Segnosaurus was described in 1979 by Dr. A. Perle. Three specimens (consisting of a mandible, pelvis, hindlimb, scapulocoracoid, incomplete forelimb, and vertebrae) were recovered from the Baynshirenstaya Svita of the Mongolian People's Republic in sediments dated between the Cenomanian to Turonian (Cretaceous). Segnosaurus can be distinguished from other segnosaurs on the basis of mesial mandibular teeth that are markedly flattened and only slightly recurved and by the moderate compression of the pedal unguals. The latero-dorsal shelf on the dentary starts at the fourteenth dentary tooth position and runs backwards for half the length of the lower jaw, unlike the shelf in Erlikosaurus which starts at the fifth tooth position. This would have indicated that Segnosaurus did not have as extensive "cheeks" as Erlikosaurus would have had.