Temporal range: Late Paleocene–Late Eocene 
|Sites where Miacis fossils have been found.|
Miacis is a genus of extinct carnivorous mammals that appeared in the late Paleocene and continued through the Eocene. The genus Miacis is not monophyletic but a diverse collection of species that belong to the stemgroup within the Carnivoramorpha. As such, most Miacis species belong to the group of early carnivores that represent the ancestors of the modern order, the crown-group Carnivora. However, the species Miacis cognitus (now Gustafsonia) is placed not in the stem-group but among the Caniformia, one of the two suborders of the crown-group Carnivora.
Miacis species were five-clawed, about the size of a weasel (~30 cm), and lived on the North American and Eurasian continents. They retained some primitive characteristics such as low skulls, long slender bodies, long tails, 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, and had limbs and joints that resemble those of modern carnivorans. Miacis was probably a very agile forest dweller that preyed upon smaller animals, such as small mammals, reptiles, and birds, and might have also have eaten eggs and fruits.
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 Carnivoramorpha. 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 Miacis species in chronological order of their original description and notes the reassignments to other genera.
|Species||Authority||Type locality||Status and notes|
|M. parvivorus||Cope, 1872||Black's Fork of Green River, Bridger Formation (Wyoming, USA)||Type species. Alteratively Viverravus parvivorus and Vulpavus parvivorus|
|M. sylvestris||Marsh, 1872||Bridger Formation (Wyoming, USA)||Harpalodon sylvestris according to J. L. Wortman 1901|
|M. vulpinus||Scott & Osborn, 1887||Uinta Basin (Utah, USA)||Described as Amphicyon vulpinum; assigned to Miacis by Matthew (1909)|
|M. uintensis||Osborn 1895||Uinta Basin (Utah, USA)||now assigned to Prodaphaenus uintensis Friscia & Rasmussen 2010|
|M. hargeri||Wortman, 1901||Bridger Formation (Wyoming, USA)|
|M. medius||Matthew, 1909||Bridger Formation (Wyoming, USA)|
|M. exiguus||Matthew & Granger, 1915||Clark's Fork Basin (Wyoming, USA)|
|M. invictus||Matthew & Granger, 1925||Irdin Manha Formation (Inner Mongolia, China)|
|M. hookwayi||Stock, 1934||Tapo Canyon (California, USA)|
|M. gracilis||Clark, 1939||Uinta Basin (Utah, USA)||now assigned to Procynodictis vulpiceps|
|M. latouri||Quinet, 1966||Dormaal (Flemish Brabant), Belgium||now assigned to Dormaalocyon latouri|
|M. lushiensis||Chow, 1975||Shanghuang Quarry (Jiangsu, China)|
|M. deutschi||Gingerich, 1983||Clark's Fork Basin (Wyoming, USA)|
|M. winkleri||Clark's Fork Basin, Wyoming||Assigned to new genus as type species Gracilocyon winkleri |
|M. australis||Gustafson, 1986||Rifle Range Hollow or Blue Cliff Horizon (Texas, USA)||now assigned to Angelarctocyon australis|
|M. cognitus||Reeves Bonebed (Texas, USA)||now assigned to Gustafsonia cognita in Caniformia|
|M. boqinghensis||Huang et al., 1986||Huoshipo, Guojiazhuang Village, Hedi Formation (China)|
|M. thailandicus||Ducrocq et al 1992|
|M. rosei||Heinrich et al., 2008||Recombined as Gracilocyon rosei|
|M. rundlei||Hooker, 2010||Abbey Wood, England||now assigned to Gracilocyon rundlei |
|M. solei||Smith & Smith, 2010||Dormaal (Flemish Brabant), Belgium||Gracilocyon solei|
A phylogenetic analysis of "Miacis" species and other carnivoramorphans reveals the paraphyletic nature of the genus Miacis. Some are found in a basal position among the stem carnivoraform groups, others are clustered in the middle near Miacis parvivorous, and one, "M". cognitus, within Caniform family Amphicyonidae. The cladogram is based on a morphological analysis of dental, cranial, and postcranial features.
|Wikimedia Commons has media related to Miacis.|
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