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Creodonta ("meat teeth") is a former order of Extinction carnivorous Placentalia that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia 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 Oxyaenodonta and the Hyaenodonta, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.
Creodonts were the dominant carnivorous mammals from , peaking in diversity and prevalence during the Eocene.
The first large, obviously carnivorous mammals appeared with the radiation of the oxyaenids in the late Paleocene. During the Paleogene, "creodont" species were the most abundant terrestrial carnivores in the Old World. 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. 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 often assumed to have been outcompeted by carnivorans, there is little empirical support for this. The last genus, Dissopsalis, became extinct about .
Most modern paleontologists agree both "creodont" families are Sister group 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 Hypercarnivore species may evolve similar shapes through convergent evolution, to deal with the mechanics of eating meat.
"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.
Hyaenodontidae was not included among the creodonts until 1909. William Diller Matthew regarded Creodonta as a suborder of order Carnivora, divided in three groups:
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, 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 . By 1969, Creodonta contained only the oxyaenids and the hyaenodontids.
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 group to Carnivoramorpha (carnivorans and their stem-relatives) within clade Ferae (in mirorder Ferae), split in two groups: order Oxyaenidae as one group and order Hyaenodonta plus its stem-relatives (genera Altacreodus and Simidectes) in the other.Prevosti, F. J., & Forasiepi, A. M. (2018). "Introduction. Evolution of South American Mammalian Predators During the Cenozoic: Paleobiogeographic and Paleoenvironmental Contingencies" 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 ( and their stem-relatives).
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. 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.
Complicating this arrangement is the tentative endorsement by Gunnell
of the erection of a third family, Limnocyonidae. The group includes taxa that were once considered oxyaenids, such as Limnocyon, Thinocyon and Prolimnocyon. In this paper the authors rename Marsh's Limnocyon protenus as Didymictis protenus and include it among the miacids Wortman had even erected a subfamily of Limnocyoninae within the oxyaenids. Van Valen nests the same subfamily (including Oxyaenodon) within Hyaenodontidae. Gunnell is agnostic whether Limnocyonidae is a group within Hyaenodontidae (although a sister group to the rest of hyaenodontids) or entirely separate.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 Talus bone articulates with the cuboid bone. The phalanges are compressed and fissured at the tip.
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.
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.
Creodonts have two or three pairs of carnassial. One pair performed the largest cutting function (either M1/m2 or M2/m3). This arrangement is unlike modern carnivorans, which use P4 and m1 for carnassials.
This difference suggests convergent evolution among meat-eaters, with a separate evolutionary history and an order-level distinction,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. The difference in which teeth form the carnassials is a major argument for the polyphyly of Creodonta.
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.
The largest North American creodont is Patriofelis. A specimen of P. ferox collected in the Bridger Basin of southern Wyoming was the size of a full-grown black bear with a head almost the size of an adult male lion.
During the Central Asia Expedition of 1930 by the American Museum of Natural History, the largest creodont ever discovered was collected: Sarkastodon mongoliensis. Its dimensions were described as 50% greater than the Patriofelis to which it bore many similarities. It has been estimated that Sarkastodon attained the body mass of twice the largest American lion.
In the Carnivora, the last upper premolar and the first lower molar are the , allowing the rearmost molar teeth to evolve adaptations for feeding on non-meat foods. In creodonts, either the first upper and second lower molars, or the second upper and third lower molars, were the primary carnassials, and the rear teeth formed a carnassial series. This structure committed them to eating meat almost exclusively, which may have limited their ability to exploit mesocarnivore and omnivore ecological niches. These differences may have caused environmental changes to affect hyaenodonts and oxyaenids differently than they did many carnivorans, as the former would have been restricted to largely or entirely faunivorous diets, while many (though not all) carnivoran lineages were/are able to subsist on plant matter as well.
A study conducted on creodont and carnivoran dietary niches in the Cypress Hills Formation showed that only the smallest creodont in the faunal assemblage had any significant dietary overlap with carnivorans and that the niches of the other creodonts were extremely distinct from those of the carnivorans they lived alongside, with the study concluding that it was highly unlikely that the extinction of creodonts in North America can be attributed to competition with carnivorans.
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