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, while hyaenodonts hail from the late Paleocene, or Late Cretaceous, of Europe.
Creodonts were the dominant carnivorous mammals from , peaking in diversity and prevalence during the Eocene. The first large, hypercarnivorous mammals appeared with the radiation of the oxyaenids in the late Paleocene. 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.
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.
"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. Cope originally placed creodonts within the Insectivora. In 1884, however, he regarded them as a basal group from which both carnivorans and insectivorans arose.
Hyaenodontidae was not included among the creodonts until 1909. 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, 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.
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. 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).
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 Wortman had even erected a subfamily of Limnocyoninae within the oxyaenids. Van Valen nests the same subfamily (including Oxyaenodon) within Hyaenodontidae. The canines are always large and pointed. The lateral incisors are large, while the medial incisors are usually small. This difference suggests convergent evolution among meat-eaters, with a separate evolutionary history and an order-level distinction, 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.
Size
left|thumb|Size comparison between [[Simbakubwa kutokaafrika and a human]]
Creodonts ranged in size from the size of a small cat to Sarkastodon and the large hyainailourines. one study estimated that it could’ve weighed , although it may have been an overestimate. The largest North American creodont, was Hemipsalodon grandis, which could’ve weighed .
The larger oxyaenids, however, were not known until late in the Paleocene which saw a radiation of oxyaenids, On the other hand, the largest known hyaenodonts didn’t appear until the early Miocene.
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 suggesting that they were probably opportunistic feeders, eating such things as eggs, birds, small mammals, insects and possibly plant matter as well, Similarly, some of the youngest hyaenodonts in the Miocene, have shown extreme specialization towards hypercarnivory.
Extinction
Creodonts, as a whole, began to experience a decline in the Eocene, with oxyaenids going extinct during the middle Eocene. Some experts suggested their extinction was due to competition with nimravids, In addition, the last records of machaeroidines predate the earliest records of nimravids in North America. 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. Some experts argued that carnivorans outcompeted hyaenodonts in mesocarnivore niches which forced hyaenodonts to become larger, more specialized hypercarnivores. The discovery of Simbakubwa suggests that their large size was due to changes in the herbivore fauna rather than competition with carnivorans. In Europe, Hyaenodon and amphicyonids preferred different habitats, with the former hunting in more open environments. Instead, it’s now thought that hyaenodonts in Europe died out because of climatic changes instead of competition with carnivorans.