A New Early Cretaceous Mammal from Western Siberia

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  • 0012-4966/02/0910- $27.00 2002 MAIK Nauka /Interperiodica0475

    Doklady Biological Sciences, Vol. 386, 2002, pp. 475477. Translated from Doklady Akademii Nauk, Vol. 386, No. 5, 2002, pp. 715717.Original Russian Text Copyright 2002 by Maschenko, Lopatin, Voronkevich.

    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 P1P5M1M3. Occlusal surface of P4M2 V-shaped, ectof-lexus of M1M2 sharp and deep. P5 molariform, withlarge and high stylocone and well-developed lingualcingulum. M1M3 double-rooted. Preparacrista ofM1M2 positioned obliquely to axis of tooth row.Metacone absent. Lingual cingulum of M1M2 well

    developed. 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 M1M2 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, P1P5, andM1M3; 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 P1P5;and the three posterior teeth, as molars M1M3. 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). P1M3 aredouble-rooted. The P1P3 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

    GENERAL BIOLOGY

    A New Early Cretaceous Mammal from Western Siberia

    E. N. Maschenko*, A. V. Lopatin*, and A. V. Voronkevich**

    Presented by Academician V.N. Bolshakov April 16, 2002

    Received April 27, 2002

    * Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia** Paleontological Museum,Tomsk State University, pr. Lenina 36, Tomsk, 643050 Russia

  • 476

    DOKLADY BIOLOGICAL SCIENCES

    Vol. 386

    2002

    MASCHENKO

    et al

    .

    cusp is massive, worn apically and mesially. The poste-rior cusp is worn distolingually. Anterior to the maincusp, there is a large wear facet. The buccal cingulumis narrow and connects the anterior and posterior stylarcuspules. The lingual cingulum is poorly pronounced.

    P5 is molarized to a greater extent than the anteriorpremolars. The occlusal view is bean-shaped. There arethree main cusps, which are more or less aligned. Theseare the central (paracone, cusp A), distal (paracone,cusp C), and mesial (supposedly, large stylocone,cusp B) cusps. The paracone is approximately twice asmassive and 1.5 times higher than the other main cusps.A small and low accessory cuspule with a flattenedapex is located mesiobuccal to the stylocone and closeto the parastyle. A well-developed posterior accessorycuspule is present. It is conical and located distobucca-lly to the base of cusp C. The parastyle and metastyleare small. The buccal cingulum is well developed. Thelingual cingulum is weak.

    M1 and M2 are characterized by a well-developedlarge stylar lobes. M1 is somewhat shorter and widerthan P5. The parastylar and metastylar lobes are equallywell developed, the ectoflexus is deep, and the buccal

    cingulum is narrow. The tooth is heavily worn. Facet 1ahas a subtransversely oriented depression at the bound-ary between the wear surfaces of the parastylar lobe andthe anterior side of the paracone, as in

    Peramus

    [3, 6].Facet 2 extends from the paracone to the metastyle. Atthe base of the mesiolingual side of the paracone, thereis a protrusion, probably a remnant of the anterior partof the lingual cingulum or a rudimentary protocone.

    M2 is distinguished from M1 by a better developedparastylar lobe, shallower ectoflexus, and better pro-nounced stylar cuspules on the buccal cingulum. M2 isless worn than M1; large facet 1, stylocone, styles, buc-cal cingulum, and cusp C are visible on its occlusal sur-face. Cusp C is located somewhat buccal to the para-cone. The lingual cingulum is short but stout and has asmall projection at the paracone level; perhaps, this isan initial stage of the protocone formation. M3 is con-siderably reduced. The crown is oval, the stylar lobesare weakly developed, the ectoflexus is not deep. Theparacone is relatively large and located at the center ofthe occlusal surface, cusp C is small and rudimentary,and cingula are absent.

    0

    0

    0

    1 mm

    1 mm

    1 mm

    (a)

    (b)

    (c)

    (d)

    Fig. 1.

    Kiyatherium cardiodens

    gen. et sp. nov., (a) and (b) holotype, PM TGU, no. 16/2-50, fragmentary left maxilla with canine,P1P5, and M1M3; Lower Cretaceous, Ilek Formation; Kemerovo Region, Shestakovo 3: (a) buccal view; (b) P4M3 occlusalview; (c) and (d) specimen PM TGU, no. 16/6-22, isolated left P5; Lower Cretaceous, Ilek Formation; Kemerovo Region, Shesta-kovo 1: (c) occlusal view, (d) lingual view.

  • DOKLADY BIOLOGICAL SCIENCES

    Vol. 386

    2002

    A NEW EARLY CRETACEOUS MAMMAL FROM WESTERN SIBERIA 477

    An isolated upper tooth from Shestakovo 1(Figs. 1c, 1d; PM TGU no. 16/6-22) is comparable toP5 of the holotype in size and structure. The styloconeis conical and half as large and high as the paracone. Anaccessory cuspule of the preparastyle is located mesialto the stylocone, within the parastylar lobe. It corre-sponds to the anterior accessory cuspule of P5 of theholotype. The true parastyle occupies a mesiobuccalposition. The posterior accessory cuspule is located atthe base of the distobuccal edge of cusp C and is con-nected to the bicuspid metastyle by a high crest. Thelingual cingulum is well-defined, has two small projec-tions on a level with the notches between the maincusps, a small accessory cuspule at the preparastyle,and a distinct cingular cuspule in the distal part. Thetooth has two roots, which are short, rounded in crosssection, and closely spaced. In morphology, this toothcorresponds to the upper premolar of

    Peramus

    sp. fromthe Lower Cretaceous of Morocco [3; Figs. 29, 30];however, it essentially differs from the latter in havinga very large stylocone and no metacone.

    Measurements (mm).

    Holotype: length of CM3is 14.0, P1M3, 11.9; P2M3, 10.2; P5M3, 5.6; M1M3, 3.95; M1M2, 3.2; M2M3, 2.5; length ofdiastema C/P1 is 1.6, P1/P2, 0.6; length

    width of C is0.65

    0.5; P1, 1.3

    0.45; P2, 1.5

    0.6; P3, 1.65

    0.8;P4, 1.9

    1.1; P5, 1.9

    1.1; M1, 1.65

    1.3; M2, 1.8

    1.2; M3, 0.75

    0.65. Specimen PM TGU no. 16/6-22:length is 1.8, width is 1.0.

    Material.

    In addition to the holotype, P5 fromShestakovo 1.

    These findings enhance our knowledge of the mor-phological diversity and geographical distribution ofthe Peramuridae. The presence of an unerupted fifthpostcanine in the holotype of

    Kiyatherium

    suggests theinterpretation of the dental formula of the Peramuridaeas P1P5 M1M3 [3, 6, 7] rather than P1P4 M1M4[4].

    Kiyatherium

    compared to

    Peramus

    demonstratesthe following specialized (advanced) characters: asmall canine, molariform P5, and a relatively stout lin-gual cingulum on M1 and M2 with an elevation at the

    base of the paracone, suggesting a rudimentary proto-cone (absent in all known peramurids). At the sametime,

    Kiyatherium

    compared to

    Peramus

    and themajority of known Peramuridae shows a number ofprimitive characters. These are the shape of the molars,absence of true metacone (replaced by cusp C of thesymmetrodont type), and oblique position of thepreparacrista. Such a mosaic pattern of the uppermolars of

    Kiyatherium

    implies the complex evolutionof pretribosphenic mammals and probably indicatesindependent development of the tribosphenic tooth pat-tern in different clades.

    ACKNOWLEDGMENTSWe are grateful to the Academician L.P. Tatarinov

    (Paleontological Institute, Russian Academy of Sci-ences) and Dr. A.O. Averyanov (Zoological Institute,Russian Academy of Sciences) for helpful advice. Thiswork was supported by the Russian Foundation forBasic Research (projects nos. 00-15-97754, 01-04-49548, and 01-04-06241).

    REFERENCES

    1. Maschenko, E.N. and Lopatin, A.V.,

    Bull. Inst. Roy. Sci.Natur. Belg. Sci. Terre

    , 1998, vol. 68, pp. 233236.2. Maschenko, E.N., Lopatin, A.V., and Voronkevich,

    A.V.,in

    Tezisy dokladov. XLII sessiya Paleontologicheskogoobshchestva

    (Abstracts, XLII Session of the Paleonto-logical Society), St. Petersburg, 2001, pp. 5961.

    3. Sigogneau-Russell, D.,

    Geodiversitas

    , 1999, vol. 21,no.

    1, pp. 93127.4. Clemens, V.A. and Mills, J.R.E.,

    Bull. Brit. Museum(Natur. Hist.) Geol.,

    1971, vol. 20, no. 3, pp. 87113.5. Crompton, A.W.,

    Early Mammals

    , London: Academic,1971, pp. 6587.

    6. Bown, T.M. and Kraus, M.J.,

    Mesozoic Mammals

    , Berk-ley: Univ. California Press, 1979, pp. 172181.

    7. McKenna, M.C.,

    Phylogeny of the Primates

    , New York:Plenum, 1975, pp. 2146.

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