title: A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and 'amphilestid' eutriconodonts.
abstract: We report the discovery of Juchilestes liaoningensis, a new genus and species of eutriconodont mammal from the Lujiatun Site of the Lower Cretaceous Yixian Formation (123.2 +/- 1.0 Ma; Lower Aptian). The holotype preserves a partial skull and full dentition. Among eutriconodonts, its lower dentition is similar to taxa formerly assigned to the paraphyletic group of 'amphilestids'. Some have considered 'amphilestid' molars to represent the structural intermediate between the lower molars of the 'triconodont' pattern of cusps in alignment and the fully triangulate and more derived therian molars. However, 'amphilestid' taxa were previously represented only by the lower dentition. Our study reveals, for the first time, the upper dentition and skull structure of an 'amphilestid', and shows that at least some eutriconodonts have an obtuse-angled cusp pattern on molars in middle positions of the long molar series. Its petrosal is similar to those of other eutriconodonts and spalacotheroid 'symmetrodonts'. Our phylogenetic analyses suggest that (i) Juchilestes is most closely related to the Early Cretaceous Hakusanodon from Japan, in the same Eastern Asiatic geographic region; (ii) 'amphilestids' are not monophyletic; and (iii) eutriconodonts might not be a monophyletic group, although this hypothesis must be further tested.
authors.affiliation: Dalian Museum of Natural History, No. 40 Xicun Street, Shahekou District, Dalian 116023, People's Republic of China.
authors.forename: Chun-Ling
authors.initials: CL
authors.lastname: Gao
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Wilson
authors.forename: Zhe-Xi
authors.initials: ZX
authors.lastname: Luo
authors.forename: A Murat
authors.initials: AM
authors.lastname: Maga
authors.forename: Qingjin
authors.initials: Q
authors.lastname: Meng
authors.forename: Xuri
authors.initials: X
authors.lastname: Wang
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002681:China; D003817:Dentition; D005580:Fossils; D021621:Imaging, Three-Dimensional; D008322:Mammals / Q000033:anatomy & histology* / Q000145:classification; D008334:Mandible / Q000033:anatomy & histology; D008963:Molar / Q000033:anatomy & histology*; D010802:Phylogeny; D012886:Skull / Q000033:anatomy & histology*