Isolated dinosaur teeth from the Lower Cretaceous Shahai and Fuxin formations of northeastern China
Introduction
Since the late 1990s, extensive field collections focused on finding Mesozoic mammals were carried out in small coal mines in Badaohao (Heishan County) and the Fuxin City area in western Liaoning Province, northeastern China, by joint Chinese–Japanese research teams (Fig. 1a). During these excavations, many isolated dinosaur remains were recovered from seven mines, but little attention has been paid to them (Wang et al., 1995, Xu et al., 1998, Zhao and Zhao, 1999), most of the effort being devoted to articulated dinosaur fossils coming from the underlying Jehol Group. Here we provide a detailed description of 37 well preserved isolated dinosaur teeth from six localities of the Shahai and Fuxin formations, and discuss their possible environmental and ecological implications.
Dinosaur teeth were collected from the Shahai Formation at a small coal mine in Badaohao (Heishan County) and from the Fuxin Formation at small coal mines (Dongfang #1, Hanjiadian #6, Nanhuang #2, Nanhuang #3 and Mingda coal mines) in Fuxin City area (Fig. 1a). Late Mesozoic non-marine sediments distributed in western Liaoning Province mainly consists of the Tuchengzi Formation, the Yixian and Jiufotang formations of the Jehol Group, and the Shahai, Fuxin and Sunjiawan formations, in stratigraphic ascending order (e.g., Wang et al., 1989, Jin, 1996, Yang et al., 1997; Fig. 1b). The Tuchengzi Formation is correlated to the ?Upper Jurassic–Lower Cretaceous, and the other five formations are Early Cretaceous in age (Wang et al., 1989, Jin, 1996, Yang et al., 1997, Swisher et al., 2002). The Shahai Formation is widely distributed, but not well exposed, in the Fuxin-Yixian-Jinzhou Basin. It conformably (e.g., Wang et al., 1989, Jin, 1996) or unconformably (e.g., Chen, 1988) overlies the Jiufotang Formation (belonging to the Jehol Group) and is conformably overlain by the Fuxin Formation (Wang et al., 1989, Jin, 1996). Numerous fossils have been collected from the middle part of the formation, which mainly consists of sandstones and mudstones with intercalated coal measures. Vertebrate remains from the formation contain fishes, turtles, lizards, dinosaurs (e.g., Wang et al., 1995, Jin, 1996) and various mammals including “symmetrodontans” (Hu et al., 2005), “eupantotherians” (Li et al., 2005) and multituberculates (Kusuhashi et al., 2009b). The Fuxin Formation is mainly exposed in the Fuxin-Yixian-Jinzhou Basin. The formation conformably overlies the Shahai Formation and is conformably (Jin, 1996) or unconformably (Yang et al., 1997) overlain by the Sunjiawan Formation. Jiang and Sha (2006) divided the Sunjiawan Formation into two formations and indicated that the lower one disconformably overlies the Fuxin Formation. The Haizhou Formation, referred to by several authors (e.g., Wu et al., 1992, Zhu and Zhang, 1992), is considered to be synonymous with the Fuxin Formation (Yang et al., 1997). The Fuxin Formation is mainly composed of mudstones, sandstones and conglomerates, numerous intercalated coal measures (e.g., Wang et al., 1989, Wu et al., 1992), and abundant vertebrate fossils have been collected from several coal horizons. These fossils include remains of fishes, turtles, lizards, dinosaurs (e.g., Shikama, 1947, Young, 1960, Wang et al., 1995) and mammals including eutherians (Shikama, 1947), multituberculates (e. g., (Kusuhashi et al., 2009b) and “triconodonts” (e. g., Kusuhashi et al., 2009a). The depositional ages of the Shahai and Fuxin formations remain ambiguous. Neither reliable radiometric ages nor available index fossils have been reported from these formations, and thus their ages are necessarily based on the ages of underlying formations. From the Jehol Group, radiometric ages of −130 to −120 Ma have been reported by several authors (e.g., Smith et al., 1995, Swisher et al., 1999, He et al., 2004, He et al., 2006, Chang et al., 2009), and the group is now generally thought to be Barremian to Aptian in age. On the basis of this correlation of the underlying Jehol Group, the Shahai and Fuxin formations are interpreted as Aptian or younger in age. Although there is no secure evidence to constrain an upper limit for the depositional age of the Shahai and Fuxin formations, considering the age uncertainty of the overlying Sunjiawan Formation (considered either as late Early Cretaceous (e.g., Sha, 2007) or early Late Cretaceous (e.g., You et al., 2003a)), they were tentatively attributed to the Aptian–Albian time span (Kusuhashi et al., 2009a, Kusuhashi et al., 2009b).
Section snippets
Theropods
Theropod dinosaurs are represented by isolated tooth crowns of two size ranges, large (from about 3.5 to 4 cm long apico-basally) and small (from 0.5 to 2 cm long apico-basally). As large teeth are too broken to be described properly, only small teeth are considered.
SAURISCHIA Seeley, 1887
THEROPODA Marsh, 1881
MANIRAPTORA Gauthier, 1986
OVIRAPTOROSAURIA Barsbold, 1976
INCISIVOSAURUS Xu et al., 2002a
Cf. Incisivosaurus.
General discussion and conclusion
Despite the fragmentary nature of the Shahai and Fuxin dinosaur remains and the relatively poor diagnostic characteristics of isolated dinosaur teeth, significant taxonomic, biostratigraphic and paleoecological information can be inferred from the collected specimens. First, the Shahai and Fuxin dinosaur faunas show a transitional state between the vertebrate communities of the Jehol Biota and Late Cretaceous dinosaur faunas. Some taxa such as the oviraptorosaur Incisivosaurus, basal
Acknowledgements
The authors are indebted to Hiroko Kusuhashi who prepared the specimens during her free time, and to Eric Buffetaut, Richard Butler, Dong Zhiming, David Hone, Tomoyuki Ohashi, Corwin Sullivan, Toru Sekiya, Olivier Maridet, for constructive discussions, and Paul Barret and two anonymous reviewers that greatly helped to improve our manuscript. Specimens described here were collected by members of joint Japanese–Chinese research into the Badaohao and Fuxin areas and local coal miners. This work
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