Therizinosaurus

Taxobox
name = "Therizinosaurus"

---

fossil_range = fossil range|72|68Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
familia = Therizinosauridae
genus = "Therizinosaurus"
genus_authority = Maleev, 1954
subdivision_ranks = Species
subdivision = "T. cheloniformis" Maleev, 1954 (type)

"Therizinosaurus" (pronEng|θɛˌrɪzɨnoʊˈsɔrəs '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. Known from very incomplete remains, it is estimated to have grown up to 9.6 meters (32 ft) long and reach 3-6 tonnes (3-7 short tons) in weight.Mortimer, M. (2003), [http://dml.cmnh.org/2003Jul/msg00355.html "And the Largest Theropod Is...."] , discussion group, The Dinosaur Mailing List, viewed July 21, 2003. http://dml.cmnh.org/.] "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").

Discovery and species

The first fossil remains of "Therizinosaurus" were discovered in the late 1940s by a joint Soviet-Mongolian fossil expedition, in the Nemegt Formation of southwestern Mongolia. The expedition unearthed several giant claws that measured up to a meter in length. These were described by Russian paleontologist Evgeny Maleev in 1954, who thought they belonged to a large, turtle-like reptile.Maleev, E.A. (1954). "New turtle−like reptile in Mongolia [in Russian] ." "Priroda", 1954(3): 106–108.] However, it was not known what creature these belonged to until the early 1950s, when further expeditions unearthed more fossils: several more sets of claws and parts of the fore and hind limbs. Subsequent finds in northern China allowed paleontologists to assemble the general skeletal structure of the animal, which was determined to be a dinosaur and not a turtle.

The discovery of the enigmatic "segnosaurs", including "Alxasaurus" in 1993 and "Beipiaosaurus" in 1996, helped clarify the relationships of "Therizinosaurus". Various theories had been proposed to explain the ancestry of the segnosaurids, with some scientists even suggesting they were descendents of the sauropodomorphs - but these new, well-preserved finds, which provided details about the bird-like pelvis, feet and skulls, 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.

Characteristics

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, with a bipedal gait and a heavy, deep body (as evidenced by the wide pelvis of other therizinosaurids). Its forelimbs may have reached a length of 2.5 meter (8 ft) long.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.] Its hind limbs ended in four weight-bearing toes, unlike other theropod groups, in which the first toe was reduced to a dewclaw.

The most distinctive feature of "Therizinosaurus" was the presence of three gigantic claws on each digit of its front limbs. These were especially large in "Therizinosaurus", and while the largest claw specimens are incomplete, they probably reached just under 1 meter (3.28 feet) in length.Barsbold, R. (1983). "Carnivorous dinosaurs from the Cretaceous of Mongolia [in Russian] ." "Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ èkspediciâ", 19: 1–120.] 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.]

Paleobiology

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.Svarney, T.E. and Svarney, P.B. (2003). "The Handy Dinosaur Answer Book", 1st ed. Canton, MI: Visible Ink Press.] There are other possible functions that could have been served by the claws of "Therizinosaurus", such as defense against predators (e.g. the contemporary "Tarbosaurus") and in intraspecific fighting, such as fighting for territory or for mating. The claws may even have served all these functions.

References