We provide a detailed description of the dental morphology of Gobiconodon zofiae based on the holotype and clarify its diagnostic features in comparison with other species in the genus. We also report a new species, Gobiconodon gongzhulingensis sp. nov., from the lower Upper Cretaceous Quantou Formation in Gongzhuling City, Jilin Province, based on a maxilla with five molariforms. The dental morphologies of both species allow us to reassess tooth assignments in Gobiconodon and support a dental formula of 2.1.3.4/2.1.3.5 for the genus. The molariforms of Gobiconodon exhibit a distinct type of tooth widening that is achieved primarily through cusp inflation, without pronounced cusp rotation or the addition of new cusps. In addition to the differences in occlusal pattern, embrasure shearing dominated by an orthal power stroke, accompanied by a labiolingually directed component of relative displacement of the lower teeth during mastication also distinguishes Gobiconodon from other eutriconodontans, particularly triconodontids, suggesting an insectivorous and/or omnivorous diet for Gobiconodon. The tooth shapes and wear patterns described here indicate diverse ecomorphological specializations and species diversification within eutriconodontans.

Key words: Mammalia, Gobiconodontidae, morphology, Quantou Formation, Upper Cretaceous, Jilin Province.

Wenhao Wu [wenhao.wu@foxmail.com; ORCID: https://orcid.org/0000-0003-0970-9713], Jun Chen [cj@jlu.edu.cn; ORCID: https://orcid.org/0000-0003-1019-3881], College of Earth Sciences, Research Centre of Palaeontology and Stratigraphy, Dinosaur Evolution Research Center, Jilin University, Changchun 130061, Jilin Province, China. Fangyuan Mao [maofangyuan@ivpp.ac.cn; ORCID: https://orcid.org/0000-0002-8208-3473] (corresponding author), Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; Division of Paleontology, American Museum of Natural History, New York, New York 10024, USA. Jin Meng [jmeng@amnh.org; ORCID: https://orcid.org/0000-0002-3385-83833], Division of Paleontology, American Museum of Natural History, New York, New York 10024, USA; Earth and Environmental Sciences, Graduate Center, City University of New York, New York, 10016, USA.