Baidabatyr clivosus, gen. et sp. nov.
Alexander Averianov, Alexey Lopatin, Pavel Skutschas, Stepan Ivantsov, Elizaveta Boitsova & Ivan Kuzmin (2017)
An enigmatic multituberculate mammal from the Early Cretaceous of Siberia, Russia.
Journal of Vertebrate Paleontology: e1293070
Baidabatyr clivosus, gen. et sp. nov. (Multituberculata incertae sedis), is described on the basis of an ultimate upper premolar (P5) from the Lower Cretaceous Ilek Formation at Bol'shoi Kemchug 3 locality in Krasnoyarsk Territory, Russia. The new taxon differs from all known multituberculates by the cusp formula of the ultimate upper premolar (4:5:5), cusps well separated by valleys of flat crown surface, and three roots. It shares with a few non-cimolodontan multituberculates such rare characters of the ultimate upper premolar as elongated crown with length to width ratio of 2.0 and smooth enamel. Baidabatyr, gen. nov., is plesiomorphically similar to Paulchoffatiidae in having a horizontal profile of the ultimate upper premolar in lateral view. It likely represents a late survival of the Jurassic paulchoffatiid radiation of multitituberculates. Baidabatyr, gen. nov., is another relict taxon in the Early Cretaceous mammal fauna of the Ilek Formation, otherwise dominated by docodontans, eutriconodontans, and symmetrodontans.
Fang-Yuan Mao, Yuan-Qing Wang, Shun-Dong Bi, Jian Guan & Jin Meng (2017)
Tooth enamel microstructures of three Jurassic euharamiyidans and implications for tooth enamel evolution in allotherian mammals.
Journal of Vertebrate Paleontology: e1279168
Incisor enamel microstructures of three euharamyidans, Shenshou lui, Xianshou linglong, and X. songae, from the early Late Jurassic Yanliao Biota, Liaoning Province, China, are reported. The enamel of the three species consists of columnar divergence units that are delimited by planes of crystallite convergence and have irregular shapes and sizes, but there is no distinct line or plane along the divergent axis of crystallites in the unit. Of the three species, the enamel of S. lui is most primitive in having simpler enamel units that are roughly perpendicular to the enamel dentine junction. In Xianshou, the enamel units are oblique apically, and crystallites in the inner zone of enamel show greater differentiation to form erratically spaced clusters that resemble incipient prism-like; seam-like and sheath-like structures are also present. This enamel type may represent a transitional stage between prismless and prismatic enamel. Mapping enamel types from selected taxa of basal mammaliaforms on a simplified phylogeny, the columnar enamel in Thomasia, Shenshou, and some ‘plagiaulacoid’ multituberculates is interpreted as the plesiomorphic condition for allotherians, from which evolved the transitional enamel, as represented by Xianshou and the ‘plagiaulacoid’ Paulchoffatia, and the plesiomorphic prismatic enamel as in some post-‘plagiaulacoid’ multituberculates and gondwanatherians. The prismatic enamel in advanced multituberculates and other gondwanatherians may have evolved independently. Despite the new enamel morphologies revealed in euharamiyidans, the amelogenesis mechanism of how prisms, seams, and sheaths evolved within mammals remains unclear.