Miacis ("small point") is an extinct genus of placental mammals from clade Carnivoraformes, that lived in North America from the early to middle Eocene.J. J. Flynn (1998.) "Early Cenozoic Carnivora ("Miacoidea")." In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.) "Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals." Cambridge University Press, Cambridge.
Description Miacis was five-clawed, similar in size to a stoat (~30 cm, tail not included), weighed between 1 and 7 kg, and likely had highly reversible hind feet that assisted in its arboreal lifestyle, similar to those of a squirrel. It retained some primitive characteristics such as a low skull, a long slender body, a long tail, and short legs. Miacis retained 44 teeth, although some reductions in this number were apparently in progress and some of the teeth were reduced in size.
The hind limbs were longer than the forelimbs, the pelvis was dog-like in form and structure, and some specialized traits were present in the vertebrae. It had retractable claws, agile joints for climbing, and binocular vision. Miacis and related forms had brains that were relatively larger than those of the creodonts, and the larger brain size as compared with body size probably reflects an increase in intelligence.
Like many other early carnivoramorphans, it was well suited for an arboreal climbing lifestyle with needle-sharp claws, limbs, and joints resembling modern carnivorans. Miacis was probably a very agile forest dweller that preyed upon smaller animals, such as small mammals, reptiles, and birds, and might also have eaten eggs and fruits.
Classification and phylogeny Classification Genus: †Miacis Species: Distribution of the species and type locality: Age:†M. parvivorus E. D. Cope (1872.) "Third account of new Vertebrata from the Bridger Eocene of Wyoming Territory." Proceedings of the American Philosophical Society 12:469-472 Colorado, Utah,M. R. Thorpe (1923) "New species of Uinta Carnivora from White River, Utah." American Journal of Science 5(27):218-224Anthony R. Friscia and D. Tab Rassmussen (2010) "Middle Eocene Carnivoramorpha of the Uinta Basin, Utah". Annals of Carnegie Museum, vol. 79 (1), pp. 51-63 and Wyoming (Black's Fork of Green River, Bridger Formation)K. D. Rose, A. E. Chew, R. H. Dunn, M. J. Kraus, H. C. Fricke and S. P. Zack (2012) "Earliest Eocene mammalian fauna from the Paleocene-Eocene Thermal Maximum at Sand Creek Divide, southern Bighorn Basin, Wyoming." University of Michigan Papers on Paleontology 36:1-12250,0 to 46,2 Ma
History of taxonomy
Since Edward Drinker Cope first described the genus Miacis in 1872, at least twenty other species have been assigned to Miacis. However, these species share few synapomorphies other than plesiomorphic characteristics of miacids in general. This reflects the fact that Miacis has been treated as a wastebasket taxon and contains a diverse collection of species that belong to the stemgroup within the Carnivoraformes. Many of the species originally assigned to Miacis have since been assigned to other genera and, apart from the type species, Miacis parvivorus, the remaining species are often referred to with Miacis in quotations (e.g. "Miacis" latidens). The following table lists the former Miacis species in chronological order of their original description and notes the reassignments to other genera.
Species: Type locality: Status and notes:M. sylvestris O. C. Marsh (1872.) "Preliminary description of new Tertiary mammals. Part II." American Journal of Science 4(21):202-224Bridger Formation (Wyoming, USA)now assigned to genus Harpalodon as Harpalodon sylvestrisM. vulpinus W. B. Scott and H. F. Osborn (1887.) "Preliminary Report on the Vertebrate Fossils of the Uinta Formation, Collected by the Princeton Expedition of 1886." Proceedings of the American Philosophical Society 24(126):255-264Uinta Basin (Utah, USA)Described as Amphicyon vulpinum; later assigned to Prodaphaenus and Miacis; now recognised as synonym of Miocyon scottiM. uintensis H. F. Osborn (1895) "Fossil mammals of the Uinta Basin. Expedition of 1894." Bulletin of the American Museum of Natural History 7(2):71-105Uinta Basin (Utah, USA)now assigned to genus Prodaphaenus as Prodaphaenus uintensisM. hargeri J. L. Wortman (1901.) "Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum." The American Journal of Science, series 4 12:193-206Bridger Formation (Wyoming, USA)recognised as close relative to genus LycarionM. washakius Bridger Formation (Wyoming, USA)now assigned to genus Neovulpavus as Neovulpavus washakiusM. medius W. D. Matthew (1909) "The Carnivora and Insectivora of the Bridger Basin, middle Eocene." Memoirs of the American Museum of Natural History 9:289-567Bridger Formation (Wyoming, USA)now assigned to genus Lycarion as Lycarion mediusM. exiguus W. D. Matthew and W. Granger (1915.) "A revision of the Lower Eocene Wasatch and Wind River faunas." Bulletin of the American Museum of Natural History 34(1):1-103Clark's Fork Basin (Wyoming, USA)recognised as close relative to genus DormaalocyonM. latidens Clark's Fork Basin (Wyoming, USA)classified as a species of carnivoraform mammals outside of genus MiacisM. invictus Matthew W. D. & Granger W. (1925.) "New mammals from the Irdin Manha Eocene of Mongolia." American Museum Novitates 198:1–10.Irdin Manha Formation (Inner Mongolia, China)classified as a species of carnivoraform mammals outside of genus MiacisM. hookwayi C. Stock (1934) "New creodonta from the Sespe upper Eocene, California." Proceedings of the National Academy of Sciences 20(7):423-427Tapo Canyon (California, USA)classified as a species of carnivoraform mammals outside of genus MiacisM. gracilis Clark, John (1939.) "Miacis gracilis, a new carnivore from the Uinta Eocene." Annals of The Carnegie Museum 27, 349-370Uinta Basin (Utah, USA)classified as a species of carnivoraform mammals outside of genus MiacisM. latouri G. E. Quinet (1966) "Les mammifères du Landénien continental belge, second tome. Etude de la morphologie dentaire comparée des carnivores de Dormaal." Mémoires de l'Institut Royal des Sciences Naturelles Belges, 158:1-64.Dormaal (Flemish Brabant, Belgium)now assigned to genus Dormaalocyon as Dormaalocyon latouriM. lushiensis Shanghuang Quarry (Jiangsu, China)classified as a species of carnivoraform mammals outside of genus MiacisM. deutschi P. D. Gingerich (1983) "Systematics of Early Eocene Miacidae (Mammalia, Carnivora) in the Clark's Fork Basin, Wyoming." Contributions from the Museum of Paleontology, University of Michigan 26(10):197-225Clark's Fork Basin (Wyoming, USA)classified as a species of carnivoraform mammals outside of genus MiacisM. petilus Clark's Fork Basin (Wyoming, USA)classified as a species of carnivoraform mammals outside of genus MiacisM. winkleri Clark's Fork Basin (Wyoming, USA)now assigned to genus Gracilocyon as type species Gracilocyon winkleriM. australis E. P. Gustafson (1986.) "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66Rifle Range Hollow or Blue Cliff Horizon (Texas, USA)now assigned to genus Angelarctocyon as Angelarctocyon australis in family AmphicyonidaeM. cognitus Reeves Bonebed (Texas, USA)now assigned to genus Gustafsonia as Gustafsonia cognita in family AmphicyonidaeM. thailandicus Ducrocq S., Buffetaut E., Buffetaut-Tong H., Helmcke-Ingavat R., Jaeger J.-J., Jongkanchanasoontorn Y. and Suteethorn V. (1992) "A lower Tertiary vertebrate fauna from Krabi (South Thailand)." Neues Jahrbuch fuer Geologie und Palaeontologie Abhandlungen 184(1): 101–122.Krabi (South Thailand)now assigned to genus Xinyuictis as Xinyuictis thailandicusM. boqinghensis X.-S. Huang, Y.-S. Tong and J.-W. Wang (1999.) "A new Miacis (Mammalia Carnivora, Miacidae) from the Middle Eocene of Yuanqu Basin, Shanxi Province." Vertebrata PalAsiatica 37(4):291-299Huoshipo, Guojiazhuang Village, Hedi Formation (China)classified as a species of carnivoraform mammals outside of genus MiacisM. rosei Wyoming, USAnow assigned to genus Gracilocyon as Gracilocyon roseiM. rundlei Abbey Wood, England, UKnow assigned to genus Gracilocyon as Gracilocyon rundleiM. solei Dormaal (Flemish Brabant, Belgium)now assigned to genus Gracilocyon as Gracilocyon solei
Phylogeny The phylogenetic relationships of genus Miacis are shown in the following cladogram:
See also
Mammal classification Carnivoraformes Miacidae
References