page_title: Segnosaurus
section_title: Paleobiology
hierarchical_section_title: Segnosaurus / Paleobiology
caption_attribution_description: Therizinosaur nest from Dinosaurland, Lyme Regis, England.
context_page_description: 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 Gobi Desert in the 1970s, and in 1979 the genus and species Segnosaurus galbinensis were named. The generic name Segnosaurus means "slow lizard" and the specific name galbinensis refers to the Galbin region. The known material of this dinosaur includes the lower jaw, neck and tail vertebrae, the pelvis, shoulder girdle, and limb bones. Parts of the specimens have gone missing or become damaged since they were collected.
  Segnosaurus was a large-bodied therizinosaur that is estimated to have been about 6–7 m long and to have weighed about 1.3 t. It would have been bipedal, with the trunk of its body tilted upwards. The head was small with a beak at the tip of the jaws, and the neck was long and slender. The lower jaw was down-turned at the front and the teeth were distinct in having additional denticles as well as third cutting edges in some of the hindmost teeth.
context_section_description: In 1979 and 1981, Barsbold and Perle said the short, massive metatarsus and unusually large, splayed toes indicated that Segnosaurus and its relatives were not adapted for rapid locomotion, perhaps because it was not required by their lifestyle; Barsbold and Perle suggested they could have been amphibious. Barsbold and Maryańska agreed in 1990 the short, broad feet and bulky trunks of the group indicated they were slow-moving animals. Paul depicted a prosauropod-like "segnosaur" skeleton (a composite of various genera) in a quadrupedal posture in 1988. Based on the more complete remains of Alxasaurus and the articulation of its vertebral column, Russell concluded in 1993 that Paul's skeletal restoration was inaccurate and that the arms of therizinosaurs were held clear off the ground. In 1995, Nessov suggested the elongated claws of therizinosaurs were used for defense against predators and that their young could have used their claws for arboreal locomotion along trunks and in tree crowns in a similar manner to sloths.
  In a 2012 study of the endocranial anatomy of Erlikosaurus and other therizinosaurs that preserve braincases, Stephan Lautenschlager and colleagues found these dinosaurs had well-developed senses of smell, hearing, and balance. The former two senses may have played a role in foraging, predator evasion, and social behavior. These senses were also well-developed in earlier coelurosaurs, so therizinosaurs may have inherited these traits from their carnivorous ancestors and used them for different dietary purposes. In a 2014 study of the function of therizinosaur hand claws, Lautenschlager found that these would not have been used for digging, which would have been done with the foot claws because, since as in other maniraptorans, feathers on the forelimbs would have interfered with this function. He could neither confirm nor disregard that the hand claws could have been used for defense, combat, stabilization by grasping tree trunks during high browsing, sexual display, or gripping mates during copulation. He largely ruled out that they dug burrows, due to their size.
  Dinosaur eggs with embryos of the Dendroolithidae type from the Nanchao Formation of China were identified as belonging to therizinosaurs and described by Martin Kundrát and colleagues in 2007. The development of the embryos and the fact that no adults were found in association with the nests indicate that therizinosaur hatchlings were precocial (capable of locomotion from birth) and able to leave their nests to feed alone, independently of their parents. In a 2013 conference abstract, Yoshitsugu Kobayashi and colleagues reported a nesting ground of theropod dinosaurs from the Javkhlant Formation of Mongolia that contained at least 17 egg clutches within an area 22 by 52 meters (72 ft × 171 ft). Each clutch contained eight spherical eggs with rough surfaces; the eggs were in contact with each other and arranged in a circular structure with no central opening. The researchers identified the eggs as dendroolithid, and therefore therizinosaurian. Though therizinosaurs are not known from the formation, it overlies the Bayan Shireh Formation where Segnosaurus, Erlikosaurus, and Enigmosaurus were found. The multiple clutches indicate some therizinosaurs were colonial nesters like hadrosaurs, prosauropods, titanosaurs, and birds. The eggs were found in a single stratigraphic layer, suggesting the dinosaurs nested at the site on a single occasion and did not exhibit site fidelity (always returning to the same site to breed).
caption: Nest attributed to therizinosaurs, Dinosaurland Fossil Museum
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