With the exception of Antarctica, Australia, New Zealand, Madagascar, Japan, and most oceanic islands, native populations of cats are found worldwide, and one species, domestic cats, have been introduced nearly everywhere humans currently exist. Although some authorities recognize only a few genera, most accounts of Felidae recognize 18 genera and 36 species. With the exception of the largest cats, most are adept climbers, and many are skilled swimmers. Most felids are solitary. Often, felids are separated into two distinct subgroups, large cats and small cats. Generally, small cats are those that, due to a hardening of the hyoid bone, have an inability to roar. Felidae consists of 2 subfamilies, Pantherinae (e.g., lions and tigers) and Felinae (e.g., bobcats, pumas, and cheetahs).
Felids are perhaps the most morphologically specialized hunters of all carnivores, often taking prey as large as themselves and occasionally taking prey several times their own size. Unlike other carnivores, felids rely almost exclusively on prey that they have killed themselves. They are agile hunters, hunting mostly at night, with diets consisting of fresh meat or carrion. Felids are found in all terrestrial habitats except treeless tundra and polar ice caps.
The first cat-like mammals appeared around 60 million years ago (MYA) during the Eocene and culminated in the most specialized of the saber-tooths, Barbourofelis fricki. However, the phylogeny of saber-tooths and their ancestors (Nimravidae) is the subject of considerable debate and fossil evidence for these cat-like mammals does not exist after the Miocene. True felids first appeared during the early Oligocene and, although early ancestors of present day felids had short upper canines, felid radiations that occurred during the Miocene and Pliocene, such as Smilodon, appeared to specialize on large herbivores and had large, saber-like upper canines. Early felids were divided into two subfamilies, Machairodontinae (saber-toothed cats) and Felinae (conical-toothed cats). The many genera of saber-toothed cats are divided into three tribes (Metailurini, Homotheriini, and Smilodontini). Living and extinct conical-toothed cats are placed in one subfamily and one tribe, the Felini, but controversy surrounds generic-level classification of felids. Modern cats are closely related to hyenas, mongooses, and civets. These families, including the families Eupleridae and Nandiniidae, are in the suborder Feliformia.