page_title: Segnosaurus
section_title: Postcranial skeleton
hierarchical_section_title: Segnosaurus / Description / Postcranial skeleton
caption_attribution_description: English: Fig. 1. Segnosaurus galbinensis Perle, 1979; holotype (GIN 100/80); Amtgay, SE Mongolia, Bayan, Shireh svita, Upper Cretaceous: left lateral view of pelvis, right dorsal view of metatarsus; is ischium, pu pubis.
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: The scapula (shoulder blade) of Segnosaurus was straight and flat at the upper end, and was fused to the coracoid bone, forming the scapulocoracoid. The coracoid was very wide, rectangular in outline and thick at the middle. The massive humerus was 560 mm (22 in) in length; it had an almost-cylindrical shaft and well-defined condyles for articulation with the radius and ulna of the lower arm. The deltopectoral crest, where the deltoid muscle was attached to the upper front of the humerus, was well-developed. The humerus was distinct from those of other therizinosaurs, being straight rather than sigmoid shaped and not expanded or deflected forwards at its upper end. The humerus was also not expanded at the middle, and the entepicondyle was not well-developed. The lack of these features was more similar to ornithomimosaurs and troodontids than to other therizinosaurs. The radius was also massive—about 60 percent of the humerus—with a straight shaft. The ulna was thicker than the radius and slightly longer—about 70 percent of the humerus—and slightly twisted along its middle axis. The hand was tridactyl (three-fingered). The phalanx bones of the fingers were flattened from top to bottom and the articular depressions on their sides were not very developed. The first phalanx of the first finger was long and thin while the first and second phalanxes of the second finger were short. The ungual of the third finger was somewhat longer than the second phalanx and quite flat from top to bottom, which may have been a unique feature of Segnosaurus. This ungual was sharpy curved, very pointed, and compressed from side to side. The lower tubercle, where the flexor tendons attached to the ungual, was thick and robust.
  The pelvis of Segnosaurus was robust and had sharply sideways-directed lobes at the front. The pelvis was shortened at the front, a feature found among bird-like theropods but uncommon among theropods as a whole. The pubic bone was directed backwards and down in parallel with the ischium; this backwards orientation of the pubic bone is known as the opisthopubic condition. This feature is only known from birds and their closest coelurosaurian relatives while other theropod dinosaurs had forwards-directed pubic bones. The pubic bone was elongated, flattened sideways, and had an ellisoid projection or "boot" at the front of its lower end. The pelvis was distinct from those of other therizinosaurs in that the upper margin of the ilium had a pronounced overhang on the lower side and that the hindwards projecting process of the ischium was extensive, almost 50 percent of the front-to-back length of the obturator process. Some features of the pelvis were similar to that of Nothronychus, particularly the ischia, but it is uncertain whether these similarities were due to them having a common ancestor to the exclusion of other derived therizinosaurids, or because they retained basal features since lost in other relatives. The ischium of Segnosaurus was distinct from that of Nothronychus in that it had an almost-rectangular obturator process and an almost-circular obturator foramen. The pelvis was distinct from that of Enigmosaurus by its deep obturator process not fusing with its counterpart at the middle, by its unfused pubic boot, and because the lower part of the pubic shaft was wide from front to back. Segnosaurus was distinct from both Nothronychus and Enigmosaurus in having a deep brevis fossa (a groove where the caudofemoralis brevis muscle of the tail originated) and because its pubic boot lacked a well developed hindwards projection.
  The femur was straight with an oval cross-section and was 840 mm (33 in) in length. The head of the femur was placed on a long "neck" and the lower condyles were well-defined. The tibia was straight, slightly shorter than the femur, and twisted along its axis. The fibula was long and narrowed towards its lower end. The metatarsus of the foot was short, massive, and consisted of five bones—four of which functioned as support elements and terminated in four toes. Functionally tetradactyl (four-to
caption: Reconstructed holotype pelvis in left side view and metatarsus in top view
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