ISSN 0012-4966, Doklady Biological Sciences, 2007, Vol. 417, pp. 432–434. © Pleiades Publishing, Ltd., 2007.Original Russian Text © A.V. Lopatin, A.O. Averianov, 2007, published in Doklady Akademii Nauk, 2007, Vol. 417, No. 1, pp. 136–138.

432

A unique recent event in paleomammalogy was thediscovery in 2000 of a Middle Jurassic mammal assem-blage in the upper part of the Itat Formation of theBerezovsk quarry, southern Krasnoyarsk krai [1–4].This fauna provides an insight into an early stage of thedevelopment of the class Mammalia in Russia and con-tains at least two docodont taxa (

Itatodon tatarinovi

Lopatin et Averianov, 2005 and Docodonta indet.), thefirst Asiatic dryolestid (Dryolestoidea indet.) and sev-eral other presently undetermined taxa (Mammaliaindet.). This study describes a new member of themammal fauna from the Itat Formation that is the earli-est known Asiatic pretribosphenic mammal and the sec-ond Jurassic mammal species from Russia.

CLASS MAMMALIA LINNAEUS, 1758

Legion Cladotheria McKenna, 1975

Clade Zatheria McKenna, 1975

Order Amphitheria Kermack, Kermack et Mussett,1968

Family Amphitheriidae Owen, 1846Genus Amphibetulimus Lopatin et Averianov,

gen. nov.

Etymology.

From the Greek

amphi

(on both sides),the Latin

betula

(birch, allusion to Berezovsk quarry),and

mus

(mouse).

Type species.

A. krasnolutskii

sp. nov.

Diagnosis.

The genus is characterized by the fol-lowing combination of (–) primitive and (+) advanced

structural characters of the lower molars: (1) paraconidlarger and higher than metaconid (+); (2) mesiolingualcuspule

e

well developed, forming anterior edge ofparaconid (+); and (3) lingual cingulid absent (–).

Species composition.

Type species.

Comparison.

Amphibetulimus

gen. nov. differsfrom

Amphitherium

Blainville, 1838 and

Palaeoxon-odon

Freeman, 1976 in characters 1 and 2 and from

Kennetheredium

Sigogneau-Russell, 2003 in charac-ters 1 and 3.

Remarks.

There are two alternative points of viewconcerning the phylogenetic position of Amphitheri-idae, i.e., (1) affinity to dryolestids and assignment tothe superorder Dryolestoidea Butler, 1939 [5, 6]; and(2) affinity to the lineage leading to tribosphenic mam-mals (clade Zatheria McKenna, 1975) [7–13]. Weadhere to the second hypothesis and regard Amphith-eriidae as the earliest and most primitive pretri-bosphenic mammals.

Amphibetulimus

is assigned to Amphitheriidaebased on the following set of characters: the talonid islarger than that of Dryolestoidea, but probably smallerthan in more advanced Zatheria; the paraconid isdirected vertically (in Dryolestidae Marsh, 1879, it isinclined anteriorly; in Paurodontidae Marsh, 1887, it islow shelflike); the talonid cusp occupies a labial posi-tion posterior to the protoconid (in Dryolestidae, it ispositioned lingually; in Paurodontidae, it is at the mid-line); the posterior root of the lower molars is onlyslightly smaller than the anterior root (in Dryolestidae,it is much smaller).

Amphibetulimus

gen. nov. probably differs fromother amphitheriids in the shorter talonid; however, thetalonid is broken off in the sole available tooth; there-fore, this character is not included in the generic diag-nosis.

Amphibetulimus

is the most primitive representa-tive of the order, which retains a well-developed

e–d–f

interlocking lower molars and a relatively large trigonidangle. The new genus is similar to

Palaeoxonodon

from

GENERALBIOLOGY

The Earliest Asiatic Pretribosphenic Mammal (Cladotheria, Amphitheriidae)

from the Middle Jurassic of Siberia

A. V. Lopatin

a

and A. O. Averianov

b

Presented by Academician E.I. Vorob’eva May 24, 2007

Received June 5, 2007

DOI:

10.1134/S0012496607060063

a

Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia e-mail: alopat@paleo.ru

b

Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034 Russia e-mail: lepus@zin.ru

DOKLADY BIOLOGICAL SCIENCES

Vol. 417

2007

THE EARLIEST ASIATIC PRETRIBOSPHENIC MAMMAL 433

the Bathonian of Great Britain in the structure of lowermolars. The molars of

Palaeoxonodon

vary within awide range and some specimens (for example, [11:Fig. 3D]) closely resemble those of

Amphibetulimus

gen. nov.

Amphibetulimus

gen. nov. is the first representativeof Amphitheria recorded beyond Great Britain (all ofthem are dated Middle Jurassic).

Amphibetulimus krasnolutskii

Lopatin et Averianov,sp. nov.

Etymology.

The species is named in honor ofS.A. Krasnolutskii, who discovered the Berezovsklocality in 2000.

Holotype.

PIN, no. 5087/3, right dentary fragmentwith one molar (presumably M

3

) and alveoli and rootsof adjacent teeth (M

1

, M

2

, M

4

, and M

5

); Russia, Kras-noyarsk krai, Sharypovskii raion, 500 m south of thevillage of Nikol’skoe, Berezovsk quarry; Middle Juras-sic, Bathonian Stage, upper part of the Itat Formation.

Description

(Fig. 1). The dentary is relatively low,only slightly higher than M

3

, gradually increasing indepth towards the coronoid process. The lingual side ofthe dentary is smooth, convex, lacking facets forparadentary bones. A distinct and narrow, almostthreadlike Meckel’s groove extends along the lowermargin of the bone. Anterior to the line of the mandib-ular foramen, the Meckel’s groove curves ventrally for2

°

–3

°

and slightly expands. Then, on the pterygoidcrest, it decreases in depth; slightly posterior to thefragment preserved of the dentary, the groove probablydisappeared. The mandibular foramen is located con-siderably above the Meckel’s groove in the anterodorsalcorner of a small pterygoid fossa; on the lingual side,the foramen is invisible. On the labial side of the den-tary, the masseteric fossa is poorly pronounced, with analmost indiscernible ventral margin; the massetericcrest is low. Several small vascular foramina are posi-tioned along the masseteric crest in the massetericfossa. A large mental foramen is located in line with theposterior root of M

1

, close to the ventral margin of thedentary (the posterior border of the foramen is pre-served, with the mandibular canal exposed anteriorly).

Judging from the sizes of alveoli and the roots pre-served, M

3

was the largest lower molar; M

2

and M

4

were larger than M

1

and M

5

, respectively. The crown ofM

3

is high, with a dominating trigonid and very smalltalonid. The crown height is much greater on the labialside than on the lingual side. The protoconid is thehighest cusp, with its base occupying most of the trigo-nid. The labial slope of the protoconid is convex, whilethe lingual slope is flattened, almost vertical. The para-conid is vertical, substantially higher and larger thanthe metaconid. The bases of the paraconid and meta-conid are widely spaced. The crown base lacks a traceof the cingulid. The anterior cingulid cuspules

e

and

f

are high vertical crests on the sides of a deep groove onthe anterior wall of the crown, which contains the tal-onid cusp of the preceding tooth. The mesiolingual cus-

pule

e

is much better developed and forms the anterioredge of the paraconid. The high position of the cuspules

e

and

f

is evidence that the talonid cusp of M

2

was posi-tioned much higher than that of M

3

. The talonid is rela-tively small; despite the fact that its distal end is brokenoff, the size of the fragment preserved allows the con-clusion that the talonid was unicuspid and probablylacked a basin. It is evident that the talonid cusp waspositioned labial to the line of the apex of the proto-

prd

0 1 mm

pad

f e

f

prd

1 + 3

td

pad med

M3

1 + 3

td

prd

2

prdpad

mede

f

td

1 + 3

mdf

ptf

Mgrmdf

M5

0 1 mm

M4

M3

M2M1

mc

msf

pmf

(a)

(b)

(c)

Fig. 1.

Amphibetulimus krasnolutskii

, sp. nov., holotypePIN, no. 5087/3, right dentary fragment with M

3

and alveoliand roots of M

1

, M

2

, M

4

, and M

5

: (a) lingual view and mag-nified M

3

, anterior, occlusal (the upper figure is in strictlyocclusal view, the lower figure with a slight anterior inclina-tion), labial, and posterior views; (b) occlusal view; and(c) labial view. Designations: (

e

) mesiolingual cuspule

e

;(

f

) mesiolabial cuspule

f

; (M

1

–M

5

) lower molars; (

mc

) mas-seteric crest; (

mdf

) mandibular foramen; (

med

) metaconid;(

Mgr

) Meckel’s groove; (

msf

) masseteric fossa; (

pad

) para-conid; (

pmf

) posterior mental foramen; (

prd)

protoconid;(

ptf

) pterygoid fossa; (

td

) talonid; and (1+3 and 2) numbersof wear facets. Scale bar, 1 mm.

434

DOKLADY BIOLOGICAL SCIENCES

Vol. 417

2007

LOPATIN, AVERIANOV

conid. The lingual wall of the talonid is vertical. Thelabial slope of the talonid is almost entirely occupied byan extensive facet 1+3, which is produced by the para-cone. Most of the posterior wall of the metaconid is alsoworn; therefore, the wall is almost vertical. Another rel-atively small wear facet 2 is seen on the labial slope ofthe protoconid near its apex. The tooth is double-rooted, the anterior root is slightly larger than the pos-terior root.

Measurements

of the holotype in mm: M

3

: crownlength, 1.75; crown width, 0.87.

Remarks.

The dental formula of

Amphibetulimus

gen. nov. is established based on the position of a largeposterior mental foramen under M

1

of

Amphitherium.

The posteriormost molar (M

5

) of the holotype of

A. krasnolutskii

sp. nov. erupted shortly before the ani-mal’s death, since the bone septum between the roots isnot formed. It is not improbable that at later ontogeneticstages, the number of molars of

Amphibetulimus

gen.nov. increased up to six or seven, as in

Amphitherium

[12].Note that, despite a significant wear of M

3

of theholotype of

A. krasnolutskii

sp. nov. in the region of themetaconid and talonid (facet 1+3), it lacks a facet A onthe paraconid; this facet is characteristic of amphitheri-ids [9, 11]. Because of considerable wear of the poste-rior wall of the metaconid, it is uncertain whether or notthe tooth had a distal metacristid.

Kennetheredium

lacks the distal metacristid, while

Amphitherium

and

Palaeoxonodon

have it.

Material.

Holotype; found by S.A. Krasnolutskii in2006.

ACKNOWLEDGMENTSThis study was supported by the Board of the Presi-

dent of the Russian Federation (MD-255.2003.4, MD-

3050.2007.4, NSh-6228.2006.4), the Russian Founda-tion for Basic Research (project nos. 04-04-49637, 04-04-49113, 05-04-48493, 07-04-00393), and the Rus-sian Science Support Foundation.

REFERENCES

1. Averianov, A.O., Lopatin, A.V., Skutschas, P.P., et al.,

Acta Palaeontol. Pol.,

2005, vol. 50, no. 4, pp. 789–797.2. Lopatin, A.V. and Averianov, A.O.,

Dokl. Biol. Sci.

,2005, vol. 405, no. 2, pp. 434–436 [

Dokl. Akad. Nauk

,2005, vol. 405, no. 2, pp. 277–279].

3. Averianov, A.O. and Lopatin, A.V.,

Paleontol. Zh.,

2006,no. 6, pp. 81–90.

4. Lopatin, A.V. and Averianov, A.O., in IX Int. Symp. onMesozoic Terrestrial Ecosystems and Biota: Abstractsand Proceedings Volume, Manchester, 2006, pp. 67–70.

5. Prothero, D.R., Bull. Am. Museum Nat. Hist., 1981,vol. 167, pp. 281–325.

6. Kielan-Jaworowska, Z., Cifelli, R.L., and Luo, Z.-X.,Mammals from the Age of Dinosaurs: Origins, Evolu-tion, and Structure, New York: Columbia Univ. Press,2004.

7. Butler, P.M., Proc. Zool. Soc. London, Ser. B, 1939,vol. 109, pp. 329–356.

8. Mills, J.R.E., Proc. Linnean Soc. London, 1964,vol. 175, pp. 117–133.

9. Crompton, A.W., Zool. J. Linnean Soc., 1971, vol. 50,suppl. 1, pp. 65–87.

10. Sigogneau-Russell, D., Geodiversitas, 1999, vol. 21,no. 1, pp. 93–127.

11. Sigogneau-Russell, D., Geodiversitas, 2003, vol. 25,no. 3, pp. 501–537.

12. Butler, P.M. and Clemens, W.A., Palaeontology, 2001,vol. 44, no. 1, pp. 1–20.

13. Luo, Z.-X., Kielan-Jaworowska, Z., and Cifelli, R.L.,Acta Palaeontol. Pol., 2002, vol. 47, no. 1, pp. 1–78.