Miacis
Miacis is an extinct genus of placental mammals from clade Carnivoraformes, that lived in North America from the early to middle Eocene.
Description
Miacis was five-clawed, similar in size to a stoat, 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
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. 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 | Bridger Formation | now assigned to genus Harpalodon as Harpalodon sylvestris |
| M. vulpinus | Uinta Basin | Described as Amphicyon vulpinum; later assigned to Prodaphaenus and Miacis; now recognised as synonym of Miocyon scotti |
| M. uintensis | Uinta Basin | now assigned to genus Prodaphaenus as Prodaphaenus uintensis |
| M. hargeri | Bridger Formation | recognised as close relative to genus Lycarion |
| M. washakius | Bridger Formation | now assigned to genus Neovulpavus as Neovulpavus washakius |
| M. medius | Bridger Formation | now assigned to genus Lycarion as Lycarion medius |
| M. exiguus | Clark's Fork Basin | recognised as close relative to genus Dormaalocyon |
| M. latidens | Clark's Fork Basin | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. invictus | Irdin Manha Formation | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. hookwayi | Tapo Canyon | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. gracilis | Uinta Basin | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. latouri | Dormaal | now assigned to genus Dormaalocyon as Dormaalocyon latouri |
| M. lushiensis | Shanghuang Quarry | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. deutschi | Clark's Fork Basin | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. petilus | Clark's Fork Basin | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. winkleri | Clark's Fork Basin | now assigned to genus Gracilocyon as type species Gracilocyon winkleri |
| M. australis | Rifle Range Hollow or Blue Cliff Horizon | now assigned to genus Angelarctocyon as Angelarctocyon australis in family Amphicyonidae |
| M. cognitus | Reeves Bonebed | now assigned to genus Gustafsonia as Gustafsonia cognita in family Amphicyonidae |
| M. thailandicus | Krabi | now assigned to genus Xinyuictis as Xinyuictis thailandicus |
| M. boqinghensis | Huoshipo, Guojiazhuang Village, Hedi Formation | classified as a species of carnivoraform mammals outside of genus Miacis |
| M. rosei | Wyoming, USA | now assigned to genus Gracilocyon as Gracilocyon rosei |
| M. rundlei | Abbey Wood, England, UK | now assigned to genus Gracilocyon as Gracilocyon rundlei |
| M. solei | Dormaal | now assigned to genus Gracilocyon as Gracilocyon solei |