page_title: Therizinosauridae
section_title: Postcranial skeleton
hierarchical_section_title: Therizinosauridae / Description / Postcranial skeleton
caption_attribution_description: Fossil Therizinosaurus arms from Mongolia, exhibited in Experimentarium, Denmark.
context_page_description: Therizinosauridae is a family of derived therizinosauroid dinosaurs whose fossil remains have been found in mostly Late Cretaceous boundary. Even though representative fossils have only been found throughout Asia and North America, the range of Therizinosauridae is believed to have spanned much of the supercontinent of Laurasia based on several footprints and isolated remains on Europe and Africa. Therizinosauridae compromises currently seven described and named taxa.
  Therizinosauridae was named in 1954 by the Evgeny Maleev after the large, claw-bearing unguals of the type species Therizinosaurus cheloniformis. Therizinosaurids were generally large and very robustly built animals that had a near convergent body plan with the more recent ground sloths. The largest genera of the group are Therizinosaurus and Segnosaurus, which were about 10 m and 7 m 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.
context_section_description: In therizinosaurids, the shoulder girdle was robustly specialized than in other maniraptorans and less bird-like. The scapula (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 suture, on the coracoid, a large foramen is present. The coracoid is a wide and broad element that is slightly convex and thickened near of the scapulocoracoid suture. The humerus (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 attachment) was strongly built. The antebrachium was relatively straight in most members, particularly on Therizinosaurus. The reduced carpal block on therizinosaurids enabled an enhanced hand flexion. Manual phalanges are relatively standard in shape among maniraptorans with a formula of digits I, II and III. However, a new and as-yet unnamed therizinosaurid specimen from the Bayan Shireh Formation preserves a reduced third digit that is almost vestigial on both hands. The other two digits are regular in constitution indicating that this species had indeed, a functionally didactyl hand like some tyrannosaurids, which makes it to differ from all other known therizinosaurs.
  The manual unguals (claws) are proportionally larger than the phalanges, strongly flattened from side to side, and recurved with more degrees of specialization than therizinosauroids. Most therizinosaurids had sharply pointed and recurved unguals with very robust tubercles (flexor tendons 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 1 m (3.3 ft) 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 2.4 m (7.9 ft).
  The vertebral column 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 with relatively short neural spines and platycoelous (concave at both ends) to opisthocoelus (concave posterior ends) centra that were elongated and had some degree of pneumacity. In dorsal vertebrae 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 proggresively reduce in size. Some species like N. graffami had a narrow hump-like structure on their back as indicated by the very elongated neural spines of the first dorsals. In therizinosaurids, the sacrum was composed by about six sacral vertebrae with broad centra that have rounded facets. The caudal vertebrae 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 constriction, which indicates a shorter and flexible tail.
  Therizinosaurids had wide torsos supported by a broad, sloth-like pelvis. The ribcage was very round and composed by elongated ribs 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 and ornithischians. The ilium was larger than the ischium and pubis, having very deflected and pronounced iliac blades. The prominent extension of the ilium shows that th
caption: Frontal view of the arms in Therizinosaurus IGM 100/15
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