New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan

Abstract

New specimens of two non-therian (non-tribosphenidan) mammals are described from the Lower Cretaceous Kitadani Formation in the upper part of the Tetori Group, Katsuyama, Fukui Prefecture, Japan. Despite their poor preservation, these specimens represent undescribed species from Japan, suggesting additional mammalian diversity in the Tetori Group. Previously, four mammal taxa had been formally described from this rock unit: a spalacotheriid ‘symmetrodont’, two eobaatarid multituberculates and a eutriconodont mammal. One of the new specimens is a damaged left p4 of a ‘plagiaulacidan’ grade multituberculate assignable to the family Eobaataridae. The Kitadani eobaatarid is a large species distinguished from the two previously described eobaatarids, Tedoribaatar and Hakusanobaatar, which are known from the stratigraphically lower Kuwajima Formation of the Tetori Group, Hakusan, Ishikawa Prefecture, Japan. It also differs from Sinobaatar, Heishanobaatar and Liaobaatar described from the Early Cretaceous of China. Another specimen, a partial right dentary with a faint Meckelian groove, is assigned to a eutriconodontan that is larger than and morphologically distinguishable from the eutriconodont Hakusanodon from the Kuwajima Formation. The Kitadani eutriconodontan is potentially related to the family Triconodontidae. The additional specimens from the Kitadani Formation shed new light on Early Cretaceous mammalian faunal change and dispersal in East Asia.

Keywords::

• Early Cretaceous
• Eobaataridae
• Eutriconodonta
• Kitadani Formation
• Tetori Group
• Triconodontidae

Acknowledgements

We profoundly thank Drs Zhe-Xi Luo (Department of Organismal Biology and Anatomy, University of Chicago, USA), K. Christopher Beard (Biodiversity Institute, University of Kansas, USA) and the two reviewers (Drs Meng Chen, Department of Biology, University of Washington, USA and Nao Kusuhashi, Department of Earth's Evolution and Environment, Ehime University, Japan) for their helpful comments and suggestions, which greatly improved the manuscript of this paper. Dr. Gregg F. Gunnell (Division of Fossil Primates, Duke University Lemur Center, Durham, USA) generously improved the early manuscript. Hakusan City Board of Education, Hakusan, Japan, helped K. Miyata access to the comparative mammalian collection from the Kuwajima Formation. The scanning electron microscope photographs (Figure 3) were taken with support of Dr. Shin-ichi Sano (FPDM), and he also provided helpful comments and references regarding the geochronology of the Tetori Group. Mr Mitsuhisa Seino (TESCO Co.) gave us the technical support regarding resolution of CT scanning.

Disclosure statement

No potential conflict of interest was reported by the authors.