Felidae Oligocene, about 25 million years ago, with the appearance of "Proailurus" and "Pseudaelurus". The latter species complex was ancestral to two main lines of felids, the cats in the extant subfamilies and a third major group of extinct cats, which are assigned to the subfamily Machairodontinae. The machairodonts included the saber-toothed cats such as the "Smilodon". The "false sabre toothed cats", the Barbourofelidae and Nimravidae, are not true cats, but are closely related and together with Felidae and other cat-like carnivores (hyaenas, viverrids and mongooses) make up the feliform carnivores. Results of mitochondrial analysis indicates that all the Felidae descended
International scientific vocabulary root before another root or prefix that starts with a vowel, e.g. gastroenteritis; but elision happens in gastrectomy (not gastroectomy). The Greek word τέρας (τέρατο-) = "monster" is usually used to mean "monster (abnormal)" (e.g. teratology, teratogen), but some biological names use it to mean "monster (enormous)" (e.g. the extinct animals "Teratornis" (a condor with a 12-foot wingspan) and "Terataspis" (a trilobite 2 feet long)). International scientific vocabulary International scientific vocabulary (ISV) comprises scientific and specialized words whose language of origin may or may not be certain, but which are in current use in several modern languages (that is, translingually).