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''Temnodontosaurus'' (Greek for “cutting-tooth lizard” - temno, meaning “to cut”, odont meaning “tooth” and sauros meaning “lizard”) is an extinct genus of Ichthyosaurs from the Early Jurassic, ranging between 198 and 185 million years ago (Hettangian - Toarcian), and known from Europe (England, France, Germany and Belgium). They lived in the deeper areas of the open ocean.〔Motani R.(2000). “Rulers of the Jurassic seas”. Scientific American. 283 (6): 52-59〕 University of Bristol paleontologist Jeremy Martin described the genus ''Temnodontosaurus'' as “one of the most ecologically disparate genera of Ichthyosaurs”.〔J.E. Martin et al.(2010). ''A longirostrine Temnodontosaurus (Ichthyosauria) with comments on Early Jurassic ichthyosaur niche partitioning and disparity.'' Palaeontology 55 (5), 995–1005〕 ''Temnodontosaurus'' are known for being gigantic Ichthyosaurs. According to the paleontologist Michael Maisch, species of ''Temnodontosaurus'' were large, exceeding 12 meters (40 ft) in length.〔Maisch MW, Matzke AT. (2000). The Ichthyosauria. ''Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie)'' 298: 1-159〕 There is a possibility that they reached a similar size to another Ichthyosaur genus, ''Shonisaurus'' who are known as the largest Ichthyosaurs.〔McGowan C. (1996). "Giant ichthyosaurs of the Early Jurassic". Canadian Journal of Earth Sciences 33(7): 1011-1021〕 There seems to be a general consensus between paleontologists that they could at least have reached 9m.〔McGowan, C. (1995). "Temnodontosaurus risor is a Juvenile of ''T. platyodon'' (Reptilia: Ichthyosauria)". Journal of Vertebrate Paleontology. 14 (4): 472–479〕 ''Temnodontosaurus'' are known for their incredibly large eyes. Their eyes are thought to be the largest of any animal ever known.〔Sander,P.M.(2000). "Ichthyosauria: their diversity, distribution, and phylogeny", Paläontologische Zeitschrift 74: 1–35〕 ''Temnodontosaurus'' eyes were approximately 20 cm (8 in) in diameter making them some of the largest of any known vertebrate. They have a tail bend which is characteristic of Jurassic age Ichthyosaurs.〔McGowan, C. (1992). Dinosaurs, Spitfires and Sea Dragons. Harvard University Press〕 and they have many conical teeth that fill their jaw and are set in a continuous groove.〔 ''Temnodontosaurus'' species are sometimes mistaken for dolphin relatives due to their similar overall morphology. However, the morphological traits are convergent. ''Temnodontosaurus'' were not mammals but were large marine reptiles and their ancestors were land dwelling reptiles.〔 ''Temnodontosaurus'' do have morphological traits which differ from Cetacea also. ''Temnodontosaurus tail would beat laterally side to side, instead of up and down.〔 ''Temnodontosaurus'' skull's also have nostrils that are placed in front of the eyes instead of on the dorsal side of the head like Cetaceans.〔 Though reptiles, ''Temnodontosaurus'' can also be mistaken for fish due to their fins and elongate undifferentiated body, but unlike fish ''Temnodontosaurus'' are air breathers and must go to the water’s surface for air.〔 Also ''Temnodontosaurus'', like other Ichthyosaurs, are viviparous.〔 The number or names of ''Temnodontosaurus'' species have varied since their discovery. Christopher McGowan in 1992 said that there were around thirteen species in the genus ''Temnodontosaurus''.〔 Michael Maisch in 2000 listed ''T. platyodon, T. trigonodon, T. acutirostris, T. nuertingensis'' and ''T. eurychephalus'' as the valid species of ''Temnodontosaurus''.〔Maisch MW and Matzke AT. (2000). ''The Ichthyosauria''. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159〕 ==Description and Paleobiology== ''Temnodontosaurus'' have a Thunniform body form.〔 Their bodies are described as long, robust and slender.〔 The tail is either as long as the body or longer.〔 The vertebral count is roughly less than 90 according to Christopher McGowan.〔 For stabilization purposes while swimming, the axis and atlas of the vertebrae are fused together.〔Emily A. Buchholtz (2000). ''Swimming styles in Jurassic Ichthyosaurs''. Journal of Vertebrate Paleontology, 21, 63-71〕 ''T. trigonodon'' shows unicipital ribs near the sacral region while they have bicipital ribs more anteriorly. This helps increase flexibility with swimming.〔 ''Temnodontosaurus'' do not have gastralia.〔 ''Temnodontosaursus'' forefins and hindfins are roughly the same length and are rather narrow and elongate.〔〔 The fins have strong hyperphalangy.〔 This is unlike other post Triassic Ichthyosaurs like Thunnosauria which has forefins are at least twice the length of the hindfins〔〔 The pelvic girdle too with ''Temnodontosaurus'' is not reduced unlike post-Triassic Icthyosaurs.〔 ''Temnodontosaurus'' species reduced their digits to 3 primary digits compared to ''Ichthyosaurus'' which had 6 to 7 digits.〔 They also have one postaxial accessory digit.〔 The proximal elements of the fin make a mosaic pattern while the more distal elements are relatively rounder.〔 There are two notches on the fin’s anterior margin.〔〔 The paired fins were used to steer and stabilize them while swimming instead of paddling or propulsion devices.〔 Their pelvic girdle is tripartite.〔 They have a triangular shaped dorsal fin. ''Temnodontosaurus'' have the largest eyes of the Ichthyosaurs and any animal measured.〔Motani R.(2005). ''Evolution of fish-shaped reptiles (Reptilia : Ichthyopterygia) in their physical environments and constraints.'' Annual Review of Earth and Planetary Sciences. 33: 395-420〕 The largest eyes measured were from the species ''T. platyodon''.〔 Despite the impressive size of their eyes, ''Temnodontosaurus'' had blind spots directly above their head due to the angle at which their eyes were pointed. ''Temnodontosaurus'' had shletotic rings.〔 According to Ryosuke Motani, the schlerotic rings of T. platyodon are at least 25 cm in diameter.〔 It is assumed that ''Temnodontosaurus'' had high visual capacity.〔 McGowan hypothesized that Icthyosuars have a scherotic ring to give the eye rigidity.〔 According to McGowan Ichthyosaurs, and so ''Temnodontosaurus'', used vision as their main sense and it would have been unlikely that they could do echolocation to sense out prey.〔 The ''Temnodontosaurus'' had a robust long snout with an antorbital constriction.〔 They also had an elongated maxilla,〔 a long cheek region〔 and a long post orbital segment.〔 The carotid foramina in the basisphenoid in the skull is paired and is separated by the parasphenoid.〔 Also, the parasphenoid has a processus cultriformis〔 The largest ''T. platyodon'' skulls can range from 1m to 1.5m long.〔McGowan, C. (1995). "Temnodontosaurus risor is a Juvenile of T. platyodon (Reptilia: Ichthyosauria)". Journal of Vertebrate Paleontology. 14 (4): 472–479〕 Species such as ''T. eurycephalus'' however had a shorter rostrum and a deeper skull.〔 This build of skull seems to have been made for crushing prey.〔 ''T. platyodon'' had a very long snout which is slightly curved on its dorsal side.〔 The species ''T. trigadon’s'' snout is also very long but can be ventrally curved.〔 ''T. acutirostris’'' snout is slender with a more pointed tip.〔 ''Temnodontosaurus'' had many, pointed conical shaped teeth that are set in a continuous grooves which called aulacodont mode of plantation of teeth. This is instead of having teeth in individual sockets.〔〔 The teeth have two or three carinae.〔 The species ''T. nuertingensis'' however did not have carinae.〔 ''T. eurycephalus’'' teeth have bulbous roots.〔 ''Temnodontosaurus'' did have a tail bend and it is described by the paleontologist Michael Maisch as being not very strong and less than 35°.〔 The tail is described as being semi-lunate〔 or lunate.〔 The tail is made up of two lobes. The lower lobe is skeletally supported and the upper lobe is unsupported.〔 The tail is used as a propulsive force for movement while the fins are not involved with propulsion of the body.〔 Feeding Mechanisms and Diet ''Temnodontosaurus'' were the top predators in the Early Jurassic seas.〔 Their diet was mainly vertebrate prey and it seems they were the only Jurassic Ichthyosaurs to have such a diet.〔 They were ram-feeding predators.〔Scheyer, Torsten M. et al. (2014). ''Early Triassic Marine Biotic Recovery: The Predators’ Perspective.'' PLoS ONE 9.3 (2014): e88987〕 They had rapid jaw movements and probably used snapping rather than chewing mechanisms to eat prey.〔 The diet of ''Temnodontosaurus'' is not completely known but probably included squid like molluscs, fishes and marine reptiles.〔 They probably fed on Plesiosaurs and other Ichthyosaurs too.〔 A ''T. trigonodon'' fossil (from the Staatliches Museum für Naturkunde in Stuttgart) shows remains of a Stenopterygian, an Ichthyosaur, in its abdominal cavity.〔Thies, D. & Hauff, R.B. (2013). ''A Speiballen from the Lower Jurassic Posidonia Shale of South Germany”. – N. Jb. Geol. Paläont. Abh., 267: 117–124; Stuttgart〕 According to McGowan ''T. eurycephalus'' had more robust teeth and a deeper jaw and therefore probably ate the larger prey such as other Ichthyosaurs, while species such as ''T. platyodon'' had pointed but modest sized teeth and therefore ate more soft-bodied prey and fish.〔 They were powerful swimmers with great stamina and could descend into the deepest areas in the Jurassic sea to catch their prey. Swimming and Movement Style Like other Ichthyosaurs, ''Temnodontosaurus'' species were fast cruisers or swimmers.〔 Jurassic Ichthyosaurs, like ''Temnodontosaurus'' species, swim with lateral oscillation of their caudal fluke on a flexible tail stock.〔 The body form for swimming of ''T. trigonodon'' were described by Emily Buchholtz. ''T. trigonodon'' species had highly flexible, long, thin bodies with a high vertebral count and modest regional differentiation.〔 They used their large limbs as rudders.〔 The style of swimming was thunniform, (unlike the earlier Ichthyosaurs which did anguilliform styled swimming instead).〔 This is shown in ''Temnodontosaurus'' and other forms in the Jurassic and after because of their semi-lunate tail fin and shortened body relative to the tail.〔 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「Temnodontosaurus」の詳細全文を読む スポンサード リンク
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