Felids are members of the biological family Felidae, the broader family of cats. The family includes two subfamilies, Pantherinae, also called the "big cats," (lions, tigers, jaguars, leopards), and Felinae (cougars, cheetah, lynxes, the caracal, and the familiar Domestic Cat). Felids evolved during the Oligocene, approximately 25 million years ago. Up until just about 10,000 years ago, there was another subfamily of cats, the Machairodontinae, which included the famous saber-toothed cats, but they were probably driven to extinction by humans.
Today, there are 40 species of felids, all thought to have descended from a common ancestor that lived about 10.8 million years ago. This group evolved in Asia and spread throughout the world via land bridges. At least 10 distinction migrations occurred. Like many taxa of placental mammals, the natural range of felids includes all continents except for Australia and Antarctica. Felids are usually not found in small islands far from the coast unless introduced by humans.
As members of Order Carnivora, felids are meat-eaters, but even more specially adapted for hunting and meat-eating than any other family within the order. Felids require meat to live, as the parts of their intestine capable of processing vegetative matter have long been selected out. Felids mainly subsist on the consumption of other vertebrates, including birds, rodents, and larger animals like gazelles, deer, elk, bighorn sheep, and wildebeest. Three-quarters of cats live in forested terrain, where they climb trees and act as ambush predators. Except for lions and the Domestic Cat, all felids are solitary.
Felids are extremely skilled hunters. Except for the cheetah, they have retractable claws, which lets them walk easily but extend their claws when going in for the kill. They possess large eyes with excellent night vision, provided in part by the tapetum lecidum, a reflective membrane inside the eye that helps direct light onto the retina under low-light conditions. This is what causes the characteristic eyeshine of felids. Because of their eyeshine, felids can be found easily at night by humans shining a flashlight and looking for the characteristic reflective eyes.
The most successful of the felids in terms of numbers is of course the Domestic Cat, which have spread throughout the world as human pets and vermin-killers. Cats are the world's most popular pet, with a population approaching one billion. The relationship between humans and cats goes back at least 9,500 years, maybe more. Through thousands of years of selective breeding, there are now about 73 distinct breeds of cats.