ISSN 0031-0301, Paleontological Journal, 2009, Vol. 43, No. 4, pp. 453462. Pleiades Publishing, Ltd., 2009.Original Russian Text A.V. Lopatin, A.O. Averianov, E.N. Maschenko, S.V. Leshchinskiy, 2009, published in Paleontologicheskii Zhurnal, 2009, No. 4, pp. 92100.
is a memberof the Early Cretaceous Shestakovo Vertebrate Assem-blage of Western Siberia, which has been studiedintensely during the past years (Maschenko and Lopa-tin, 1998; Maschenko et al., 2002, 2003; Lopatin et al.,2005; Lopatin and Averianov, 2007; see also referencesin these papers). This species was described based onthree mandibular fragments, one of which (holotypePM TGU, no. 16/5-22) contains two deciduous premo-lars and
and others have more posterior molars, pre-sumably identified as M
in specimen PM TGU,no. 16/5-14 and as M
in specimen PM TGU,no. 16/5-2 (Maschenko et al., 2003). The holotypeadditionally has four alveoli of two relatively smalldouble-rooted teeth; therefore, the lower cheek teethformula of
was initially deter-mined as P
. In 2004, E.N. Maschenko (PIN) andA.S. Rezvyi (SPbGU) found a new dentary fragment of
(specimen PM TGU, no. 120/9-34) in theShestakovo 1 locality. This specimen has M
, threeposterior premolars, the posterior alveolus of thecanine, and six small alveoli (with partially preservedroots) of three anterior premolars. Close to the dentaryfragment in the matrix, there were three isolated pre-molars and a fragment of the symphyseal region of thedentary, with a strongly damaged large double-rootedtooth, which was identified as the canine, and an alveo-lus of a single-rooted tooth anterior to it (which pre-sumably contained the ultimate incisor). As the speci-men was prepared, the breaks of roots of the isolatedpremolars fit into the fragments preserved in the alve-oli; thus, these teeth were glued to the dentary. The den-
tary fragment with the canine, alveolus of the incisor,and partial symphysis also belongs to this hemimandi-ble; they come in contact just anterior to the alveoli ofthe anterior premolar. This allowed the establishment ofthe structure and number of the lower premolars of
and variation in the structure of the lowermolars and correctness of identification of M
. Anotherimportant find is a maxillary fragment with the penulti-mate and ultimate molars (specimen PM TGU,no. 120/5-Sh1-5), which were found by P.P. Skuchas(SPbGU), A.S. Rezvyi, and other researchers in 2005 inthe Shestakovo 1 locality. In addition, in 2007, Shesta-kovo 1 yielded another isolated upper molar (specimenPM TGU, no. 120/7-Sh1-3). These specimens allow thestructure of the upper molars of
to bedescribed for the first time. The present study revisesthe morphology of
based on all knownspecimens, including new finds listed above and others.
In the description, we use the dental nomenclatureand terminology of Docodonta developed by Butler(1997) and modified by us (Averianov et al., 2009; seealso Fig. 1) based on subsequent works (Hu et al., 2007;Luo and Martin, 2007). The letter designations of den-tal cusps correspond to those accepted by some otherresearchers (Kermack et al., 1987; Sigogneau-Russell,2001, 2003; Kielan-Jaworowska et al., 2004): in thelower molars, cusp
is the main cusp, cusp
is themesiolabial cusp, cusp
is the distolingual cusp, cusp
is the mesiolingual cusp, cusp
is the anterior cusp,cusp
is an additional anterolingual cingular cusp, cusp
is the distolabial cusp or labial talonid cusp, cusp
is the lingual talonid cusp; in the upper molars, cusp
is the mesiolabial cusp, cusp
is the labial cingularcusp, cusp
is the distolabial cusp, cusp
is the distal
Early Cretaceous Mammals of Western Siberia: 2. Tegotheriidae
A. V. Lopatin
, A. O. Averianov
, E. N. Maschenko
, and S. V. Leshchinskiy
Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russiae-mail: email@example.com
Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034 Russia
Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia
Received July 21, 2008
New specimens of the tegotheriid docodont
Maschenko et al., 2003, includ-ing a maxillary fragment with two posterior teeth, an isolated upper molar, and mandibular fragments with teeth fromthe Early Cretaceous Shestakovo locality are described. The dental formula of
1 + ?
. Theupper molars of
, with two main labial and three lingual cusps, are convergently similar to themolars of tribosphenic mammals. In the dentary, the symphysis is short and Meckels groove is reduced.
is similar in the structure of lower teeth to
from the Upper Jurassic of Mongolia; itis the latest known representative of Docodonta.
: Docodonta, Tegotheriidae, Lower Cretaceous, Western Siberia.
LOPATIN et al.
stylar cusp, cusp
is the mesial stylar cusp, cusp
isthe mesiolingual cusp, and cusp
is the distolingualcusp (homologues of the cusp
have not been recog-nized). The crests between particular cusps are desig-nated as follows:
ab, ag, ac, ad, bg, bbb, bbg,cd, ddd, ddc, AB, AC, CD, BE, XZ
We use the following abbreviations: (L) maximumlength of the tooth crown; (W) maximum width of thetooth crown, (H) height of the tooth crown along thelabial side of the cusp
; and (h) depth of the horizontalramus of the lower jaw on the labial side.
The material described and discussed in the presentstudy is stored in the Paleontological Museum ofTomsk State University (PM TGU), Tomsk, Russia.
Order Docodonta Kretzoi, 1946
Family Tegotheriidae Tatarinov, 1994
Tegotheriidae: Tatarinov, 1994, p. 104; Maschenko et al., 2003,p. 76.
Ty p e g e n u s.
Tatarinov, 1994,Upper Jurassic of Mongolia.
D i a g n o s i s. Upper molars with cusp
; lower molars with cusp
and largepseudotalonid basin bordered by crests
, without crest
G e n e r i c c o m p o s i t i o n. In addition to thetype genus,
Sigogneau-Russell, 2003 fromthe Middle Jurassic of England and
Maschenko, Lopatin et Voronkevich, 2003 from theLower Cretaceous of Western Siberia.
C o m p a r i s o n. The family Tegotheriidae differsfrom other docodonts in the presence of the cusp
andthe absence of the crest
on the upper molars, thepresence of the cusp
and the formation of walls ofthe pseudotalonid basin by the crests
combined with the absence of a crest
onthe lower molars.
R e m a r k s. The family Tegotheriidae was consid-ered to include
Martin et Averianov,2004 from the Middle Jurassic of Kyrgyzstan and
Lopatin et Averianov, 2005 from the MiddleJurassic of Western Siberia (Martin and Averianov,2004; Lopatin and Averianov, 2005; Averianov andLopatin, 2006). At present, based on new phylogeneticanalysis, we regard these genera as Docodonta incertaesedis, assuming a basal position of
amongdocodonts (Averianov et al., 2009).
Maschenko, Lopatin et Voronkevich, 2003
: Maschenko et al., 2003, p. 76.
Ty p e s p e c i e s.
Maschenko, Lopatin et Voronkevich, 2003, Lower Cre-taceous of Western Siberia.
D i a g n o s i s. Upper molars with strongly trans-versely expanded lingual projection. In lower molars,cusp
larger than cusp
incomplete, reduced, crest
or distinct cusp
well developed, crest
present or absent,supplementary crests of posterior basin absent, lingualcingulid well developed.
S p e c i e s c o m p o s i t i o n. Type species.C o m p a r i s o n.
in the shorter crest
, reduced crest
, and well-developed crest
It differs from
in the more strongly expanded lingual pro-jection of the upper molars, the reversed size ratio ofcusps
, the absence of crest
and distinct cusp
, possible presence of crest
, the absence of sup-plementary crests of the posterior basin, and in thewell-developed lingual cingulid of the lower molars.
Maschenko, Lopatin et Voronkevich, 2003
Plate 12, figs. 16
[sic, incorrect ending of the species epi-thet]: Maschenko et al., 2003, p. 77, text-figs. 14.
: Lopatin and Averianov, 2007, p. 263.
H o l o t y p e. PM TGU, no. 16/5-22, left dentaryfragment with DP
1, and alveoli of (D)P3 and(D)P4; Russia, Kemerovo Region, Chebulinskii Dis-trict, Shestakovo 1 locality (5554'12'' N, 8757'28'' E,1.5 km downstream from the village of Shestakovo onthe right bank of the Kiya River); Lower Cretaceous,Ilek Formation.
D e s c r i p t i o n (Figs. 26). The upper teeth areknown from a maxillary fragment with two posteriormolars (specimen PM TGU, no. 120/5-Sh1-5) and anisolated upper molar (specimen PM TGU, no. 120/7-Sh1-3). Although tentative number of lower molars ofSibirotherium has been determined (presumably six,see Maschenko et al., 2003), we refrain from thehomologization of the posterior upper molars, since, indocodonts, the number of upper and lower molars maydiffer by one or even two (Kielan-Jaworowska et al.,
B A C
b a d() (b)
Fig. 1. Designations of dental cusps of Docodonta, usingSibirotherium rossicum Maschenko, Lopatin et Voronkevich,2003 as an example: (a) left upper molar and (b) left lowermolar.
PALEONTOLOGICAL JOURNAL Vol. 43 No. 4 2009
EARLY CRETACEOUS MAMMALS OF WESTERN SIBERIA: 2. TEGOTHERIIDAE 455
2004). The isolated molar under study occupied a moreanterior position in the jaw than the two posterior.
The upper molars are transversely expanded, theectoflexus is weak (Pl. 12, figs. 1, 2; Fig. 2). The labialpart of the crown is formed of the central cusps A and Cand the anterior cusp B in specimen PM TGU,no. 120/7-Sh1-3. In this specimen, the cusp B is locatedon a well-developed anterolabial projection (Pl. 12,fig. 1; Fig. 2a), which is an analogue of the parastylarlobe of the tribosphenic teeth. Lingual to the cusp B, theanterior cingulum has a well-developed cingular cuspE. The space between the walls of the cusps A, B, and Eis occupied by a deep and extensive depression, whichforms a fissure in the anterior wall of the cusp A just lin-gual to the crest AB. The anterior wall of the cusp Ahas subvertical enamel crenulations (Fig. 2b). In bothposterior molars of specimen PM TGU, no. 120/5-Sh1-5,the anterolabial projection of the crown is completelyabsent, the cusp B is reduced to a small cingular prom-inence, which is positioned anterolabial to the cusp A(Pl. 12, fig. 2; Fig. 2f). In the penultimate molar, thecusp B is positioned close to the stylar cusp E, the api-ces of these cusps are connected in a single crestlikestructure; however, a superficial groove separating thebases of these cusps is observed on the anterior side(Fig. 2g). In the ultimate molar, the apices of the cusps
B and E are differentiated and connected by a shortcrest.
On the labial side of specimen PM TGU, no. 120/7-Sh1-3, the cusps A and C are separated by a well-pro-nounced triangular depression (Fig. 2d). In specimenPM TGU, no. 120/5-Sh1-5, this depression is weaker;however, it has a distinctive narrow depression at thebase of the anterior side of the cusp A, which is partic-ularly well developed in the penultimate tooth (Fig. 2h).
The cusp C is approximately half as high as the cuspA in specimen PM TGU, no. 120/7-Sh1-3 and in thepenultimate tooth of specimen PM TGU, no. 120/5-Sh1-5 (in the ultimate tooth, it is damaged). The cingu-lar cusp D is very small, hardly discernible. In speci-men PM TGU, no. 120/7-Sh1-3, the crest CD is verystrong, with a wear facet along the entire length. Lin-gual to the bases of the labial cusps, the crown is nar-rowed considerably longitudinally (at the point of nar-rowing, the length is 48% of the labial length of thecrown in specimen PM TGU, no. 120/7-Sh1-3 and 57%in the penultimate tooth of specimen PM TGU,no. 120/5-Sh1-5; at the same time, the length of the lin-gual projection is accordingly 48 and 63% of the labiallength of the crown, respectively). The center of the lin-gual projection of the crown is occupied by a large cuspX, which is approximately equal in height to the cusp C
() (b) (c)
(h)0 1 mm
Fig. 2. Sibirotherium rossicum Maschenko, Lopatin et Voronkevich, 2003: (ae) specimen PM TGU, no. 120/7-Sh1-3, isolated leftupper molar: (a) occlusal, (b) anterior, (c) posterior, (d) labial, and (e) lingual views; (fh) specimen PM TGU, no. 120/5-Sh1-5,left upper penultimate and ultimate molars: (f) occlusal view; (g) penultimate molar, anterior view; (h) molars, labial view; Shesta-kovo 1 locality; Lower Cretaceous, Ilek Formation.
PALEONTOLOGICAL JOURNAL Vol. 43 No. 4 2009
LOPATIN et al.
(Fig. 2e). Two smaller cusps are located at the base ofthe cusp X: the anterolabial cusp Z and posterolabialcusp Y. The cusp Z is somewhat larger than the cusp Y.Labially, the cusps Z and Y are connected by transversemarginal crests to the anterior and posterior portions ofa strong cingulum, respectively; in specimen PM TGU,no. 120/5-Sh1-5, this cingulum borders the entire labiallobe of the crown (anteriorly, posteriorly, and labially).In specimen PM TGU, no. 120/7-Sh1-3, the labial cin-gulum is restricted to the posterior half of the crown; itsanterior end has a distinct cingular cuspule opposite themiddle of the cusp A. Between the labial and lingualcusps and transverse cingula, the central part of thecrown is occupied by an extensive basin. In specimenPM TGU, no. 120/5-Sh1-3, the cusps Z and Y have nar-row crests inside the basin, which are analogues of themedial wings of conules of tribosphenic mammals(Pl. 12, fig. 1; Fig. 2a). In specimen PM TGU, no.120/5-Sh1-5, either tooth has only a weak anterolabialprojection of the cusp Y (Pl. 12, fig. 2; Fig. 2f).
The crests AB and CD and the anterior portion ofthe crest AC are well developed. A long transversecrest, which extends from the apex of the cusp A andborders anteriorly a superficial basin of the lingual pro-jection (anterolingual crest: Sigogneau-Russell, 2003;it is better developed in specimen PM TGU, no. 120/5-Sh1-5), is also distinct. Other crests (XZ, XY, and theposterior portion of AC of three available molars, thelabial crest of the cusp A, and the crest BE of the ulti-mate molar of specimen PM TGU, no. 120/5-Sh1-5)are shorter and weaker. In specimen PM TGU, no.
120/5-Sh1-5, the ultimate...