Therizinosauria

Therizinosaurs (or segnosaurs) were theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China, western North America and possibly Australia.[2] Various features of the forelimbs, skull and pelvis unite these finds as both theropods and as maniraptorans, close relatives to birds.

The name therizinosaur is derived from the Greek θερίζω[3] therízein, meaning 'to reap' or 'to cut off', and σαῦρος[4] saûros meaning 'lizard'. The older name segnosaur is derived from the Latin segnis meaning 'slow' or 'sluggish', and σαῦρος.

Therizinosauria
Temporal range: EarlyLate Cretaceous, 130–66 Ma
Possible Early Jurassic record[1]
Nothronychus (1)
Reconstructed skeleton of Nothronychus graffami
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Aveairfoila
Clade: Therizinosauria
Russell, 1997
Subgroups
Synonyms

Segnosauria Barsbold, 1980
Segnosaurischia Dong, 1987

Description

Beipiao1mmartyniuk
Life restoration of Beipiaosaurus inexpectus.

Therizinosaurs had a very distinctive, often confusing set of characteristics. Their long necks, wide torsos, and hind feet with four toes used in walking resembled those of basal sauropodomorph dinosaurs. Their unique hip bones, which pointed backwards and were partially fused together, initially reminded paleontologists of the "bird-hipped" ornithischians. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of around one meter in Therizinosaurus. The unusual range of motion in therizinosaur forelimbs, which allowed them to reach forward to a degree other theropods could not achieve, also supports the idea that they were mainly herbivorous. Therizinosaurs may have used their long reach and strongly curved claws to grasp and shear leafy branches, in a manner similar to large mammals that lived later on, such as chalicotheres, ground sloths, great apes, and giant pandas.[5]

Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down-like feathers similar to those seen in the compsognathid Sinosauropteryx, as well as longer, simpler, quill-like feathers that may have been used in display.[6][7] Therizinosaurs spanned a large range of sizes, from the small Beipiaosaurus (which measured 2.2 m [7 ft 3 in] in length),[8] to the gigantic Therizinosaurus, which at an approximate 10 m (33 ft) long and an estimated weight of 5 tonnes,[9] was among the largest-known theropods.

History of research

Erlikosaurus
Outdated reconstruction of a quadrupedal and prosauropod-like Erlikosaurus. Therizinosaurs were often depicted this way until more complete specimens were found

Because early finds were incomplete, the strange suite of anatomical features combining features typical of theropods, prosauropods and ornithischians led some scientists, such as Gregory S. Paul, to conclude that segnosaurs (as they were called before Therizinosaurus was recognized as part of the group) represented a late-surviving suborder of primitive dinosaurs, sometimes thought of as intermediates between prosauropods and ornithischians. Because of their suspected relationship with prosauropods, early depictions of segnosaurs (including illustrations by Paul) portrayed them as semi-quadrupedal, a mode of locomotion now known to have been impossible given the bird-like nature of their wrists.[10] It also led Paul to include segnosaurs within paleontologist Robert T. Bakker's Phytodinosauria in 1986, a superorder which was to include ornithischians, prosauropods, and sauropods, typified by their "blunt, spoon-crowned teeth suitable for cropping plants."[10]

It was not until the mid-1990s, after Alxasaurus was discovered and shown to possess more typically theropod features, and Therizinosaurus was recognized as a member of the segnosaur group, that their true identity as herbivorous descendants of the carnivorous theropods became generally accepted.[11] The relation between the more derived therizinosaurids and other theropods was greatly elucidated by the discovery of primitive members of the group, such as Beipiaosaurus in 1999 and Falcarius in 2005.[6] The scientists who described Falcarius noted that it seemed to represent an intermediate stage between carnivorous and herbivorous theropods, a sort of "missing link" between predatory maniraptorans and plant-eating therizinosaurs.[12] Although they are now classified as theropods, therizinosaurs had skulls similar to those of sauropods and the shape of their teeth and jaws make it likely that they were herbivores.

Systematics

Therizinosaur skeletons
Skeletons to scale

Taxonomy

Barsbold and Perle named the group Segnosauria as an infraorder of Theropoda in 1980.[13] Dong Zhiming (1992) went further, placing the segnosaurs in their own order, Segnosaurischia. This name has been abandoned since the discovery that segnosaurs are a specialized group within the suborder Theropoda. Clark et al. in 2004 considered Segnosaurischia a synonym of Therizinosauroidea.

The superfamily Therizinosauroidea had been established by Maleev in 1954, to include only the bizarre, giant-clawed theropod Therizinosaurus. When it was later realized that Therizinosaurus was an advanced segnosaur, Therizinosauroidea was given a phylogenetic definition to include both groups, and has largely replaced the use of the older name Segnosauria in phylogenetic studies, mainly because of the association of the name Segnosauria with the discredited idea that these animals were relatives of prosauropods.

The following taxonomy follows Zanno, 2010 unless otherwise noted.[14]

Phylogeny

Therizinosauria hips variation
Hips from different genera.

The clade Therizinosauria was first defined by Dale Russell in 1997 as Alxasaurus, Enigmosaurus, Erlikosaurus, Nanshiungosaurus, Segnosaurus, Therizinosaurus, and all taxa closer to them than to oviraptorosaurs, ornithomimids, and troodontids. Paul Sereno, in 2005, modified this definition to the most inclusive clade containing Therizinosaurus but not Ornithomimus, Oviraptor, Shuvuuia, Tyrannosaurus, or Troodon.[16]

Therizinosauroidea, previously named as a superfamily with no phylogenetic definition, was first defined by Zhang et al. in 2001, as the clade containing all theropods more closely related to Therizinosaurus than to birds (effectively replacing the older name Segnosauria, which has not yet been defined as a clade). This definition, however, defines the same group as the pre-existing Therizinosauria. An alternate definition was given by Clark in 2004 (as the last common ancestor of Therizinosaurus and Beipiaosaurus and all its descendants), comprising a narrower group that excludes more primitive therizinosaurs, such as Falcarius, and allows the name Therizinosauria to remain in use for the larger group comprising all therizinosaurs. This definition was followed by Teresa Maryańska and Barsbold (2004), Sereno (2005), Zanno et al. (2009) and Zanno (2010),[14][16][17][18] though other subsequent studies, such as Senter (2007, 2012) have continued to use Therizinosauroidea for the therizinosaur "total group".[19]

The following cladogram follows an analysis by Phil Senter, 2007.[19]

Therizinosauroidea

Falcarius

unnamed

Beipiaosaurus

unnamed

Alxasaurus

unnamed

Nanshiungosaurus

Therizinosauridae

Erliansaurus

Nothronychus

unnamed

Neimongosaurus

unnamed

Segnosaurus

unnamed

Erlikosaurus

Therizinosaurus

The cladogram below follows the extensive phylogenetic analysis of Therizinosauria, by Lindsay E. Zanno, 2010.[14]

Therizinosauria

Falcarius

Therizinosauroidea

Beipiaosaurus

unnamed

Alxasaurus

unnamed

Erliansaurus

unnamed

Neimongosaurus

unnamed

Enigmosaurus

unnamed

Suzhousaurus

Therizinosauridae

Nanshiungosaurus

Segnosaurus

Erlikosaurus

Therizinosaurus

Nothronychus

Nothronychus mckinleyi

Nothronychus graffami

The following cladogram is based on the phylogenetic analysis by Phil Senter et al., 2012.[20]

Therizinosauroidea

Falcarius

Beipiaosaurus

Martharaptor

Alxasaurus

Therizinosauridae

Nanshiungosaurus

Suzhousaurus

Nothronychus

Segnosaurus

Neimongosaurus

Erliansaurus

Erlikosaurus

Therizinosaurus

The cladogram below is the most recent cladogram based on the phylogenetic analysis of Therizinosauria conducted by Hanyong Pu et al., 2013.[21]

Therizinosauria

Falcarius

unnamed

Jianchangosaurus

Therizinosauroidea

Beipiaosaurus

unnamed

Alxasaurus

Therizinosauridae

Erliansaurus

Nanshiungosaurus

Neimongosaurus

Segnosaurus

Erlikosaurus

Suzhousaurus

Enigmosaurus

Therizinosaurus

Nothronychus mckinleyi

Nothronychus graffami

Paleobiology

Therizinosauroid behavior is quite poorly understood, but 20th-century studies and subsequent finds have revealed some aspects of their behavior. Nests with sub-spherical eggs have been found, and evidence points to the eggs being buried and abandoned by the parents. And studies of neonates indicate they were well developed and likely precocial—able to leave the nest shortly after birth and suggesting little to no parental care.[22]

CT scans published in 2012 by Stephan Lautenschlager et al. focused on the skull and brain cavity of Erlikosaurus, revealing it to have a large forebrain, and suggesting it had well developed senses of balance, hearing and smell, all of which would have been useful in evading predators, finding food, or in performing complex social behavior.[23]

In 2011, a nesting ground containing 17 clutches of eggs was found in Mongolia's Gobi Desert, with a total of 75 eggs uncovered during excavation. The eggs were 5 inches in diameter and contained no embryos; and there was evidence—in the form of egg shells that had been broken out of—that the young had hatched and left, presumably with their parents. The presence of so many fossilized eggs in one venue implies that therizinosaurs probably were social animals that came together for nesting; and that some genera may have performed parental care. This find, described by Yoshitsugu Kobayashi et al., and mass-death quarries such as those containing Falcarius, augments evidence that therizinosauroids were social, herding animals. Adult therizinosaurs are estimated to have weighed around 500 kg (1,100 lb).[24][25]

References

  1. ^ Xu, X., Zhao, X., & Clark, J. (2001). A New Therizinosaur from the Lower Jurassic Lower Lufeng Formation of Yunnan, China. Journal of Vertebrate Paleontology, 21(3): 477-483.
  2. ^ http://theropoddatabase.com/Therizinosauroidea.htm
  3. ^ θερίζω. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  4. ^ σαύρα. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  5. ^ * Burch, S. (2006). "The range of motion of the glenohumeral joint of the therizinosaur Neimongosaurus yangi (Dinosauria: Theropoda)." Chicago Biological Investigator, 3(2): 20. (Abstract).
  6. ^ a b Xu, X.; Tang, Z-L.; Wang, X-L. (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature. 399 (6734): 350–354. Bibcode:1999Natur.399..350X. doi:10.1038/20670.
  7. ^ Xu X., Zheng X.-t. and You, H.-l. (2009). "A new feather type in a nonavian theropod and the early evolution of feathers." Proceedings of the National Academy of Sciences (Philadelphia), . doi:10.1073/pnas.0810055106 PMID 19139401
  8. ^ Xu, X.; Tang, Z-L.; Wang, X-L. (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature. 399 (6734): 350–354. Bibcode:1999Natur.399..350X. doi:10.1038/20670.
  9. ^ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 160
  10. ^ a b Paul, G.S. (1988). Predatory Dinosaurs of the World, a Complete Illustrated Guide. New York: Simon and Schuster. 464 p.
  11. ^ Russell, D.A.; Dong, Z. (1993). "The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People's Republic of China." In Currie, P.J. (ed.)". Results from the Sino-Canadian Dinosaur Project. Canadian Journal of Earth Sciences. 30 (10): 2107–2127. Bibcode:1993CaJES..30.2107R. doi:10.1139/e93-183.
  12. ^ Kirkland, J.I.; Zanno, L.E.; Sampson, S.D.; Clark, J.M.; DeBlieux, D.D. (2005). "A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah". Nature. 435 (7038): 84–87. Bibcode:2005Natur.435...84K. doi:10.1038/nature03468. PMID 15875020.
  13. ^ Barsbold, R.; Perle, A. (1980). "Segnosauria, a new infraorder of carnivorous dinosaurs". Acta Palaeontologica Polonica. 25 (2): 187–195.
  14. ^ a b c 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.
  15. ^ Paul, G. S. (2016). The Princeton field guide to dinosaurs, second edition. Princeton University Press.
  16. ^ a b Sereno, P. C. 2005. Stem Archosauria—TaxonSearch Archived 2009-01-15 at the Wayback Machine [version 1.0, 2005 November 7]
  17. ^ Clark, J.M., Maryanska, T., and Barsbold, R. (2004). "Therizinosauroidea." Pp. 151– 164 in Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria, Second Edition. University of California Press., 861 pp.
  18. ^ Zanno, L.E., Gillette, D.D., Albright, L.B., and Titus, A.L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution." Proceedings of the Royal Society B, Published online before print July 15, 2009, doi:10.1098/rspb.2009.1029.
  19. ^ a b Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology, 5: 429-463 (doi:10.1017/S1477201907002143).
  20. ^ Senter, P.; Kirkland, J. I.; Deblieux, D. D. (2012). Dodson, Peter (ed.). "Martharaptor greenriverensis, a New Theropod Dinosaur from the Lower Cretaceous of Utah". PLoS ONE. 7 (8): e43911. Bibcode:2012PLoSO...743911S. doi:10.1371/journal.pone.0043911. PMC 3430620. PMID 22952806.
  21. ^ Pu, H.; Kobayashi, Y.; Lü, J.; Xu, L.; Wu, Y.; Chang, H.; Zhang, J.; Jia, S. (2013). Claessens, Leon (ed.). "An Unusual Basal Therizinosaur Dinosaur with an Ornithischian Dental Arrangement from Northeastern China". PLoS ONE. 8 (5): e63423. Bibcode:2013PLoSO...863423P. doi:10.1371/journal.pone.0063423. PMC 3667168. PMID 23734177.
  22. ^ Paul, G.S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 157.
  23. ^ "Inside the head of a dinosaur: Research reveals new information on the evolution of dinosaur senses". ScienceDaily.
  24. ^ "Nests of Big-Clawed Dinosaurs Found in Mongolia". Yahoo News. 5 November 2013.
  25. ^ "Nests of Big-Clawed Dinosaurs Found in Mongolia". LiveScience.com.

External links

Alxasaurus

Alxasaurus (; "Alxa Desert lizard") is a genus of therizinosauroid alxasaurid theropod dinosaur from the Early Cretaceous (Albian) Bayin-Gobi Formation in Inner Mongolia. It is one of the earliest known members of the superfamily Therizinosauroidea, but it already possessed the body shape - including the long neck, short tail, and long hand claws - of later therizinosauroids. Like other members of this group, it was a bipedal herbivore with a large gut to process plant material. Several specimens are known and the largest was a little over 3.8 metres (12 feet) long. According to Gregory S. Paul, it was 4 metres (13 feet) long and its weight was about 400 kilograms (880 pounds).

Beipiaosaurus

Beipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China. Before the discovery of Yutyrannus, it was among the largest dinosaurs known from direct evidence to be feathered.

The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical theropods. Beipiaosaurus, being considered to be a primitive therizinosauroid, has features which suggest that all therizinosauroids, including the more derived Therizinosauridae, to be coelurosaurian theropods, not sauropodomorph or ornithischian relatives as once believed.

Bostobe Formation

The Bostobe Formation (Kazakh: Boztóbe svıtasy) is a geological formation in Kazakhastan whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation. It is about 45 metres thick and consists primarily of clay with interbeds of sand, representing an estuarine environment.

Enigmosaurus

Enigmosaurus (meaning "Riddle Lizard") is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of Mongolia, central Asia. It is a herbivorous bipedal dinosaur.

The holotype, IGM 100/84, was collected in the Bayan Shireh Formation (=Baynshirenskaya) in Khara Khutul, southeastern Mongolia, dating from the Cenomanian and the Turonian stages, around 98-89.8 million years ago. It was first reported in 1979. It consists of a partial skeleton, lacking the skull, which includes a nearly complete pelvis with part of the right ischium missing.The type species, Enigmosaurus mongoliensis, was named in 1983, by Rinchen Barsbold and Altangerel Perle. The generic name was stated to be derived from Greek αἴνιγμα, ainigma, "riddle", after the puzzling and unusual shape of its pelvis (hips); at the time little was known about therizinosauroids. The specific name refers to the provenance from Mongolia.Enigmosaurus reached a length of five to seven metres, and a weight of one tonne. It is a considerably larger dinosaur than the related Erlikosaurus. The obturator process on the front edge of the ischium is horizontally elongated and low.

Enigmosaurus was by the describers assigned to a separate Enigmosauridae but later considered a member of the Segnosauridae which are today called the Therizinosauridae. Lindsay Zanno in 2010 recovered a position more basal in the Therizinosauroidea.

Erliansaurus

Erliansaurus is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of China.

Erlikosaurus

Erlikosaurus is a genus of herbivorous theropod dinosaur from the late Cretaceous Period, belonging to the Therizinosauridae. Its fossils, a skull and some post-cranial fragments, were found in the Bayan Shireh Formation of Mongolia, dating to around 90 million years ago.

Eshanosaurus

Eshanosaurus is a genus of therizinosaurian dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be the earliest known coelurosaur.

Falcarius

Falcarius is a genus of therizinosaurian dinosaur found in the Cretaceous of east-central Utah, United States. Its name is derived from the word "sickle", falcarius in Latin being a sickle cutter, which scientists have used to describe its large clawed hands.

Falcarius was a 4-meter-long (13 ft), bipedal herbivore. It had a small head and a long neck and tail.

The description of Falcarius (2005), following that of therizinosauroid Beipiaosaurus from the Early Cretaceous of China in 1999, clarifies the early evolution of the Therizinosauria and their relationship with the larger group of theropod dinosaurs, because Falcarius is a transitional form between older theropods and the much changed Therizinosauridae.

Jianchangosaurus

Jianchangosaurus is a genus of therizinosaurian dinosaur that lived approximately 126 million years ago during the early part of the Cretaceous Period from the Yixian Formation in what is now China. The nearly complete juvenile specimen was missing only the distal tail. Jianchangosaurus was a small, lightly built, bipedal, ground-dwelling herbivore, that could grow up to an estimated 2 m (6.6 ft) long and was 1 m (3.3 ft) high at the hips.

Lingyuanosaurus

Lingyuanosaurus (meaning "the lizard of Lingyuan") is a genus of therizinosaurian theropod dinosaur from the Early Cretaceous of China. It contains a single species, L. sihedangensis. It was found within a layer of the Jehol Group.

According to Mickey Mortimer, Lingyuanosaurus may have been an oviraptorosaur.

Maniraptora

Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period (see Eshanosaurus), and are regarded as surviving today as living birds.

Maniraptoriformes

Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptors. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of Ornithomimus and birds, and all descendants of that common ancestor."

Nanshiungosaurus

Nanshiungosaurus is a genus of therizinosaurian theropod dinosaur from the Cretaceous of China.

Two species have been named in the genus: the type species Nanshiungosaurus brevispinus and Nanshiungosaurus bohlini.

Neimongosaurus

Neimongosaurus ("Nei Mongol lizard") is a genus of herbivorous therizinosaur theropod dinosaur known from the Upper Cretaceous of Nei Mongol, China.

Neimongosaurus is a therizinosauroid which is known from the holotype LH V0001, a partially preserved skull and skeleton, consisting of a partial braincase, the front of the right lower jaw, a nearly complete axial column, a furcula, the shoulder girdle, both humeri, a left radius, parts of the pelvis and parts of the hindlimbs. The specimen was in 1999 collected in the Sanhangobi in Inner Mongolia from the Iren Dabasu Formation dating from the Santonian stage about 85 million years ago. A second specimen, LH V0008, consisting of a sacrum with ilia, was assigned as the paratype.The type species, Neimongosaurus yangi, was formally named and described by Zhang Xiaohong, Xu Xing, Paul Sereno, Kwang Xuewen and Tan Lin in 2001. The generic name is derived from Nei Mongol, the Chinese name for Inner Mongolia. The specific name honours Yang Zhongjian.Neimongosaurus was bipedal. The teeth in its deep lower jaw, coarsely serrated, indicate an herbivorous diet. It had elongated cervical vertebrae. Its scapula had a tapering end. Neimongosaurus is thought to have been about 2.3 meters in length.

The original describers of the genus assigned Neimongosaurus to the Therizinosauroidea, in a basal position. Subsequent cladistic analyses have indicated a position in the more derived Therizinosauridae, but an analysis in 2010 by Lindsay Zanno confirmed the original placement.

Nothronychus

Nothronychus is a genus of theropod dinosaur classified in the group Therizinosauria, from the Cretaceous of North America.

The type species of this dinosaur, Nothronychus mckinleyi, was described by James Kirkland and Douglas G. Wolfe in 2001. It was recovered near New Mexico's border with Arizona, in an area known as the Zuni Basin, from rocks assigned to the Moreno Hill Formation, dating to the late Cretaceous period (mid-Turonian stage), around 91 million years ago. A second specimen, described in 2009 as a second species, Nothronychus graffami, was found in the Tropic Shale of Utah, dating to the early Turonian, between one million and a half million years older than N. mckinleyi.

The name Nothronychus, is derived from Greek, meaning "slothful claw."Nothronychus was a herbivorous theropod with a beak, a bird-like hip (resembling that of the non-related ornithischians) and four-toed feet, with all four toes facing forward.

Segnosaurus

Segnosaurus ('slow lizard') is a genus of herbivorous theropod dinosaur belonging to the Therizinosauridae from the Cretaceous of Mongolia.

Suzhousaurus

Suzhousaurus is a genus of herbivorous therizinosauroid theropod dinosaur from the Early Cretaceous-age Xinminbao Group of the Yujingzi Basin, Gansu, China.

Therizinosauridae

Therizinosauridae ("reaper lizards") is a family of theropod dinosaurs whose fossil remains have been dated to the Mid-to-Late Cretaceous period (100 to 70 mya). Even though representative fossils have only been found throughout China, Mongolia, and the United States, the range of Therizinosauridae was believed to have spanned much of the supercontinent of Laurasia at its height.Therizinosauridae was named after the large, claw-bearing ungual found on the manus of members in the group. This feature has led to little insight about the ecology of the family, and the purpose of the claw remains unknown. Other notable aspects of the physiology of these animals include a modified pelvis, robust hind-limbs, and a highly derived, nearly avian inner-ear. Moreover, the larger superfamily of Therizinosauroidea is believed to be the earliest group in which simple feathers have been documented.Research into therizinosaurids has also focused on uncovering more about the unique ecology and paleobiology of the family. A fair portion of modern research has concentrated on the feeding-patterns of these dinosaurs, as they are considered to be the best regarded candidate for the emergence of herbivory within Theropoda. While many closely related taxa are carnivorous, it is thought that the members of Therizinosauroidea, including Therizinosauridae, diverged and adopted either an herbivorous or omnivorous lifestyle.The current scientific consensus is that therizinosaurids evolved from small, bird-like maniraptorans, and thus they fall within the coelurosaurian clade called Maniraptora. Most studies have concluded that within Maniraptora, Therizinosaurians were the first of five major groups to diverge.

Therizinosaurus

Therizinosaurus (; 'scythe lizard', from Ancient Greek θερίζω, meaning 'to reap', and σαῦρος, meaning 'lizard') is a genus of very large theropod dinosaurs. Therizinosaurus comprises the single species T. cheloniformis, which lived in the late Cretaceous Period (early Maastrichtian stage, around 70 million years ago), and was one of the last and largest representatives of its unique group, the Therizinosauria. Fossils of this species were first discovered in Mongolia and 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.

Therizinosauria
Basal therizinosaurs
Therizinosauroidea

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