therizinosaur
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Therizinosaurs (once called segnosaurs) were large herbivorous theropod
dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
whose fossils have been found across the
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to
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
deposits in
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and
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. Various features of the forelimbs, skull and pelvis unite these finds as both theropods and
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, Oviraptoros ...
ns, close relatives to
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s. The name of the representative genus, ''
Therizinosaurus ''Therizinosaurus'' (; meaning 'scythe lizard') is a genus of very large therizinosaurid that lived in Asia during the Late Cretaceous period in what is now the Nemegt Formation around 70 million years ago. It contains a single species, ''Therizi ...
'', is derived from the Greek (, 'to reap' or 'scythe')Translated paper
and (, 'lizard'). The older representative, ''Segnosaurus'', is derived from the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
('slow') and the Greek .


History of research

Therizinosaurs were long considered an enigmatic group, whose mosaic of features resembling those of various different dinosaur groups, and scarcity of their fossils, led to controversy over their evolutionary relationships for decades after their initial discovery. The first genus, ''
Therizinosaurus ''Therizinosaurus'' (; meaning 'scythe lizard') is a genus of very large therizinosaurid that lived in Asia during the Late Cretaceous period in what is now the Nemegt Formation around 70 million years ago. It contains a single species, ''Therizi ...
'', was originally identified as a turtle when described from forelimb elements in 1954. Perle noted in 1979 that the ''Segnosaurus'' fossils were possibly representative of a new family of dinosaurs, which he tentatively classified as theropods (traditionally thought of as the "meat-eating" dinosaurs). He named the family Segnosauridae, with ''
Segnosaurus ''Segnosaurus'' is a genus of therizinosaurid dinosaur that lived in what is now southeastern Mongolia during the Late Cretaceous, about 102–86 million years ago. Multiple incomplete but well-preserved specimens were discovered in the Go ...
'' as type genus and sole member. He distinguished Segnosauridae from the theropod families Deinocheiridae and Therizinosauridae (then only known from the genera ''
Deinocheirus ''Deinocheirus'' ( ) is a genus of large ornithomimosaur that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the Ne ...
'' and ''Therizinosaurus'', both mainly represented by large forelimbs found in Mongolia) by features of their humeri and hand claws. Later in 1979, Barsbold and Perle found the pelvic features of segnosaurids and dromaeosaurids so different from those of "true" theropods that they should be separated into three taxa of the same rank, possibly at the level of infraorder within Saurischia (one of the two main divisions of dinosaurs, the other being
Ornithischia Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
). In 1980, Barsbold and Perle named the new theropod infraorder Segnosauria, containing only Segnosauridae. In the same article, they named the new genus ''
Erlikosaurus ''Erlikosaurus'' (meaning "Erlik's lizard") is a genus of therizinosaurid that lived in Asia during the Late Cretaceous period. The fossils, a skull and some post-cranial fragments, were found in the Bayan Shireh Formation of Mongolia in 1972, da ...
'' (known from a well-preserved skull and partial skeleton) which they tentatively considered a segnosaurid, and reported a partial pelvis of an undetermined segnosaurian, both from the same formation as ''Segnosaurus''. Combined, the specimens provided relatively complete data on this group; they were united by their opisthopubic pelvis, slender mandible, and the toothless front of their jaws. Barsbold and Perle stated that though some of their features resembled those of ornithischians and sauropods, these similarities were superficial, and were distinct when examined in detail. While they were essentially different from other theropods (perhaps due to diverging from them relatively early), and therefore warranted a new infraorder, they did show similarities with them. Since the ''Erlikosaurus'' specimen lacked a pelvis, the authors were unsure if that of the undetermined segnosaurian could belong to it, in which case they would consider it part of a separate family. Though ''Erlikosaurus'' was difficult to compare directly to ''Segnosaurus'' due to the incompleteness of their remains, Perle stated in 1981 that there was no justification for separating it into another family. In 1982, Perle reported hindlimb fragments similar to those of ''Segnosaurus'', and assigned them to ''Therizinosaurus'', whose forelimbs had been found in almost the same location. He concluded that Therizinosauridae, Deinocheiridae, and Segnosauridae, which all had enlarged forelimbs, represented the same taxonomic group. ''Segnosaurus'' and ''Therizinosaurus'' were particularly similar, leading Perle to suggest they belonged in a family to the exclusion of Deinocheiridae (today, ''Deinocheirus'' is recognized as an ornithomimosaur).Translated paper
/ref> Barsbold retained ''Segnosaurus'' and ''Erlikosaurus'' in the family Segnosauridae in 1983, and named the new genus '' Enigmosaurus'' based on the previously undetermined segnosaurian pelvis, which he placed in its own family, Enigmosauridae, within Segnosauria. Though the structure of the pelvis of ''Erlikosaurus'' was unknown, Barsbold considered it unlikely the ''Enigmosaurus'' pelvis belonged to it, since ''Erlikosaurus'' and ''Segnosaurus'' were so similar in other respects, while the pelvis of ''Enigmosaurus'' was very different from that of ''Segnosaurus''. Barsbold found that segnosaurids were so peculiar compared to more typical theropods that they were either a very significant deviation in theropod evolution, or that they went "beyond the borders" of this group, but opted to retain them within Theropoda.Translated paper
/ref> In the same year, Barsbold stated that the segnosaurian pelvis deviated strongly from the theropod norm, and found the configuration of their ilia generally similar to those of sauropods. Paleontologist Gregory S. Paul concluded in 1984 that segnosaurs did not possess any theropodan features, but were instead derived, late-surviving
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
prosauropods with adaptations similar to those of ornithischians. He found segnosaurs similar to prosauropods in the morphology of their snout, mandible, and hindfoot, and to ornithischians in their cheek, palate, pubis, and ankle, and similar to early dinosaurs in other respects. He proposed that ornithischians were descended from prosauropods, and that the segnosaurs were an intermediate relict of this transition, which supposedly took place during the
Triassic period The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
. In this way, he considered segnosaurians to be to herbivorous dinosaurs what
monotremes Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brains, ...
are to mammals. He did not rule out that segnosaurs could be derived from theropods, or that segnosaurs, prosauropods and ornithischians were each independently derived from early dinosaurs, but found these options unlikely. He considered the common descent of these groups as support for the idea that dinosaurs were a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
(natural) group, which was contested by some paleontologists at the time (who instead thought different dinosaurs groups evolved independently from thecodonts). Paleontologist
David B. Norman David Bruce Norman (born 20 June 1952 in the United Kingdom) is a British paleontologist, currently the main curator of vertebrate paleontology at the Sedgwick Museum, Cambridge University. From 1991 to 2011, Norman has also been the Sedgwick Mus ...
considered Paul's idea a contentious claim "bound to provoke much argument" in 1985. In 1988, Paul maintained that segnosaurs were late surviving ornithischian-like prosauropods, and proposed a segnosaurian identity for ''Therizinosaurus''. He also placed segnosauria within
Phytodinosauria Phytodinosauria is a group of dinosaurs proposed in 1986, combining the Sauropodomorpha and Ornithischia as sister groups, conceptualized as a superorder of herbivorous dinosaurs excluding the carnivorous Theropoda. This hypothesis has been refu ...
, a
superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
that paleontologist Robert Bakker had created in 1985 to retain all plant-eating dinosaurs. In a 1986 study of the interrelationships of saurischian dinosaurs, paleontologist
Jacques Gauthier Jacques Armand Gauthier (born June 7, 1948 in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology. Life and career Gauthier is the so ...
concluded that segnosaurs were prosauropods. While he conceded they had similarities with ornithischians and theropods, he proposed these featured had evolved independently. In a 1989 conference abstract about sauropodomorph interrelationships, paleontologist
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
also considered segnosaurs as prosauropods, based on skull features. In a 1990 review article, Barsbold and paleontologist Teresa Maryańska found Segnosauria to be a rare and aberrant group of saurischians, in an unresolved position among sauropodomorphs and theropods, probably closer to the former. They therefore listed them as Saurischia ''sedis mutabilis'' ("position subject to change"). Though they agreed the hindlimbs assigned to ''Therizinosaurus'' in 1982 were segnosaurian, they did not consider this justification for ''Therizinosaurus'' itself being a segnosaur, since it was only known from forelimbs. In 1993, paleontologists Dale A. Russell and Dong Zhi-Ming described the new genus ''
Alxasaurus ''Alxasaurus'' (; meaning " Alxa lizard") is a genus of therizinosauroid theropod dinosaurs from the Early Cretaceous (Albian age) Bayin-Gobi Formation of Inner Mongolia. History of discovery The fossil remains were first discovered in 1988 and ...
'' from China, at the time the most complete large theropod from its time and place. While it was similar to prosauropods in some respects, the detailed morphology of its limbs linked it to ''Therizinosaurus'' and segnosaurs. Since it preserved both fore and hindlimbs, ''Alxasaurus'' showed that Perle's assignment of segnosaurian hindlimbs to ''Therizinosaurus'' was probably correct. Russell and Dong therefore proposed that Segnosauridae was a
junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of Therizinosauridae (since the latter name was older), with ''Alxasaurus'' being the most completely known representative so far, providing a better understanding of the group. They also named the new higher taxonomic rank Therizinosauroidea to contain ''Alxasaurus'' and Therizinosauridae (since the new genus was somewhat different from its relatives), which they placed in the group Tetanurae within Theropoda. They considered therizinosaurs most closely related to ornithomimids, troodontids, and oviraptorids, which they placed together in the group
Oviraptorosauria Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or wit ...
(since they found
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, Oviraptoros ...
, the conventional grouping of these, invalid, and the higher level taxonomy of theropods was in flux at the time). The synonymy of Segnosauridae with Therizinosauridae was accepted by Perle himself and co-authors of a redescription of the holotype skull of ''Erlikosaurus'' in 1994, and they considered therizinosaurs maniraptoran theropods, the group that also includes modern birds (since they did find Maniraptora to be valid through their analysis). They also discussed the previous ornithischian and sauropod hypotheses for therizinosaur affinities in detail and demonstrated various faults with them. Palaeontologist Lev Alexandrovich Nessov rejected that therizinosaurs were theropods in 1995, and instead considered them a distinct group within saurischia.Nessov, L. A., 1995, Dinosaurs of northern Eurasia: New data about assemblages, ecology and paleobiogeography. Saint Petersburg In 1996, paleontologist
Thomas R. Holtz Jr. Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorp ...
found therizinosaurs to group with oviraptorosaurs in a phylogenetic analysis of coelurosauria. In 1999, paleontologist Xing Xu and colleagues described a small, basal therizinosauroid from China, ''
Beipiaosaurus ''Beipiaosaurus'' is a genus of therizinosauroid theropod dinosaurs that lived in Asia during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the discovery of ''Yutyrannus ...
'', which confirmed that the group belonged among the coelurosaurian theropods, and that similarities with prosauropods had evolved independently. They published the first ever cladogram showing the evolutionary relationships of Therizinosauria, and demonstrated that ''Beipiaosaurus'' had features of more basal theropods, coelurosaurs, and therizinosaurs. Sereno found Therizinosaurs to be basal Ornithomimosaurian theropods during the year 1999. By the early 21st century, many more therizinosaur taxa had been discovered, including outside Asia (the first being ''Nothronychus'' from North America), as well as various basal taxa that helped understanding of the early evolution of the group (such as ''Falcarius'', also from North America). Therizinosaurs were not considered as rare or aberrant anymore, but more diverse than previously thought (including in size), and their classification as maniraptoran theropods was generally accepted. The placement of Therizinosauria within Maniraptora continued to be unclear; in 2007, paleontologist Alan H. Turner and colleagues found them to group with oviraptorosaurs, while Zanno and colleagues found them to be the most basal clade within Maniraptora in 2009, bracketed by
Ornithomimosauria Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...
and
Alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
. Despite the additional fossil material, the interrelations within the group were also still uncertain by 2010, when Zanno conducted the most detailed phylogenetic analysis of the Therizinosauria until that point. She cited the inaccessibility, damage, potential loss of holotype specimens, scarcity of cranial remains, and fragmentary specimens with few overlapping elements as the most significant obstacles to resolving the evolutionary relationships within the group.


Uncertain species

In 1979 Dong Zhiming named a new species of the
megalosaurid Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relative ...
'' Chilantaisaurus'', ''C. zheziangensis'', based on specimen ZhM V.001. This specimen was recovered in 1972 from the
Tangshang Formation The Tangshang Formation is a Late Cretaceous Mesozoic geologic Formation (geology), formation in China. Dinosaur and pterosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation. The formation ...
and consists of a partial tibia and partial right pes (foot) largely lacking metatarsals. Dong referred it to the genus mainly based on similarities between the unguals of this specimen and those of ''C. tashuikouensis''.Translated paper
/ref> Barsbold and Maryanska in 1990 considered ''C. zheziangensis'' as a tentative segnosaur (later known as therizinosaurs) based on its relatively short and robust pedal phalanges and enlarged, strongly curved unguals, mostly similar to ''Segnosaurus''. As this taxon may lie outside the genus ''Chilantaisaurus'', they listed this species as ''"Chilantaisaurus" zheziangensis''. Although Glut (1997) stated this specimen may have been based on part of the holotype of Nanshiungosaurus brevispinus (based on a pers. comm from Dong to Molnar in 1984), Dong in 1979 described both taxa from largely different formations and localities. Zanno in 2010 argued that the notorious side to side compression of the unguals reflect therizinosaur affinities, although examinations to the preserved tibia are required for further conclusions. In 2012 Mai-Ping Qian and colleagues placed ''"C". zheziangensis'' in the family Therizinosauridae based on its pes morphology, which is consistent to other therizinosaurids. They also illustrated most of the preserved pes. Hartman with team in 2019 added ''"C". zheziangensis'' to a phylogenetic analysis and recovered it within Therizinosauroidea in a polytomy with ''Alxasaurus'', ''Enigmosaurus'' and therizinosaurids. In 1997 Dong Zhiming and You Hailu named and described a supposed second species of ''
Nanshiungosaurus ''Nanshiungosaurus'' (meaning "Nanxiong's lizard") is a genus of therizinosaurid that lived in what is now Asia during the Late Cretaceous of South China. The type species, ''Nanshiungosaurus brevispinus'', was first discovered in 1974 and descri ...
'', ''N. bohlini'', based on specimen IVPP V 11116 found in 1992 at
Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145  Ma to 100.5 Ma. Geology Pro ...
strata from the Zhonggou Formation,
Xinminbao Group The Xīnmínbǎo Group () is a group of geological formations in north central China. They occur across a large depression (geology), depression between the Altai mountains of Mongolia to the north and the Qilian Shan, Qilian mountains of the Qing ...
. It consists of 11 cervical and 5 dorsal vertebrae with some ribs. In order to contain both ''N. brevispinus'' and ''N. bohlini'' they coined the Nanshiungosauridae family. Dong and Yu presented no clear evidence regarding the assignment of this new species to ''Nanshiungosaurus''. Li and colleagues in their 2007 description of ''
Suzhousaurus ''Suzhousaurus'' (meaning "Suzhou lizard") is a genus of large therizinosauroid dinosaur from the Early Cretaceous of China. The genus is known from two specimens discovered on the Xiagou Formation and Zhonggou Formation—which are situated in ...
'' pointed out that ''N. bohlini'' might be synonymous with the former, as both are found in the same geological group and also incompletely known. As per terms of taxonomic priority, the species name would be ''Suzhousaurus bohlini''. However, they noted that a direct comparison between specimens is difficult to near impossible because there is no overlapping material (besides dorsal vertebrae) and the holotype of ''N. bohlini'' is apparently lost. Li and team disagree in that this species belong to ''Nanshiungosaurus'' and listed it as ''"Nanshiungosaurus" bohlini''. Zanno in 2010 indicated that the anatomical traits that were originally used to characterize ''"N." bohlini'' are now known to be present in other therizinosaur taxa. Hartman with colleagues in 2019 recovered ''"N." bohlini'' as a therizinosaurid in a clade joined by ''Segnosaurus'' and ''Nothronychus''. Around 2005 partial therizinosaur material was collected from the
Laijia Formation The Liangtoutang Formation, also referred to as the Laijia Formation is a geological formation located in Zhejiang, China. Its strata date back to the Albian to Cenomanian stages of the Cretaceous period. In 1998
Zhao Xijin Zhao Xijin (赵喜进; born c. 1935 died July 21, 2012) was a Chinese paleontologist notable for having named numerous dinosaurs. He was a professor at Beijing's Institute of Vertebrate Paleontology and Paleoanthropology. Biography Zhao Xijin was ...
and Xu Xing briefly discovered a partial lower jaw with teeth (IVPP V11579) from the Early Jurassic-aged Lufeng Formation in
Yunnan Yunnan , () is a landlocked Provinces of China, province in Southwest China, the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is ...
, and concluded that this specimen represented the oldest known record of a coelurosaurian theropod. Based mainly on teeth morphology, they indicated therizinosaur affinities. The specimen was latter described in depth in 2001 and used as the holotype specimen for the new genus and species ''
Eshanosaurus deguchiianus ''Eshanosaurus'' is a genus of a dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be a therizinosaurian, and if so the earliest known coelurosaur. Discovery and naming The t ...
'', named by Xing and colleagues. The team reinforced therizinosaur relationships, arguing that the teeth morphology of ''Eshanosaurus'' can be differentiated from sauropodomorphs. In the same 2001 however, James I. Kirkland and
Douglas G. Wolfe Douglas may refer to: People * Douglas (given name) * Douglas (surname) Animals *Douglas (parrot), macaw that starred as the parrot ''Rosalinda'' in Pippi Longstocking *Douglas the camel, a camel in the Confederate Army in the American Civil W ...
noted that the holotype of ''Eshanosaurus'' preserves traits only seen in sauropodomorphs.
Paul M. Barrett {{Short pages monitor