A new early cretaceous mammal from western Siberia.

Abstract

The first Mesozoic mammal in Siberia (and in Rus-sia) was discovered by E.N. Maschenko in 1995 in theEarly Cretaceous Shestakovo locality (ChebulinskiiDistrict, Kemerovo Region) [1]. Representatives of atleast six mammalian species belonging to Gobicon-odontidae, Docodonta, and Peramura have been discov-ered in Shestakovo [2]. The majority of specimensbelong to Gobiconodon , a “triconodont” genus, whichwas widespread in the Early Cretaceous of the northernHemisphere.Here, we describe a new member of the family Per-amuridae established as a special group, Peramura(sublegion Zatheria, legion Cladotheria, infraclassHolotheria, subclass Theriiformes) [3]. Peramura ismost closely related to tribosphenic mammals [3, 4]and, therefore, important for the understanding of theirorigin and early evolution. This paraphyletic taxoncomprises forms with dental structures that fill themorphological gap between the Symmetrodonta andTribosphenida. To date, it has only been known fromthe Jurassic and Lower Cretaceous of Europe andAfrica [3, 4].The nomenclature of dental structures is given afterSigogneau-Russell [3], the designations of wear facetsare given after Crompton [5]. Measurements, mm,( L ) length and ( W ) width.Family Peramuridae Kretzoi, 1946.Genus Kiyatherium Maschenko, Lopatin, etVoronkevich, gen. nov. Etymology. From the Kiya River. Type species. Kiyatherium cardiodens Maschenko, Lopatin, et Voronkevich, sp. nov. Diagnosis. Dental formula of postcanines P1–P5M1–M3. Occlusal surface of P4–M2 V-shaped, ectof-lexus of M1–M2 sharp and deep. P5 molariform, withlarge and high stylocone and well-developed lingualcingulum. M1–M3 double-rooted. Preparacrista ofM1–M2 positioned obliquely to axis of tooth row.Metacone absent. Lingual cingulum of M1–M2 welldeveloped. Buccal part of molars relatively slightlyexpanded. Parastylar lobe of M3 considerably reduced.Prominent diastema present between canine and P1. Species composition. Type species. Comparison. Differs from Peramus Owen, 1871, Palaeoxonodon Freeman, 1979, Abelodon Brunet et al. ,1991, Magnimus Sigogneau-Russell, 1999, and Afriquiamus Sigogneau-Russell, 1999, in the well-developed lingual cingulum of M1–M2 and in theabsence of true metacone. From all these genera, exceptfor Afriquiamus , it differs by the oblique rather thantransverse preparacrista of M1 and M2. In addition, itdiffers from Magnimus in the double-rooted M1 andM2 and from Peramus in the presence of a prominentdiastema between C and P1, the shape of P4 and P5, thestructure of P5, and in a less expanded buccal part ofM1 and M2 and more reduced M3. Kiyatherium cardiodens Maschenko, Lopatin, etVoronkevich, sp. nov. Etymology. Latin cardium (heart) and dens (tooth). Holotype. Paleontological Museum of the TomskState University (PM TGU), no. 16/2-50 (Figs. 1a, 1b);fragmentary left maxilla with the canine, P1–P5, andM1–M3; Kemerovo Region, Shestakovo 3 locality;Lower Cretaceous, Ilek Formation. Description. Nine teeth are preserved in the upperjaw, the anteriormost of which is located in the proxim-ity of the incisor foramen and identified as a canine.The fifth postcanine is characterized by an incompleteeruption, and the two successive teeth are considerablyworn and expanded buccolingually. Therefore, the fiveanterior postcanines are interpreted as premolars P1–P5;and the three posterior teeth, as molars M1–M3. Theanterior part of the maxilla deviates ventrally at thelevel of P1, similarly to that of Peramus tenuirostris Owen [4]. The large infraorbital foramen is located aboveP3. The incisor foramen is oval and relatively large.The canine is small, single-rooted, chisel-shaped,with a simple conical crown, and strongly curved dis-tally (perhaps, as a result of deformation). P1–M3 aredouble-rooted. The P1–P3 crowns are elongated mesio-distally. P3 shows a massive main cusp (paracone),which is worn apically and distally, and an accessorydistal cuspule. A large wear facet ascends along the dis-tolingual side of the crown. P4 is bicuspid; the main