- Email: [email protected]
A gigantic caenagnathid oviraptorosaurian (Dinosauria: Theropoda) from the Upper Cretaceous of the Gobi Desert, Mongolia
Cretaceous Research 56 (2015) 60e65
Contents lists available at ScienceDirect
Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes
A gigantic caenagnathid oviraptorosaurian (Dinosauria: Theropoda) from the Upper Cretaceous of the Gobi Desert, Mongolia Takanobu Tsuihiji a, *, Mahito Watabe b, Rinchen Barsbold c, Khishigjav Tsogtbaatar c a
Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113-0033, Japan Department of Geosciences, Osaka City University, Osaka 558-8585, Japan c Mongolian Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar 210351, Mongolia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 December 2014 Accepted in revised form 26 March 2015 Available online
A large, isolated symphyseal region of fused dentaries of an oviraptorosaurian was found in the Upper Cretaceous Bayn Shire Formation at Tsagaan Teg in the Mongolian Gobi Desert. A phylogenetic analysis places this specimen within Caenagnathidae. This specimen is comparable in size and morphology to the gigantic caenagnathid Gigantoraptor erlianensis from the Iren Dabasu Formation in China and is likely closely related to it. The occurrence of the specimen with possible affinities to G. erlianensis in the Bayn Shire Formation is consistent with the hypothesized correlation between the Bayn Shire and Iren Dabasu formations based on the co-occurrences of vertebrate fossils, especially turtles. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Caenagnathidae Oviraptorosauria Bayn Shire Formation
1. Introduction Oviraptorosauria is a clade of mostly small to medium-sized maniraptoran theropods, with body lengths that rarely exceeded lska et al., 2004). More recently, however, large-bodied 2 m (Osmo caenagnathid oviraptorosaurians have been described. Anzu wyliei, from the upper Maastrichtian Hell Creek Formation of the western United States, is approximately 3.5 m in total length (Lamanna et al., 2014). Unguals of similarly sized caenagnathids have also been described from the upper Campanian Dinosaur Park and the Maastrichtian Frenchman formations of Canada (Bell et al., 2015). An even larger-bodied taxon is Gigantoraptor erlianensis, from the Iren Dabasu Formation of Inner Mongolia in China, estimated to be approximately 8 m in total length (Xu et al., 2007), revealing a body-size variation within Caenagnathidae much larger than expected before. In 2008, a fused symphyseal region of the two dentaries was found in strata of the Bayn Shire Formation in the Tsagaan Teg region of the central part of Eastern Gobi Aimag, Mongolia (Fig. 1) by the Hayashibara Museum of Natural Sciences-Mongolian Paleontological Center Joint Expedition. Although fragmentary, this specimen possesses several derived features characterizing the
* Corresponding author. Department of Earth and Planetary Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Tel.: þ81 3 5841 4519. E-mail address: [email protected] (T. Tsuihiji). http://dx.doi.org/10.1016/j.cretres.2015.03.007 0195-6671/© 2015 Elsevier Ltd. All rights reserved.
clade Oviraptorosauria, especially Caenagnathidae. A remarkable aspect of this specimen is its size: the dorsoventral height at the symphyseal region is 97 mm, much larger than the corresponding bones in most oviraptorosaurians but comparable in size to that of Gigantoraptor. In fact, the present specimen is similar to the corresponding part of Gigantoraptor in overall morphology and indeed likely represents a taxon that is closely related to it. This finding is another example of closely related vertebrate taxa co-occurring in the Iren Dabasu and Bayn Shire Formations and is thus consistent with the hypothesized correlation between these formations (Jerzykiewicz and Russell, 1991; Currie and Eberth, 1993; Averianov and Sues, 2012). Institutional Abbreviation: MPC, Mongolian Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia. 2. Material MPC-D 107/17, isolated symphyseal region of fused dentaries. 3. Locality and age The specimen examined is from Tsagaan Teg, Eastern Gobi Aimag, Mongolia (Fig. 1). This locality is situated approximately 20 km southwest of Dzun Bayan Somon and consists of the main outcrop and a second outcrop called Tsagaan Teg West (Watabe et al., 2010). The present specimen was found at the latter outcrop in a layer of medium-to coarse-grained sandstone. The
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
Fig. 1. Map of Mongolia showing the Tsagaan Teg locality as well as Saihangaobi in China, where the holotype of Gigantoraptor erlianensis was found (modified from Tsubamoto et al., 2010).
horizon exposed in the Tsagaan Teg region is correlated with the Bayn Shire Formation (Jerzykiewicz and Russell, 1991; Tumoanova, 1993; Watabe et al., 2010), the age of which is inferred to be the Cenomanian to Santonian (Hicks et al., 1999; Averianov and Sues, 2012). 4. Description MPC-D 107/17 consists of the symphyseal part of fused dentaries of a large oviraptorosaurian (Fig. 2AeF). It is mediolaterally compressed and is crushed around the symphysis (Fig. 2B) so that the left ramus is pushed against the lingual aspect of the mesialmost part of the right ramus, obscuring a detailed morphology of the lingual aspect around the symphysis (Fig. 2F). Teeth are completely lacking. No clear suture is present on the symphysis, indicating that the dentaries are completely fused as in caenagnathids more derived than Microvenator celer such as Caenagnathus collinsi, ‘Caenagnathus’ sternbergi, Caenagnathasia martinsoni, Leptorhynchos gaddisi, Anzu and Gigantoraptor (e.g., Currie et al., 1994; Xu et al., 2007; Longrich et al., 2013; Lamanna et al., lska et al., 2004) such as Cit2014), but unlike oviraptorids (Osmo ipati sp. (MPC-D 100/42) and Rinchenia mongoliensis (MPC-D 100/ 321), in which such a suture between the dentaries is discernable. The symphysis is dorsoventrally deep (97 mm) relative to the maximum anteroposterior length of the preserved part (142 mm). The labial surface is generally smooth except for numerous foramina of various sizes (Fig. 2C). Similar to the condition described in derived caenagnathids by Currie et al. (1994), two rows of relatively large foramina extend parallel to the dorsal and ventral margins of the bone. Toward the anterior end, the ventral row curves upwards. The third row of foramina extends anteroposteriorly approximately 20e25 mm dorsal to the ventral row. In addition, three relatively large foramina cluster anterior to a depression ventral to the lateral flange. As in Gigantoraptor (Xu et al., 2007), the lateral flange is present on the posterodorsal corner of the preserved part, extending posterodorsally (Fig. 2C). As in Gigantoraptor (Xu et al., 2007), but unlike in Anzu (Lamanna et al., 2014), this flange does not extend to the symphysis. Ventral to this flange, there is a large depression as in Gigantoraptor (Xu et al., 2007). The lateral surface of this depression is crushed, but CT data suggests that there is likely a foramen that leads into a pneumatic space inside the bone (Fig. 3), as in derived caenagnathids (Currie et al., 1994). A lingually extended symphyseal shelf, characterizing most, if not all, oviraptorosaurians (e.g., Lamanna et al., 2014), is present,
61
although it is not nearly as extensive as those in Caenagnathus collinsi or Anzu (Currie et al., 1994; Lamanna et al., 2014). The dorsal or occlusal edge of the dentaries is sharp. Unlike in derived caenagnathids (Currie et al., 1994; Longrich et al., 2013; Lamanna et al., 2014), the lingual ridge (Currie et al., 1994) or triturating shelf (Longrich et al., 2013) is not distinctly developed in the present specimen. Anterior occlusal grooves and ridges described in derived caenagnathids (Currie et al., 1994; Lamanna et al., 2014) are apparently absent in the symphysis area. More distally (posteriorly), however, a series of dorsoventrally elongated depressions, eight on the better-preserved right ramus, occur on the lingual surface just below the dorsal edge of the bone (Fig. 2A). These depressions topologically correspond to lateral occlusal grooves in derived caenagnathids, including Caenagnathus collinsi, ‘Caenagnathus’ sternbergi, Leptorhynchos and Caenagnathasia (Currie et al., 1994). The ventral aspect of the symphyseal area bears a depression, which has been described as hourglass- or dumbbell-shaped in derived caenagnathids (Currie et al., 1994), demarcated by a sharp ridge on either side (Fig. 2E). On the lingual side of the bone and posterodorsal to this depression, the Meckelian groove extends posteriorly. Dorsal to the Meckelian groove lies a tab-like process on each side of the sagittal line (Figs. 2E, F, 4A). Posterior to this tablike process on the lingual side of the bone, an anteroposteriorly elongate articular surface for the splenial is ventrally demarcated by a ridge (Fig. 4A). A large, anteroposteriorly elongated foramen (maximum diameter up to 10 mm) is present dorsal to the splenial articular surface on the posteriormost part on the preserved bone (Fig. 4A). The same foramen was interpreted as being for the inferior alveolar nerve and internal mandibular artery in derived caenagnathids by Currie et al. (1994). The base of a flange of bone is preserved dorsal to this foramen (Fig. 4A). This flange would have lingually overlapped the surangular and/or articular. A homologous flange was described in derived caenagnathids by Currie et al. (1994). While still in a plaster jacket, the specimen was scanned on the TESCO TXS320-ACTIS micro CT scanner at the National Museum of Nature and Science, Tokyo, Japan at 290 kv and 290 mA. The CT scan data revealed numerous, presumably pneumatic chambers developed inside the otherwise dense bone (Fig. 3). 5. Discussion Several characteristics of the present specimen have been identified as synapomorphies of Oviraptorosauria or more exclu lska et al. (2004) sive clades in past analyses. For example, Osmo identified a U-shaped mandibular symphysis and the absence of teeth on the dentary as oviraptorosaurian synapomorphies, although the latter feature turned out to characterize a more exclusive clade because the basal-most oviraptorosaurian Incisivosaurus gauthieri possesses dentary teeth (Xu et al., 2002a). To confirm such synapomorphies, character optimization was conducted based on the data matrix and most parsimonious tree topology of Lamanna et al. (2014) using MacClade 4 Version 4.08 (Maddison and Maddison, 2005). First, a U-shaped mandibular symphysis and the presence of the symphyseal shelf in the present specimen were optimized as oviraptorosaurian synapomorphies. The absence of teeth on the dentary characterized the clade consisting of oviraptorosaurians more derived than Incisivosaurus. As identified by Lamanna et al. (2014), the fused symphysis between the dentaries is a synapomorphy for caenagnathids more derived than Microvenator (and, convergently, in Incisivosaurus as well). These characteristics present in MPC-D 107/17, therefore, strongly indicate its oviraptorosaurian affinity. The hierarchical distribution of these characteristics also suggests that MPC-D 107/17 belongs to
62
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
Fig. 2. MPC-D 107/17, symphyseal part of fused dentaries of a caenagnathid. A, dorsal view; B, anterior view; C, right lateral view; D, left lateral view; E, ventral view; F, lingual view of the anteriormost region. Abbreviations: dlog, depressions probably corresponding to lateral occlusal grooves in derived caenagnathids; b, breakage; lf, lateral flange; ld, lateral depression; ?pf, possible pneumatic foramen (crushed); mg, Meckelian groove; tp, tab-like processes; vd, ventral depression.
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
63
Fig. 3. A CT image slice showing an oblique frontal section of MPC-D 107/17, with the position of the slice indicated in the inset figure. Abbreviations: lr, left ramus; pj, plaster jacket; ?pf, possible pneumatic foramen; ps, pneumatic space; rr, right ramus; s, sediment.
Fig. 4. MPC-D 107/17, symphyseal part of fused dentaries of a caenagnathid. A, oblique lingual view of the right ramus; B, preserved part of the specimen in relation to the entire lower jaw in right lateral view. The profile of the lower jaw is based on the morphology of Gigantoraptor erlianensis illustrated in Xu et al. (2007). Abbreviations: a, angular; assp, articular surface for the splenial; bf, base of a bony flange; d, dentary; fiav, foramen for the inferior alveolar nerve and internal mandibular artery; sac, surangular-articular-coronoid complex; tp, tab-like processes.
Caenagnathidae. Furthermore, MPC-D 107/17 appears to possess a fossa with a pneumatic foramen on the lateral surface of the dentary, which was identified as a synapomorphy for Caenagnathidae by Lamanna et al. (2014). The lateral flange dorsal to this fossa is also present in Gigantoraptor and Anzu. Based on the difference in detailed morphology, such as its anterior extent, Lamanna et al. (2014) considered the presence of this flange as convergently evolved in these two taxa, which was corroborated by the most parsimonious tree topologies obtained in their analysis conducted by omitting all of those caenagnathid taxa for which no mandibular material is known (Lamanna et al., 2014, fig. 6B). The lateral flange
in MPC-D 107/17 is more similar to that in Gigantoraptor than in Anzu in being restricted to the middle part of the dentary dorsal to the lateral depression and not extending farther anteriorly to the symphyseal region. The caenagnathid affinities of MPC-D 107/17 were further confirmed by adding this specimen to the dataset of Lamanna et al. (2014), in which caenagnathid taxa without known mandibular material were omitted, and conducting a cladistic analysis with equally weighted parsimony using TNT v. 1.0 (Goloboff et al., 2008; see Appendix for coding of this specimen). One thousand replicates of tree bisection reconnection branch swapping were run holding
64
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
10 trees per replicate with all zero-length branches collapsed. The search resulted in 152 most parsimonious trees (MPTs) of 502 steps (CI 0.534, RI 0.700). Because some replicates encountered more than 10 most parsimonious trees, further branch-swapping starting from the 152 most parsimonious trees in memory was conducted, with nine additional optimal topologies found. Branch support was estimated with bootstrap values (5000 replicates). The strict consensus tree of these 161 most parsimonious trees had the same topology as that in Lamanna et al. (2014, figure 6B). The exception was that caenagnathids more derived than Microvenator comprised a large, unresolved polytomy, including MPC-D 107/17, although the bootstrap valuesdnine for Caenagnathidae and 15 for this polytomydwere rather low. The size is similar between MPC-D 107/17 and the corresponding part of Gigantoraptor. Based on the illustration in Xu et al. (2007), the entire lower jaw of Gigantoraptor is approximately 40e45 cm in length. Assuming a Gigantoraptor-like morphology, the entire length of the lower jaw from which MPC-D 107/17 was derived would likely have been 45e50 cm in length (Fig. 4B). The overall morphology is also similar between MPC-D 107/17 and Gigantoraptor. In particular, MPC-D 107/17 and Gigantoraptor share one derived characteristic, the lateral flange, which is otherwise present only in Anzu among oviraptorosaurians according to Lamanna et al. (2014). On the other hand, MPC-D 107/17 lacks a fossa on the lateral surface of the dentary near the symphysis (anterior fossa), which Xu et al. (2007) regarded as one of the diagnostic features of Gigantoraptor. Because the fragmentary nature of MPC-D 107/17 prevents a more detailed phylogenetic assessment, it is here regarded as Caenagnathidae gen. et sp. indet. The correlation of the Iren Dabasu Formation (which produced Gigantoraptor) in China with other formations in the Gobi Basin has been debated. Van Itterbeeck et al. (2005) correlated the Iren Dabasu Formation with the Nemegt Formation in Mongolia based on charophyte and ostracode assemblages and inferred the age of these formations to be the latest Campanian to early Maastrichtian. In doing so, Van Itterbeeck et al. (2005) questioned the previous correlation by Jerzykiewicz and Russell (1991) and Currie and Eberth (1993) of the Iren Dabasu Formation with the Bayn Shire Formation in Mongolia based on vertebrate assemblages. Sues and Averianov (2009) and Averianov and Sues (2012), however, regarded the correlation between the Iren Dabasu and Nemegt formations problematic, citing that the stratigraphic ranges of many microfossil taxa used for this correlation by Van Itterbeeck et al. (2005) were not necessarily restricted to the Maastrichtian and that similarity in the composition of such microfossil taxa between the Iren Dabasu and Nemegt formations are likely due to a similarity in depositional and climatic settings, not age, between these formations. Sues and Averianov (2009) and Averianov and Sues (2012) instead supported a correlation among the Bissekty Formation in Uzbekistan, the upper part of the Bayn Shire Formation, and the Iren Dabasu Formation, as proposed by Nessov (1995) and Averianov (2002) based on vertebrates, especially turtles. Because the age of the Bissekty Formation is well constrained as middle to late Turonian based on marine intercalation (Nessov, 1995; Averianov and Sues, 2012), the correlation among these formations would contradict the latest Campanian to early Maastrichtian age for the Iren Dabasu Formation proposed by Van Itterbeeck et al. (2005). If confirmed, occurrences of Gigantoraptor in both the Iren Dabasu and Bayn Shire Formations would be consistent with the correlation between these formations. Importantly, whereas such correlation is reasonably well supported based on turtle genera common to these formations (Currie and Eberth, 1993; Averianov, 2002), occurrences of most dinosaur genera that Currie and
Eberth (1993) proposed or cited as shared between these two formations have not been confirmed or have since been dismissed. For example, Currie and Eberth (1993) suggested the presence of Garudimimus brevipes in the Iren Dabasu Formation based on metatarsals found from this formation that were originally considered to belong to Archaeornithomimus asiaticus. Kobayashi and Barsbold (2005), however, noted the difference in morphology between these metatarsals and those of the holotype of Garudimimus described from the Bayn Shire Formation. Accordingly, they dismissed the presence of Garudimimus in the Iren Dabasu Formation. Perle (1977) referred tyrannosauroid material from the Bayn Shire Formation to Alectrosaurus olseni based on the gracile proportions of its hindlimb elements, the holotype of which was found in the Iren Dabasu Formation. Mader and Bradley (1989) and Holtz (2004), however, cast doubt on this referral of the Bayn Shire material. Finally, Currie and Eberth (1993) referred isolated elements of therizinosaurians from the Iren Dabasu Formation to Erlicosaurus andrewsi, Segnosaurus galbiensis and possibly Enigmosaurus mongoliensis, all of which were described based on holotypes from the Bayn Shire Formation. Since then, new therizinosaurians, namely, Neimongosaurus yangi and Erliansaurus bellamanus have been described from the Iren Dabasu Formation (Zhang et al., 2001; Xu et al., 2002b). Accordingly, the taxonomy of the Iren Dabasu therizinosaurian specimens cited by Currie and Eberth (1993) needs to be reexamined based on autapomorphies of the named taxa not only from the Bayn Shire Formation but also from the Iren Dabasu Formation. In summary, there is currently no evidence for dinosaurian genera shared by the two formations. If more material confirms the affinity of MPC-D 107/17 with Gigantoraptor, this would be among the first definite records of a dinosaurian taxon occurring in both the Iren Dabasu and Bayn Shire formations. The finding of MPC-D 107/17 also suggests that the theropod diversity in the Bayn Shire Formation could be increased by future paleontological work. Several studies have described the remains of large-bodied (body length of approximately 3.5 m) caenagnathids from the Campanian and Maastrichtian strata in North America (Zanno and Sampson, 2005; Lamanna et al., 2014; Bell et al., 2015). Based on these findings, Bell et al. (2015) concluded that caenagnathids of large body size were widespread in North America during these ages. The Tsagaan Teg and Saihangaobi localities, which produced MPC-D 107/17 and the holotype of G. erlianensis, respectively, are approximately 240 km apart (Fig. 1) and are located in separate basins (Eastern Gobi and Erlian basins, respectively) formed during the late Mesozoic intracontinental extension (Meng et al., 2003). Regardless of the age of the Iren Dabasu Formation (either latest Campanian to early Maastrichtian or Cenomanian to Santonian), the discovery of MPC-D 107/17 shows that giant caenagnathids were not restricted to a single locality and that large-bodied caenagnathids were widely distributed across North America and Asia in the Late Cretaceous. The Bayn Shire Formation yielding MPC-D 107/17 and the Iren Dabasu Formation yielding Gigantoraptor both consist mainly of fluvial sediments (e.g., Jerzykiewicz and Russell, 1991; Currie and Eberth, 1993; Jerzykiewicz, 2000), as do the Campanian and Maastrichtian strata in North America from which large-bodied caenagnathids have been found (Zanno and Sampson, 2005; Lamanna et al., 2014; Bell et al., 2015). In contrast, most oviraptorids of smaller sizes have been found from sediments deposited under semi-arid and arid environments (e.g., Longrich et al., 2010; Lamanna et al., 2014). Taken at face value, such data might be interpreted as suggesting that large-bodied caenagnathids inhabited more mesic environments than other, small-bodied oviraptorosaurians. However, two factors confound such an interpretation. First, both large and smaller forms of caenagnathids
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
occur in fluvial sediments (e.g., Longrich et al., 2013). It is therefore possible that caenagnathids in general preferred fluvial-dominated environments for their habitats (e.g., Lamanna et al., 2014). Second, a strong taphonomic bias against the preservation of small-bodied taxa has been well-documented in fluvial systems (e.g., Brown et al., 2013). Therefore, relatively rare occurrences of smallbodied oviraptorosaurians in fluvial sediments may simply reflect the fact that skeletons of such taxa rarely survived high-energy fluvial processes (e.g., Lamanna et al., 2014). Further exploration of theropod faunas and sedimentology in localities of large-bodied caenagnathids, including the Tsagaan Teg region, will contribute to clarifying the still enigmatic paleoecology of this clade of theropods. 6. Conclusions A large, fused symphyseal region of dentaries found in the Bayn Shire Formation in the Tsagaan Teg region of Mongolia belongs to a caenagnathid oviraptorosaurian. Although fragmentary, this specimen is likely closely related to Gigantoraptor erlianensis, known from the Iren Dabasu Formation in China. Co-occurrences of Gigantoraptor and its close ally in the Iren Dabasu and Bayn Shire formations is consistent with the hypothesized correlation between these formations based on other vertebrate fossils. As recently recognized, large caenagnathids appear to have been widespread in Asia and North America. Acknowledgments We are grateful to K. Hayashibara (former president of the Hayashibara Company Limited, Okayama, Japan) for his continuous financial support of the Japanese-Mongolian Joint Paleontological Expedition since 1993. Thanks are also due to the Japanese (Hayashibara Museum of Natural Sciences) and Mongolian (MPC) members of the joint expedition team for their help in the field and laboratories. Olympus, Mitsubishi Motor Company, and Panasonic supported the expedition. We thank M. Manabe (National Museum of Nature and Science, Tokyo) for access to the CT scanner under his care. Two anonymous reviewers made constructive suggestions that greatly improved the clarity of the manuscript. The English translation of Nessov (1995) was by T. Platanova and H.-D. Sues and was obtained courtesy of the Polyglot Paleontologist website (http://www.paleoglot.org). This paper is Japanese-Mongolian Joint Paleontological Expedition Contribution Number 87. References Averianov, A.O., 2002. An ankylosaurid (Ornithischia: Ankylosauria) braincase from the Upper Cretaceous Bissekty Formation of Uzbekistan. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique Sciences de la Terre 72, 97e110. Averianov, A., Sues, H.-D., 2012. Correlation of Late Cretaceous continental vertebrate assemblages in Middle and Central Asia. Journal of Stratigraphy 36, 462e485. Bell, P.R., Currie, P.J., Russell, D.A., 2015. Large caenagnathids (Dinosauria, Oviraptorosauria) from the uppermost Cretaceous of western Canada. Cretaceous Research 52, 101e107. Brown, C.M., Evans, D.C., Campione, N.E., O'Brien, L.J., Eberth, D.A., 2013. Evidence for taphonomic size bias in the Dinosaur Park Formation (Campanian, Alberta), a model Mesozoic terrestrial alluvial-paralic system. Palaeogeography, Palaeoclimatology, Palaeoecology 372, 108e122. Currie, P.J., Eberth, D.A., 1993. Palaeontology, sedimentology and palaeoecology of the Iren Dabasu Formation (Upper Cretaceous), Inner Mongolia, People's Republic of China. Cretaceous Research 14, 127e144. Currie, P.J., Godfrey, S.J., Nessov, L., 1994. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences 30, 2255e2272.
65
Goloboff, P.A., Farris, J.S., Nixon, K.C., 2008. TNT, a free program for phylogenetic analysis. Cladistics 24, 774e786. Hicks, J.F., Brinkman, D.L., Nichols, D.J., Watabe, M., 1999. Paleomagnetic and palynologic analyses of Albian to Santonian strata at Bayn Shireh, Burkhant, and Khuren Dukh, eastern Gobi Desert, Mongolia. Cretaceous Research 20, 829e850. Holtz Jr., T.R., 2004. Tyrannosauroidea; pp. 111e136. In: Weishampel, D.B., lska, H. (Eds.), The Dinosauria, second edition. University of Dodson, P., Osmo California Press, Berkeley, California. Jerzykiewicz, T., 2000. Lithostratigraphy and sedimentary settings of the Cretaceous dinosaur beds of Mongolia; pp. 279e296. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., Kurochkin, E.N. (Eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge. Jerzykiewicz, T., Russell, D.A., 1991. Late Mesozoic stratigraphy and vertebrates of the Gobi Basin. Cretaceous Research 12, 345e377. Kobayashi, Y., Barsbold, R., 2005. Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences 42, 1501e1521. Lamanna, M.C., Sues, H.-D., Schachner, E.R., Lyson, T.R., 2014. A new large-bodied oviraptorosaurian theropod dinosaur from the latest Cretaceous of Western North America. PLoS One 9, e92022. Longrich, N.R., Currie, P.J., Dong, Z.-M., 2010. A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia. Palaeontology 53, 945e960. Longrich, N.R., Barnes, K., Clark, S., Millar, L., 2013. Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a revision of the Caenagnathinae. Bulletin of the Peabody Museum of Natural History 54, 23e49. Maddison, D.R., Maddison, W.P., 2005. MacClade 4: analysis of phylogeny and character evolution. Version 4.08. Sinauer Associates, Sunderland, Massachusetts. Mader, B.J., Bradley, R.T., 1989. A redescription and revised diagnosis of the syntypes of the Mongolian tyrannosaur Alectrosaurus olseni. Journal of Vertebrate Paleontology 9, 41e55. Meng, Q.-R., Hu, J.-M., Jin, J.-Q., Zhang, Y., Xu, D.-F., 2003. Tectonics of the late Mesozoic wide extensional basin system in the China-Mongolia border region. Basin Research 15, 397e415. Nessov, L.A., 1995. Dinosaurs of northern Eurasia: new data about assemblages, ecology and paleobiogeography. Izdatel’stvo Sankt-Peterburgskogo Universiteta, St Petersburg, Russia, p. 156 [Russian]. lska, H., Currie, P.J., Barsbold, R., 2004. Oviraptorosauria; pp. 165e183. In: Osmo lska, H. (Eds.), The Dinosauria. University of Weishampel, D.B., Dodson, P., Osmo California Press, Berkeley, California. Perle, A., 1977. On the first discovery of Alectrosaurus (Tyrannosauridae, Theropoda) from the Late Cretaceous of Mongolia. Problemy Mongol'skoi Geologii 3, 104e113 [Russian]. Sues, H.-D., Averianov, A., 2009. A new basal hadrosauroid dinosaur from the Late Cretaceous of Uzbekistan and the early radiation of duck-billed dinosaurs. Proceedings of the Royal Society B: Biological Sciences 276, 2549e2555. Tsubamoto, T., Saneyoshi, M., Tsogtbaatar, K., Chinzorig, T., Khatanbaatar, P., Mainbayar, B., Suzuki, S., 2010. Report of the HMNS-MPC Joint Paleontological Expedition in 2008. Hayashibara Museum of Natural Sciences Research Bulletin 3, 29e39. Tumoanova, T.A., 1993. Concerning a new armored dinosaur from the southeastern Gobi. Paleontologicheskii Zhurnal 1993, 92e98 [Russian]. Van Itterbeeck, J., Horne, D.J., Bultynck, P., Vandenberghe, N., 2005. Stratigraphy and palaeoenvironment of the dinosaur-bearing Upper Cretaceous Iren Dabasu Formation, Inner Mongolia, People's Republic of China. Cretaceous Research 26, 699e725. Watabe, M., Tsogtbaatar, K., Suzuki, S., Saneyoshi, M., 2010. Geology of dinosaurfossil-bearing localities (Jurassic and Cretaceous: Mesozoic) in the Gobi Desert: results of the HMNS-MPC Joint Paleontological Expedition. Hayashibara Museum of Natural Sciences Research Bulletin 3, 41e118. Xu, X., Cheng, Y.-N., Wang, X.-L., Chang, C.-H., 2002a. An unusual oviraptorosaurian dinosaur from China. Nature 419, 291e293. Xu, X., Zhang, X.-H., Sereno, P., Zhao, X.-J., Kuang, X.-W., Han, J., Tan, L., 2002b. A new therizinosauroid (Dinosauria, Theropoda) from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol. Vertebrata PalAsiatica 40, 228e240. Xu, X., Tan, Q., Wang, J., Zhao, X., Tan, L., 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature 447, 844e847. Zanno, L.E., Sampson, S.D., 2005. A new oviraptorosaur (Theropoda, Maniraptora) form the Late Cretaceous (Campanian) of Utah. Journal of Vertebrate Paleontology 25, 897e904. Zhang, X.-H., Xu, X., Zhao, X.-J., Sereno, P., Kuanng, X.-W., Tan, L., 2001. A longnecked therizinosauroid dinosaur from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol, People's Republic of China. Vertebrata PalAsiatica 39, 282e290.
Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10. 1016/j.cretres.2015.03.007.
Contents lists available at ScienceDirect
Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes
A gigantic caenagnathid oviraptorosaurian (Dinosauria: Theropoda) from the Upper Cretaceous of the Gobi Desert, Mongolia Takanobu Tsuihiji a, *, Mahito Watabe b, Rinchen Barsbold c, Khishigjav Tsogtbaatar c a
Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113-0033, Japan Department of Geosciences, Osaka City University, Osaka 558-8585, Japan c Mongolian Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar 210351, Mongolia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 December 2014 Accepted in revised form 26 March 2015 Available online
A large, isolated symphyseal region of fused dentaries of an oviraptorosaurian was found in the Upper Cretaceous Bayn Shire Formation at Tsagaan Teg in the Mongolian Gobi Desert. A phylogenetic analysis places this specimen within Caenagnathidae. This specimen is comparable in size and morphology to the gigantic caenagnathid Gigantoraptor erlianensis from the Iren Dabasu Formation in China and is likely closely related to it. The occurrence of the specimen with possible affinities to G. erlianensis in the Bayn Shire Formation is consistent with the hypothesized correlation between the Bayn Shire and Iren Dabasu formations based on the co-occurrences of vertebrate fossils, especially turtles. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Caenagnathidae Oviraptorosauria Bayn Shire Formation
1. Introduction Oviraptorosauria is a clade of mostly small to medium-sized maniraptoran theropods, with body lengths that rarely exceeded lska et al., 2004). More recently, however, large-bodied 2 m (Osmo caenagnathid oviraptorosaurians have been described. Anzu wyliei, from the upper Maastrichtian Hell Creek Formation of the western United States, is approximately 3.5 m in total length (Lamanna et al., 2014). Unguals of similarly sized caenagnathids have also been described from the upper Campanian Dinosaur Park and the Maastrichtian Frenchman formations of Canada (Bell et al., 2015). An even larger-bodied taxon is Gigantoraptor erlianensis, from the Iren Dabasu Formation of Inner Mongolia in China, estimated to be approximately 8 m in total length (Xu et al., 2007), revealing a body-size variation within Caenagnathidae much larger than expected before. In 2008, a fused symphyseal region of the two dentaries was found in strata of the Bayn Shire Formation in the Tsagaan Teg region of the central part of Eastern Gobi Aimag, Mongolia (Fig. 1) by the Hayashibara Museum of Natural Sciences-Mongolian Paleontological Center Joint Expedition. Although fragmentary, this specimen possesses several derived features characterizing the
* Corresponding author. Department of Earth and Planetary Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Tel.: þ81 3 5841 4519. E-mail address: [email protected] (T. Tsuihiji). http://dx.doi.org/10.1016/j.cretres.2015.03.007 0195-6671/© 2015 Elsevier Ltd. All rights reserved.
clade Oviraptorosauria, especially Caenagnathidae. A remarkable aspect of this specimen is its size: the dorsoventral height at the symphyseal region is 97 mm, much larger than the corresponding bones in most oviraptorosaurians but comparable in size to that of Gigantoraptor. In fact, the present specimen is similar to the corresponding part of Gigantoraptor in overall morphology and indeed likely represents a taxon that is closely related to it. This finding is another example of closely related vertebrate taxa co-occurring in the Iren Dabasu and Bayn Shire Formations and is thus consistent with the hypothesized correlation between these formations (Jerzykiewicz and Russell, 1991; Currie and Eberth, 1993; Averianov and Sues, 2012). Institutional Abbreviation: MPC, Mongolian Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia. 2. Material MPC-D 107/17, isolated symphyseal region of fused dentaries. 3. Locality and age The specimen examined is from Tsagaan Teg, Eastern Gobi Aimag, Mongolia (Fig. 1). This locality is situated approximately 20 km southwest of Dzun Bayan Somon and consists of the main outcrop and a second outcrop called Tsagaan Teg West (Watabe et al., 2010). The present specimen was found at the latter outcrop in a layer of medium-to coarse-grained sandstone. The
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
Fig. 1. Map of Mongolia showing the Tsagaan Teg locality as well as Saihangaobi in China, where the holotype of Gigantoraptor erlianensis was found (modified from Tsubamoto et al., 2010).
horizon exposed in the Tsagaan Teg region is correlated with the Bayn Shire Formation (Jerzykiewicz and Russell, 1991; Tumoanova, 1993; Watabe et al., 2010), the age of which is inferred to be the Cenomanian to Santonian (Hicks et al., 1999; Averianov and Sues, 2012). 4. Description MPC-D 107/17 consists of the symphyseal part of fused dentaries of a large oviraptorosaurian (Fig. 2AeF). It is mediolaterally compressed and is crushed around the symphysis (Fig. 2B) so that the left ramus is pushed against the lingual aspect of the mesialmost part of the right ramus, obscuring a detailed morphology of the lingual aspect around the symphysis (Fig. 2F). Teeth are completely lacking. No clear suture is present on the symphysis, indicating that the dentaries are completely fused as in caenagnathids more derived than Microvenator celer such as Caenagnathus collinsi, ‘Caenagnathus’ sternbergi, Caenagnathasia martinsoni, Leptorhynchos gaddisi, Anzu and Gigantoraptor (e.g., Currie et al., 1994; Xu et al., 2007; Longrich et al., 2013; Lamanna et al., lska et al., 2004) such as Cit2014), but unlike oviraptorids (Osmo ipati sp. (MPC-D 100/42) and Rinchenia mongoliensis (MPC-D 100/ 321), in which such a suture between the dentaries is discernable. The symphysis is dorsoventrally deep (97 mm) relative to the maximum anteroposterior length of the preserved part (142 mm). The labial surface is generally smooth except for numerous foramina of various sizes (Fig. 2C). Similar to the condition described in derived caenagnathids by Currie et al. (1994), two rows of relatively large foramina extend parallel to the dorsal and ventral margins of the bone. Toward the anterior end, the ventral row curves upwards. The third row of foramina extends anteroposteriorly approximately 20e25 mm dorsal to the ventral row. In addition, three relatively large foramina cluster anterior to a depression ventral to the lateral flange. As in Gigantoraptor (Xu et al., 2007), the lateral flange is present on the posterodorsal corner of the preserved part, extending posterodorsally (Fig. 2C). As in Gigantoraptor (Xu et al., 2007), but unlike in Anzu (Lamanna et al., 2014), this flange does not extend to the symphysis. Ventral to this flange, there is a large depression as in Gigantoraptor (Xu et al., 2007). The lateral surface of this depression is crushed, but CT data suggests that there is likely a foramen that leads into a pneumatic space inside the bone (Fig. 3), as in derived caenagnathids (Currie et al., 1994). A lingually extended symphyseal shelf, characterizing most, if not all, oviraptorosaurians (e.g., Lamanna et al., 2014), is present,
61
although it is not nearly as extensive as those in Caenagnathus collinsi or Anzu (Currie et al., 1994; Lamanna et al., 2014). The dorsal or occlusal edge of the dentaries is sharp. Unlike in derived caenagnathids (Currie et al., 1994; Longrich et al., 2013; Lamanna et al., 2014), the lingual ridge (Currie et al., 1994) or triturating shelf (Longrich et al., 2013) is not distinctly developed in the present specimen. Anterior occlusal grooves and ridges described in derived caenagnathids (Currie et al., 1994; Lamanna et al., 2014) are apparently absent in the symphysis area. More distally (posteriorly), however, a series of dorsoventrally elongated depressions, eight on the better-preserved right ramus, occur on the lingual surface just below the dorsal edge of the bone (Fig. 2A). These depressions topologically correspond to lateral occlusal grooves in derived caenagnathids, including Caenagnathus collinsi, ‘Caenagnathus’ sternbergi, Leptorhynchos and Caenagnathasia (Currie et al., 1994). The ventral aspect of the symphyseal area bears a depression, which has been described as hourglass- or dumbbell-shaped in derived caenagnathids (Currie et al., 1994), demarcated by a sharp ridge on either side (Fig. 2E). On the lingual side of the bone and posterodorsal to this depression, the Meckelian groove extends posteriorly. Dorsal to the Meckelian groove lies a tab-like process on each side of the sagittal line (Figs. 2E, F, 4A). Posterior to this tablike process on the lingual side of the bone, an anteroposteriorly elongate articular surface for the splenial is ventrally demarcated by a ridge (Fig. 4A). A large, anteroposteriorly elongated foramen (maximum diameter up to 10 mm) is present dorsal to the splenial articular surface on the posteriormost part on the preserved bone (Fig. 4A). The same foramen was interpreted as being for the inferior alveolar nerve and internal mandibular artery in derived caenagnathids by Currie et al. (1994). The base of a flange of bone is preserved dorsal to this foramen (Fig. 4A). This flange would have lingually overlapped the surangular and/or articular. A homologous flange was described in derived caenagnathids by Currie et al. (1994). While still in a plaster jacket, the specimen was scanned on the TESCO TXS320-ACTIS micro CT scanner at the National Museum of Nature and Science, Tokyo, Japan at 290 kv and 290 mA. The CT scan data revealed numerous, presumably pneumatic chambers developed inside the otherwise dense bone (Fig. 3). 5. Discussion Several characteristics of the present specimen have been identified as synapomorphies of Oviraptorosauria or more exclu lska et al. (2004) sive clades in past analyses. For example, Osmo identified a U-shaped mandibular symphysis and the absence of teeth on the dentary as oviraptorosaurian synapomorphies, although the latter feature turned out to characterize a more exclusive clade because the basal-most oviraptorosaurian Incisivosaurus gauthieri possesses dentary teeth (Xu et al., 2002a). To confirm such synapomorphies, character optimization was conducted based on the data matrix and most parsimonious tree topology of Lamanna et al. (2014) using MacClade 4 Version 4.08 (Maddison and Maddison, 2005). First, a U-shaped mandibular symphysis and the presence of the symphyseal shelf in the present specimen were optimized as oviraptorosaurian synapomorphies. The absence of teeth on the dentary characterized the clade consisting of oviraptorosaurians more derived than Incisivosaurus. As identified by Lamanna et al. (2014), the fused symphysis between the dentaries is a synapomorphy for caenagnathids more derived than Microvenator (and, convergently, in Incisivosaurus as well). These characteristics present in MPC-D 107/17, therefore, strongly indicate its oviraptorosaurian affinity. The hierarchical distribution of these characteristics also suggests that MPC-D 107/17 belongs to
62
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
Fig. 2. MPC-D 107/17, symphyseal part of fused dentaries of a caenagnathid. A, dorsal view; B, anterior view; C, right lateral view; D, left lateral view; E, ventral view; F, lingual view of the anteriormost region. Abbreviations: dlog, depressions probably corresponding to lateral occlusal grooves in derived caenagnathids; b, breakage; lf, lateral flange; ld, lateral depression; ?pf, possible pneumatic foramen (crushed); mg, Meckelian groove; tp, tab-like processes; vd, ventral depression.
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
63
Fig. 3. A CT image slice showing an oblique frontal section of MPC-D 107/17, with the position of the slice indicated in the inset figure. Abbreviations: lr, left ramus; pj, plaster jacket; ?pf, possible pneumatic foramen; ps, pneumatic space; rr, right ramus; s, sediment.
Fig. 4. MPC-D 107/17, symphyseal part of fused dentaries of a caenagnathid. A, oblique lingual view of the right ramus; B, preserved part of the specimen in relation to the entire lower jaw in right lateral view. The profile of the lower jaw is based on the morphology of Gigantoraptor erlianensis illustrated in Xu et al. (2007). Abbreviations: a, angular; assp, articular surface for the splenial; bf, base of a bony flange; d, dentary; fiav, foramen for the inferior alveolar nerve and internal mandibular artery; sac, surangular-articular-coronoid complex; tp, tab-like processes.
Caenagnathidae. Furthermore, MPC-D 107/17 appears to possess a fossa with a pneumatic foramen on the lateral surface of the dentary, which was identified as a synapomorphy for Caenagnathidae by Lamanna et al. (2014). The lateral flange dorsal to this fossa is also present in Gigantoraptor and Anzu. Based on the difference in detailed morphology, such as its anterior extent, Lamanna et al. (2014) considered the presence of this flange as convergently evolved in these two taxa, which was corroborated by the most parsimonious tree topologies obtained in their analysis conducted by omitting all of those caenagnathid taxa for which no mandibular material is known (Lamanna et al., 2014, fig. 6B). The lateral flange
in MPC-D 107/17 is more similar to that in Gigantoraptor than in Anzu in being restricted to the middle part of the dentary dorsal to the lateral depression and not extending farther anteriorly to the symphyseal region. The caenagnathid affinities of MPC-D 107/17 were further confirmed by adding this specimen to the dataset of Lamanna et al. (2014), in which caenagnathid taxa without known mandibular material were omitted, and conducting a cladistic analysis with equally weighted parsimony using TNT v. 1.0 (Goloboff et al., 2008; see Appendix for coding of this specimen). One thousand replicates of tree bisection reconnection branch swapping were run holding
64
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
10 trees per replicate with all zero-length branches collapsed. The search resulted in 152 most parsimonious trees (MPTs) of 502 steps (CI 0.534, RI 0.700). Because some replicates encountered more than 10 most parsimonious trees, further branch-swapping starting from the 152 most parsimonious trees in memory was conducted, with nine additional optimal topologies found. Branch support was estimated with bootstrap values (5000 replicates). The strict consensus tree of these 161 most parsimonious trees had the same topology as that in Lamanna et al. (2014, figure 6B). The exception was that caenagnathids more derived than Microvenator comprised a large, unresolved polytomy, including MPC-D 107/17, although the bootstrap valuesdnine for Caenagnathidae and 15 for this polytomydwere rather low. The size is similar between MPC-D 107/17 and the corresponding part of Gigantoraptor. Based on the illustration in Xu et al. (2007), the entire lower jaw of Gigantoraptor is approximately 40e45 cm in length. Assuming a Gigantoraptor-like morphology, the entire length of the lower jaw from which MPC-D 107/17 was derived would likely have been 45e50 cm in length (Fig. 4B). The overall morphology is also similar between MPC-D 107/17 and Gigantoraptor. In particular, MPC-D 107/17 and Gigantoraptor share one derived characteristic, the lateral flange, which is otherwise present only in Anzu among oviraptorosaurians according to Lamanna et al. (2014). On the other hand, MPC-D 107/17 lacks a fossa on the lateral surface of the dentary near the symphysis (anterior fossa), which Xu et al. (2007) regarded as one of the diagnostic features of Gigantoraptor. Because the fragmentary nature of MPC-D 107/17 prevents a more detailed phylogenetic assessment, it is here regarded as Caenagnathidae gen. et sp. indet. The correlation of the Iren Dabasu Formation (which produced Gigantoraptor) in China with other formations in the Gobi Basin has been debated. Van Itterbeeck et al. (2005) correlated the Iren Dabasu Formation with the Nemegt Formation in Mongolia based on charophyte and ostracode assemblages and inferred the age of these formations to be the latest Campanian to early Maastrichtian. In doing so, Van Itterbeeck et al. (2005) questioned the previous correlation by Jerzykiewicz and Russell (1991) and Currie and Eberth (1993) of the Iren Dabasu Formation with the Bayn Shire Formation in Mongolia based on vertebrate assemblages. Sues and Averianov (2009) and Averianov and Sues (2012), however, regarded the correlation between the Iren Dabasu and Nemegt formations problematic, citing that the stratigraphic ranges of many microfossil taxa used for this correlation by Van Itterbeeck et al. (2005) were not necessarily restricted to the Maastrichtian and that similarity in the composition of such microfossil taxa between the Iren Dabasu and Nemegt formations are likely due to a similarity in depositional and climatic settings, not age, between these formations. Sues and Averianov (2009) and Averianov and Sues (2012) instead supported a correlation among the Bissekty Formation in Uzbekistan, the upper part of the Bayn Shire Formation, and the Iren Dabasu Formation, as proposed by Nessov (1995) and Averianov (2002) based on vertebrates, especially turtles. Because the age of the Bissekty Formation is well constrained as middle to late Turonian based on marine intercalation (Nessov, 1995; Averianov and Sues, 2012), the correlation among these formations would contradict the latest Campanian to early Maastrichtian age for the Iren Dabasu Formation proposed by Van Itterbeeck et al. (2005). If confirmed, occurrences of Gigantoraptor in both the Iren Dabasu and Bayn Shire Formations would be consistent with the correlation between these formations. Importantly, whereas such correlation is reasonably well supported based on turtle genera common to these formations (Currie and Eberth, 1993; Averianov, 2002), occurrences of most dinosaur genera that Currie and
Eberth (1993) proposed or cited as shared between these two formations have not been confirmed or have since been dismissed. For example, Currie and Eberth (1993) suggested the presence of Garudimimus brevipes in the Iren Dabasu Formation based on metatarsals found from this formation that were originally considered to belong to Archaeornithomimus asiaticus. Kobayashi and Barsbold (2005), however, noted the difference in morphology between these metatarsals and those of the holotype of Garudimimus described from the Bayn Shire Formation. Accordingly, they dismissed the presence of Garudimimus in the Iren Dabasu Formation. Perle (1977) referred tyrannosauroid material from the Bayn Shire Formation to Alectrosaurus olseni based on the gracile proportions of its hindlimb elements, the holotype of which was found in the Iren Dabasu Formation. Mader and Bradley (1989) and Holtz (2004), however, cast doubt on this referral of the Bayn Shire material. Finally, Currie and Eberth (1993) referred isolated elements of therizinosaurians from the Iren Dabasu Formation to Erlicosaurus andrewsi, Segnosaurus galbiensis and possibly Enigmosaurus mongoliensis, all of which were described based on holotypes from the Bayn Shire Formation. Since then, new therizinosaurians, namely, Neimongosaurus yangi and Erliansaurus bellamanus have been described from the Iren Dabasu Formation (Zhang et al., 2001; Xu et al., 2002b). Accordingly, the taxonomy of the Iren Dabasu therizinosaurian specimens cited by Currie and Eberth (1993) needs to be reexamined based on autapomorphies of the named taxa not only from the Bayn Shire Formation but also from the Iren Dabasu Formation. In summary, there is currently no evidence for dinosaurian genera shared by the two formations. If more material confirms the affinity of MPC-D 107/17 with Gigantoraptor, this would be among the first definite records of a dinosaurian taxon occurring in both the Iren Dabasu and Bayn Shire formations. The finding of MPC-D 107/17 also suggests that the theropod diversity in the Bayn Shire Formation could be increased by future paleontological work. Several studies have described the remains of large-bodied (body length of approximately 3.5 m) caenagnathids from the Campanian and Maastrichtian strata in North America (Zanno and Sampson, 2005; Lamanna et al., 2014; Bell et al., 2015). Based on these findings, Bell et al. (2015) concluded that caenagnathids of large body size were widespread in North America during these ages. The Tsagaan Teg and Saihangaobi localities, which produced MPC-D 107/17 and the holotype of G. erlianensis, respectively, are approximately 240 km apart (Fig. 1) and are located in separate basins (Eastern Gobi and Erlian basins, respectively) formed during the late Mesozoic intracontinental extension (Meng et al., 2003). Regardless of the age of the Iren Dabasu Formation (either latest Campanian to early Maastrichtian or Cenomanian to Santonian), the discovery of MPC-D 107/17 shows that giant caenagnathids were not restricted to a single locality and that large-bodied caenagnathids were widely distributed across North America and Asia in the Late Cretaceous. The Bayn Shire Formation yielding MPC-D 107/17 and the Iren Dabasu Formation yielding Gigantoraptor both consist mainly of fluvial sediments (e.g., Jerzykiewicz and Russell, 1991; Currie and Eberth, 1993; Jerzykiewicz, 2000), as do the Campanian and Maastrichtian strata in North America from which large-bodied caenagnathids have been found (Zanno and Sampson, 2005; Lamanna et al., 2014; Bell et al., 2015). In contrast, most oviraptorids of smaller sizes have been found from sediments deposited under semi-arid and arid environments (e.g., Longrich et al., 2010; Lamanna et al., 2014). Taken at face value, such data might be interpreted as suggesting that large-bodied caenagnathids inhabited more mesic environments than other, small-bodied oviraptorosaurians. However, two factors confound such an interpretation. First, both large and smaller forms of caenagnathids
T. Tsuihiji et al. / Cretaceous Research 56 (2015) 60e65
occur in fluvial sediments (e.g., Longrich et al., 2013). It is therefore possible that caenagnathids in general preferred fluvial-dominated environments for their habitats (e.g., Lamanna et al., 2014). Second, a strong taphonomic bias against the preservation of small-bodied taxa has been well-documented in fluvial systems (e.g., Brown et al., 2013). Therefore, relatively rare occurrences of smallbodied oviraptorosaurians in fluvial sediments may simply reflect the fact that skeletons of such taxa rarely survived high-energy fluvial processes (e.g., Lamanna et al., 2014). Further exploration of theropod faunas and sedimentology in localities of large-bodied caenagnathids, including the Tsagaan Teg region, will contribute to clarifying the still enigmatic paleoecology of this clade of theropods. 6. Conclusions A large, fused symphyseal region of dentaries found in the Bayn Shire Formation in the Tsagaan Teg region of Mongolia belongs to a caenagnathid oviraptorosaurian. Although fragmentary, this specimen is likely closely related to Gigantoraptor erlianensis, known from the Iren Dabasu Formation in China. Co-occurrences of Gigantoraptor and its close ally in the Iren Dabasu and Bayn Shire formations is consistent with the hypothesized correlation between these formations based on other vertebrate fossils. As recently recognized, large caenagnathids appear to have been widespread in Asia and North America. Acknowledgments We are grateful to K. Hayashibara (former president of the Hayashibara Company Limited, Okayama, Japan) for his continuous financial support of the Japanese-Mongolian Joint Paleontological Expedition since 1993. Thanks are also due to the Japanese (Hayashibara Museum of Natural Sciences) and Mongolian (MPC) members of the joint expedition team for their help in the field and laboratories. Olympus, Mitsubishi Motor Company, and Panasonic supported the expedition. We thank M. Manabe (National Museum of Nature and Science, Tokyo) for access to the CT scanner under his care. Two anonymous reviewers made constructive suggestions that greatly improved the clarity of the manuscript. The English translation of Nessov (1995) was by T. Platanova and H.-D. Sues and was obtained courtesy of the Polyglot Paleontologist website (http://www.paleoglot.org). This paper is Japanese-Mongolian Joint Paleontological Expedition Contribution Number 87. References Averianov, A.O., 2002. An ankylosaurid (Ornithischia: Ankylosauria) braincase from the Upper Cretaceous Bissekty Formation of Uzbekistan. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique Sciences de la Terre 72, 97e110. Averianov, A., Sues, H.-D., 2012. Correlation of Late Cretaceous continental vertebrate assemblages in Middle and Central Asia. Journal of Stratigraphy 36, 462e485. Bell, P.R., Currie, P.J., Russell, D.A., 2015. Large caenagnathids (Dinosauria, Oviraptorosauria) from the uppermost Cretaceous of western Canada. Cretaceous Research 52, 101e107. Brown, C.M., Evans, D.C., Campione, N.E., O'Brien, L.J., Eberth, D.A., 2013. Evidence for taphonomic size bias in the Dinosaur Park Formation (Campanian, Alberta), a model Mesozoic terrestrial alluvial-paralic system. Palaeogeography, Palaeoclimatology, Palaeoecology 372, 108e122. Currie, P.J., Eberth, D.A., 1993. Palaeontology, sedimentology and palaeoecology of the Iren Dabasu Formation (Upper Cretaceous), Inner Mongolia, People's Republic of China. Cretaceous Research 14, 127e144. Currie, P.J., Godfrey, S.J., Nessov, L., 1994. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences 30, 2255e2272.
65
Goloboff, P.A., Farris, J.S., Nixon, K.C., 2008. TNT, a free program for phylogenetic analysis. Cladistics 24, 774e786. Hicks, J.F., Brinkman, D.L., Nichols, D.J., Watabe, M., 1999. Paleomagnetic and palynologic analyses of Albian to Santonian strata at Bayn Shireh, Burkhant, and Khuren Dukh, eastern Gobi Desert, Mongolia. Cretaceous Research 20, 829e850. Holtz Jr., T.R., 2004. Tyrannosauroidea; pp. 111e136. In: Weishampel, D.B., lska, H. (Eds.), The Dinosauria, second edition. University of Dodson, P., Osmo California Press, Berkeley, California. Jerzykiewicz, T., 2000. Lithostratigraphy and sedimentary settings of the Cretaceous dinosaur beds of Mongolia; pp. 279e296. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., Kurochkin, E.N. (Eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge. Jerzykiewicz, T., Russell, D.A., 1991. Late Mesozoic stratigraphy and vertebrates of the Gobi Basin. Cretaceous Research 12, 345e377. Kobayashi, Y., Barsbold, R., 2005. Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences 42, 1501e1521. Lamanna, M.C., Sues, H.-D., Schachner, E.R., Lyson, T.R., 2014. A new large-bodied oviraptorosaurian theropod dinosaur from the latest Cretaceous of Western North America. PLoS One 9, e92022. Longrich, N.R., Currie, P.J., Dong, Z.-M., 2010. A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia. Palaeontology 53, 945e960. Longrich, N.R., Barnes, K., Clark, S., Millar, L., 2013. Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a revision of the Caenagnathinae. Bulletin of the Peabody Museum of Natural History 54, 23e49. Maddison, D.R., Maddison, W.P., 2005. MacClade 4: analysis of phylogeny and character evolution. Version 4.08. Sinauer Associates, Sunderland, Massachusetts. Mader, B.J., Bradley, R.T., 1989. A redescription and revised diagnosis of the syntypes of the Mongolian tyrannosaur Alectrosaurus olseni. Journal of Vertebrate Paleontology 9, 41e55. Meng, Q.-R., Hu, J.-M., Jin, J.-Q., Zhang, Y., Xu, D.-F., 2003. Tectonics of the late Mesozoic wide extensional basin system in the China-Mongolia border region. Basin Research 15, 397e415. Nessov, L.A., 1995. Dinosaurs of northern Eurasia: new data about assemblages, ecology and paleobiogeography. Izdatel’stvo Sankt-Peterburgskogo Universiteta, St Petersburg, Russia, p. 156 [Russian]. lska, H., Currie, P.J., Barsbold, R., 2004. Oviraptorosauria; pp. 165e183. In: Osmo lska, H. (Eds.), The Dinosauria. University of Weishampel, D.B., Dodson, P., Osmo California Press, Berkeley, California. Perle, A., 1977. On the first discovery of Alectrosaurus (Tyrannosauridae, Theropoda) from the Late Cretaceous of Mongolia. Problemy Mongol'skoi Geologii 3, 104e113 [Russian]. Sues, H.-D., Averianov, A., 2009. A new basal hadrosauroid dinosaur from the Late Cretaceous of Uzbekistan and the early radiation of duck-billed dinosaurs. Proceedings of the Royal Society B: Biological Sciences 276, 2549e2555. Tsubamoto, T., Saneyoshi, M., Tsogtbaatar, K., Chinzorig, T., Khatanbaatar, P., Mainbayar, B., Suzuki, S., 2010. Report of the HMNS-MPC Joint Paleontological Expedition in 2008. Hayashibara Museum of Natural Sciences Research Bulletin 3, 29e39. Tumoanova, T.A., 1993. Concerning a new armored dinosaur from the southeastern Gobi. Paleontologicheskii Zhurnal 1993, 92e98 [Russian]. Van Itterbeeck, J., Horne, D.J., Bultynck, P., Vandenberghe, N., 2005. Stratigraphy and palaeoenvironment of the dinosaur-bearing Upper Cretaceous Iren Dabasu Formation, Inner Mongolia, People's Republic of China. Cretaceous Research 26, 699e725. Watabe, M., Tsogtbaatar, K., Suzuki, S., Saneyoshi, M., 2010. Geology of dinosaurfossil-bearing localities (Jurassic and Cretaceous: Mesozoic) in the Gobi Desert: results of the HMNS-MPC Joint Paleontological Expedition. Hayashibara Museum of Natural Sciences Research Bulletin 3, 41e118. Xu, X., Cheng, Y.-N., Wang, X.-L., Chang, C.-H., 2002a. An unusual oviraptorosaurian dinosaur from China. Nature 419, 291e293. Xu, X., Zhang, X.-H., Sereno, P., Zhao, X.-J., Kuang, X.-W., Han, J., Tan, L., 2002b. A new therizinosauroid (Dinosauria, Theropoda) from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol. Vertebrata PalAsiatica 40, 228e240. Xu, X., Tan, Q., Wang, J., Zhao, X., Tan, L., 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature 447, 844e847. Zanno, L.E., Sampson, S.D., 2005. A new oviraptorosaur (Theropoda, Maniraptora) form the Late Cretaceous (Campanian) of Utah. Journal of Vertebrate Paleontology 25, 897e904. Zhang, X.-H., Xu, X., Zhao, X.-J., Sereno, P., Kuanng, X.-W., Tan, L., 2001. A longnecked therizinosauroid dinosaur from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol, People's Republic of China. Vertebrata PalAsiatica 39, 282e290.
Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10. 1016/j.cretres.2015.03.007.