Therizinosauroidea ( Maleev, 1954 )

Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, Special papers in palaeontology 69, pp. 1-213 : 41-42

Therizinosauroidea ( Maleev, 1954)

Included taxa. Alxasaurus elesitaiensis Russell and Dong, 1993a ; Beipiaosaurus inexpectus Xu, Tang and Wang, 1999 . Therizinosauridae Maleev, 1954 : Enigmosaurus mongoliensis Barsbold and Perle, 1983 ; Erlikosaurus andrewsi Perle, 1980 (in Barsbold and Perle 1980); ‘Nanshiungosaurus’ bohlini Dong and Yu, 1997; Nanshiungosaurus brevispinus Dong, 1979 ; Nothronychus mckinleyi Kirkland and Wolfe, 2001 ; Segnosaurus galbinensis Perle, 1979 ; Therizinosaurus cheloniformis Maleev, 1954 .

Temporal range. Barremian-Maastrichtian.

Occurrence. Bayin Gobi Formation, Nei Mongol Zizhiqu, China; Yixian Formation, Liaoning, China; Baynshiren Svita, Omnogov and Domogov, Mongolia; Xinminbao Group, Gansu, China; Nanxiong Formation, Guandong, China; Nemegt Formation, Omnogov, Mongolia; White beds of Khermeen Tsav, Bayankhongor, Mongolia.

Diagnosis. Mandibular teeth set off from the lateral margin of the jaw posteriorly (convergently present in o rn ithischians and some prosauropods); teeth leaf-shaped with large, blunt marginal denticles (convergently present in prosauropods); anterior dorsal vertebrae with elevated neural arches such that the zygapophyseal articulation is more than three-quarters the height of the centrum above the neurocentral suture; manual unguals flat-sided and deep proximally; anterior end of iliac blade strongly expanded dorsoventrally; prominent lateral tuberosity on the postacetabular iliac blade dorsally; medial surface of Mt I hollowed to articulate with the convex lateral surface of the shaft of Mt II.

Remarks. The genus Therizinosaurus , based on isolated claws from the Upper Cretaceous of Mongolia, was described in 1954 by Maleev as a new genus of giant turtle. It was not until 1970 that the theropod nature of these remains was recognized (Rozhdestvensky 1970). However, despite the description of some new material referable to this genus ( Barsbold 1976 c), its affinities and most of its anatomy remained unknown until recently.

In 1979, Perle proposed a new family of enigmatic Late Cretaceous theropods from Mongolia, Segnosauridae , to include a new genus, Segnosaurus . Subsequently, Enigmosaurus , Erlikosaurus , and Nanshiungosaurus from the Upper Cretaceous of central Asia were referred to this family (Barsbold and Perle 1980, 1983; Perle 1981; Barsbold and Maryanska 1990). Paul (1984) questioned the theropod affinities of segnosaurids and regarded them as ‘relics of the prosauropod-ornithischian transition’ ( Paul 1984, p. 507). Other subsequent workers pointed out similarities between segnosaurids and prosauropods ( Gauthier 1986; Sereno 1989), and Barsbold and Maryanska (1990) listed them as Saurischia sedis mutabilis.

In 1993, Russell and Dong (1993 a) described a new species from the upper Lower Cretaceous of China, Alxasaurus elesitaiensis , and demonstrated that Therizinosaurus is closely related to segnosaurids and consequently changed the family name to the senior synonym Therizinosauridae . Alxasaurus , in its own family Alxasauridae , and therizinosaurids were united in the superfamily Therizinosauroidea. Russell and Dong also made a strong case for assigning therizinosauroids to the Theropoda , the similarities between them and prosauropods being interpreted as adaptations to similar ecological conditions. This view was supported by Clark et al. (1994) in their detailed analysis of the skull of Erlikosaurus ( Text-fig. 6g ), and is followed here. A new therizinosauroid from the Lower Cretaceous of Liaoning, China, with integumentary filaments preserved, was recently described by Xu et al. (1999). This specimen shows a more conservative theropodan pes morphology and a very maniraptoran-like manus, thus furthermore strengthening the theropod affinities of therizinosauroids.

Recently, Xu et al. (2001) described a new supposed therizinosaur, Eshanosaurus deguchiianus , from the Lower Jurassic Lufeng Formation of China. However, the only material known for this taxon, an incomplete lower jaw, shows many similarities with the mandibles of prosauropods, which are the most common dinosaur fossils in this formation. Of the 11 characters listed by Xu et al. in support for therizinosaur affinities, six are clearly also present in prosauropods (characters 3, 6 and 8-11 of Xu et al. f one represents a plesiomorphy for dinosaurs ancestrally (character 4), and the rest are debatable in either their distribution or significance. For example, character 1 of Xu et al. (anterior teeth larger than middle or posterior teeth) might also be present in juvenile prosauropods, as noted by Upchurch (1998, p. 56). Likewise, the shape of the tooth crowns in mesial view (character 5) and the relative size of the root (character 7) might vary within one dentition depending on the position of the tooth. Indeed, some o rn ithischian teeth have roots that are wider than the crown (Rauhut, unpublished data). The number of teeth (character 2) is highly variable in reptiles in general and might vary significantly within one species or even on the left and right side of a single individual (e.g. Colbert 1990; Galton 1990), so a slightly higher number of teeth than in any known prosauropod might not be too significant. Furthermore, the type of Eshanosaurus shows one character that is not present in therizinosauurs, or in any other theropod, but occurs in prosauropods: the presence of a medial ridge on the tooth crowns (Lamanna, pers. comm, in Kirkland and Wolfe 2001). In conclusion, Eshanosaurus is based on an intriguing specimen from the Lower Jurassic Lufeng Formation with a remarkable combination of characters, but more material is needed to confirm its therizinosaur affinities. Therefore, it has not been taken into consideration here.

Figures

text-fig. 6. Skull reconstructions of representatives of Cretaceous OTUs in left lateral view, a, abelisaurid Camotaurus sastrei, Late Cretaceous (Campanian), Gorro Frigio Formation, Argentina; based on Bonaparte et al. (1990) and MACN CH 894. b, composite skull of a generalized baryonychid; mainly based on Suchomimus tenerensis (MNN GDF 501, 503-506) and Irritator challenged (SMNS 58022), with some elements reconstructed after Baryonyx walkeri (BMNH R 9951). c, carcharodontosaurid Carcharodontosaurus sahariens, Late Cretaceous (Cenomanian), Kem Kem beds, Morocco; based on Sereno et al. (1996) and SGM-Din 1, unpreserved elements shaded. D, dromaeosaurid Velociraptor mongoliensis, Late Cretaceous (Campanian), Djadokhta Formation, Mongolia; based on Barsbold (1983), Barsbold and Osmólska (1999), and AMNH 6515. e, ornithomimosaur Dromiceiomimus brevitertius, Late Cretaceous (Maastrichtian), Horseshoe Canyon Formation, Alberta, Canada; redrawn from Russell (1972). F, oviraptorosaur Oviraptor philoceratops, Late Cretaceous (Campanian), Djadokhta Formation, Mongolia; redrawn from Barsbold et al. (1990). G, therizinosauroid Erlikosaurus andrewsi, Late Cretaceous (Cenomanian- Turonian), Baynshiren Svita, Mongolia; based on Clark et al. (1994). H, tyrannosaurid Gorgosaurus libratus, Late Cretaceous (Campanian), Judith River Formation, Alberta, Canada, redrawn from Molnar et al. (1990). Abbreviations as in Text-figures 4 and 5, and: acc. op., accessory opening of unknown function in the premaxilla of Oviraptor (Barsbold et al. 1990); amf, anterior maxillary foramen; pn, pneumatic openings. Scale bars represent 50 mm (d-g) and 100 mm (a-c, h).