New fossils of early and middle Miocene Choerolophodon from northern China reveal a Holarctic distribution of Choerolophodontidae

ABSTRACT

As one of the three major groups of gomphotheres, the Miocene Choerolophodontidae were long considered to have been distributed in Europe, Africa, and South Asia, with a few localities in East Asia, whereas choerolophodontids never extended into North America during the Miocene. In this paper, we report new Choerolophodon fossil materials from the early and middle Miocene of China, which suggest morphological similarities to the enigmatic North American Gnathabelodon thorpei. The new fossils were recovered from the lower Miocene of Linxia (C. guangheensis) and the middle Miocene of Junggar (Choerolophodon sp.) basins, suggesting the persistence of this genus in East Asia during the early–middle Miocene. The cheek tooth morphology of the new specimens resembles that of early–middle Miocene Choerolophodon from elsewhere (i.e., C. palaeindicus, C. kisumuensis, and C. chioticus), in addition to striking affinities with Gnathabelodon thorpei. The upper tusk and mandibular characters of G. thorpei, which include upwardly bent maxillary tusks without enamel bands, and elongated and trough-like mandibular symphysis without mandibular tusks, also support its relationship with the choerolophodontids. The occurrence of a possible member of Choerolophodontidae in the late Miocene of North America (i.e., G. thorpei) reveals intercontinental dispersals of choerolophodontids from East Asia across Beringia possibly between 16.0 and 11.0 Ma, at roughly the same time as other proboscideans, e.g., Mammutidae, Amebelodontidae, and Gomphotheriidae. Together, these new materials significantly revise previously established models of the geographic distribution, taxonomic diversity, and ecological adaptations of Choerolophodontidae within China and elsewhere across the Holarctic.

ACKNOWLEDGMENTS

We thank P. Tassy and L. Costeur for access to specimens in MNHN and NMB for comparison, respectively; G. Zazula (Yukon Government) for the careful review and editing of the manuscript; J. Ye for his great guidance and suggestions; Q. G. Jiang-Zuo for the discussions on this work; X. D. Cui for the advice about figures; D. Su for the assistance in fossil preparation; and L. E. Wilson and C. Byrd (SMNH) for providing pictures of Gnathabelodon specimens. We are grateful to the reviewer G. E. Konidaris and an anonymous reviewer for constructive advice and suggestions. This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (grant nos. XDB26000000, XDA20070203, QYZDY-SSW-DQC022, 2019Q2KK0705), the National Natural Science Foundation of China (grant nos. 41430102, 41372001, 41625005).

ORCID

Xijun Ni http://orcid.org/0000-0002-4328-8695