92(3):305-321
19. L. Van Valen (1967). "New Paleocene insectivores and insectivore classification." Bulletin of the American Museum of Natural History 135(5):217-284
20. Huang, Xue-Shi; Zhu, Bao-Cheng (15 March 2002). "Creodont (mammalia) remains from the Early Oligocene of Ulantatal, Nei Mongol". Vertebrata PalAsiatica. 40 (1): 17. ISSN   2096-9899 . Retrieved 19 November 2023.
21. Malcolm C. McKenna, Susan K. Bell (1997). "Classification of Mammals: Above the Species Level", Columbia University Press, New York, 631 pages. Hyaenodon
22. Pfaff, Cathrin; Nagel, Doris; Gunnell, Gregg; Weber, Gerhard W.; Kriwet, Jürgen; Morlo, Michael; Bastl, Katharina (25 September 2016). "Palaeobiology of Hyaenodon exiguus (Hyaenodonta, Mammalia) based on morphometric analysis of the bony labyrinth". Journal of Anatomy . 230 (2): 282–289. doi:10.1111/joa.12545. PMC   5244453 . PMID   27666133.
23. Bastl, Katharina Anna; Morlo, Michael; Nagel, Doris (2011). "Differences in the Tooth Eruption Sequence in Hyaenodon ('Creodonta': Mammalia) and Implications for the Systematics of the Genus". Journal of Vertebrate Paleontology. 31 (1): 181–192. doi:10.1080/02724634.2011.540052.
24. Li, Qiang; Sheng, Jia Q.; Bi, Alexander; Li, Qi (2025). "A new small hyaenodon (Hyaenodonta: Hyaenodontinae) from the Eocene Lingbao Basin, Henan Province, China". The Anatomical Record. 308 (10): 2669–2679. doi:10.1002/ar.25668.
25. Henri Marie Ducrotay de Blainville (1841.) "Ostéographie ou description iconographique comparée du squelette et du système dentaire des mammifères récents et fossiles." Tome 2: Secondates et Subursus, 123 p.; Viverras, 100 p. et atlas, 117 pl. Baillėte édit. Paris.
26. Dashzeveg D. (1985.) "Nouveau Hyaenodontinae (Creodonta, Mammalia) du Paléogène de Mongolie." Annales de Paléontologie 71:223–256
27. Filhol, H. (1873.) "Sur les Vertébrés fossiles trouvés dans les dépôts de phosphate de chaux du Quercy." Bull. Soc. Pholomath. Paris (6) 10, 85-89.
28. Matthew W. D. & Granger W. (1925.) "New creodonts and rodents from the Ardyn Obo Formation of Mongolia." American Museum Novitates 193:1–11.
29. Gervais P. (1873.) "Mammifères dont les ossements accompagnent les dépôts de chaux phosphatée des départements du Tarn-et.Garonne et du Lot." Journal de Zoologie, Paris, 2:356-380
30. M. Schlosser (1887.) "Die Affen, Lemuren, Chiropteren, Insectivoren, Marsupialier, Creodonten und Carnivoren des Europaischen Tertiars." Beitrage zur Paleontologie Osterreich-Ungarns un des Orients 6:1-224
31. R. Martin (1906.) "Revision der obereocænen und unteroligocænen Creodonten Europas." Rev. Suisse Zool., 14, (3), pp. 405-500
32. H. Filhol (1876.) "Recherches sur les phospohorites du Quercy. Étude des fossiles qi'on y rencontre et spécialement des Mammifères." Annales des Sciences Géologiques, Paris, 7(7):220 p., pl. 11-36; 1877:art. 1, 340 p., 28 pl.
33. Laizer, L. D. and Parieu, D. (1838.) "Description et détermination d'une mâchoire fossile appartenant à un mammifère jusqu'à présent inconnu, Hyaenodon leptorhynchus." Comptes Rendus de l'Académie des Sciences Paris, 7:442
34. Li, Q.; Sheng, J. Q.; Bi, A.; Li, Q. (2025). "A new small Hyaenodon (Hyaenodonta: Hyaenodontinae) from the Eocene Lingbao Basin, Henan Province, China" . The Anatomical Record ar.25668. doi:10.1002/ar.25668. PMID   40186436.
35. Lange-Badré, B. (1979.) "Les créodontes (Mammalia) d'Europe occidentale de l'Éocène supérieur à l'Oligocène supérieur." Mémoires du Muséum National d'Histoire Naturelle 42: 1–249
36. W. D. Matthew and W. Granger (1924.) "New Carnivora from the Tertiary of Mongolia." American Museum Novitates 104:1-9
37. A. V. Lavrov (2019). "New material on small hyenodons Hyaenodontinae, Creodonta) from the Paleogene of Mongolia" . Paleontological Journal. 53 (4): 418–431. Bibcode:2019PalJ...53..418L. doi:10.1134/S0031030119040063. S2CID   201654889.
38. Gervais P. (1846.) "Mémoire sur quelques Mammifères fossiles du Vaucluse." Comptes rendus hebdomadaires des séances de l'Académie des sciences, Paris, T. 22, pp. 845-846.
39. X. Wang, Z. Qiu and B. Wang (2005.) "Hyaenodonts and carnivorans from the early Oligocene to early Miocene of the Xianshuihe Formation, Lanzhou Basin, Gansu Province, China." Palaeontologia Electronica, Vol. 8, Issue 1; 6A: Pages 1-14
40. C. Young (1937.) "An early Tertiary vertebrate fauna from Yuanchü." Bulletin of the geological society of China 17(3-4):413-438
41. M. R. Thorpe (1922.) "A new genus of Oligocene Hyaenodontidae." American Journal of Science 3(16):277-287
42. Leidy, J. (1853.) "Remarks on a collection of fossil Mammalia from Nebraska." Proceedings of the Academy of Natural Sciences, Philadelphia, 6:392-394.
43. J. S. Mellett (1977.) "Paleobiology of North American Hyaenodon (Mammalia, Creodonta)." Contributions to Vertebrate Evolution 1:1-134
44. D. Dashzeveg (1964.) "On two Oligocene Hyaenodontidae from Erghilyin-Dzo (Mongolian People's Republic)." Acta Palaeontologica Polonica 9(2):263-274
45. E. Douglass (1902.) "Fossil Mammalia of the White River beds of Montana." Transactions of the American Philosophical Society 20:237-279
46. C. Stock (1933.) "Hyaenodontidae of the Upper Eocene of California." Proceedings of the National Academy of Sciences 19(4):434-440
47. J. R. Macdonald (1970.) "Review of the Miocene Wounded Knee faunas of southwestern South Dakota." Bulletin of the Los Angeles County Museum of Natural History, Science 8:165-82
48. William Berryman Scott (1894.) "The osteology of Hyaenodon" Journal of Academy of Natural Sciences, Philadelphia (2), 9, 291-323
49. E. P. Gustafson (1986.) "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66
50. Egi, Naoko (2001). "Body mass estimates in extinct mammals from limb bone dimensions: the case of North American hyaenodontids". Palaeontology. 44 (3): 497–528. Bibcode:2001Palgy..44..497E. doi: 10.1111/1475-4983.00189 . S2CID   128832577.
51. Solé; Dubied; Le Verger; Mennecart (2018). "Niche partitioning of the European carnivorous mammals during the paleogene" . PALAIOS. 33 (11): 514–523. Bibcode:2018Palai..33..514S. doi:10.2110/palo.2018.022.
52. Christison, Brigid E; Gaidies, Fred; Pineda-Munoz, Silvia; Evans, Alistair R; Gilbert, Marisa A; Fraser, Danielle (2022-01-25). Powell, Roger (ed.). "Dietary niches of creodonts and carnivorans of the late Eocene Cypress Hills Formation". Journal of Mammalogy . 103 (1): 2–17. doi:10.1093/jmammal/gyab123. ISSN   0022-2372. PMC   8789764 . PMID   35087328 . Retrieved 17 October 2024– via Oxford Academic.
53. Tsubamoto, Takehisa; Watabe, Mahito; Tsogtbaatar, Khishigjav (2009). "Hyaenodon chunkhtensis and The Hyaenodontid Fauna From The Upper Eocene Ergilin Dzo Formation Of Mongolia". Journal of Vertebrate Paleontology. 2: 559–564. doi:10.1671/0272-4634(2008)28[559:HCATHF]2.0.CO;2.
54. Morlo, Michael; Nagel, Doris (2006). "New remains of Hyaenodontidae (Creodonta, Mammalia) from the Oligocene of Central Mongolia". Annales de Paléontologie. 92 (3): 305–321. doi:10.1016/j.annpal.2005.12.001.
55. Bastl, Katharina A. (2012). Ecomorphology of the European Hyaenodon (PhD thesis). University Vienna.
56. Solé, Floréal; Amson, Eli; Borths, Matthew; Vidalenc, Dominique; Morlo, Michael; Bastl, Katharina (2015-09-23). Friedman, Matt (ed.). "A New Large Hyainailourine from the Bartonian of Europe and Its Bearings on the Evolution and Ecology of Massive Hyaenodonts (Mammalia)". PLOS ONE. 10 (9) e0135698. doi: 10.1371/journal.pone.0135698 . ISSN   1932-6203. PMC   4580617 . PMID   26398622.
57. Ginsburg, Léonard (1980). "Hyainailouros sulzeri, mammifère créodonte du Miocène d'Europe". Annales de Paléontologie. 66 (1): 19–73.
58. Stefen, Clara (September 1997). "The enamel of Creodonta, Arctocyonidae, and Mesonychidae (Mammalia), with special reference to the appearance of Hunter-Schreger-Bands" . Paläontologische Zeitschrift . 71 (3–4): 291–303. doi:10.1007/BF02988497. ISSN   0031-0220 . Retrieved 15 September 2024– via Springer Nature Link.
59. Bastl, Katharina; Semprebon, Gina; Nagel, Doris (1 September 2012). "Low-magnification microwear in Carnivora and dietary diversity in Hyaenodon (Mammalia: Hyaenodontidae) with additional information on its enamel microstructure" . Palaeogeography, Palaeoclimatology, Palaeoecology . 348–349: 13–20. Bibcode:2012PPP...348...13B. doi:10.1016/j.palaeo.2012.05.026 . Retrieved 7 November 2024– via Elsevier Science Direct.
60. Wang, Xiaoming; Tedford, Richard H. (2008). Dogs: Their Fossil Relatives and Evolutionary History. New York: Columbia University Press. p. 1. doi:10.7312/wang13528. ISBN   978-0-231-13528-3. JSTOR   10.7312/wang13528.
61. Tseng, Zhijie Jack; DeSantis, Larisa R. G. (2024). "Relationship between tooth macrowear and jaw morphofunctional traits in representative hypercarnivores". PeerJ . 12 e18435. doi: 10.7717/peerj.18435 . PMC   11562772 . PMID   39544419.
62. Bastl, Katharina Anna (2013). "First evidence of the tooth eruption sequence of the upper jaw in Hyaenodon (Hyaenodontidae, Mammalia) and new information on the ontogenetic development of its dentition". Paläontologische Zeitschrift. 88 (4): 481–494. doi:10.1007/s12542-013-0207-z. S2CID   85304920.
63. Andersson, Ki; Werdelin, Lars (December 2003). "The evolution of cursorial carnivores in the Tertiary: Implications of elbow-joint morphology". Proceedings of the Royal Society B: Biological Sciences . 270 (Suppl 2): S163-5. doi:10.1098/rsbl.2003.0070. PMC   1809930 . PMID   14667370.
64. Castellanos, Miguel (2025). "Hunting types in North American Eocene–Oligocene carnivores and implications for the 'cat-gap'" . Journal of Mammalian Evolution . 32 (2): 1–12. doi:10.1007/s10914-025-09767-2.
65. Morlo, Michael; Gunnell, Gregg F.; Nagel, Doris (2010). "10 - Ecomorphological analysis of carnivore guilds in the Eocene through Miocene of Laurasia". Carnivoran Evolution. Cambridge University Press. pp. 269–310. ISBN   978-1-139-19343-6.
66. Van, Valkenburgh B. (1999). "Major patterns in the history of carnivorous mammals". Annual Review of Earth and Planetary Sciences. 27: 463–493. Bibcode:1999AREPS..27..463V. doi:10.1146/annurev.earth.27.1.463.
67. Flink, Therese; Cote, Susanne; Rossie, James B.; Kibii, Job M.; Werdelin, Lars (March 2021). "The neurocranium of Ekweeconfractus amorui gen. et sp. nov. (Hyaenodonta, Mammalia) and the evolution of the brain in some hyaenodontan carnivores". Journal of Vertebrate Paleontology . 41 (2) e1927748. Bibcode:2021JVPal..41E7748F. doi: 10.1080/02724634.2021.1927748 . S2CID   237518007.
68. Dubied, Morgane; Solé, Floréal; Mennecart, Bastien (29 July 2019). "The cranium of Proviverra typica (Mammalia, Hyaenodonta) and its impact on hyaenodont phylogeny and endocranial evolution". Palaeontology. 62 (6): 983–1001. Bibcode:2019Palgy..62..983D. doi: 10.1111/pala.12437 .
69. Joeckel, R. M.; Bond, H. W.; Kabalka, G. W. (1997). "Internal anatomy of the snout and paranasal sinuses of Hyaenodon (Mammalia, Creodonta)". Journal of Vertebrae Paleontology. 17 (2): 440–446. doi:10.1080/02724634.1997.10010989.
70. Kort, Anne E. (2019). "The Paleoecology of Patriofelis ulta and Implications for Oxyaenid Extinction (thesis)". Indiana University .
71. Castellanos, Miguel (2024). Hunting Types in North American Eocene and Oligocene Carnivores and Implications for Nimravid Extinction (Graduate Research Thesis & Disserations)
72. Bryant, Harold N. (1993). "Carnivora and Creodonta of the Calf Creek Local Fauna (Late Eocene, Chadronian), Cypress Hills Formation, Saskatchewan". Journal of Paleontology. 67 (6): 1032–1046. Bibcode:1993JPal...67.1032B. doi:10.1017/S0022336000025361. JSTOR   1306120.
73. Holman, J. Alan (1972). "Herpetofauna of the Calf Creek Local Fauna (Lower Oligocene: Cypress Hills Formation) of Saskatchewan" . Canadian Journal of Earth Sciences. 9 (12): 1612–1631. doi:10.1139/e72-143.
74. PBDB: Calf Creek
75. PaleoBiology Database: Brule Formation
76. Retallack, Gregory J. (2014-07-14), Prothero, Donald R.; Berggren, William A. (eds.), "19. Paleosols and Changes in Climate and Vegetation across the Eocene/Oligocene Boundary" , Eocene-Oligocene Climatic and Biotic Evolution, Princeton University Press, pp. 382–398, doi:10.1515/9781400862924.382, ISBN   978-1-4008-6292-4 , retrieved 2024-12-06
77. John W. Hoganson and Jeff Person (2010). "Tooth puncture marks on a skull of Dinictis (Nimravidae) from the Oligocene Brule Formation of Northe Dakota attributed to predation by Hyaenodon (Hyaenodontidae)", North Dakota Geological Survey
78. John W. Hoganson and Jeff Person (2011). "Tooth puncture marks on a 30 million year old Dinictis skull.", Geo News, p. 12-17
79. Solé, Floréal; Fischer, Valentin; Le Verger, Kévin; Mennecart, Bastien; Speijer, Robert P.; Peigné, Stéphane; Smith, Thierry (2022). "Evolution of European carnivorous mammal assemblages through the Paleogene". Biological Journal of the Linnean Society. 135 (4): 734–753. doi:10.1093/biolinnean/blac002.
80. PaleoBiology Database: La Debruge (Eocene of France)
81. Sun, Jimin; Ni, Xijun; Bi, Shundong; Wu, Wenyu; Ye, Jie; Meng, Jin; Windley, Brian F. (2014). "Synchronous turnover of flora, fauna, and climate at the Eocene-Oligocene Boundary in Asia". Scientific Reports. 4 (7463): 7463. Bibcode:2014NatSR...4.7463S. doi:10.1038/srep07463. PMC   4264005 . PMID   25501388.
82. Toumoulin, Agathe; Tardif, Delphine; Donnadieu, Yannick; Licht, Alexis; Ladant, Jean-Baptiste; Kunzmann, Lutz; Dupont-Nivet, Guillaume (2022). "Evolution of continental temperature seasonality from the Eocene greenhouse to the Oligocene icehouse –a model–data comparison". Climate of the Past. 18 (2): 341–362. Bibcode:2022CliPa..18..341T. doi: 10.5194/cp-18-341-2022 .
83. Hooker, Jerry J.; Collinson, Margaret E.; Sille, Nicholas P. (2004). "Eocene–Oligocene mammalian faunal turnover in the Hampshire Basin, UK: calibration to the global time scale and the major cooling event" (PDF). Journal of the Geological Society. 161 (2): 161–172. Bibcode:2004JGSoc.161..161H. doi:10.1144/0016-764903-091. S2CID   140576090. Archived (PDF) from the original on 2023-08-08. Retrieved 2023-08-31.
84. Blondel, Cécile (2001). "The Eocene-Oligocene ungulates from Western Europe and their environment" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 168 (1–2): 125–139. Bibcode:2001PPP...168..125B. doi:10.1016/S0031-0182(00)00252-2.
85. Schmidt-Kittler, Norbert; Godinot, Marc; Franzen, Jens L.; Hooker, Jeremy J. (1987). "European reference levels and correlation tables". Münchner geowissenschaftliche Abhandlungen A10. Pfeil Verlag, München. pp. 13–31.
86. Hooker, Jerry J. (2010). "The 'Grande Coupure' in the Hampshire Basin, UK: taxonomy and stratigraphy of the mammals on either side of this major Palaeogene faunal turnover". In Whittaker, John E.; Hart, Malcolm B. (eds.). Micropalaeontology, Sedimentary Environments and Stratigraphy: a Tribute to Dennis Curry (1912–2001). Vol. 4. Geological Society of London. pp. 147–215. doi:10.1144/TMS004.8. ISBN   978-1-86239-622-7.
87. Lange-Badré, Brigitte (1979). "Les Creodontes (Mammalia) d'Europe occidentale de l'Eocene superieur a l'Oligocene superieur". Mémories du Muséum National d'Historie Naturelle, Série C, Sciences de la Terre. 42: 1–249.
88. Solé, Floréal; Fischer, Fischer; Denayer, Julien; Speijer, Robert P.; Fournier, Morgane; Le Verger, Kévin; Ladevèze, Sandrine; Folie, Annelise; Smith, Thierry (2020). "The upper Eocene-Oligocene carnivorous mammals from the Quercy Phosphorites (France) housed in Belgian collections". Geologica Belgica. 24 (1–2): 1–16. doi: 10.20341/gb.2020.006 . S2CID   224860287.
89. Rivals, Florent; Belyaev, Ruslan I.; Basova, Vera B.; Prilepskaya, Natalya E. (2023). "Hogs, hippos or bears? Paleodiet of European Oligocene anthracotheres and entelodonts". Palaeogeography, Palaeoclimatology, Palaeoecology. 611 111363. Bibcode:2023PPP...61111363R. doi: 10.1016/j.palaeo.2022.111363 . S2CID   254801829.
90. Becker, Damien (2009). "Earliest record of rhinocerotoids (Mammalia: Perissodactyla) from Switzerland: systematics and biostratigraphy". Swiss Journal of Geosciences . 102 (3): 489–504. doi: 10.1007/s00015-009-1330-4 . S2CID   67817430.
91. Mennecart, Bastien; Geraads, Denis; Spassov, Nikolai; Zagorchev, Ivan (2018). "Discovery of the oldest European ruminant in the late Eocene of Bulgaria: Did tectonics influence the diachronic development of the Grande Coupure?" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 498: 1–8. Bibcode:2018PPP...498....1M. doi:10.1016/j.palaeo.2018.01.011. S2CID   134845249.
92. Mennecart, Bastien (2012). The Ruminantia (Mammalia, Cetartiodactyla) from the Oligocene to the Early Miocene of Western Europe: systematics, palaeoecology and palaeobiogeography (PDF) (PhD). Université de Fribourg.
93. Escarguel, Gilles; Legendre, Serge; Sigé, Bernard (2008). "Unearthing deep-time biodiversity changes: The Palaeogene mammalian metacommunity of the Quercy and Limagne area (Massif Central, France)" . Comptes Rendus Geoscience340. 340 (9–10): 602–614. doi: 10.1016/j.crte.2007.11.005 .
94. Mennecart, Bastien (2015). "The European Ruminants during the "Microbunodon Event" (MP28, Latest Oligocene): Impact of Climate Changes and Faunal Event on the Ruminant Evolution". PLoS ONE. 10 (2). doi: 10.1371/journal.pone.0116830 . PMC   4334963 .
95. Tsubamoto, Takehisa; Tsogtbaatar, Khishigjav; Chinzorig, Tsogtbaatar; Egi, Naoko (2022). "A brief review of the updated fossil vertebrate fauna of the upper Eocene Ergilin Dzo Formation, southeastern Mongolia" (PDF). Memoirs of the Faculty of Science, Ehime University. 24: 64–83.
96. Tsubamoto, T., Saneyoshi, M., Watabe, M., Tsogbataar, K., Mainbayar, B. (2011). The Entelodontid Artiodactyl Fauna from the Eocene Ergilin Dzo Formation of Mongolia with Comments on Brachyhyops and the Khoer Dzan Locality. Paleontological Research, 15(4):258-268
97. PBDB: Khoer Dzan slope
98. Friscia, Anthony; Van, Valkenburgh B. (2010). "Ecomorphology of North American Eocene carnivores: evidence for competition between Carnivorans and Creodonts". Carnivoran Evolution. Cambridge University Press. pp. 311–341. doi:10.1017/CBO9781139193436.012. ISBN   978-0-521-51529-0.
99. Van Valkenburgh, Blaire (1994). "Extinction and replacement among predatory mammals in the North American late Eocene and Oligocene: Tracking a paleoguild over twelve million years" . Historical Biology. 8 (1–4): 129–150. Bibcode:1994HBio....8..129V. doi:10.1080/10292389409380474 . Retrieved 12 April 2022.
100. Solé, Floréal; Fischer, Fischer; Denayer, Julien; Speijer, Robert P.; Fournier, Morgane; Le Verger, Kévin; Ladevèze, Sandrine; Folie, Annelise; Smith, Thierry (2020). "The upper Eocene-Oligocene carnivorous mammals from the Quercy Phosphorites (France) housed in Belgian collections". Geologica Belgica. 24 (1–2): 1–16. doi: 10.20341/gb.2020.006 . S2CID   224860287.
101. Serio, Carmela; Brown, Richard P.; Clauss, Marcus; Meloro, Carlo (2024). "Morphological disparity of mammalian limb bones throughout the Cenozoic: the role of biotic and abiotic factors". Palaeontology. 67 (4) e12720. Bibcode:2024Palgy..6712720S. doi: 10.1111/pala.12720 .
102. Lang, Andreas Johann; Engler, Thomas; and Martin, Thomas (November 2021). "Dental topographic and three-dimensional geometric morphometric analysis of carnassialization in different clades of carnivorous mammals (Dasyuromorphia, Carnivora, Hyaenodonta)". Journal of Morphology. 283 (5): 91–108. doi: 10.1002/jmor.21429 . hdl: 20.500.11811/10981 . PMID   34775616.
103. Frisica, Anthony R.; Macharwas, Mathew; Muteti, Samuel; Ndiritu, Francis; Rasmussen, D. Tab (2 November 2020). "A Transitional Mammalian Carnivore Community from the Paleogene–Neogene Boundary in Northern Kenya" . Journal of Vertebrate Paleontology. 40 (5) e1833895. Bibcode:2020JVPal..40E3895F. doi:10.1080/02724634.2020.1833895.
104. Wattinne, Aurélia; Lécuyer, Christophe; Vennin, Emmanuelle; Chateauneuf, Jean-Jacques; Martineau, François (2018). "Environmental changes around the Oligocene/Miocene boundary in the Limagne graben, Massif Central, France". Bulletin de la Société Géologique de France. 189 (4–6). doi: 10.1051/bsgf/2018019 .
105. Hullot, Manon; Martin, Céline; Blondel, Cécile; Becker, Damien; Rössner, Gertrud E. (2024). "Evolutionary palaeoecology of European rhinocerotids across the Oligocene–Miocene transition". The Royal Society Publishing. 11 (10): 1–24. doi: 10.1098/rsos.240987 . PMC   11461060 .