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Creodonta is an extinct, apparently polyphyletic〔Morlo, M., Gunnell G., and P.D. Polly. 2009. What, if not nothing, is a creodont? Phylogeny and classification of Hyaenodontida and other former creodonts. Journal of Vertebrate Paleontology 29(Supplement 3): 152A. 〕〔Polly, P.D. 1994. What, if anything, is a creodont? Journal of Vertebrate Paleontology 14(Supplement 3): 42A.〕〔Polly, P.D. 1996. The skeleton of Gazinocyon vulpeculus gen. et comb. nov. and the cladisitic relationships of Hyaenodontidae (Eutheria, Mammalia). Journal of Vertebrate Paleontology 16: 303–319. 〕〔Grohé et al. 2012〕〔Katharina Anna Bastl, 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 (Impact Factor: 1.1). 10/2013; 88:481-494. DOI: 10.1007/s12542-013-0207-z〕〔Camille Grohé, Michael Morlo, Yaowalak Chaimanee, Cécile Blondel, Pauline Coster, Xavier Valentin, Mustapha Salem, Awad A. Bilal, Jean-Jacques Jaeger, and Michel Brunet, New Apterodontinae (Hyaenodontida) from the Eocene Locality of Dur At-Talah (Libya): Systematic, Paleoecological and Phylogenetical Implications, Published online 2012 Nov 21. doi: 10.1371/journal.pone.0049054〕 wastebasket taxon order of carnivorous mammals that lived from the Paleocene to the Miocene epochs. Because they both possess carnassial teeth, creodonts and carnivorans were once thought to have shared a common ancestor, but given that different teeth are involved in making up the carnassials (both between creodonts and carnivorans and between the main groups of creodonts), this appears to be a case of evolutionary convergence. Carnassials are also known in other mammal clades, such as in the extinct bat ''Necromantis''. Two distinct families were historically thought to compose the order: Oxyaenidae and Hyaenodontidae. They may both represent separate orders of fossil mammals related to carnivoramorphs or are descended from more basal taxa. Creodonts 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 early Eocene through late Miocene in Asia, and from the Paleocene to the late Miocene in Africa. Creodonts were the first large, obviously carnivorous mammals with the radiation of the oxyaenids in the late Paleocene. During the Paleogene, they were the most abundant form of terrestrial carnivore in the Old World. In Oligocene Africa, they were the dominant predatory group. They competed with the Mesonychids and the Entelodonts and ultimately outlasted them by the start of the Oligocene and by the middle of the Miocene respectively, but lost ground to the carnivorans. The last genus became extinct , and carnivorans now occupy their ecological niches. == Systematics == "Creodonta" was coined by Edward Drinker Cope in 1875. Cope included the oxyaenids and the viverravid ''Didymictis'' but omitted the hyaenodontids. In 1880. he expanded the term to include Miacidae, Arctocyonidae, Leptictidae (now Pseudorhyncocyonidae), Oxyaenidae, Ambloctonidae and Mesonychidae. 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.〔: Matthew used the term "Pseudocreodi" for what is now called Creodonta. He regarded Pseudocreodi and the mesonychids as "Inadaptive Creodonta", which together with "Adaptive Creodonta" (made up of the miacids and the taxa included in the wastebasket "Arctocyonidae") and "Primitive Creodonta" (made up of Oxyclaenidae) comprised the suborder of Creodonta, itself within the order Carnivora.〕 Over time, various groups were removed, and by 1969 it contained, as it does today, only the oxyaenids and the hyaenodontids. One view of the position of the group is that Creodonta and Carnivora are sister taxa (within a superorder Ferae). Others have argued that insectivorans are more closely related to carnivorans, and creodonts, therefore, are basal eutherians. Others have suggested that Creodonta might not be monophyletic. 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 myacids.〕 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 astragalus 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 artiuclates 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. Currently, "Creodonta" is considered to be a polyphyletic assemblage of mammals, not a natural group. Oxyaenids are laurasiatheres - the same group of mammals that includes carnivorans, as well as other groups like ungulates, eulipotyphlans and bats -, of uncertain affinities within that clade but assumed to be basal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Creodonta」の詳細全文を読む スポンサード リンク
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