Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals 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 oxyaenids and the hyaenodonts, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.[10]
Creodonts were the dominant carnivorous mammals from 55to35 million years ago, peaking in diversity and prevalence during the Eocene.[11] The first large, obviously carnivorous mammals appeared with the radiation of the oxyaenids in the late Paleocene.[12] During the Paleogene, "creodont" species were the most abundant terrestrial carnivores in the Old World.[13] 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.[14] 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 800kg.[15]
Though often assumed to have been outcompeted by carnivorans, there is little empirical support for this. The last genus, Dissopsalis, became extinct about 11.1million years ago.
Most modern paleontologists agree both "creodont" families are related toCarnivora, 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.[16]
"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.[19]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,[20] 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.[21]
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 (family Wyolestidae and genera Altacreodus, Simidectes and Tinerhodon) in the other.[22][23][24][25][26] 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).[27]
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.[28] 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.[12]
Complicating this arrangement is the tentative endorsement by Gunnell[14] of the erection of a third family, Limnocyonidae.[29] The group includes taxa that were once considered oxyaenids, such as Limnocyon, Thinocyon[19] and Prolimnocyon.[30] Wortman had even erected a subfamily of Limnocyoninae within the oxyaenids.[31] Van Valen nests the same subfamily (including Oxyaenodon) within Hyaenodontidae.[21] Gunnell is agnostic whether Limnocyonidae is a group within Hyaenodontidae (although a sister group to the rest of hyaenodontids) or entirely separate.[14]
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.[14]
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.[14]
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.[14]
Morphology
Dentition
Among primitive creodonts the dental formula is 3.1.4.33.1.4.3, but later forms often had reduced numbers of incisors, premolars and/or molars.[32] The canines are always large and pointed. The lateral incisors are large, while the medial incisors are usually small.[14] Premolars are primitive, with one primary cusp and various secondary cusps.[13]
Creodonts have two or three pairs of carnassial teeth. One pair performed the largest cutting function (either M1/m2 or M2/m3).[14] This arrangement is unlike modern carnivorans, which use P4 and m1 for carnassials.[33] This difference suggests convergent evolution among meat-eaters, with a separate evolutionary history and an order-level distinction,[34] 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 batNecromantis, 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.[19] The difference in which teeth form the carnassials is a major argument for the polyphyly of Creodonta.
Comparison of carnassial teeth of wolf and typical hyaenodontid and oxyaenid
Upper teeth of creodonts from Middle Eocene Bridger Basin, Wyoming
Sinopa fossils: (1) Right upper cheek teeth, P2-M2; (2) Left ramus of mandible (p2-m2); (3) Right ramus of mandible (c-m2)
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).[14] Many creodonts had proportionately large heads.[13] In primitive forms, the auditory bullae was not ossified. Generally the temporal fossae were very broad.[14]
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.[14]
Mount of oxyaenid Patriofelis ferox from the American Museum of Natural History
Reconstruction of Patriofelis ferox
Mounted skeleton of the hyaenodontid Sinopa rapax from Bridger Basin
Size
Creodonts ranged in size from the size of a small cat to the 800-kilogram (1,800lb)Sarkastodon. The larger animals, however, were not known until late in the Paleocene with the radiation of the oxyaenids,[12] such as the puma-sized Dipsalidictis and the probably bone-crushing scavenger Dipsalodon.[35]
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.[36]
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.[37]
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.[38] It has been estimated that Sarkastodon attained the body mass of twice the largest American lion.[15]
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[39] suggesting that they were probably opportunistic feeders, eating such things as eggs, birds, small mammals, insects and possibly plant matter as well,[14] possibly like extant viverrids.[32] 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.[39] A similar development can be seen by comparing Oxyaena, Prototomus and Limnocyon with the smaller, more generalized feeders among the creodonts.[14]
Several theories have suggested that hyaenodonts and oxyaenids became extinct because they were outcompeted by the newly-evolved Carnivora. However, there is no direct evidence that the existence of large Carnivora caused the extinction of these taxa, and in many cases (in Africa throughout the Early and Middle Miocene, and in North America and Eurasia during much of the Oligocene), hyaenodonts thrived in environments in which large carnivorans such as nimravids and (later) larger amphicyonids were also present as competitors. Theories that suggest they were outcompeted by the Carnivora include that their smaller brains limited their intelligence, but carnivoran brain sizes have not always been consistently large throughout their evolution, and the importance of brain size as a factor in intelligence has been vastly overestimated in the past when these ideas were published. Other speculations focus on their limb structure, which limited leg movement to a vertical plane, as in ungulates; they were unable to turn their wrists and forearms inward to trip, slash, or grab prey as some modern carnivores can. Creodonts had to depend entirely on their jaws to capture prey, which may be why creodonts generally had a larger head size in relation to their bodies than carnivores of similar stature. However, many carnivorans, such as large canids, are also dependent on their jaws alone to capture prey yet do so effectively even in situations where they must tackle large prey alone, so this also fails to provide a satisfactory explanation.
In the Carnivora, the last upper premolar and the first lower molar are the carnassials, 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.[40]
Related Research Articles
Carnivora is an order of placental mammals that have specialized in primarily eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species on every major landmass and in a variety of habitats, ranging from the cold polar regions of Earth to the hyper-arid region of the Sahara Desert and the open seas. Carnivorans exhibit a wide array of body plans, varying greatly in size and shape.
Sarkastodon is an extinct genus of placental mammals from extinct subfamily Oxyaeninae within extinct family Oxyaenidae, that lived in Asia during the middle Eocene. It was a genus of large, carnivorous animals known only from a skull and jawbones. Sarkastodon was probably a hypercarnivore that preyed on large mammals in its range during the Middle Eocene, such as brontotheres, chalicotheres, and rhinoceroses. Its weight is estimated at 800 kg (1,800 lb), and its length at 3 m (10 ft).
Mesonychia is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychians first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct.
Oxyaenidae is a family of extinct carnivorous placental mammals. Traditionally classified in order Creodonta, this group is now classified in its own order Oxyaenodonta within clade Pan-Carnivora in mirorder Ferae. The group contains four subfamilies comprising fourteen genera. Oxyaenids were the first to appear during the late Paleocene in North America, while smaller radiations of oxyaenids in Europe and Asia occurred during the Eocene.
Megistotherium is an extinct genus of hyaenodont belonging to the family Hyainailouridae that lived in Africa.
Hyaenodon ("hyena-tooth") is an extinct genus of carnivorous placental mammals from extinct tribe Hyaenodontini within extinct subfamily Hyaenodontinae, that lived in Eurasia and North America from the middle Eocene, throughout the Oligocene, to the early Miocene.
Ferae is a mirorder of placental mammals in grandorder Ferungulata, that groups together clades Pan-Carnivora and Pholidotamorpha.
Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified fourth upper premolar and the first lower molar. These teeth are also referred to as sectorial teeth.
Miacidae is a former paraphyletic family of extinct primitive placental mammals that lived in North America, Europe and Asia during the Paleocene and Eocene epochs, about 65–33.9 million years ago. These mammals were basal to order Carnivora, the crown-group within the Carnivoraformes.
Oxyaena is an extinct genus of placental mammals from extinct subfamily Oxyaeninae within extinct family Oxyaenidae, that lived in Europe, Asia and North America during the early Eocene.
Carnivoramorpha is a clade of placental mammals of clade Pan-Carnivora from mirorder Ferae, that includes the modern order Carnivora and its extinct stem-relatives.
Mesonychidae is an extinct family of small to large-sized omnivorous-carnivorous mammals. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of large carnivorous mammals in Asia. Once considered a sister-taxon to artiodactyls, recent evidence now suggests no close connection to any living mammal. Mesonychid taxonomy has long been disputed and they have captured popular imagination as "wolves on hooves", animals that combine features of both ungulates and carnivores. Skulls and teeth have similar features to early whales, and the family was long thought to be the ancestors of cetaceans. Recent fossil discoveries have overturned this idea; the consensus is that whales are highly derived artiodactyls. Some researchers now consider the family a sister group either to whales or to artiodactyls, close relatives rather than direct ancestors. Other studies define Mesonychia as basal to all ungulates, occupying a position between Perissodactyla and Ferae. In this case, the resemblances to early whales would be due to convergent evolution among ungulate-like herbivores that developed adaptations related to hunting or eating meat.
Didymictis is an extinct genus of placental mammals from extinct subfamily Didymictinae within extinct family Viverravidae, that lived in North America and Europe from the late Paleocene to middle Eocene.
Pterodon is an extinct genus of hyaenodont in the family Hyainailouridae, containing five species. The type species Pterodon dasyuroides is known exclusively from the late Eocene to the earliest Oligocene of western Europe. The genus was first erected by the French zoologist Henri Marie Ducrotay de Blainville in 1839, who said that Georges Cuvier presented one of its fossils to a conference in 1828 but died before he could make a formal description of it. It was the second hyaenodont genus with taxonomic validity after Hyaenodon, but this resulted in taxonomic confusion over the validities of the two genera by other taxonomists. Although the taxonomic status of Pterodon was revised during the late 19th and early 20th centuries, it became a wastebasket taxon for other hyaenodont species found in Africa and Asia. Today, only the type species is recognized as belonging to the genus while four others are pending reassessment to other genera.
Gustafsonia is an extinct genus of carnivoran belonging to the family Amphicyonidae. The type species, Gustafsonia cognita, was described in 1986 by Eric Paul Gustafson, who originally interpreted it as a miacid and named it Miacis cognitus. It was subsequently considered to be the only species of the diverse genus Miacis that belonged to the crown-group Carnivora, within the Caniformia, and it was ultimately assigned to the family Amphicyonidae. The type specimen or holotype was discovered in Reeve's bonebed, western Texas, in the Chambers Tuff Formation in 1986. The University of Texas holds this specimen. It is the only confirmed fossil of this species.
Palaeonictis is an extinct genus of placental mammals from extinct subfamily Palaeonictinae within extinct family Oxyaenidae, that lived in Europe and North America from the late Paleocene to the early Eocene.
Hyaenodonta is an extinct order of hypercarnivorous placental mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that arose during the early Paleocene in Europe and persisted well into the late Miocene.
Tytthaena is an extinct genus of placental mammals from extinct subfamily Tytthaeninae within extinct family Oxyaenidae, that lived in North America from the late Paleocene to early Eocene.
Machaeroidinae ("dagger-like") is an extinct subfamily of carnivorous sabre-toothed placental mammals from extinct family Oxyaenidae, that lived from the early to middle Eocene of Asia and North America. Traditionally classified as hyaenodonts, this group is now classified as a member of the family Oxyaenidae.
Palaeonictinae is an extinct subfamily of placental mammals from extinct family Oxyaenidae, that lived from the late Paleocene to early Eocene of Europe and North America.
↑ T. C. Winkler (1893.) "De Gewervelde Dieren van Het Verleden." Palaeontologische Studiën in Telyer's Museum 1-291
↑ Kenneth E. Kinman (1994.) "The Kinman System: Toward a Stable Cladisto-Eclectic Classification of Organisms: Living and Extinct, 48 Phyla, 269 Classes, 1,719 Orders", Hays, Kan. (P. O. Box 1377, Hays 67601), 88 pages
↑ Miklos Kretzoi (1945) "Bemerkungen über das Raubtiersystem." Annales Historico-Naturales Musei Nationalis Hungarici, Budapest, vol. 38, pp. 59-83.
↑ Romer, A. S. (1966.) "Vertebrate Paleontology." University of Chicago Press, Chicago; 3rd edition ISBN0-7167-1822-7
↑ Kretzoi, N. (1929.) "Materialien zur phylogenetischen Klassifikation der Aeluroïdeen. X Congres International de Zoologie, Budapest 1927., 2, 1293–1355.
↑ Trouessart, E. L. (1879.) "Catalogue des mammifères vivants et fossiles. III. Insectivora." Rev. Mag. Zool. 3è ser. 7: 219 – 285.
↑ Solé, F.; Lhuillier, J.; Adaci, M.; Bensalah, M.; Mahboubi, M.; Tabuce, R. (2013). "The hyaenodontidans from the Gour Lazib area (?Early Eocene, Algeria): implications concerning the systematics and the origin of the Hyainailourinae and Teratodontinae". Journal of Systematic Palaeontology. 12 (3): 303–322. doi:10.1080/14772019.2013.795196. S2CID84475034.
1 2 3 Janis, Christine M.; Baskin, Jon A.; Berta, Annalisa; Flynn, John J.; Gunnell, Gregg F.; Hunt, Robert M. Jr.; Martin, Larry D.; Munthe, Kathleen (1998). "Carnivorous mammals". In Janis, Christine M.; Scott, Kathleen M.; Jacobs, Louis L. (eds.). Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Evolution of Tertiary Mammals of North America. Vol.1. Cambridge: Cambridge University Press. pp.73–90. ISBN978-0-521-35519-3.
1 2 3 Rose, Kenneth David; Archibald, J. David (2005). The Rise of Placental Mammals: Origins and relationships of the major extant clades. Baltimore, MD: Johns Hopkins University Press.
1 2 3 4 5 6 7 8 9 10 11 12 13 Gunnell, Gregg F. (1998). "Creodonta". In Janis, Christine M.; Scott, Kathleen M.; Jacobs, Louis L. (eds.). Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Evolution of Tertiary Mammals of North America. Cambridge, UK: Cambridge University Press. pp.91–109. ISBN978-0-521-35519-3.
↑ Cope, E. D. (March–December 1880). "On the Genera of the Creodonta". Proceedings of the American Philosophical Society. 19 (107): 76–82. JSTOR982610.
↑ Russell, Loris S. (1954). "Evidence of Tooth Structure on the Relationships of the Early Groups of Carnivora". Evolution. 8 (2): 166–171. doi:10.2307/2405640. ISSN0014-3820. JSTOR2405640.
↑ Solé, Floréal; Ladevèze, Sandrine (2017). "Evolution of the hypercarnivorous dentition in mammals (Metatheria,Eutheria) and its bearing on the development of tribosphenic molars". Evolution & Development. 19 (2): 56–68. doi:10.1111/ede.12219. PMID28181377. S2CID46774007.
↑ Matthew, William Diller; Granger, Walter (1915). "A revision of the Lower Eocene Wasatch and Wind River faunas". Bulletin of the American Museum of Natural History. 34: 4–103. hdl:2246/1373. In this paper the authors rename Marsh's Limnocyon protenus as Didymictis protenus and include it among the miacids
↑ Turner, Alan; Antón, Mauricio (2004). Evolving Eden: An Illustrated Guide to the Evolution of the African Large-Mammal Fauna. New York: Columbia University Press. p.77. ISBN978-0-231-11944-3.
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