Russian J. Theriol. 2 (1): 1525 © RUSSIAN JOURNAL OF THERIOLOGY, 2003 The revision of the Early Miocene beavers (Castoridae, Rodentia, Mammalia) from the North Aral Region Alexey V. Lopatin ABSTRACT. The results of the revision of the Early Miocene beavers (Castoridae) from the Aral Svita of the Akespe and Altynshokysu localities (North Aral Region, Kazakhstan) show the presence of three species: Steneofiber kumbulakensis (Lytshev, 1970), S. schokensis (Bendukidze, 1993) and Asiacastor sp. The study of the dental morphology variability of S. kumbulakensis during the wear process suggests that Capacikala sajakensis Bendukidze, 1993 is the junior subjective synonymous of this species. Capatanka schokensis Bendukidze, 1993 is transferred to the genus Steneofiber. KEY WORDS. Steneofiber, Asiacastor, Castoridae, Rodentia, Early Miocene, North Aral Region, Western Kazakhstan. Alexey V. Lopatin [[email protected]], Paleontological Institute, Russian Academy of Sciences, ul. Profsoyuznaya 123, Moscow 117647, Russia. Ðåâèçèÿ ðàííåìèîöåíîâûõ áîáðîâ (Castoridae, Rodentia, Mammalia) Ñåâåðíîãî Ïðèàðàëüÿ À.Â. Ëîïàòèí ÐÅÇÞÌÅ.  ðåçóëüòàòå ðåâèçèè ðàííåìèîöåíîâûõ áîáðîâ (Castoridae) èç àðàëüñêîé ñâèòû ìåñòîíàõîæäåíèé Àêåñïå è Àëòûíøîêûñó (Ñåâåðíîå Ïðèàðàëüå, Êàçàõñòàí) óñòàíîâëåíî ïðèñóòñòâèå òðåõ âèäîâ: Steneofiber kumbulakensis (Lytshev, 1970), S. schokensis (Bendukidze, 1993) è Asiacastor sp. Èçó÷åíèå èçìåí÷èâîñòè ìîðôîëîãèè çóáîâ S. kumbulakensis â ïðîöåññ ñòèðàíèÿ ïîêàçàëî, ÷òî Capacikala sajakensis Bendukidze, 1993 ÿâëÿåòñÿ ìëàäøèì ñóáúåêòèâíûì ñèíîíèìîì ýòîãî âèäà. Capatanka schokensis Bendukidze, 1993 îòíåñåí ê ðîäó Steneofiber. ÊËÞ×ÅÂÛÅ ÑËÎÂÀ: Steneofiber, Asiacastor, Castoridae, Rodentia, ðàííèé ìèîöåí, Ñåâåðíîå Ïðèàðàëüå, Çàïàäíûé Êàçàõñòàí. Introduction The dental terminology follows Lytshev & Shevyreva (1994) (Fig. 1). The systematics of the beavers follows Korth (2002). The main material is housed in the collection of the At present the families Aplodontidae, Sciuridae, Paleontological Institute of the Russian Academy of Sciences Eomyidae, Zapodidae, Cricetidae, Tachyoryctoididae, (PIN) in Moscow, Russia. Several samples were collected Ctenodactylidae and Castoridae make up the rodent Dr. Th. Bolliger from Paleontological Institute of the Univer- assemblage of the Early Miocene (~MN1) Aral Fauna sity of Zurich (PIUZ) from Altynshokysu in 1994; they belong of Western Kazakhstan, North Aral Region (Ben- to the PIUZ collection. dukidze, 1993, 1997; Lopatin, 1996, 1997, 1999, 2000). In quantity of remains, the beavers are dominated Systematic Paleontology among large-sized rodents. Eight forms of Castoridae were described from the Aral Svita by previous inves- Order Rodentia Bowdich, 1821 tigators (Lytshev, 1970; Bendukidze, 1993): Steneofi- ber kumbulakensis (Lytshev, 1970), Palaeocastor sp., Capatanka schokensis Bendukidze, 1993, Capatanka Family CASTORIDAE Hemprich, 1820 aff. schokensis, Capacikala sajakensis Bendukidze, 1993, Capacikala aff. sajakensis, Capacikala cf. sci- Subfamily Castorinae Hemprich, 1820 uroides (Matthew, 1907) and Asiacastor aff. orientalis Lytshev, 1987. The study of the new and large material, Genus Steneofiber Geoffroy, 1833 collected by the author in Altynshokysu and Akespe localities in 19911993, revealed the stages of the Steneofiber kumbulakensis (Lytshev, 1970) ontogenetic development of the occlusal surface struc- Figs. 13, 4AM, 5. ture in the most common Aralian castorid, Steneofiber Propalaeocastor kumbulakensis: Lytshev, 1970: 84, fig.1; 1987: kumbulakensis, and allowed to revise the taxa earlier 70, fig.1. described on this base. Steneofibercf. viciacensis : Lytshev & Aubekerova, 1971: 14, fig.3. 16 Alexey V. Lopatin and the postmesofossette. Parafossette consists of three isolated fossettes. Metafossette region is located dorsal- ly to the main plane of the occlusal surface. Metafos- sette is separated from the postmesofossette by a low crest. The walls of the folds are irregular in shape and plicated. In the initial wear stage (n=2; Fig. 4B), the plane of occlusal surface of P4 is flat. The connection of anter- oflexus and anterior arm of mesoflexus is preserved. Also, these folds are communicated with the end of hypoflexus. Posterior arm of the mesoflexus connects with a small rounded mark, which is located in the Figure 1. The dental structure of the Castoridae after the posterolingual corner of the occlusal surface. The heights example of the middle worn premolars of Steneofiber kum- of the flexi are approximately the same as those in bulakensis (Lytshev, 1970). unworn tooth. Occasionally, the metafossette is ex- A right P4; B left p4. 1 paracone, 2 metacone, 3 protocone, 4 hypocone, 5 hypostria, 6 hypoflexus, 7 pressed by a small flexus with minute metastria. Parafos- anterostria, 8 anteroflexus and anterofossette (parafossette by Hu- sette consists of two or three small marks. The place of gueney, 1999), 9 parafossette (subparafossette by Hugueney, 1999), postmesofossette is occupied by three small oval or 10 mesostria, 11 mesoflexus, 12 postmesofossette, 13 drop-shaped marks. metafossette, 14 protoconid, 15 metaconid, 16 hypoconid, 17 The little worn P4 (n=2; Fig. 4C) has well developed entoconid, 18 hypostriid, 19 hypoflexid, 20 parafossettid roots and it is characterized by relatively deep hypos- (proparafossettid by Hugueney, 1999), 21 metafossettid (parafos- tria, which does not connects to the anteroflexus and settid by Hugueney, 1999), 22 premesofossettid, 23 mesostriid, 24 mesoflexid, 25 postmesofossettid, 26 entofossettid (metafos- posterior arm of mesoflexus. By a more prominent wear settid by Hugueney, 1999). these two folds are connecting lingually. Anterostria is shortened. Posterior portion of mesoflexus adjoins (or Steneofiber aff. kumbulakensis: Bendukidze, 1993: 79, pl.23, associates) postmesofossette, or, correctly, the largest fig.6; pl.24, figs.13. fossette consisting it. There is one additional small Capacikala sajakensis: Bendukidze, 1993: 92, pl.27, figs.1, 2, 4. mark between labial portion of mesoflexus and that of Capacikala aff. sajakensis: Bendukidze, 1993: 94. postmesofossette. Parafossette consists of two small Holotype. Institute of Zoology of the Ministry of Education and Sciences of Republic of Kazakhstan, M-2020/66-Àã, frag- marks. Metafossette is located slightly dorsally to the mented skull with P4M3 and p4m3. main plane of occlusal surface or at same level. Referred material. A left dentary fragment with p4m1 P4 in a middle wear stage (n=2; Figs. 2A, 4D, E) has (PIN 210/767), and isolated M2 (PIN 210/768) and m2 (PIN a very small anterostria. Anteroflexus is compressed in 210/769) from Akespe; isolated m2 (PIN 4516/122) and m3 (PIN 4516/121) from Altynshokysu, bone-bearing level I; a right the middle point and considerably enlarged lingually. dentary fragment with m1m2 (PIN 4516/320) and 38 isolated Parafossette is a small mark with irregular shape. teeth and tooth fragments, eight P4 (PIN 4516/1012, 307, 308, Anteroflexus and mesoflexus are dissociated, and me- 315, 316, 339), sixth M1 (PIN 4516/24, 312, 313, 323, 330, 331), soflexus has a small anterior process. Postmesofossette three M2 (PIN 4516/314, 317, 322), sixth M3 (4516/29, 310, is separated from the mesoflexus, which is curved 319, 332, 336, 337), four p4 (PIN 4516/23, 37, 38, 309), seven m1 (PIN 4516/39, 324, 326, 328, 329, 334, 338), four m2 (PIN backward. Postmesofossette is expressed by a small 4516/301, 318, 326, 335) and one m3 (4516/333) from oval mark, as well as the metafossette. In the next stage, Altynshokysu, bone-bearing level IV. hypoflexus became deeper and directed more posterior- Type locality. Kumbulak, North Aral Region, Ka- ly, anteroflexus divided in two parts, the lingual anter- zakhstan. ofossette and the labial anteroflexus, connecting with Stratigraphic level. Aral Svita, Lower Miocene. small anterostria, the anterior process of mesoflexus Description. Cheek teeth are relatively low crowned disappeared, and the parafossette became rounded. In (mesodont), without cement. P4 has rectangular shape. this stage, hypostria extends across one fourth to half of The unworn occlusal surface is uneven, complex, with the lingual crown height. The thickness of the enamel a great number of folds. There is one specimen exhib- walls became increased. In heavily worn teeth (n=1), iting this wear stage (n=1; Fig. 4A). Hypostria ascends the enamel walls of fossettes are strongly elevated above on the two thirds of the lingual crown height. Mesostria the dentine field, and mesoflexus is closed and forms a and anterostria extend dorsally across two thirds of the mesofossette. A mark is detached from the posterior labial height and approximately one third of the antero- end of mesofossette. Moreover, the hypoflexus became labial height, respectively. Hypoflexus is not very deep, closed. directed sharply anteriorly. It communicates with point The unworn M1 is similar to P4 (n=1). Hypoflexus of connection of the anteroflexus and anterior arm of is a little deepening into the occlusal surface. There are the mesoflexus (in anterolingual corner of the occlusal three distinct transverse fossettes in anterior lobe, i.e. surface) by narrow groove. Posterior arm of the mesof- wide anterofossette, relatively narrow parafossette, and lexus is sharply turned posteriorly. It is separated from small premesofossette. They are delimited by small the postmesofossette by very thin crest. There are two uneven crests. An isolated longitudinal rounded fos- small fossettes between