Editing Segnosaurus (section)

===Diet and feeding===
[[File:Therizinosaurian mandibular morphology.png|thumb|left|Right half of the holotype mandible shown from the inner side (A), the top (C), and bottom (D), and the left half shown from the inner side (B), compared with the mandibles of other therizinosaurs (to scale in lower right)]]

The unusual features of therizinosaurs have led to several interpretations of their feeding behavior; there is no direct evidence of their diet, such as stomach contents and feeding traces. In 1970, [[Anatoly K. Rozhdestvensky]] suggested ''Therizinosaurus''—the only member of the group known at the time—used its large claws to open [[termite mounds]] or gather fruits from trees.<ref name="Dinosauria2"/> Barsbold and Perle pointed out in 1979 and 1980 that their peculiar features probably reflected a different evolutionary direction than those of more typical theropods, many of which were considered effective, active predators. Their delicate jaws, small, weak teeth and beaks, and short, compact feet indicated they would not have used the armaments of other theropods to procure food but could have preyed on fish.<ref name="Barsbold&Perle1979" /><ref name="perle&barsbold80" /> In 1983, Barsbold said the horny beak at the front of the jaws and weakened teeth at the back were common features among herbivorous dinosaurs but not of carnivorous theropods, and speculated this might indicate segnosaurs had shifted to herbivory.<ref name=barsbold1983/> In 1984, Paul suggested they were herbivorous due to the similarities of their skulls to those of prosauropod and ornithischian dinosaurs, which include horny beaks, inset rows of teeth, and a shelf at the side of the jaws that indicated the presence of cheeks. Like ornithischians, they could, therefore, crop, manipulate, and chew plants in a sophisticated manner. He also suggested the ilia of the pelvis had sideways-flaring blades at the front similar to those of sauropods to support a large gut that was used to ferment and process food.<ref name="Paul1984"/> Norman stated in 1985 the possibility ''Segnosaurus'' was an aquatic fish-eater could explain its small, pointed teeth and broad and perhaps webbed feet, but found it mysterious why it should have a horny beak.<ref name="DBN85"/>

[[File:Segnosaurus Restoration.jpg|thumb|Restoration showing large area behind the legs caused by the backwards directed [[pubic bone]]; therizinosaurs may have "sat" on their pelvises during feeding]]
In 1993, Russell and Dong considered the small size of the head, blunt beaks and large body weights of therizinosaurs consistent with herbivory.<ref name="Alxasaurus"/> In 1993 and 1997, Russell suggested therizinosaurs would have "sat" on their pelvises and supported their bodies on their hind limbs while using their long arms, claws, and flexible necks to reach leaves from trees and bushes with their beaks. They could have reached even higher while standing and browsing bipedally. This parallels the way some herbivorous mammals use their forelimbs to manipulate vegetation; Russell considered the extinct [[chalicotheres]] and [[ground sloth]]s, as well as [[gorilla]]s, adaptively convergent with therizinosaurs. Because therizinosaur remains are often found in [[sediments]] deposited in river and lake environments, Russell said they may have browsed on [[riparian]] bushes and trees.<ref name=Russell1997>{{cite book |last=Russell |first=D. A. |year=1997 |chapter=Therizinosauria |editor=[[Phil Currie|Currie, Philip J.]] |editor2=Padian, Kevin |title=Encyclopedia of Dinosaurs |publisher= Academic Press |location=San Diego |pages=729–730 |isbn=978-0-12-226810-6}}</ref><ref name="NatGeo">{{Cite journal |last1=Russell |first1=D. A. |last2=Russell |first2=D. E. |year=1993 |title=Mammal-dinosaur convergence |journal=National Geographic Research |volume=9 |pages=70–79 |issn=8755-724X}}</ref> Based on the assemblage of fossils in the [[Bissekty Formation]] of Uzbekistan, Nessov suggested in 1995 that therizinosaurs could have been part of its nutrient-rich aquatic ecosystems, though perhaps indirectly, by feeding on wasps which had themselves fed on carrion of aquatic vertebrates. He found this consistent with Rozhdestvensky's suggestion that therizinosaurs may have fed on [[social insects]].<ref name="Nessov" /> In a 2006 conference abstract, Sara Burch presented the inferred range of motion in the arms of the therizinosaur ''Neimongosaurus'' and concluded the overall motion at the {{Dinogloss|glenoid}}-humeral joint at the shoulder was roughly circular, 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 therizinosars reach and grasp for foliage.<ref name="burch2006">{{Cite conference |last=Burch |first=S. |year=2006 |title=The range of motion of the glenohumeral joint of the therizinosaur ''Neimongosaurus yangi'' (Dinosauria: Theropoda) |conference=Chicago Biological Investigator |volume=3 |issue=2 |pages=20}}</ref>

In 2009, Zanno and colleagues stated therizinosaurs were the most-widely regarded candidates for herbivory among theropods and listed features associated with this diet. These included small, densely packed, coarse serrations; lanceolate (lance-shaped) teeth with a low replacement rate; a beak at the front of the jaws; an inset tooth row that suggests fleshy cheeks; an elongated neck; a small skull; a very large gut capacity as indicated by the rib circumference at the trunk and the outwards flaring processes of the ilia; and the loss of [[cursorial]] (related to running) adaptations in the hind limbs, including development of functionally tetradactyl feet. Zanno and colleagues found the clades at the base of Maniraptora—Ornithomimosauria, Therizinosauria, and Oviraptorosauria—had either direct or morphological evidence for herbivory, 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.<ref name="Zanno2009">{{cite journal |last1=Zanno |first1=L. E. |last2=Gillette |first2=D. D. |last3=Albright |first3=L. B. |last4=Titus |first4=A. L. |author1-link=Lindsay Zanno |title=A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution |journal=Proceedings: Biological Sciences |date=2009 |volume=276 |issue=1672 |pages=3505–3511 |issn=0962-8452|jstor=30244145 |doi=10.1098/rspb.2009.1029 |pmid=19605396 |pmc=2817200 }}</ref> Zanno and Peter J. Makovicky found, in 2011, therizinosaurs and some other groups of herbivorous dinosaurs that had beaks and retained teeth were unable to lose their teeth completely because they lacked [[gastric mill]]s (gizzards) and needed the teeth to process food, and that the high-fiber [[folivorous]] (leaf-based) diet of therizinosaurs and other [[archosaurs]] may also have precluded the evolution of a complete beak.<ref>{{cite journal |last1=Zanno |first1=L. E. |last2=Makovicky |first2=P. J. |author1-link=Lindsay Zanno |title=Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution |journal=Proceedings of the National Academy of Sciences |date=2011 |volume=108 |issue=1 |pages=232–237 |doi=10.1073/pnas.1011924108|pmid=21173263 |pmc=3017133 |bibcode=2011PNAS..108..232Z |doi-access=free }}</ref> Lautenschlager found in 2014 the hands of therizinosaurs 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 make sense if lower parts of long branches were pulled down to access out-of-reach parts of trees.<ref name="Claws"/>

[[File:Dentary teeth of Segnosaurus.png|thumb|upright|Hindmost dentary teeth showing the third cutting edge (lc), unique to ''Segnosaurus'' among theropods]]
Zanno and colleagues stated in 2016 that therizinosaurs were generally accepted to fall within the spectrum of [[omnivory]] and herbivory, with a trend towards intensified herbivory. While various anatomical features have been used to support this idea, tooth morphology had been considered relatively simplistic and with few unique specializations compared to other herbivorous dinosaurs. The few modifications include the increased symmetry in the teeth of ''Erlikosaurus'' and the enlargement of denticles in ''Segnosaurus''. Zanno and colleagues identified novel, complex features in the dentary teeth of ''Segnosaurus'', including the presence of additional carinae and folded carinae with denticulated front edges, which indicate ''Segnosaurus'' had a higher degree of oral food processing than other therizinosaurs. These traits together created a roughened, shredding surface near the base of the tooth crowns that was unique to ''Segnosaurus'' and suggest it consumed unique food resources or used highly specialized feeding strategies. Because multiple geological formations show evidence of [[sympatric]] therizinosaur species—related species that lived in the same area at the same time—it is possible [[niche partitioning]] between them could have played a role in the group's evolutionary success. This is supported by ''Segnosaurus'' with its highly specialized dentition being a contemporary of ''Erlikosaurus'' with its relatively indistinct teeth, indicating their partitioning in food acquisition, processing, or resources. This conclusion is also strengthened by the large difference in estimated body masses of sympatric therizinosaurs in the Bayan Shireh Formation, which was up to 500%.<ref name="Zanno2016"/>

In a 2017 study of niche partitioning in therizinosaurs through digital simulations, Lautenschlager found the dentaries of ''Segnosaurus'' experienced one of the lowest stress magnitudes during extrinsic feeding scenarios. ''Segnosaurus'' and ''Erlikosaurus'' were aided by the down-turned tip of the lower jaws and symphyseal regions, and probably also by beaks, which are known to mitigate stress and strain. By contrast, the straighter and more elongated dentaries of basal therizinosaurs—typical of their coelurosaurian ancestors—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 ''Segnosaurus'' and ''Erlikosaurus'' with their stress-mitigating jaws. Difference in relative bite force between the sympatric ''Segnosaurus'' and ''Erlikosaurus'' show the former would have been able to feed on tougher vegetation while the overall robustness of the latter suggests greater flexibility in its manner of feeding, because stress levels stayed low across feeding simulations. Lautenschlager agreed the two taxa were adapted to different modes of feeding and food selection; ''Segnosaurus'' was more adapted to using its dentition to procure or process food while ''Erlikosaurus'' mostly used its beak for cropping and its neck musculature while foraging. The difference in size between ''Segnosaurus'' and ''Erlikosaurus'' (the former of which is estimated to have weighed more than the latter) indicates these effects were increased and that there were further mechanisms partitioning their resources, such as different heights. Because other therizinosaur taxa were more divided in time and space, other factors than competition within their group may also have contributed to their variation, such as adaptations to different flora and competition with other kinds of herbivores.<ref name="Niche">{{cite journal |last1=Lautenschlager |first1=S. |title=Functional niche partitioning in Therizinosauria provides new insights into the evolution of theropod herbivory |journal=Palaeontology |date=2017 |volume=60 |issue=3 |pages=375–387 |doi=10.1111/pala.12289 |bibcode=2017Palgy..60..375L |s2cid=90965431 |url=http://pure-oai.bham.ac.uk/ws/files/39402933/FUNCTIONAL_NICHE_PARTITIONING_IN_THERIZINOSAURIA_REVISED2.pdf |archive-date=January 28, 2021 |access-date=December 23, 2019 |archive-url=https://web.archive.org/web/20210128051751/http://pure-oai.bham.ac.uk/ws/files/39402933/FUNCTIONAL_NICHE_PARTITIONING_IN_THERIZINOSAURIA_REVISED2.pdf |url-status=live }}</ref>

In 2018, Loredana Macaluso and colleagues pointed out that the hips of therizinosaurs were peculiar because the shaft of the pubic bone was rotated backwards whereas the pubic boot was strongly projected forwards. While the larger gut associated with herbivory was able to push the shaft backwards, they suggested the pubic boot was restrained by [[ventilatory muscles]] that were crucial for cuirassal ventilation—breathing with extra [[air sacs]]—which shows the importance of this mode of respiration.<ref name="Macaluso">{{cite journal |last1=Macaluso |first1=L. |last2=Tschopp |first2=E. |last3=Mannion |first3=P. |title=Evolutionary changes in pubic orientation in dinosaurs are more strongly correlated with the ventilation system than with herbivory |journal=Palaeontology |date=2018 |volume=61 |issue=5 |pages=703–719 |doi=10.1111/pala.12362|bibcode=2018Palgy..61..703M |s2cid=133643430 }}</ref> In a 2019 study of jaw musculature, Ali Nabavizadeh concluded therizinosaurs were mainly orthal feeders—moving their jaws up and down—and raised their jaws isognathously whereby the upper and lower teeth of each side [[Occlusion (dentistry)|occluded]] (contacted each other) at once. The origin and insertion sites of their jaw muscles also added strength to their jaw closure.<ref name="Nabavizadeh">{{cite journal |last1=Nabavizadeh |first1=A. |title=Cranial musculature in herbivorous dinosaurs: a survey of reconstructed anatomical diversity and feeding mechanisms |journal=The Anatomical Record |date=2019 |volume=303 |issue=4 |pages=1104–1145 |doi=10.1002/ar.24283|pmid=31675182 |s2cid=207815224 |doi-access=free }}</ref> David J. Button and Zanno found in 2019 herbivorous dinosaurs mainly followed two distinct modes of feeding, either processing food in the gut—characterized by gracile skulls and low bite forces—or the mouth, characterized by features associated with extensive processing. ''Segnosaurus'', along with [[diplodocoid]] and titanosaur sauropods, deinocheirid and ornithomimid ornithomimosaurs, and [[caenagnathids]], was found to be in the former category, whereas ''Erlikosaurus'' was more similar to some sauropodomorph and ornithischian taxa, indicating these two therizinosaurs were functionally separated and occupied different niches.<ref name="DivergentHerbivory">{{cite journal |last1=Button |first1=D. J. |last2=Zanno |first2=L. E. |author2-link=Lindsay Zanno |title=Repeated evolution of divergent modes of herbivory in non-avian dinosaurs |journal=Current Biology |volume=30 |issue=1 |pages=158–168.e4|date=2019 |doi=10.1016/j.cub.2019.10.050|pmid=31813611 |s2cid=208652510 |doi-access=free }}</ref>