Eoletes tianshanicus, Averianov & Godinot, 2005

Averianov, Alexander O. & Godinot, Marc, 2005, Ceratomorphs (Mammalia, Perissodactyla) from the early Eocene Andarak 2 locality in Kyrgyzstan, Geodiversitas 27 (2), pp. 221-237 : 222-226

Eoletes tianshanicus n. sp. ( Fig. 2 A-I)

Eomoropus sp. – Averianov & Udovichenko 1993: 141.

Schlosseria magister – Averianov & Udovichenko 1993: 141.

Eoletes sp. – Averianov & Godinot 1998: 212.

Eomoropus ? sp. or?cf. Propachynolophus sp. – Averianov & Godinot 1998: 212.

HOLOTYPE. — ZIN 32754, left maxillary fragment with P2-M2 and alveolus of P1. Andarak 2 locality, Osh Province, Kyrgyzstan. Lower Alay beds, latest early Eocene (Ypresian).

ETYMOLOGY. — After the Tian Shan mountains in Middle Asia.

REFERRED MATERIAL. — ZIN 35282, right maxillary fragment with P1 and the alveoli of P2 ; ZIN 35283, left M2 ; ZIN 34023, right M2 ; ZIN 32760, posterior portion of left M2 ; ZIN 35284, incomplete left M3 ; ZIN 32758, right m1 or m2 ; ZIN 32755, left astragalus ; ZIN 34024, right astragalus ; ZIN 34025, right astragalus of juvenile animal. Locality as for the holotype .

DIFFERENTIAL DIAGNOSIS. — Eoletes tianshanicus n. sp. differs from the type species, E. gracilis Biryukov, 1974 from the middle Eocene of Kazakhstan ( Biryukov 1974;

Lucas et al. 1997) by its smaller size ( Table 1), its lower and anteriorly situated infraorbital foramen (above P3 instead of above the anterior part of P 4 in E. gracilis ), a two-rooted P1 (three-rooted in E. gracilis ), and an interrupted lingual cingulum on P3-4. From E. xianensis ( Zhang & Qi, 1981) from the middle(?) Eocene of China ( Zhang & Qi 1981; Lucas et al. 1997), Eoletes tianshanicus n. sp. differs by its smaller size, lower placed anterior zygomatic root and infraorbital foramen, a longer bony palate, extending behind M2 (between M1 and M 2 in E. xianensis ), and the presence of a P1.

REMARKS

L u c a s e t a l. (2 0 0 1) r e f e r r e d t h e s o -c a l l e d hyrachyid Subhyrachyus tshakpaktasensis Gabunia, 1999 from the Arshantan Chakpaktas Svita in the Zaisan Basin, eastern Kazakhstan ( Gabunia 1999) to the lophialetid genus Eoletes . However, this taxon clearly differs from Eoletes and other lophialetids by the presence of a crista on the ectoloph of the upper molars and premolars. Whether or not this taxon belongs to Eoletes , it differs from Eoletes tianshanicus n. sp. by this character and its noticeably larger size.

DESCRIPTION

The palatal portion of the maxilla (ZIN 32754) appears to be very narrow. The intermaxillar suture is preserved in the region of P1-2. At the level of M1-2 there is a thick maxillary-palatine suture, which indicates that the end of the bony palate was probably far more posteriorly. The infraorbital foramen is located relatively low and anteriorly, 8.7 mm above the anterior half of P3. The anterior root of the zygomatic arch begins above M2 and relatively low, only slightly above the tooth row.

The P1 is a two-rooted tooth, as can be seen from both the alveoli on the holotype and the tooth on the maxillary fragment ZIN 35282. The tooth is relatively small, its width being less than half of the width of P2. The crown is dominated by one cusp (paracone), without traces of a metacone. There is a very small protocone which is placed lingually and posteriorly to the paracone center and above the posterior tooth root.

The P2-4 are quite uniform in morphology. They differ mainly by a slight posterior increase in size. These premolars are non-molariform (sensu Radinsky 1967). They have a relatively straight to slightly sinuous ectoloph, and the protoloph-metaloph loop characteristic of the Lophialetidae . The parastyle is relatively well separated. On P2 the paracone is noticeably larger than the metacone; on P3-4 both cusps are of equal size. The anterior and posterior cingula are well developed on P2-4, but a lingual cingulum is present only on P2. The ectoflexus is very shallow on P2-3 and almost absent on P4.

The M1-2 are similar in morphology, differing mostly in proportions (M1 is squarish, M2 is more trapezoid, antero-posteriorly elongated). The parastyle is relatively large, but about two times lower than the paracone. The paracone is higher than the metacone, but on M2 the latter has a longer base. On both teeth the metacone is considerably deflected lingually. The metastyle is almost indistinct. In occlusal view, the ectoloph runs antero-posteriorly above the paracone, then makes an almost right angle and runs parallel to the metaloph until the summit of the metacone, and posteriorly it is bent postero-labially. It is more confluent with the metaloph on M2 than on M1. The protoloph connects the parastyle. The metaloph connects nearly the paracone on M1 and midway between paracone and metacone on M2. The hypocone is higher than the protocone. There is a strong anterior cingulum and a weaker posterior cingulum. A very small lingual cingulum is present only on ZIN 35283 ( Fig. 2D ), confined to an embrasure between the bases of the protocone and hypocone.

ZIN 35284 is an M3 with a broken off parastylar region and most of the lophs. It was possibly not fully erupted as the preserved parts of the protoloph and metaloph are unworn and the roots apparently were not developed. The metacone is deflected lingually and the postmetacrista is relatively short. The protocone is higher than the hypocone. There are remnants of anterior and posterior cingula; the enamel is lacking on the lingual side.

The crown of m1-2 is rectangular in outline, with a somewhat rounded anterior side. The paralophid is relatively long but low. The trigonid basin is very narrow and short. The protolophid and the hypolophid are almost perpendicular to the crown longitudinal axis. The hypolophid is distinctly lower than the protolophid. The cristid obliqua is well developed, joining the protolophid at the center. The hypoconulid is a distinct, transversely wide ridge, connected to the hypolophid by a short posthypocristid. There is a faint anterior cingulid below the paralophid and a very short labial cingulid, between the bases of protoconid and hypoconid.

The astragalus is typical of ceratomorph perissodactyls, having a well developed trochlea, a short neck, and a saddle-shaped astragalar head (navicular facet). The sustentacular and distal calcaneal facets are not confluent. The adult astragali are slightly smaller than those of Lophialetes expeditus ( Radinsky 1965; Reshetov 1979) and similar in size with those of Eoletes gracilis ( Biryukov 1974; Lucas et al. 1997).

Measurements

For upper dentition see Table 1. m1-2 (ZIN 32758): L = 10.1; WTR = 5.7; WTL = 5.8. Astragali (ZIN 32755, 34025): proximodistal height = 18.3, 17.1; distal width = 12.0, -.

DISCUSSION

Eoletes tianshanicus n. sp., with its two-rooted P1, is intermediate in the state of reduction of P1 between E. gracilis (three-rooted P1) and E. xianensis (P1 is totally lacking).

Family DEPERETELLIDAE Radinsky, 1965

Figures

FIG. 2. — A-I, Eoletes tianshanicus n. sp.; J-L, Teleolophus medius Matthew & Granger, 1925; in labial (A, G), anterior (I, L) and occlusal (B-F, H, J, K) views; Andarak 2, Kyrgyzstan, Alay beds, Irdinmanhan; A, B, ZIN 32754, holotype, left maxillary fragment with P2-M2 and alveolus of P1; C, ZIN 34023, right M1 or 2; D, ZIN 35283, left M2; E, ZIN 35284, left M3; F, ZIN 32758, right m1 or 2; G, H, ZIN 35282, right maxillary fragment with P1; I, ZIN 32755, left astragalus; J, ZIN 35285, left P2; K, L, ZIN 32756, right p3 trigonid. Scale bar: 1 cm.