Therizinosauroidea
Creators: name: Rauhut, Oliver W. M.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Saurischia

description: Therizinosauroidea (Maleev, 1954) <i>Included taxa. Alxasaurus elesitaiensis Russell and Dong, 1993a</i>; <i>Beipiaosaurus inexpectus</i> Xu, Tang and Wang, 1999. Therizinosauridae Maleev, 1954: <i>Enigmosaurus mongoliensis</i> Barsbold and Perle, 1983; <i>Erlikosaurus andrewsi</i> Perle, 1980 <i>(in</i> Barsbold and Perle 1980); <i>‘Nanshiungosaurus’ bohlini</i> Dong and Yu, 1997; <i>Nanshiungosaurus brevispinus</i> Dong, 1979; <i>Nothronychus mckinleyi</i> Kirkland and Wolfe, 2001; <i>Segnosaurus galbinensis</i> Perle, 1979; <i>Therizinosaurus cheloniformis</i> Maleev, 1954. <i>Temporal range.</i> Barremian-Maastrichtian. <i>Occurrence.</i> 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. <i>Diagnosis.</i> 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. <i>Remarks.</i> The genus <i>Therizinosaurus,</i> 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 <i>c</i>), 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, <i>Segnosaurus.</i> Subsequently, <i>Enigmosaurus, Erlikosaurus,</i> and <i>Nanshiungosaurus</i> 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 <i>sedis mutabilis.</i> In 1993, Russell and Dong (1993 <i>a</i>) described a new species from the upper Lower Cretaceous of China, <i>Alxasaurus elesitaiensis,</i> and demonstrated that <i>Therizinosaurus</i> is closely related to segnosaurids and consequently changed the family name to the senior synonym Therizinosauridae. <i>Alxasaurus,</i> 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 <i>et al.</i> (1994) in their detailed analysis of the skull of <i>Erlikosaurus</i> (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 <i>et al.</i> (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 <i>et al.</i> (2001) described a new supposed therizinosaur, <i>Eshanosaurus deguchiianus,</i> 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 <i>et al.</i> in support for therizinosaur affinities, six are clearly also present in prosauropods (characters 3, 6 and 8-11 of Xu <i>et al.</i> 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 <i>et al.</i> (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 <i>Eshanosaurus</i> 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, <i>in</i> Kirkland and Wolfe 2001). In conclusion, <i>Eshanosaurus</i> 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.
description: Published as part of <i>Rauhut, Oliver W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs, pp. 1-213 in Special papers in palaeontology 69</i> on pages 41-42, DOI: 10.5281/zenodo.3382576
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