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 the Xinminbao Group. These findings were made during field-works in 1999 and 2004. Though Suzhousaurus is known from these two specimens, an earlier named and described therizinosauroid from the adjacent basin, "Nanshiungosaurus" bohlini, may be synonymous with the former. However, Suzhousaurus can not be compared to this species due to non-overlapping material and the loss of the same. Moreover, this synonymy will result in Suzhousaurus bohlini with "N". bohlini having priority.
Suzhousaurus was an unusually large Early Cretaceous therizinosauroid reaching lengths of 6 m (20 ft) and nearly 3.1 t (3,100 kg) in weight. The upper arm (humerus) was very distinct from therizinosaurids, making Suzhousaurus to be considered as a therizinosauroid. Unlike derived (advanced) therizinosaurids, the vertebral column was not highly pneumatized, however, the pelvis shows a marked therizinosaurid-like opisthopubic build. Like other therizinosauroids, Suzhousaurus had elongated claws and neck for browsing, robust hindlimbs and a large trunk that ended on a reduced tail.
With the description of the more complete second specimen, the autapomorphies and validity of Suzhousaurus became more clear and with this, numerous anatomical traits indicate that Suzhousaurus is a non-therizinosaurid therizinosauroid, therefore, excluded from the derived Therizinosauridae. The genus is often recovered as the sister taxon of this family though.
The holotype specimen, FRDC-GSJB-99, was discovered in the Xinminbao Group at the Yujingzi Basin. It consists of a partial skeleton lacking cranial material but contains a right humerus, right scapulocoracoid, 10 dorsal vertebrae, partial ribs, nearly complete left and fragmentary right pubes, the lower end of the left ilium and several unidentified elements. The specimen was described in 2007 by Li Daqing, Peng Cuo, You Hailu, Matthew Lamanna, Jerrald Harris, Kenneth Lacovara and Zhang Jianping, also naming the type species Suzhousaurus megatherioides. In terms of etymology, the generic name, Suzhousaurus, is derived from Suzhou which is the old name for the Jiuquan area. The specific name, megatherioides, indicates a resemblance to the giant ground sloths Megatherium. Li and colleagues pointed out that Suzhousaurus might be identical to "Nanshiungosaurus" bohlini, an earlier named therizinosauroid found in the same geological group and also known from limited remains. If so, the resulting species name would be Suzhousaurus bohlini under the terms of priority. However, a direct comparison is difficult because there is no overlapping material and the holotype of "N". bohlini is apparently lost.[1]
In 2008, a new and fairly more complete skeleton was described. The specimen FRDC-GSJB-2004-001 which contains the last three dorsal vertebrae, the sacrum composed of five sacral vertebrae, the first six caudal vertebrae, a very complete pelvic girdle composed of the left ilium, pubis and ischium, and both femora (right femur is fragmented), was discovered in 2004 by a field team of the Fossil Research and Development Center of Geology and Mineral Resources Exploration of Gansu Province also at the Xinminbao Group. Since the left pubis of both specimens share similar traits, these fossil remains represent another specimen for the taxon.[2] Although both specimens lack cranial material, Button and colleagues reported an isolated dentary tooth referred to Suzhousaurus that was collected in the Yujingzi Basin near the area of the two specimens,[3] which was described in detail by the same team and You Hailu in 2017.[4]