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A saber-toothed cat (alternatively spelled sabre-toothed cat)〔See for example "sabre-toothed cat" Encyclopædia Britannica. 2009. (Encyclopædia Britannica Online. 26 Oct. 2009 ).〕 is any member of various extinct groups of predatory mammals that were characterized by long, curved saber-shaped canine teeth. The large maxillary canine teeth extended from the mouth even when it was closed. The saber-toothed cats were found worldwide from the Eocene epoch to the end of the Pleistocene epoch (42 mya – 11,000 years ago), existing for about . Despite the "cat" in their name, these animals are not closely related to modern cats. These saber-toothed animals belong to three different biological orders: members of the order Carnivora, including Machairodontinae from the Felidae (cat family) as well as families Barbourofelidae and Nimravidae from the "cat-like" suborder Feliformia; taxa of the order Creodonta, specifically from genus ''Machaeroides''; and two families from the extinct order Sparassodonta, which are more closely related to marsupials than to the placental mammals of the other orders mentioned. The Nimravidae are the oldest, entering the landscape around 42 mya and becoming extinct by 7.2 mya. Barbourofelidae entered around 16.9 mya and were extinct by 9 mya. These two would have shared some habitats. ==Morphology== These subfamilies evolved their saber-toothed characteristics entirely independently. They are most known for having maxillary canines which were, in some species, up to 50 cm (19.7 inches) long and extended down from the mouth even when the mouth was closed. Saber-toothed cats were generally more robust than today's cats and were quite bear-like in build. They were believed to be excellent hunters and hunted animals such as sloths, mammoths, and other large prey. Evidence from the numbers found at La Brea Tar Pits suggests that ''Smilodon'', like modern lions, was a social carnivore. The first late saber-tooth instance is a group of animals ancestral to mammals but not yet mammals. Known as synapsids or mammal-like reptiles, they were one of the first groups of animals to experience specialization of teeth and many had long canines. Some had two pairs of upper canines with two jutting down from each side, but most had one pair of upper extreme canines. Because of their primitiveness, they are extremely easy to tell from machairodonts. With no cononoid process, many sharp "premolars" more like pegs than scissors and a very long, lizard-like head are among several characteristics that mark them out. The second appearance of long canines is ''Thylacosmilus'', which is the most distinctive of the saber-tooth mammals and is also easy to tell apart. It differs from machairodonts in a possessing a very prominent flange and a tooth that is triangular in cross section. The root of the canines is more prominent than in machairodonts and a true sagittal crest is absent. The third instance of saber teeth is from order Creodonta. The small and slender ''Machaeroides'' bore canines that were thinner than in the average machairodont. Its muzzle was longer and narrower. The fourth saber-tooth appearance is the ancient family of carnivores, the nimravids, and they are notoriously hard to tell apart from machairodonts. Both groups have short skulls, tall sagittal crests, and their general skull shape is very similar. Some have distinctive flanges, and some have none at all, so this confuses the matter further. Machairodonts were almost always bigger, though, and their canines were longer and more stout for the most part, but exceptions do appear. The fifth appearance is the barbourofelids. These carnivores are very closely related to actual cats, and as such, they are hard to tell apart. The best known barbourofelid is ''Barbourofelis'', which differs from most machairodonts by a much heavier and more stout mandible, smaller orbits, massive and almost knobby flanges, and canines that are farther back. The average machairodont had well-developed incisors, but barbourofelids were more extreme. The sixth and last of the saber-tooth group to evolve were the machairodonts themselves. Image:Gorgonops.jpg|1st saber-tooth instance: Synapsida, the gorgonopsid ''Gorgonops'' skull Image:Thylacosmilus Atrox.jpg|2nd saber-tooth instance: Thylacosmilidae (Sparassodonta) - ''Thylacosmilus atrox'' skull Image: Machaeroides eothen.JPG|3rd saber-tooth instance: Creodonta, family undetermined - ''Machaeroides'' skull Image: Hoplophoneus primaevus 01.jpg| 4th saber-tooth instance: Nimravidae (Carnivora) - ''Hoplophoneus primaevus'' skull and upper cervical vertebrae Image:Barbourofelis loveorum.jpg|5th saber-tooth instance: Barbourofelidae (Carnivora) - ''Barbourofelis'' skeleton Image:Smilodon head.jpg|6th saber-tooth instance: Felidae (Carnivora) - ''Smilodon'' skull and upper cervical vertebrae 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「Saber-toothed cat」の詳細全文を読む スポンサード リンク
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