A new species of Tetralophodon from the Linxia Basin and the biostratigraphic significance of tetralophodont gomphotheres from the Upper Miocene of northern China
Introduction
Tetralophodont gomphotheres are an important group in the evolution of proboscideans, and proximally related to the true elephants (Tassy, 1985, Tassy, 1988, Tassy, 1996, Shoshani, 1996). Because tetralophodont gomphotheres are a paraphyletic group, the family hierarchy of this group is undetermined (Shoshani and Tassy, 2005) or they are attributed to the paraphyletic Gomphotheriidae (Gheerbrant and Tassy, 2009). They were dominant proboscideans in the Late Miocene of Eurasia (Göhlich, 1999). However, fossil records of tetralophodont gomphotheres from the Upper Miocene of northern China are rare, relatively to Western Europe and southern Asia, and the taxonomy of these specimens is controversial. For example, the classical taxon “Tetralophodon exoletus Hopwood, 1935” was erected based on the type material from the Baode region (Hopwood, 1935) (Fig. 1), and Liu et al. (1978) reported other specimens from the Lantian region (Fig. 1). However, Tobien et al. (1988) attributed the hypodigm to “Stegotetrabelodon exoletus” and referred the Lantian material to “Tetralophodon (Paratetralophodon) cf. hasnotensis”. Other researchers debated on the occurrence of Stegotetrabelodon in eastern Asia (Tassy, 1999; Ferreti et al., 2003). Recently recognized tetralophodont amebelodontid Konobelodon robustus from the Upper Miocene of the Linxia Basin (Wang et al., 2016a), which had been identified as “Tetralophodon sp.” and “Tetralophodon exoletus” (Deng et al., 2004, Deng et al., 2013), further complicated this problem (Fig. 1). For example, can Konobelodon be used to name other material of Tetralophodon from northern China? And if so, is Tetralophodon really present in northern China? These questions remain to be resolved.
Besides the above material, there are other two records of tetralophodont gomphotheres from the Upper Miocene of northern China with known horizon: Tetralophodon sp. from the Qaidam Basin (Bohlin, 1937), Tetralophodon cf. exoletus from Wuzhong (Qiu et al., 1987) (Fig. 1). The remaining specimens of tetralophodont gomphotheres, i.e., “Gomphotherium watzeensis” (Hu, 1962) and “Gomphotherium quinanensis” (Chow and Chang, 1961) (attributed to “Tetralophodon (Paratetralophodon) cf. hasnotensis” and “Stegotetrabelodon exoletus” by Tobien et al. (1988), respectively), are represented only by molar fragments, and their precise localities and horizons are unknown.
In the Hezheng Palaeozoological Museum, there is a complete mandible of a tetralophodont gomphothere (HMV 1427). It is the first complete mandible of a tetralophodont gomphothere from China, and is clearly distinguishable from K. robustus from the Liushu Formation of the Linxia Basin. On the basis of the morphology of the mandible, we attributed this specimen to Tetralophodon and erected a new species Tetralophodon euryrostris n. sp. This is definitive evidence for the occurrence of the genus Tetralophodon in northern China. Furthermore, we amended the other material of tetralophodont gomphotheres from northern China, compared their tooth morphology with the related taxa such as Konobelodon and Stegolophodon. The stratigraphic occurrences of the tetralophodont proboscideans were also discussed based on the newly established Asian biochronological framework (Qiu et al., 2013, Wang et al., 2013). Hence this work improves the study of systematic evolution and biostratigraphy of tetralophodont gomphotheres, an important group of proboscideans, from the Upper Miocene of northern China.
Section snippets
Institutional abbreviations
GPAHLD: Geologisch-Paläontologische Abteilung des Hessischen Landesmuseums, Darmstadt, Germany.
HMV: Hezheng Paleozoological Museum, Hezheng, China.
IVPP: Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China.
NMHW: Naturhistorisches Museum, Vienna, Austria.
MSB: Museo del Seminario, Barcelona, Spain.
MNM: Naturhistorisches Museum, Mainz, Germany.
PMU: Palaeontological Museum, Uppsala.
UZ: Palaeontological collection in the Zoology Department, University of the Panjab, Lahore,
Systematic paleontology
Order Proboscidea Illiger, 1811
Family Gomphotheriidae Hay, 1922
Genus Tetralophodon Falconer, 1857
Type species: Tetralophodon longirostris (Kaup, 1832).
Type locality and horizon: Eppelsheim of the “Deinotherium” sand, Germany, Vallesian (early Late Miocene) (Tassy, 1985).
Tetralophodon euryrostris n. sp.
(Fig. 3, Fig. 4)
Etymology: eury-, wide; rostris, mouth or nose that is anteriorly protruded. The name indicates the wide mandibular symphysis and mandibular tusks relative to the other species of
Comparison of mandibles and tusks
Mandibles of tetralophodont proboscideans (including Konobelodon and Stegolophodon) are rarely discovered from northern China. Wang et al. (2016a) reported K. robustus from the early Late Miocene of the Linxia Basin, which seems to be contemporary with the new material. The mandibular tusks of K. robustus (Fig. 5c and l) having a dorsally concave cross-section are significantly flatter and wider than those of T. euryrostris. The exposed length of the tusks is much longer than the symphyseal
Conclusions
In this article we reported a new species of T. euryrostris from the Upper Miocene of the Linxia Basin. This is the only unequivocal record of Tetralophodon in northern China. The new species is characterized by an elongated and wide mandibular symphysis within Tetralophodon and by its convergence with Stegolophodon in tooth morphology. The age of T. euryrostris is postulated to be the early Late Miocene (MN10); however, the precise locality cannot be traced. Besides T. euryrostris, there are
Acknowledgements
We thank Tao Deng, Zhan-Xiang Qiu, Bo-Yang Sun, Su-Kuan Hou, Qin-Qin Shi, IVPP, China; U. Göhlich, Naturhistorisches Museum Wien, Austria for discussions and advice on this work. We thank Prof. Xue-Ping Ji, and an anonymous reviewer for their great suggestions in their review of this paper. This work was supported by the National Basic Research Program of China (Grant No. 2012CB821900), the Chinese Academy of Sciences (Grant No. XDB03020104), the National Natural Science Foundation of China
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