Therizinosaurus
| Therizinosaurus Temporal range: Late Cretaceous, 70 Ma |
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| Fossil forelimbs, Experimentarium, Denmark | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Family: | †Therizinosauridae |
| Genus: | †Therizinosaurus Maleev, 1954 |
| Species: | †T. cheloniformis |
| Binomial name | |
| Therizinosaurus cheloniformis Maleev, 1954 |
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Therizinosaurus (
/θɛˌrɪzɨnɵˈsɔrəs/; 'scythe lizard', from the Greek therizo meaning 'to reap' or 'to cut off' and sauros meaning 'lizard') is a genus of very large theropod dinosaur. Therizinosaurus lived in the late Cretaceous Period (late Campanian-early Maastrichtian stages, around 70 million years ago), and was one of the last and largest representatives of its unique group, the Therizinosauria. Its fossils were first discovered in Mongolia and they were originally thought to belong to a turtle-like reptile (hence the species name, T. cheloniformis — "turtle-formed"). It is known only from a few bones, including gigantic hand claws, from which it gets its name.
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[edit] Description
Though the fossil remains of Therizinosaurus are incomplete, inferences can be made about its physical characteristics based on related therizinosaurids. Like other members of its family, Therizinosaurus probably had a small skull atop a long neck, and had a bipedal gait and a heavy, deep, broad body (as evidenced by the wide pelvis of other therizinosaurids). Its forelimbs may have reached a length of 2.5 metres (8 feet)[1] or even 3.5 metres for the largest known specimen.[2] Its hindlimbs ended in four weight-bearing toes, unlike other theropod groups, in which the first toe was reduced to a dewclaw. Gregory S. Paul in 2010 estimated the length of Therizinosaurus at ten metres, the weight at five tonnes.[2] It is the largest therizinosaur known and the largest known member of the Maniraptora.[2]
The most distinctive feature of Therizinosaurus was the presence of three gigantic claws on each digit of its frontlimbs. These were common among therizinosaurs but especially large in Therizinosaurus, and while the largest claw specimens are incomplete, they probably reached just under 1 metre (3.28 ft) in length. The claws are the longest known from any animal.[3] The claws were relatively straight, only gradually tapering into a point, and extremely narrow, transversely flattened.[4][5][6]
The feeding habits of Therizinosaurus are unknown, since no skull material has ever been found that could indicate its diet. However, like other therizinosaurs, it was probably primarily herbivorous.[7]
[edit] History
The first fossil remains of Therizinosaurus were discovered in 1948 by a joint Soviet-Mongolian fossil expedition, in the Nemegt Formation of southwestern Mongolia.[4] The expedition unearthed several giant claws that measured, including presumed horn sheaths, up to a meter in length. These were named and described by Russian paleontologist Evgeny Maleev in 1954, who thought they belonged to a large diving turtle-like reptile, 4.5 metres long, that used the claws to harvest seaweed. The holotype specimen, PIN no. 551-483, consisted of the claws.[3] However, it was not understood what general kind of creature these belonged to until 1970, when Anatoly Konstantinovich Rozhdestvensky determined it to be a theropod dinosaur and not a turtle.[5] Nevertheless, what precise kind of dinosaur it was remained a controversial issue. Some reconstructed it with a head and body like a carnosaur and a killing claw on the foot like a deinonychosaur.
Further expeditions unearthed more fossils. The first were specimens IGM 100/15-17: several more sets of claws and parts of the forelimbs, described by Rinchen Barsbold in 1976.[1] Another find was specimen IGM 100/45, consisting of hindlimbs, described by Altangerel Perle in 1982.[8] Subsequently, finds in northern China of related species allowed paleontologists to assemble the general skeletal structure of the animal. The discovery that these enigmatic segnosaurs (including Erlikosaurus and Segnosaurus) were actually theropods helped clarify the relationships of Therizinosaurus. Various theories had been proposed to explain the ancestry of the "segnosaurids," with some scientists suggesting they were descendants of the sauropodomorphs or even that they were neither saurischians nor ornithischians - but new, well-preserved finds such as Alxasaurus in 1993 and Beipiaosaurus in 1996 provided details about the bird-like pelvis, feet and skulls of primitive members, and helped confirm that segnosaurids belonged to the same group of theropod dinosaurs as Therizinosaurus (and were therefore re-named therizinosaurids), and that therizinosaurs were, more specifically, advanced, herbivorous maniraptoran theropods.
[edit] Phylogeny
Therizinosaurus was in 1954 by Maleev assigned to the Therizinosauridae, seen by him as an unique Central-Asian family of sea-turtles, the largest known.[3] Later the Therizinosauridae were identified with the Segnosauridae, the former name having priority. Relationships within the Therizinosauridae are difficult to determine, other therizinosaurids apart from Segnosaurus and Erlikosaurus being the earlier Nanshiungosaurus and Nothronychus.[9]
[edit] See also
[edit] References
- ^ a b Barsbold, R. (1976c). "New data on Therizinosaurus (Therizinosauridae, Theropoda) [in Russian]." In Devâtkin, E.V. and N.M. Ânovskaâ (eds.), Paleontologiâ i biostratigrafiâ Mongolii. Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ kspediciâ, 3: 76–92.
- ^ a b c Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 160
- ^ a b c Maleev, E.A. (1954). "New turtle−like reptile in Mongolia [in Russian]." Priroda, 1954(3): 106–108.
- ^ a b Barsbold, R. (1983). "Carnivorous dinosaurs from the Cretaceous of Mongolia [in Russian]." Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ èkspediciâ, 19: 1–120.
- ^ a b Rozhdestvensky, A.K. (1970). "On the gigantic claws of mysterious Mesozoic reptiles." Paleontologischeskii Zhurnal, 1970(1): 131-141.
- ^ Rozhdestvensky, A.K. (1970). "Giant claws of Enigmatic Mesozoic Reptiles." Paleontology Journal, 4(1): 117-125.
- ^ Svarney, T.E. and Svarney, P.B. (2003). "The Handy Dinosaur Answer Book", 1st ed. Canton, MI: Visible Ink Press.
- ^ Perle, A., 1982, "On a new finding of the hindlimb of Therizinosaurus sp. from the Late Cretaceous of Mongolia", Problems on the Geology of Mongolia, 5: 94–98
- ^ Lindsay E. Zanno (2010). "A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora)". Journal of Systematic Palaeontology 8 (4): 503–543. doi:10.1080/14772019.2010.488045. http://www.tandfonline.com/doi/abs/10.1080/14772019.2010.488045.
