Creodonta

Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the Early Paleocene (or Late Cretaceous) to the Late Miocene epochs in North America, Eurasia, and Africa. Originally thought to be a single group of animals ancestral to the modern Carnivora, this order is now usually considered a polyphyletic assemblage of two different groups, the oxyaenids and the hyaenodonts, not a natural group. Oxyaenids are first known from the early Paleocene of North America,<ref>Template:Cite journal</ref> while hyaenodonts hail from the late Paleocene, or Late Cretaceous, of Europe.<ref>Template:Cite journal</ref><ref name="Borths-2017">Template:Cite journal</ref><ref name="Borths2019">Template:Cite journal</ref>

Creodonts were the dominant carnivorous mammals from Template:Ma, peaking in diversity and prevalence during the Eocene.<ref>Template:Cite book</ref> The first large, obviously carnivorous mammals appeared with the radiation of the oxyaenids in the late Paleocene.<ref name="Janis1998" /> During the Paleogene, "creodont" species were the most abundant terrestrial carnivores in the Old World.<ref name="Rose2005">Template:Cite book</ref> In Oligocene Africa, hyaenodonts were the dominant group of large flesh-eaters, persisting until the middle of the Miocene.

"Creodont" groups had an extensive range, both geographically and temporally. They are known from the late Paleocene through the late Oligocene in North America, the early Eocene through late Oligocene in Europe, from the late Paleocene through late Miocene in Asia, and from the late Paleocene to the late Miocene in Africa.<ref name="Gunnell1998" /> While most were small-to-medium sized mammals, among their number was Sarkastodon, one of the largest mammalian land predators of all time, weighing an estimated 800 kg, though this may have been an overestimate.<ref name="Sorkin-2008">Template:Cite journal</ref> The last genus, Dissopsalis, went extinct about Template:Ma.<ref name="Barry-2025">Template:Cite book</ref>

Most modern paleontologists agree both "creodont" families are related to Carnivora, but are not their direct ancestors. It is still unclear how closely the two families are related to each other. In general, classification is complicated by the fact that relationships among fossil mammals are usually decided by similarities in the teeth, but the teeth of hypercarnivorous species may evolve similar shapes through convergent evolution, to deal with the mechanics of eating meat.<ref>Template:Cite journal</ref>

"Creodonts" share with the Carnivora, and many other predatory mammal clades, the carnassial shear, a scissors-like modification of upper and lower cheek teeth that was used to slice muscle tissue. This adaptation is also seen in other clades of predatory mammals.

Systematics and history

"Creodonta" was coined by Edward Drinker Cope in 1875.<ref name=Cope-1875/> Cope included the oxyaenids and the viverravid Didymictis but omitted the Hyaenodontidae. In 1880. he expanded the term to include families Miacidae (including Viverravidae), Arctocyonidae, Leptictidae (now Pseudorhyncocyonidae), Oxyaenidae, Ambloctonidae and Mesonychidae.<ref>Template:Cite journal</ref> Cope originally placed creodonts within the Insectivora. In 1884, however, he regarded them as a basal group from which both carnivorans and insectivorans arose.<ref>Template:Cite book</ref>

Hyaenodontidae was not included among the creodonts until 1909.<ref name="MatthewBridgerBasin">Template:Cite journal</ref> William Diller Matthew regarded Creodonta as a suborder of order Carnivora, divided in three groups:

• "Inadaptive Creodonta" (Creodonta inadaptiva), group that includes "Pseudocreodi" (oxyaenids and hyaenodontids) and the mesonychids,
• "Adaptive Creodonta" (Creodonta adaptiva), made up of the miacids and the taxa included in the wastebasket "Arctocyonidae",
• and "Primitive Creodonta" (Creodonta primitiva), made up of Oxyclaenidae.

Over time, various groups and species were removed from this order. It stabilized in the mid-20th century as representing oxyaenids, hyaenodonts, mesonychids, and arctocyonids,<ref>Template:Cite journal</ref> which were understood as the major groups of flesh-eating placental mammals that were not members of the Carnivora. It became increasingly clear that arctocyonids were a wastebasket taxon and mesonychids might be more closely related to ungulates. By 1969, Creodonta contained only the oxyaenids and the hyaenodontids.<ref name="Van Valen">Template:Cite journal</ref>

More recently, "Creodonta" had been considered to be a nonvalid polyphyletic assemblage of carnivorous placental mammals (and not a natural group), and members of Creodonta being sister taxa to Carnivoramorpha (carnivorans and their stem-relatives) within clade Pan-Carnivora (in mirorder Ferae), split in two groups: order Oxyaenodonta as one group and order Hyaenodonta plus its stem-relatives (genera Altacreodus and Simidectes) in the other.<ref name="Matthew2017">Template:Cite journal</ref><ref name="Sandrine2017">Template:Cite journal</ref><ref name="Prevosti2018">Prevosti, F. J., & Forasiepi, A. M. (2018). "Introduction. Evolution of South American Mammalian Predators During the Cenozoic: Paleobiogeographic and Paleoenvironmental Contingencies"</ref><ref name="Simbakubwa">Template:Cite journal</ref><ref name="Geodiversitas4213">Template:Cite journal</ref> However, some phylogenetic analysis recover them as a natural group, such as a phylogenetic analysis of Paleocene mammals published in 2015 that supported the monophyly of Creodonta, and placed the group as relatives of clade Pholidotamorpha (pangolins and their stem-relatives).<ref name="HallidayUpchurch2015">Template:Cite journal</ref>

Polly has argued that the only available synapomorphy between oxyaenids and hyaenodontids is a large metastylar blade on the first molar (M1), but he believes that that feature is common for all basal eutheria.<ref name="Polly">Template:Cite journal</ref> Separating Oxyaenidae from Hyaenodontidae would also comport with biogeographic evidence, since the first oxyaenid is known from the North American early Paleocene and the first hyaenodontids are from very late Paleocene of North Africa.<ref name="Janis1998">Template:Cite book</ref>

Complicating this arrangement is the tentative endorsement by Gunnell<ref name="Gunnell1998">Template:Cite book</ref> of the erection of a third family, Limnocyonidae.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The group includes taxa that were once considered oxyaenids, such as Limnocyon, Thinocyon<ref name="MatthewBridgerBasin"/> and Prolimnocyon.<ref>Template:Cite journal In this paper the authors rename Marsh's Limnocyon protenus as Didymictis protenus and include it among the miacids</ref> Wortman had even erected a subfamily of Limnocyoninae within the oxyaenids.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Van Valen nests the same subfamily (including Oxyaenodon) within Hyaenodontidae.<ref name="Van Valen"/> Gunnell is agnostic whether Limnocyonidae is a group within Hyaenodontidae (although a sister group to the rest of hyaenodontids) or entirely separate.<ref name="Gunnell1998"/>

According to Gunnell, the defining features of the oxyaenids include: A small braincase low in the skull. The occiput wide at base and narrowing dorsally (to give it a triangular shape). The lacrimal bone makes a semicircular expansion on the face. The mandibles have heavy symphysis. M1 and m2 form the carnassials, while M3/m3 are absent. The manus and pes are plantigrade or subplantigrade. The fibula articulates with the calcaneum, and the astragalus articulates with the cuboid bone. The phalanges are compressed and fissured at the tip.<ref name="Gunnell1998"/>

Likewise, Gunnell's list of defining features of hyaenodontids includes: Long, narrow skull with a narrow basicranium and a high narrow occiput. The frontal bones are concave between the orbital regions. M2 and m3 form the carnassials. M3 is present in most species, while m3 is always present. Manus and pes range from plantigrade to digitigrade. The fibula articulates with the calcaneum, while the astragalar-cuboid articulation is reduced or absent. Terminal phalanges are compressed and fissured at the tip.<ref name="Gunnell1998"/>

The limnocyonids had the following features according to Gunnell: M3/m3 were reduced or absent, other teeth were unreduced. The rostrum was elongated. The animals themselves were small to medium-sized.<ref name="Gunnell1998"/>

Morphology

Dentition

Among primitive creodonts the dental formula is Template:DentalFormula, but later forms often had reduced numbers of incisors, premolars and/or molars.<ref name="Denison">Template:Cite journal (Subscription or payment required.)</ref> The canines are always large and pointed. The lateral incisors are large, while the medial incisors are usually small.<ref name="Gunnell1998"/> Premolars are primitive, with one primary cusp and various secondary cusps.<ref name="Rose2005"/>

Creodonts have two or three pairs of carnassial teeth. One pair performed the largest cutting function (either M1/m2 or M2/m3).<ref name="Gunnell1998"/> This arrangement is unlike modern carnivorans, which use P4 and m1 for carnassials.<ref>Template:Cite book</ref> This difference suggests convergent evolution among meat-eaters, with a separate evolutionary history and an order-level distinction,<ref>Template:Cite book</ref> given that different teeth evolved as the carnassials both between creodonts and carnivorans, and between oxyaenids and hyaenodonts. Carnassials are also known in other flesh-eating mammal clades, such as in the extinct bat Necromantis, as well as highly unrelated taxa such as the flesh-eating marsupial Thylacoleo.

Different molars were involved in the two major groups of creodonts. In the Oxyaenidae, M1 and m2 that form the carnassials. Among the hyaenodontids, it is M2 and m3. Unlike most modern carnivorans, in which the carnassials are the sole shearing teeth, other creodont molars have a subordinate shearing functions.<ref name="MatthewBridgerBasin"/> The difference in which teeth form the carnassials is a major argument for the polyphyly of Creodonta.

Cranium

Creodonts had long, narrow skulls with small brains. The skull narrowed considerably behind the eyes, producing a distinct splanchnocranium and neurocranium segments of the cranium. They had large sagittal crests and usually broad mastoids (which were probably derived features for the group).<ref name="Gunnell1998"/> Many creodonts had proportionately large heads.<ref name="Rose2005"/> In basal forms, the auditory bullae was not ossified. Generally the temporal fossae were very broad.<ref name="Gunnell1998"/>

Postcranial skeleton

Creodonts had generalized postcranial skeletons. Their limbs were mesaxonic (with the axis of the foot provided by the middle of their five digits). Their method of locomotion ranged from plantigrade to digitigrade. The terminal phalanges were fused claws.<ref name="Gunnell1998"/>

Within oxyaenids, many taxa within the family remained adaptations. Hyaenodonts, on the other hand, showed transition from plantigrade to digitigrade throughout their evolutionary history.<ref name="Solé-2015">Template:Cite journal</ref><ref name="Borths20192">Template:Cite journal</ref> Template:Multiple image

Size

Creodonts ranged in size from the size of a small cat to the Template:Convert Sarkastodon, however this has been considered to possibly be an overestimate.<ref name="Sorkin-2008" /> Its dimensions were described as 50% greater than the Patriofelis to which it bore many similarities.<ref name="Granger1938">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Other large creodonts include Megistotherium, Hyainailouros, and Simbakubwa.<ref name="Borths20193">Template:Cite journal</ref><ref name="Antunesa2006">Template:Cite journal</ref><ref name="Sorkin-2008" /><ref name="Savage1973">Template:Cite journal</ref> The largest North American hyaenodonta, as well as creodont, was Hemipsalodon, which could’ve weighed Template:Convert.<ref name="Egi-2001">Template:Cite journal</ref>

The larger oxyaenids, however, were not known until late in the Paleocene which saw a radiation of oxyaenids,<ref name="Janis1998" /> such as the puma-sized Dipsalidictis and the probably bone-crushing scavenger Dipsalodon.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> On the other hand, the largest known hyaenodonts didn’t appear until the early Miocene.<ref name="Borths20193" />

Certain creodonts (Arfia, Prolimnocyon and Palaeonictis) seem to have experienced the dwarfing phenomenon during the Paleocene-Eocene Thermal Maximum seen in other mammal genera. A proposed explanation for this phenomenon is that the increased carbon dioxide levels in the atmosphere directly affected carnivores through increased temperature and aridity and also indirectly affected them by reducing the size of their herbivorous prey through the same selective pressures.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Biology

Diet and feeding

Early creodonts (both oxyaenids and hyaenodontids) displayed the tribosphenic molars common for basal therians. Small forms had somewhat strong postmetacrista-metastellar crests<ref name="Gingerich1989">Template:Cite journal</ref> suggesting that they were probably opportunistic feeders, eating such things as eggs, birds, small mammals, insects and possibly plant matter as well,<ref name="Gunnell1998"/> possibly like extant viverrids.<ref name="Denison"/> Larger forms had greater shearing capacity and the capacity increased over time. Arfia, one of the most common carnivorous mammals in early Eocene North America, developed a more open trigonid on M3 over the course of the Early Eocene, increasing the shearing ability of the carnassials.<ref name="Gingerich1989"/> A similar development can be seen by comparing Oxyaena, Prototomus and Limnocyon with the smaller, more generalized feeders among the creodonts.<ref name="Gunnell1998"/> However, however some of the last oxyaenids, such as Patriofelis and Machaeroidinae, showed adaptations towards hypercarnivory.<ref name="Kort-2021">Template:Cite journal</ref><ref name="Zack-2022a">Template:Cite journal</ref> Similarly, some of the youngest hyaenodonts in the Miocene, have shown extreme specialization towards hypercarnivory.<ref>Template:Cite book</ref><ref name="Frisica-2020">Template:Cite journal</ref>

Extinction

Creodonts, as a whole, began to experience a decline in the Eocene,<ref name="Friscia-2010">Template:Cite book</ref> with oxyaenids going extinct during the middle Eocene.<ref name="Kort-2019">Template:Cite journal</ref><ref name="Zack-2022b">Template:Cite journal</ref> Some experts suggested their extinction was due to competition with nimravids,<ref name="Zack-2022b" /> however other experts disagree with this hypothesis.<ref name="Van-1999a">Template:Cite journal</ref><ref name="Kort-2019" /> The excellent fossil records within North America show that oxyaenids were declining prior to the appearance of replacement taxa such as nimravids.<ref name="Van-1999b">Template:Cite journal</ref> In addition, the last records of machaeroidines predate the earliest records of nimravids in North America.<ref name="Zack-2022b" /><ref name="Poust et al.">Template:Cite journal</ref> Instead, climatic changes towards the late Eocene played a role in their extinction, as during the towards the late Eocene the climate of the planet began to cooling, resulting in more arid, open environments.<ref name="Van-1999b" /><ref name="Kort-2019" /> Because of their low mobility, oxyaenids went extinct because they weren’t adapted towards the temperate, open forest habitats.<ref name="Kort-2019" />

Hyaenodonts, the last group of creodonts, also experienced a decline in Eurasia and North America during the Eocene,<ref name="Van-1999a" /> in North America only a few species of Hyaenodon persisted into the Oligocene.<ref name="Friscia-2010" /> During the Miocene, hyainailourids experienced a massive decline after the early Miocene and went extinct by the late Miocene.<ref name="Frisica-2020" /> Many experts have argued that the extinction of hyaenodonts was due to competition with carnivorans.<ref name="Frisica-2020" /><ref name="Friscia-2010" /><ref name="Van-1999a" /><ref name="Borths20193" /><ref name="Lang-2021">Template:Cite journal</ref><ref name="Serio-2024">Template:Cite journal</ref> Some experts argued that carnivorans outcompeted hyaenodonts in mesocarnivore niches which forced hyaenodonts to become larger, more specialized hypercarnivores.<ref name="Friscia-2010" /><ref name="Frisica-2020" /> Lang et al. (2021) suggested carnivorans may have played a role in their extinction of hyaenodonts due to the adaptive potential of their carnassials.<ref name="Lang-2021" /> Serio et al. (2024) found that creodont disparity showed a degree of morphological differentiations until the middle Eocene, when disparity from carnivorans increased. They argued this suggests that carnivorans competitively replaced hyaenodonts.<ref name="Serio-2024" /> Borths and Stevens (2019) suggested that large hyainailourines may have went extinct because of loss of diversity of large herbivores and competition with gregarious carnivorans that had larger, more complex brains, which made them more adept for stealing carcasses from the hyainailourines.<ref name="Borths20193" />

However, this hypothesis has been questioned by experts.<ref name="Christison-2022" /><ref name="Morales 2008">Template:Cite journal</ref><ref name=":12">Template:Cite journal</ref> The discovery of Simbakubwa suggests that their large size was due to changes in the herbivore fauna rather than competition with carnivorans.<ref name="Borths20193" /> Additionally, overall brain sizes have little to no correlation in the sociality of carnivorans.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> In Europe, Hyaenodon and amphicyonids preferred different habitats, with the former hunting in more open environments.<ref name=":6">Template:Cite journal</ref> Instead, it’s now thought that hyaenodonts in Europe died out because of climatic changes instead of competition with carnivorans.<ref name="Frisica-2020" /> Christison et al. (2021) conducted a study on carnivoran and hyaenodont dietary niches in the Cypress Hills Formation. Their results showed that only the smallest hyaenodonts in the faunal assemblage had any significant dietary overlap with smaller carnivorans, while larger carnivorans and hyaenodonts were extremely distinct from one another, with the study concluding that it was highly unlikely that the extinction of hyaenodonts in North America can be attributed to competition with carnivorans. Instead, they argued the extinction of hyaenodonts may have been because of the preferences of large prey, such as brontotheres, in addition to the inability to adapt to more open environments due to their relatively short legs.<ref name="Christison-2022">Template:Cite journal</ref>

Further reading

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