Miacids are thought to have evolved into the modern carnivorous mammals of the order Carnivora. They were small carnivores, superficially marten-like or civet-like with long, little bodies and long tails. Some species were arboreal, while others lived on the ground.
They probably fed on invertebrates, lizards, birds, and smaller mammals like shrews and opossums. Their teeth and skulls show that the miacids were less developed than modern carnivorans. They had carnivoran-type carnassials, but lacked fully ossified auditory bullae (rounded protrusions).
Miacidae as traditionally conceived is not a monophyletic group; it is a paraphyletic array of stem taxa. Traditionally, Miacidae and Viverravidae had been classified in a superfamily, Miacoidea. Today, Carnivora and Miacoidea are grouped together in the crown-clade Carnivoramorpha, and the Miacoidea are regarded as basal carnivoramorphs. Some species of the genus Miacis are closely related to the order Carnivora, but only the species Miacis cognitus is a true carnivoran, as it is classified in the Caniformia.
The divergence of carnivorans from miacids is now inferred to have occurred in the middle-Eocene (ca. 42 million years ago). Traditionally, the Viverravidae (viverravids) had been thought to be the earliest carnivorans, with fossil records first appearing in the Paleocene of North America about 60 million years ago, but recent cranial morphology evidence now places them outside the order Carnivora. Later authorities disagreed, and propose that the viverravids arose in North America 65-60 million years ago, spread to Asia then later to Europe, and were the first carnivorans and possessed the first true pair of carnassial teeth.:p8
It has been proposed that miacids arose in North America and Europe 50-60 million years ago then later spread to Asia. Like the earlier viverravids, they possessed a true pair of carnassial teeth and therefore are related to order Carnivora. They also possessed a full set of cheek teeth, were weasel to small fox sized, and lived in forests. All modern carnivorans arose from them.:p9
Angelarctocyon is an extinct genus of Amphicyonidae (bear dog), which belongs to the order Carnivora.
It was originally interpreted as a miacid and named Miacis australis, however recent research has suggested it is an early amphicyonid . Analysis of skeletal morphology suggests it is most closely related to another taxon previously attributed to Miacidae, Miacis cognitus, and the well known New World amphicyonid, Daphoenus.Chailicyon
Chailicyon is an extinct genus in the basal Carnivoramorph family Miacidae that lived in Asia during the Middle to Late Eocene.Eosictis
Eosictis is an extinct genus of Miacidae. It was first named by Scott in 1945, and contains one species, Eosictis avinoffi.Ictognathus
Ictognathus is an extinct genus of Miacidae.Messelogale
Messelogale is an extinct genus of Miacidae. Its fossils have been found in Europe. There is one assigned species: M. kessleri.Miacoidea
Miacoidea is a paraphyletic superfamily that had been traditionally divided into two families of carnivores: Miacidae (the miacids) and Viverravidae. Miacoids were primitive carnivores that lived during the Paleocene and Eocene Epochs, about 66-33 million years ago. Today, Miacidae is recognized as a paraphyletic array of stem taxa that probably resulted in some "miacid" genera ending up just outside the order Carnivora, the crown-group within the Carnivoramorpha. Carnivoramorpha consists of both Miacoidea and Carnivora, but excludes the order Creodonta that existed alongside Carnivoramorpha. Miacoids are regarded as basal carnivoramorphs. The miacids are a paraphyletic group containing all miacoids that are not viverravids.
The transition from miacids to Carnivora was a gradual trend during the Paleocene to late Eocene, with taxa from both North America and Eurasia involved. The miacids did not appear until the very end of the Paleocene and are characterized by their shorter skull, and loss of contact between the calcaneum and fibula in the ankle.
Miacoids were mostly small carnivores superficially reminiscent of martens or civets. They probably fed on invertebrates, lizards, birds and smaller mammals like shrews and opossums, while others may have been insectivores. Some species were arboreal, others lived on the ground. Their teeth and skull show that the miacoids were less developed than modern carnivores.Miocyon
Miocyon is an extinct genus of Miacidae, primitive carnivores which lived during the Paleocene and Eocene Epoch.Oodectes
Oodectes is an extinct genus of Miacidae.Palaearctonyx
Palaearctonyx is an extinct genus of omnivorous Miacidae which inhabited North America during the Eocene living from 50.3—46.2 Ma and existed for approximately 4.1 million years.Paramiacis
Paramiacis is an extinct genus of Miacidae. Christian Mathis has defined to make a difference between the miacids from Europe and the American genus Miacis. There are two species of it, P. exilis (Henri Filhol, 1876) and P. teilhardi (Mathis, 1987) - which were long believed to be only sexual dimorphism.Procynodictis
Procynodictis is an extinct genus of Miacidae. It was first named by Jacob Lawson Wortman and William Diller Matthew in 1899, and contains two species: P. progressus and P. vulpiceps. It was identified as an ancestor of Hesperocyon.Prodaphaenus
Prodaphaenus is an extinct genus of Miacidae. The genus has at least one known species: Prodaphaenus scotti.Quercygale
Quercygale is an extinct genus of Miacidae, primitive carnivores that lived during the Eocene. The genus contains four species: Q. angustidens, Q. hastingsae, Q. helvetica, and Q. smithi. Phylogenetic analysis of the basicranial morphology of miacid carnivoramorphans suggests Quercygale is the most advanced miacid and sister to crown group Carnivora, predating the split between Feliformia and Caniformia., although another recent study places them as a stem group within Feliformia.Tapocyon
Tapocyon is an extinct genus of Miacidae, a family of primitive carnivores. Tapocyon was first discovered in Ventura County, when part of a jaw was found in the 1930s. A representative fossil of Tapocyon robustus was found in Oceanside, California. The animal was about the size of a coyote and is believed to have been a good climber that spent a lot of time in trees.Uintacyon
Uintacyon is an extinct genus of Miacidae. There are at least two species in the genus; Uintacyon rudis and Uintacyon gingerichi, the latter being recently discovered.Vassacyon
Vassacyon is an extinct genus of Miacidae. It contains two species; Vassacyon promicrodon and Vassacyon bowni. It is considered the largest of the early Eocene mammals.Vulpavus
Vulpavus ("fox grandfather") is an extinct genus of Miacidae. It measured 60–90 cm in length and had an estimated weight over 1.19 kg (in V. palustris).Xinyuictis
Xinyuictis is an extinct genus of Miacidae. It contains a species, Xinyuictis tenuis. It was once suggested that the species was the same as Miacis, but it was eventually decided that they were different.Ziphacodon
Ziphacodon is an extinct genus of Miacidae. The species Ziphacodon rugatus was first described by Marsh in 1872. Probably a junior synonym of Viverravus gracilis.