Therizinosauridae (meaning 'scythe lizards')Translated paper
is a family of derived (advanced)

therizinosauroid Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite thes ...

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 fossil remains have been found in mostly

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 ...

boundary. Even though representative fossils have only been found throughout

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, the range of Therizinosauridae is believed to have spanned much of the supercontinent of

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

based on several footprints and isolated remains on Europe and Africa. Therizinosauridae compromises currently eight described and named taxa. Therizinosauridae was named in 1954 by paleontologist

Evgeny Maleev Evgeny Aleksandrovich Maleev (, ; 25 February 1915 – 12 April 1966) was a Soviet and Russian paleontologist who did most of his research on reptiles and Asian fossils, such as the naming of the ankylosaur ''Talarurus'' and theropods ''Tarbo ...

after the large, claw-bearing

unguals An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual ...

of the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

Therizinosaurus cheloniformis ''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 ...

''. Therizinosaurids were generally large and very robustly built

animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

that had a near convergent body plan with the more recent (and also extinct)

ground sloths Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Carib ...

. The largest genera of the group are ''Therizinosaurus'' and ''

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 ...

'', which were about and long, respectively. The physiology of therizinosaurids include a broad and rounded belly supported by a wide and robust pelvis with thick hind-limbs composed of very sout, four-toed feet, a strong arm build with enhanced hand flexibility, elongated hand claws, and a highly derived, nearly avian inner-ear. Traits that are also well-known include an elongated neck, a prominent keratinous beak and a

prosauropod Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

-like dentition that differs from all theropods. In addition, therizinosaurids are estimated to have had more advanced

feathers Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier e ...

in comparison to primitive therizinosaurs (''

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 ...

'' or ''

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 m ...

''). The unique and bizarre features of the group has encouraged research into the

paleobiology Paleobiology (or palaeobiology) is an interdisciplinary field that combines the methods and findings found in both the earth sciences and the life sciences. Paleobiology is not to be confused with geobiology, which focuses more on the interactio ...

and

paleoecology Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...

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 theropod candidates for

herbivory A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. While other theropod groups are fully carnivorous, members of Therizinosauridae diverged and adopted an herbivorous and possibly

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...

lifestyle. This is even more supported by their unusual morphology. As indicated by their feet morphology and several footprints from Asia, Africa and Europe, they probably were

plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. T ...

walkers, but further examination may be required. Therizinosaurids were

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

animals that nested in colonies and laid

egg clutches __NOTOC__ A clutch of eggs is the group of eggs produced by birds, amphibians, or reptiles, often at a single time, particularly those laid in a nest. In birds, destruction of a clutch by predators (or removal by humans, for example the Cali ...

. In fact, therizinosaur

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s are particularly common on

formations, mainly in Asia. The

oofamily Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of t ...

Dendroolithidae ''Dendroolithus'' is an oogenus of Dendroolithidae, Dendroolithid dinosaur egg found in the Cenomanian, late Cenomanian Chichengshan Formation (Tiantai Group), in the Gong-An-Zhai Formation, Gong-An-Zhai and Santonian Majiacun Formations of China ...

is often attributed to therizinosaur-grade dinosaurs. Some of the first dendroolithid eggs were found on the Bayan Shireh and

Nanchao Nanzhao (, also spelled Nanchao, ) was a dynastic kingdom that flourished in what is now southern China and northern Southeast Asia during the 8th and 9th centuries. It was centered on present-day Yunnan in China. History Origins Nanzha ...

formations. Their relationships were confusing and obscure on the early years of research mainly because of the unusual traits among members. Several alternative classifications were proposed (such as the naming of Segnosauridae in 1979) until more complete specimens and other taxa were described during the 1990s, which confirmed them as

theropods Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

. Many of the shared characters within the group also showed that Segnosauridae was a junior synonym of the much earlier family Therizinosauridae. The current phylogenetic consensus is that therizinosaurids evolved from small, bird-like

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, and thus they fall within the

coelurosaurian Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...

clade called

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 ...

. Moreover, most of the traits of therizinosaurids (such as the

ear An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...

structure) were inherited by smaller, agile, carnivorous ancestors. Extensive phylogenetic analyses have concluded that within Maniraptora, therizinosaurs were the first of five major groups to diverge.

History of discovery

The first definitive therizinosaurid discovered was ''

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 ...

''. The fossil remains were discovered in 1918 during Mongolian field expedition on the

Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilian ...

of the

Gobi Desert The Gobi Desert (Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world. Geography The Gobi measures from southwest to northeast an ...

. Several claws were unearthed by the team and later described by the

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

in 1954. The claws were unusually large, approximately long if restored, very straight and flattened. Maleev considered that the claws belonged to a giant marine turtle and named the new genus and species ''Therizinosaurus cheloniformis'', also erecting the Therizinosauridae to include the new species. In the 1970s more findings were made including the naming of more taxa. Additional specimens of ''Therizinosaurus'' were referred by the

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

n paleontologist

Rinchen Barsbold , Rinchyengiin Barsbold, born December 21, 1935 in Ulaanbaatar) is a Mongolian paleontologist and geologist. He works with the Institute of Geology, at Ulaanbaatar, Mongolia. He is an expert in vertebrate paleontology and Mesozoic stratigraphy. Bar ...

in 1976. He described a set of partial arms from the Nemegt Formation and given the similarities within the claws, he referred this specimen to the genus. The Mongolian paleontologist

Altangerel Perle Altangerel Perle (born 1945) is a Mongolian palaeontologist. He is employed at the National University of Mongolia. He has described species such as ''Goyocephale lattimorei'', '' Achillobator giganticus'' and '' Erlikosaurus andrewsi''. He has ...

described and named the new genus ''

'' in 1979, based on lower jaws and much of the hindlimbs. He also coined the newer Segnosauridae (now synonym of Therizinosauridae) to contain this species.Translated paper
/ref> In the same year, paleontologist

Dong Zhiming Dong Zhiming (Chinese: 董枝明, Pinyin: ''Dǒng Zhimíng''; born January 1937) is a Chinese vertebrate paleontologist formerly employed at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing. He began working at the ...

described the genus ''

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 ...

'', but wrongly interpreted the remains to have pertained to some kind of dwarf sauropod.Translated paper
/ref> In the following year, Barsbold and Perle coined the family Segnosauria (now Therizinosauria) to contain the Segnosauridae and kin. Also, they named and briefly described ''

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 ...

'', a new genus smaller than ''Segnosaurus''. Confusingly, Perle redescribed ''Erlikosaurus'' treating the taxon as a new genus and species in 1981.Translated paper
/ref> Also, Perle described another specimen of ''Therizinosaurus'' in 1982, this time a partial hind limb. He referred the hindlimb to the genus based on the similarities with ''Segnosaurus''.Translated paper
/ref> In 2001, the new therizinosaurids ''

Neimongosaurus ''Neimongosaurus'' (meaning "Nei Mongol lizard") is a genus of herbivorous therizinosaur theropod dinosaur that lived in Asia during the Cenomanian stage of the Late Cretaceous period in what is now the Iren Dabasu Formation. Discovery and namin ...

'' and ''

Nothronychus ''Nothronychus'' (meaning "slothful claw") is a genus of therizinosaurid theropod dinosaurs that lived in North America during the Late Cretaceous period. The type species, ''Nothronychus mckinleyi'', was described by James Kirkland and Douglas ...

'' (''N. mckinleyi'') were described and named, and in the following year ''

Erliansaurus ''Erliansaurus'' (meaning "Erlian lizard") is a genus of therizinosaur theropod dinosaur that lived in Asia during the Cenomanian stage of the Late Cretaceous period in what is now Nei Mongol, Iren Dabasu Formation. Discovery and naming The r ...

'' was also described and named. Although a new species of ''Nothronychus'' (''N. graffami'') was named in 2009. With this, both species make ''Nothronychus'' the most complete therizinosaurid known.

Description

Therizinosaurids were quite advanced and robustly-built animals that reached multi-ton dimensions which make them among the largest

ns. The smallest known therizinosaurids are ''Erliansaurus'', ''Erlikosaurus'' and ''Neimongosaurus'' which were around long, furthermore the holotype skull of ''Erlikosaurus'' is about . ''Segnosaurus'' and the possible therizinosaurid ''

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 ...

'' were about the same size, in length and weighing . Slightly smaller members are represented by ''Nanshiungosaurus'' and ''Nothronychus'', estimated at long and in weight, respectively.Genus List for Holtz 2012
/ref> The related ''"Nanshiungosaurus" bohlini'' was similar in size (about long), however, its assignment to ''Nanshiungosaurus'' is unlikely and it may or not represent another species or specimen of the better known ''Suzhousaurus''. ''Therizinosaurus'' were the largest representatives, reaching the top dimensions of the group, they grew up to long weighing over . These dimensions that make the genus among the largest-known theropods. The exponential sizes obtained across the Therizinosauridae appear to have been triggered by the bulk and specialized diet within the group and early members of the Therizinosauria. Skin impressions from ''

'' and ''

'' indicate that primitive therizinosaurs were covered with a coat of down-like, sparse

similar to those seen in the

compsognathid Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other ...

Sinosauropteryx ''Sinosauropteryx'' (meaning "Chinese reptilian wing", ) is a compsognathid dinosaur. Described in 1996, it was the first dinosaur taxon outside of Avialae (birds and their immediate relatives) to be found with evidence of feathers. It was covere ...

'', as well as longer, simpler, quill-like feathers that may have been used in display. However, while the earliest known example of primitive, stage-I feathers are found among early therizinosaurs, more advanced members are thought to have possessed more developed, avian-like feathers. Although typically associated with flight, the feathers which covered these animals were not used for that purpose, instead, they assisted in either

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...

Skull

Therizinosaurids had more specialized

skulls The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

compared to primitive members such as ''

Falcarius ''Falcarius'' (meaning "sickle cutter") is a genus of primitive therizinosaur dinosaur that lived during the Early Cretaceous period in what is now North America. Its remains were first collected in the Cedar Mountain Formation in 1999, with subs ...

'', which had a generalist, beak-less snout. They had relatively elongated snouts and the tip was covered with a

rhamphotheca The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...

(keratinous beak) used during feeding. Although the extension of the beak on the dorsal surface of the snout is unknown, it is estimated that it slightly overlapped the nasal cavity as in some modern-day birds. The

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

(lower jaw) also developed a rhamphotheca, seen on the

edentulous Toothlessness, or edentulism, is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the ...

(without teeth) anterior-most end. This extension was supplied by neurovascular

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

(small pits) found on the lateral surfaces. The known specimens of the therizinosaurids ''Erlikosaurus'', ''Neimongosaurus'' and ''Segnosaurus'' preserve numerous neurovascular foramina (more notorious on ''Erlikosaurus''), indicating that a well-developed beak was present in life. Both

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

and

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

were toothed and some species of therizinosaurids had specialized, recurved dentaries such as ''Segnosaurus'' and possibly ''Neimongosaurus''.

Braincases In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria (skull), ...

are known from three therizinosaurids: ''Erlikosaurus'', ''Neimongosaurus'' and ''N. mckinleyi''. Unfortunately, the braincase of ''Neimongosaurus'' has not been described nor illustrated. The braincases are directed to the bottom, co-ossified with well-developed sideways oriented paroccipital projections, highly pneumatized and had a prominent central

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

. The

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

is another featured trait in therizinosaurids which differs from all theropod groups. At least two different

tooth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

morphologies are observed among therizinosaurids; the first is represented by relatively

homodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example ...

, oval to lanceolate-shaped teeth with moderate coarse denticles (serrations) on the

crowns A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...

(upper exposed part). This type of dentition is better represented by the complete, three-dimensional holotype skull of ''Erlikosaurus'' which features the mentioned characters. Two isolated teeth are known from ''Nothronychus'' and they are lanceolate-shaped, symmetrical, have moderate denticles, and strongly resemble those of ''Erlikosaurus''. Furthermore, they seem to derive from the dentary based on comparisons with the latter. The preserved holotype dentary tip of ''Neimongosaurus'' preserves an erupted tooth that is lanceolate-shaped with small coarse serrations, falling within this type of dentition. Another type of dental morphology is the one seen on the highly specialized ''Segnosaurus''. In this taxon, the teeth are very

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...

, leaf-shaped with relatively less denticles that are prominently developed being bigger than in the previous therizinosaurids. These denticles are composed of numerous folded carinae (cutting edges) with denticulated front edges, creating a roughened and shredding surface near the base of the tooth crowns. Most therizinosaurids appear to have had a low

tooth replacement Tooth loss is a process in which one or more teeth come loose and fall out. Tooth loss is normal for deciduous teeth (baby teeth), when they are replaced by a person's adult teeth. Otherwise, losing teeth is undesirable and is the result of injur ...

rate or not able to loose them at all.

Postcranial skeleton

In therizinosaurids, the

shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...

was robustly specialized than in other maniraptorans and less bird-like. The

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

(shoulder blade) was very straight and flattened at the upper end being fused to the coracoid bone, forming the scapulocoracoid. Near the region of the

scapulocoracoid The scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula. The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions. The scapula is commonly known as the ''shoulde ...

suture, on the coracoid, a large foramen is present. The

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

is a wide and broad element that is slightly convex and thickened near of the scapulocoracoid suture. The

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

(upper arm) was exceptionally robust and flexible with wide lower ends as seen on the humeri of the therizinosaurids ''Nothronychus'' and ''Therizinosaurus''. Not only that but the biceps muscle was prominently well-developed in ''Therizinosaurus''. In ''Segnosaurus'', the deltopectoral crest (

deltoid muscle The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle appears to be made up o ...

attachment) was strongly built. The

antebrachium The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in anat ...

was relatively straight in most members, particularly on ''Therizinosaurus''. The reduced

carpal The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...

block on therizinosaurids enabled an enhanced hand flexion. Manual

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

are relatively standard in shape among maniraptorans with a formula of digits I, II and III. Nothronychus right pes

The manual

(

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

bones) are proportionally larger than the phalanges, strongly flattened from side to side, and recurved with more degrees of specialization than

therizinosauroids Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite thes ...

. Most therizinosaurids had sharply pointed and recurved unguals with very robust

tubercles In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

(

flexor tendons A flexor is a muscle that flexes a joint. In anatomy, flexion (from the Latin verb ''flectere'', to bend) is a joint movement that decreases the angle between the bones that converge at the joint. For example, one’s elbow joint flexes when one ...

attachment). These traits are better seen on ''Nothronychus'' and ''Segnosaurus''. In ''Therizinosaurus'', however, the manual unguals were extremely elongated and straight with poor curves. Although most of them are incomplete, if restored, they would measure about long, which make them the largest hand claws of any known terrestrial animal. The tubercles are not as strongly developed as in other therizinosaurids though, in addition, ''Therizinosaurus'' had some of the longest forelimbs known for any bipedal dinosaurs: the preserved right arm in specimen IGM 100/15 has a total length of . The

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

was highly pneumatized (air-spaced) and is relatively well documented from several badly to well-preserved elements among genera but specimens of ''Nanshiungosaurus'' and ''Nothronychus'' preserve the most complete series of vertebrae. Therizinosaurids had large and robust

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

with relatively short

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

and platycoelous (concave at both ends) to opisthocoelus (concave posterior ends)

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different f ...

that were elongated and had some degree of pneumacity. In

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...

the neural spines are more elongated and stiff. Several pneumatopores (small openings leading to air pockets) are present on the dorsolateral surfaces of the centra and they progressively reduce in size. Some species like ''N. graffami'' had a narrow

hump The mountains and hills of the British Isles are categorised into various lists based on different combinations of elevation, prominence, and other criteria such as isolation. These lists are used for peak bagging, whereby hillwalkers attempt ...

-like structure on their back as indicated by the very elongated neural spines of the first dorsals. In therizinosaurids, the

sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

was composed by about six

sacral vertebrae The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

with broad centra that have rounded facets. The

caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

were stocky with stiff and rounded transverse projections. When compared to early members, therizinosaurids had a reduction in the number of caudals and a minor

chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...

constriction, which indicates a shorter and flexible

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

Therizinosaurids had wide torsos supported by a broad,

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

-like

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. The

ribcage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

was very round and composed by elongated

ribs The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

with fairly robust capitula. The most modified element within the therizinosaurid build was the possession of a unique opisthopubic pelvis (pubis and ischium extending backwards), a feature known otherwise only in

birds 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 ...

and

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 ...

ns. The ilium was larger than the

ischium The ischium () form ...

and pubis, having very deflected and pronounced iliac blades. The prominent extension of the ilium shows that therizinosaurids had massive

thighs In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of b ...

. On the bottom of the ischium, a large obturator process (ridge-like expansion) was present, most notably in ''Segnosaurus'' and ''Nothronychus''. The pubis was larger than the ischium and had a large pubic boot (wide expansion at the end). Unlike any other theropod group, the pubis and ischium were attached together forming a solid structure with a square end. Both

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

and

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

were robust in constitution. The former was relatively straight with well-developed articulations and femoral head. The tibia was slightly shorter than the femur and had a wide lower end, forming a prominent

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular join ...

. The

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

was pinched to the bottom and very stiffened. Both

astragalus ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...

and

calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...

were generally robust and elongated bones but the astragalar body was apparently reduced in this group. The astragalus has an elongated lateral

condyle A condyle (;Entry "condyle"
in
articulation with the adjacent elements such as the astragalus or distal tarsals. Another highly modified element was the

tetradactyl In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος (''dáktylos'') = "finger". Sometimes the ending "-dactylia" is used ...

pes Pes (Latin for "foot") or the acronym PES may refer to: Pes * Pes (unit), a Roman unit of length measurement roughly corresponding with a foot * Pes or podatus, a * Pes (rural locality), several rural localities in Russia * Pes (river), a river ...

: the

metatarsus The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...

was composed by four shortened, fully functionally

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...

. Metatarsals III and IV were almost equal in size, the second was slightly narrow and the first one was the shortest. There are, however, traces of metatarsal V but it is highly reduced and has no functional significance−as seen on ''Segnosaurus''. The phalangeal formula was as in other maniraptorans, IV-4, III-3, II-2 and I-1 (excluding the unguals). The pedal unguals were sharply pointed, side to side flattened and smaller than the manual unguals. In ''Erlikosaurus'' however, they are massive, combining a stiff and recurved shape with robust tubercles.

Classification

The family Therizinosauridae was coined by

in 1954 to contain the enigmatic ''

'', who interpreted this taxon as representing giant marine turtles. Relatives of ''Therizinosaurus'' were later found but not recognized as such for some time. With the description of ''

'' in 1979, the paleontologist

coined the family Segnosauridae to contain this enigmatic taxon and tentatively considered this group to represent theropods. He noted that this new family was different from Therizinosauridae based on claw and antebrachium traits. Moreover, in the same year Perle and

analyzed the pelvis structure of ''Segnosaurus'' and concluded that it was unusually different from those of "traditional" theropods. Based on these observations, they proposed that segnosaurids should be separated into a separate grouping, near the level of the main division infraorder

Saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...

. Parallel to this, the newly and also described ''

'' was assigned to the

Titanosaurinae ''Titanosaurus'' (; ) is a dubious genus of sauropod dinosaurs, first described by Richard Lydekker in 1877.R. Lydekker. (1877). Notices of new and other Vertebrata from Indian Tertiary and Secondary rocks. ''Records of the Geological Survey of I ...

based on the assumption it was a sauropod genus. In the following year, both Barsbold and Perle named the new theropod infraorder Segnosauria, containing the Segnosauridae. In this new paper they also described the new ''

'' and ''

Enigmosaurus ''Enigmosaurus'' (meaning "Enigma lizard" or "Enigmatic lizard") is a genus of therizinosauroid that lived in Asia during the Late Cretaceous period. It was a medium-sized, ground-dwelling, bipedal herbivore that represents the third therizinosa ...

'' (then unnamed) noting that segnosaurs were more similar to theropod dinosaurs and though some of their features resembled those of

ns and

sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

, these similarities were superficial and distinct when examined in detail. In 1982, Perle described a third specimen of the therizinosaurids ''Therizinosaurus''. He referred this material to the genus based on the striking similarities with the specimens of ''Segnosaurus''. Additionally, Perle acompared the forelimbs in these two taxa and concluded that they were characterized by elongated arms, possibly belonging to a single taxonomic group. However, based on osteological features, in 1984

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

proposed that segnosaurs were no theropods but Late Cretaceous

prosauropods Plateosauridae is a family (biology), family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosaurida ...

and they represented a transitional form between prosauropods and ornithischians. For instance, segnosaurs resembled prosauropods in their skull and foot morphology and were also similar to ornithischians in their snout, pubis, and ankle. In 1988 he suggested a segnosaurian classification for the therizinosaurids ''Therizinosaurus''. In a

review article A review article is an article that summarizes the current state of understanding on a topic within a certain discipline. A review article is generally considered a secondary source since it may analyze and discuss the method and conclusions i ...

on the book

The Dinosauria ''The Dinosauria'' is an extensive book on dinosaurs, compiled by David B. Weishampel, Peter Dodson, and Halszka Osmólska. It has been published in 2 editions, with the first edition published in 1990, consisting of material from 23 scientists.B ...

in 1990, Barsbold and

Teresa Maryańska Teresa Maryańska (1937 – 3 October 2019) was a Polish paleontologist who specialized in Mongolian dinosaurs, particularly pachycephalosaurians and ankylosaurians. Peter Dodson (1998 p. 9) states that in 1974 Maryanska together with Halszka ...

considered Segnosauria to be an enigmatic group of saurischians with a position subject to change. They however, disagreed with ''Therizinosaurus'' as a segnosaurian taxon since it was known from forelimb material; they corroborated the referred hindlimb material as segnosaurian though. Lastly, Barsbold and Maryańska noted the striking similarities between the pelvises of ''Nanshiungosaurus'' and ''Segnosaurus'', such as the opisthopubic condition and large iliac blade. They concluded that the former was part of the Segnosauridae. Alxasaurus elesitaiensis

With the description of the therizinosauroids ''

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 ...

'' in 1993 by

Dale A. Russell Dale Alan Russell (27 December 1937 – 21 December 2019) was an American-Canadian geologist and palaeontologist. Throughout his career Russell worked as the Curator of Fossil Vertebrates at the Canadian Museum of Nature, Research Professor at ...

and Dong Zhiming, the affinities of the group were fairly more clear. This new taxon represented the most complete member and was known from multiple specimens with numerous theropod traits. Moreover, the preserved hindlimbs in some specimens showed that the assignment of segnosaurian hindlimbs to ''Therizinosaurus'' was correct and "segnosaurs" were in fact theropods. Russell and Dong also noted the extreme similarities between Therizinosauridae and Segnosauridae and considered that the latter was a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of the former due to priority. However, ''Alxasaurus'' was a fairly more primitive genus and the superfamily

Therizinosauroidea Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite thes ...

was coined to contain it and related species. Posterior to this year, Clark and colleagues redescribed the holotype skull of ''Erlikosaurus'' and found more theropod traits than when first described. They concluded that therizinosaurs were more likely to be classified as maniraptoran theropods.

Therizinosauria Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite the ...

itself, was erected in 1997 by Rusell in order to contain all of these theropods. This new infraorder was composed of Therizinosauroidea and the more advanced Therizinosauridae. The family Therizinosauridae was first given a

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

definition by

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 ...

in 1998, who defined it as all dinosaurs closer to ''Erlikosaurus'' than to ''

Ornithomimus ''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...

''. In 2010,

Lindsay Zanno Lindsay E. Zanno is an American vertebrate paleontologist and a leading expert on theropod dinosaurs and Cretaceous paleoecosystems. She is the Head of Paleontology at the North Carolina Museum of Natural Sciences and an Associate Research Profe ...

conducted the most detailed phylogenetic analysis of the Therizinosauria to 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. The position of Segnosaurus and those of some other Asian therizinosaurids was affected by these factors; Zanno stated more well-preserved specimens and the rediscovery of missing elements would be necessary. Zanno also revised Therizinosauroidea to exclude Falcarius and retained it in the wider clade Therizinosauria, which became the senior synonym of Segnosauria. In addition, she defined Therizinosauridae as the least inclusive clade containing ''Erlikosaurus'', ''Nothronychus'', ''Segnosaurus'' and ''Therizinosaurus''. ''

'' and ''

'' are now regarded as the most primitive therizinosaurs while therizinosauroids are considered to be more derived that these two taxa, but less derived than therizinosaurids. Most phylogenetic analyses recover the family Therizinosauridae containing ''Erlikosaurus'', ''Erliansaurus'', ''Nanshiungosaurus'', ''Neimongosaurus'', ''Nothronychus'', ''Segnosaurus'' and ''Therizinosaurus''. However, ''Suzhousaurus'' is commonly recovered within the group. Therizinosauridae, along a handful of named genera, constitute the superfamily of Therizinosauroidea and finally, Therizinosauroidea falls within the higher infraorder of Therizinosauria. Although a consensus has yet to be reached, it has been proposed that therizinosaurs are the most primitive clade within

, as well as the sister clade to

oviraptorosaurs 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 ...

. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

below follows the 2019 phylogenetic analysis by Scott Hartman and colleagues, which is largely based on the work from Zanno in 2010. While most therizinosaurids are recovered in relatively traditional, well-established positions, the therizinosauroid ''"N." bohlini'' was unusually recovered as a therizinosaurid taxon: Therizinosaur skeletons

Paleobiology

Feeding

In 2009, Zanno and colleagues stated therizinosaurs were the most-widely regarded candidates for herbivory among theropods based on the small, densely packed, coarse serrations; lance-shaped teeth with a relatively low replacement rate; a well-developed keratinous beak; long neck for browsing; relatively small skulls; a very large gut capacity as indicated by the rib circumference at the trunk and the outwards flaring processes of the ilia; and the notable lack of

cursorial A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often u ...

adaptations in the hind limbs. All of these features suggest that members of this family feed on

vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic character ...

, as well as pre-processing it within their mouths to begin the breakdown of

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

and

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

. This is perhaps even more so true for therizinosaurids, which seem to have further exploited these characters. One of the most notable adaptations in advanced therizinosaurids are the four-toed feet, which had a fully functional, weight-bearing first digit that was likely adapted to slow life-style. Zanno and colleagues found that

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

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 ...

had either direct or morphological evidence for

, which would mean either this diet evolved independently multiple times in coelurosaurian theropods or that the primitive condition of the group was at least facultative herbivory with carnivory only emerging in more derived maniraptorans. The skull of therizinosaurids was specialized as well, as it was likely capped off with a beak-like

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

in the front. It has been argued that this rostrum was likely covered with a

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

ous beak, an adaption that might have helped to enhance cranial stability by mitigating the stress and strain experienced by the skull during feeding. As indicated by their respective dental morphologies, the contemporaneous therizinosaurids ''

'' and ''

'' were separated by

niche partitioning In ecology, niche differentiation (also known as niche segregation, niche separation and niche partitioning) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive excl ...

. These differentiations include the relatively indistinct and symmetrical teeth with moderate serrations ( denticles) in ''Erlikosaurus'', and the enlarged serrations in ''Segnosaurus'' composed of additional carinae and folded carinae with denticulated front edges, which together created a roughened, shredding surface near the base of the tooth crowns that was apparently unique to ''Segnosaurus'' and suggest they consumed unique food resources or used highly specialized feeding strategies, and had a higher degree of oral food processing than other therizinosaurids. In addition to these morphological differences, in 2019 Button and Zanno note that herbivorous dinosaurs followed two main distinct modes of feeding. One of these was processing food in the gut which is characterized by gracile skulls and relatively low bite forces. The second was oral food processing, characterized by features associated with extensive processing such as the lower jaws or dentition. ''Segnosaurus'' was found to be in the former mode, whereas ''Erlikosaurus'' was more likely to fall in the second group, indicating these two therizinosaurids were functionally separated and occupied different niches. During the same year, Ali Nabavizadeh concluded that most therizinosaurs were mainly orthal feeders (moving their jaws up and down and not to the sides) and raised their jaws isognathously whereby the upper and lower teeth of each side contacted each other at once. However, advanced

therizinosaurids had relatively weak bite forces compared to primitive therizinosaurs. In 2013 the paleontologist Stephan Lautenschlager performed digital reconstructions for the cranial

musculature Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

in ''Erlikosaurus'' and found the bite force of ''

Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...

'' being greater than that for the former. The lesser bite force for ''Erlikosaurus'' better served in stripping and cropping

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

, rather than active mastication. On a newer study with more therizinosaur taxa, Lautenschlager found similar conclusions. The evolutionary trends in jaw mechanics of therizinosaurs noticed a change in bite force through time, from higher bite forces in early members to lesser ones in the advanced therizinosaurids. Therizinosaurids were aided by the down-turned tip and symphyseal regions (union between bones) of the

dentaries In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, and probably also by beaks. By contrast, the straighter and more elongated dentaries of primitive therizinosaurs had the highest magnitudes of stress and strain. A downwards-pulling motion of the head while gripping vegetation was more likely than a sideways or upwards movement, though such behavior would be more likely in therizinosaurids with their stress-mitigating jaws.

Foraging

Among therizinosaurids, the forelimbs were increased in robustness and the flexibility of the

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...

was increased as well, with this, the presumed reach for

foraging Foraging is searching for wild food resources. It affects an animal's Fitness (biology), fitness because it plays an important role in an animal's ability to survive and reproduce. Optimal foraging theory, Foraging theory is a branch of behaviora ...

is likely to have lengthened. Moreover, the pectoral girdle has been modified to further augment upright reach, however the grasping ability of the animals is thought to have decreased. These adaptations are more linked to assist with their herbivorous lifestyle, as they have specialized the ability to harvest and collect vegetation. Moreover. in the therizinosaurids ''

'', the range of motion in the arms was roughly circular at the glenoid-humeral joint at the shoulder, and directed sideways and slightly downwards, which diverged from the more oval, backwards-and-downwards-directed ranges of other theropods. This ability to extend their arms considerably forwards may have helped these therizinosaurids reach and grasp for foliage. In 2014, Lautenschlager tested the biomechanical function of multiple therizinosaur claws. He noted that the hands of some therizinosaurids (such as ''Nothronyhus'' or ''Therizinosaurus'') were more effective when piercing or pulling down vegetation. The arms would have had to be able to extend the range of the animal to a point that could not be reached by the head if they were used for browsing and pulling down vegetation. In genera where both neck and forelimb elements are preserved, however, the necks were equal in length or longer than the forelimbs, so pulling vegetation would only be likely if lower parts of long branches were pulled down to access out-of-reach vegetation. Lautenschlager also found that therizinosaurid claws would not have been used for digging, which would have been done with the foot claws because, since as in other maniraptorans,

on the forelimbs would have interfered with this function. Additionally, this action leads to a higher stress tension on the dorsal area of the claw−this is more evident in ''Therizinosaurus''. However, he could neither confirm nor disregard that the hand claws could have been fully used for

sexual display A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate Mate choice, exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ( ...

, self-defense,

intraspecific competition Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals, but the more fit individual survives and is able to r ...

, mate-gripping during

mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...

or grasping stabilization when

Brain and senses

The group is also notable for adaptations to the structures of their

. The structure of their inner-ear is almost avian, with bird-like

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line of ...

s and an extended

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...

. For birds, an extended cochlea allows them to hear across an increased range of

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

, suggesting a similar function in the ponderous therizinosaurids and also allowing them a good hearing and balance, which indeed, are traits better associated with

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

. Furthermore, the lengthening of the cochlea, an adaptation which has independently evolved in a number of other theropod groups, is thought to further improve auditory acumen. The

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the Anatomical terms of location#Directional terms, rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hin ...

of therizinosaurids was fairly enlarged and developed with elongated

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...

s. The adaptations to the inner-ear and forebrain of therizinosaurids likely served a number of functions, such as well-developed senses of smell, complex

social behavior Social behavior is behavior among two or more organisms within the same species, and encompasses any behavior in which one member affects the other. This is due to an interaction among those members. Social behavior can be seen as similar to an ...

, increased alertness to the vocalizations of juveniles or even communicating with

conspecifics Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...

, moreover, the large

pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...

chambers on the sensorial areas in the skulls of therizinosaurids (''Erlikosaurus'' or ''Nothronychus mckinleyi'') indicates that the tympanic systems would result in increased and optimal

low frequency Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre wave. LF radio waves exh ...

sound reception, possibly

infrasound Infrasound, sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perce ...

. Such is the case of ''N. mckinleyi'', which had an average hearing frequency of 1100 to 1450 Hz and possible upper limits between 3000 and 3700 Hz. Features include not only extensive basicranial pneumaticity, but also the development of a basisphenoid bulla (hollow bony structure). In addition, the orientation of the horizontal semicircular canal relative to the horizontal orientation of the

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...

gave therizinosaurids a horizontal head posture that enabled

binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...

with overlapping visual fields. A vast majority of these senses were also well-developed in earlier coelurosaurs and other theropods, indicating that therizinosaurids inherited many of these traits from their small, carnivorous maniraptoran ancestors and retained the ancestral, carnivorous ear configuration to be used for their different and very specialized dietary purposes.

Locomotion

In 1964, Zakharov described and named the particular

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...

Macropodosaurus ''Macropodosaurus'' is an ichnogenus of therizinosaurid footprints from the Late Cretaceous of Asia, North America and Poland. The ichnogenus is currently monotypic only including the type ichnospecies ''M. gravis'', described and named in 1964. ...

'', which is represented by a series of four-toed

footprints Footprints are the impressions or images left behind by a person walking or running. Hoofprints and pawprints are those left by animals with hoof, hooves or paws rather than foot, feet, while "shoeprints" is the specific term for prints made by ...

. These tracks were found in beds of the

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

age at

Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...

, noting that they were made by a

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

four-toed

dinosaur 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 ...

and the toes were

webbed ''Webbed'' is a 2D computer graphics, 2D Adventure game, adventure Puzzle video game, puzzle platform game developed and published by Australian, Brisbane-based studio Sbug Games. A Physics game, physics-based game set in a fantasy version of Qu ...

or at least, very fleshy. It is unlikely that these were made by a quadrupedal animal since no manual footprints were found in association. The footprints are about long and wide. Since the research of therizinosaurs started posterior to these findings, Zakharov was not able to determine the exact type of dinosaur. Sennikov in 2006 re-examined these footprints and concluded that a therizinosaurid-grade dinosaur could have made those tracks. He compared ''Macropodosaurus'' with the articulated feet of ''Erlikosaurus'' and the referred one from ''Therizinosaurus'' revealing that when articulated in a

position they fit in the morphology of ''Macropodosaurus''. Therefore, he considered these tracks to be more associated with therizinosaurids and was one of the first in propose a plantigrade stance in therizinosaurids. An additional ''Macropodosaurus''-grade footprint was discovered in

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...

and first reported in 2008. This footprint is reminiscent of the tracks described by Zakharov and therefore assigned to ''Macropodosaurus'' sp. These tracks could indicate the presence of therizinosaurs in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

. In 2017 Masrour with colleagues reported ''Macropodosaurus'' footprints in what is now

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...

. They are similar to the original description with some degree of semiplantigradism. However, several other footprints may indicate a more digitigrade stance. Such is the case the footprints from the

Cantwell Formation The Cantwell Formation is a geologic formation in Alaska. It preserves fossils dating back to the Cretaceous period, it has also yielded numerous dinosaur tracks at Denali National Park. Contemporary therizinosaurid and hadrosaurid trackways in ...

labelled under the numbers DMNH 2010-07-01, 2013-08-04, 2013-08-06 and 2014-11-05. These impressions are composed by four toes with the first digit slightly smaller than the others which is attributed to therizinosaurids. At least one footprint, DMNH 2010-07-01, was directly compared to the relatively complete right pes of ''Erlikosaurus'' revealing a consistent morphology. However, most of the footprint was made (apparently) by the fingers and a foot pad, indicating a more upright position of the metatarsals. Nevertheless, Botelho and colleagues have also considered a plantigrade stance for therizinosaurids in 2016. Accordingly, members of the Therizinosauridae (such as ''Neimongosaurus'' or ''Nothronychus'') re-evolved a fully functional first digit that articulates to the

Reproduction

Nesting

Some of the first dendroolithid

s—which are attributed to therizinosaurs—were reported from the Bayan Shireh and

formations on the same year, 1997. These consisted of several

(a group) with an average composition of 7 or more eggs. In addition, the Bayan Shireh Formation has produced fully grown, specific therizinosaurid taxa, such as ''

'' and ''

''. The egg nests from the Nanchao Formation remained undescribed for several years, only being briefly examined but identified to contain

fossilized A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

embryos An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sper ...

. However, in 2007 these were described by paleontologist

Martin Kundrát Martin may refer to: Places * Martin City (disambiguation) * Martin County (disambiguation) * Martin Township (disambiguation) Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Austral ...

and colleagues and tentatively identified as therizinosaurids based on anatomical features such as the tooth-less premaxilla with a downturned edge, dentary with a lateral shelf, teeth with leaf-shaped crowns, humerus with a prominent deltopectoral crest, ilium with an expanded anterior end, and the elongated, sharply-pointed manual unguals. Most eggs have an average size of and given these dimensions, they likely were laid by a medium-sized female. Although several egg clutches were found, one was found containing 7 eggs of which 3 of them were preserving the embryos. In 2019, Hartman and colleagues were the first authors to include these embryos in a phylogenetic analysis and as expected, the embryos were recovered as therizinosaurids. In a 2013 conference abstract, paleontologist

Yoshitsugu Kobayashi {{Short pages monitor