A high-latitude fauna of mid-Mesozoic mammals from Yakutia, Russia

Abstract

The Early Cretaceous (?Berriasian-Barremian) Teete vertebrate locality in Western Yakutia, East Siberia, Russia, has produced mammal remains that are attributed to three taxa: Eleutherodontidae indet. cf. Sineleutherus sp. (Haramiyida; an upper molariform tooth), Khorotherium yakutensis gen. et sp. nov. (Tegotheriidae, Docodonta; maxillary fragment with three molariform teeth and dentary fragment with one molariform tooth), and Sangarotherium aquilonium gen. et sp. nov. (Eutriconodonta incertae sedis; dentary fragment with one erupted molariform tooth and one tooth in crypt). This is the second occurrence of Mesozoic mammals in high latitudes (paleolatitude estimate N 63-70°) of the Northern Hemisphere. In spite of the presumed Early Cretaceous age based on freshwater mollusks, the Teete mammal assemblage has a distinctive Jurassic appearance, being most similar to the Middle-Late Jurassic mammal assemblages known from Siberia, Russia and Xinjiang, China. The smooth transition from Jurassic to Cretaceous biota in Northern Asia is best explained by stable environmental conditions.

Fig 1. Maps showing the geographic position of the Teete locality (red dot).

Fig 2. Teeth of Stegosauria indet.

(a, b), Ornithischia indet. (c-e), and Eleutherodontidae indet. cf. Sineleutherus sp. (f, g). a, b, ZIN PH 1/246, in occlusal (a) and labial or lingual (b) views. c-e, ZIN PH 2/246, in occlusal (c), lingual (d), and mesial or distal (e) views. f, g, PIN 5614/4, left upper molariform tooth, in labial (f) and occlusal (g) views. Scale bars equal 1 mm.

Fig 3. Photograph of the Teete microvertebrate locality (left) and its geological section (right).

Fig 4

Khorotherium yakutensis gen. et sp. nov., PIN 5614/1, right maxilla fragment with the three last molariform teeth (holotype; a, b, SEM micrographs; a’, b’, explanatory drawings). Teete, Yakutia, Russia; Sangar Series, Lower Cretaceous. a, labial view. b, occlusal view. A, B, C, D, E, X, and Y–cusps of an upper molariform tooth. Scale bar equals 1 mm.

Fig 5

Khorotherium yakutensis gen. et sp. nov., PIN 5614/2, left dentary fragment with the penultimate molariform tooth, a distal fragment of the antepenultimate molariform tooth, and alveoli for the ultimate and more anterior teeth (a-d, SEM micrographs; a’-d’, explanatory drawings). Teete, Yakutia, Russia; Sangar Series, Lower Cretaceous. a, b, penultimate molariform tooth in occlusal (a) and lingual (b) views. c, d, dentary fragment in occlusal (c) and lingual (d) views. Abbreviations: Mg, Meckel's groove; rg, replacement groove. a, b, bb, c, d, dd, e, and g–cusps of a lower molariform tooth. Scale bars equal 0.1 mm for a, b, and 1 mm for c, d.

Fig 6

Sangarotherium aquilonium gen. et sp. nov., PIN 5614/3, left dentary fragment with roots of the antepenultimate molariform tooth, the penultimate molariform tooth, and the ultimate molariform tooth in crypt (holotype; a-c, SEM micrographs; d, light photograph; a’-d’, explanatory drawings). Teete, Yakutia, Russia; Sangar Series, Lower Cretaceous. a, penultimate molariform tooth in occlusal view. b-d, dentary fragment in occlusal (b), labial (c), and lingual (d) views. Abbreviations: cf, coronoid facet; mc, mandibular canal; mf, mandibular foramen; Mg, Meckel's groove. a, b, c, d, e–cusps of a lower molariform tooth. Scale bars equal 0.1 mm for a and 1 mm for b-d.