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The Nimravidae, sometimes known as false saber-toothed cats, are an extinct family of mammalian carnivores that was endemic to North America, Europe, and Asia. Not considered to belong to the true cats (family Felidae), the Nimravidae are generally considered closely related and classified as part of suborder Feliformia. Fossils have been dated from the Middle Eocene through the Late Miocene epochs (Bartonian through Tortonian stages, 40.4—7.2 mya), spanning about .〔(PaleoBiology Database: ''Nimravidae'', basic info )〕 Previously classified as a subfamily of Nimravidae, in 2004, the barbourofelids were reassigned to their own distinct family Barbourofelidae. ==Morphology and evolution== Most nimravids had muscular, low-slung, cat-like bodies, with shorter legs and tails than are typical of cats. Unlike extant Feliformia, the Nimravidae had a different bone structure in the small bones of the ear. The middle ear of true cats is housed in an external structure called an auditory bulla, which is separated by a septum into two chambers. Nimravid remains show ossified bullae with no septum, or no trace at all of the entire bulla. It is assumed that they had a cartilaginous housing of the ear mechanism. Although some nimravids physically resembled the sabre-toothed cats of the genus ''Smilodon'', they were not closely related, but evolved a similar form through parallel evolution. They possessed synapomorphies with the barbourofelids in the cranium, mandible, dentition, and postcranium. They also had a flange on the front of the mandible, not as prominent as those on ''Thylacosmilus'', that projected downward as long as the canine tooth. The ancestors of nimravids and felids diverged from a common ancestor soon after the Caniformia-Feliformia split, in the middle Eocene about 50 million years ago (mya), with a minimum constraint of 43 mya. Recognizable nimravid fossils date from the late Eocene (37 mya), from the Chadronian White River Formation at Flagstaff Rim, Wyoming, to the late Miocene (5 mya). Nimravid diversity appears to have peaked about 28 mya. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nimravidae」の詳細全文を読む スポンサード リンク
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