Multituberculata from the Early Cretaceous of Mongolia
А. В. Лопатин, Alexander O. Averianov
Abstract
The multituberculate assemblage from the Early Cretaceous Khovoor locality in Mongolia, based on the study of 112 specimens in PIN collection, includes three taxa: arginbaatarid Arginbaatar dmitrievae Trofimov, 1980 (=Monobaatar mimicus Kielan-Jaworowska et al., 1987, new synonym) and two eobaatarids, Eobaatar magnus Kielan-Jaworowska et al., 1987 and Nokerbaatar minor (Kielan-Jaworowska et al., 1987), comb. nov. Both eobaatarid taxa from Khovoor differ from other known eobaatarids by lower incisors with enamel restricted to ventrolateral side. Contrary to the previous claims, in both Eobaatar magnus and Nokerbaatar minor P5 is sectorial tooth, as in other eobaatarids, different in morphology from P4. In Eobaatar and Nokerbaatar gen. nov., there is pronounced sculpture of radiating ridges on the upper premolars, which is partially also present on the upper molars. In Nokerbaatar, there is a ventrolingual groove on the lower incisor and p3 is relatively small, lacking serrations. In Eobaatar, there is a pronounced ventrolingual ridge on the lower incisor and p3 is relatively larger, with serrations. The number of infraorbital foramina is variable in Arginbaatar, with most specimens having two foramina. In Arginbaatar, the cusp ornamentation is poorly developed or absent on upper premolars and absent on upper molars. The sectorial dP5 was likely not replacing by P5. The molars (M2, m1–2) have conical cusps. The p4 is very large and highly variable in size and number of denticles (11–18). It lacks labial cusps and has restricted enamel. The p4 rotates mesioventrally during the ontogeny, which is unique for the Multituberculata. The p2 and dp3 are shed early during the ontogeny. The p3 is fully formed but cannot erupt because it is overhang by p4. In upper dentition, there is a replacement of dP3 by P3. Arginbaataridae are currently known only from Khovoor valley in Mongolia, while Eobaataridae were widely distributed in the Early Cretaceous in Asia and Europe.