Indarctos arctoides ( Depéret, 1895 )

Geraads, Denis, Kaya, Tanju & Mayda, Serdar, 2005, Late Miocene large mammals from Yulafli, Thrace region, Turkey, and their biogeographic implications, Acta Palaeontologica Polonica 50 (3), pp. 523-544 : 523-525

Indarctos arctoides ( Depéret, 1895)

Type locality: Montredon , France .

Material from Yulafl I.—TTMEU−CY−46, an almost complete left dentary, lacking only the incisors, the tip of the canine, p1, m3, and part of the coronoid process ( Fig. 2 ).

Description.—The corpus is robust, but not extremely so, with a uniform depth from p4 to m2. The ventral border forms a rather regular curve, being only slightly more convex posteriorly. The anterior border of the coronoid process is slightly inclined backwards.

The canine is short and stout, and strongly curved. It has a weak posterior keel, and a stronger mesio−lingual one, with an enamel notch just in front of it.

The missing first premolar had a single, rather large root, strongly inclined forwards. It is separated by a short diastema from p2, which has two roots, almost fused but well distinct labially. Its crown is long, and consists of a single low cuspid, whose apex is more anterior than mid−length, so that the longitudinal cristid has a steeper mesial slope. There is a lingual cingulid, especially marked in the distal half, where it increases tooth width. A longer diastema separates p2 from p3, which has two well−distinct roots and is morphologically intermediate between p2 and p4. The main cuspid is higher and more posterior than on p3, the disto−lingual cingulid is weaker, but there is an incipient distal cingulid. In labial view, both edges of the main cuspid are convex. A short diastema separates this tooth from p4, which is much larger, but not disproportionately so. Its main cuspid is relatively still higher than on p3; there is a hint of a mesial accessory cuspid where the base of the main cristid turns inwards, and the distal cingulid is somewhat enlarged, forming a narrow shelf. The tooth is only slightly broader above the distal root.

The m1 has the usual morphology for Indarctos , with a very open trigonid, much narrower than the talonid, a reduced metaconid, and an entoconid larger and higher than the entoconulid (see Beaumont 1982). Although the teeth are slightly worn, it is clear that there was no cuspid between protoconid and hypoconid. The m2 is a large tooth, broader than m1, without paraconid, but with a transverse cristid between protoconid and metaconid.

Comparisons.—Several species of Indarctos have been named, but only a few are now currently recognised in Eurasia. Indarctos atticus ( Weithofer, 1888, ex Dames) is mostly known in the classic Turolian localities of Pikermi, Samos, and Maragha. Indarctos atticus probably includes I. salmontanus Pilgrim, 1913 , the type species, probably from the Dhok Pathan zone of the Siwaliks, I. lagrelii Zdansky, 1924 and I. sinensis Zdansky, 1924 , from Loc. 31 and Loc. 30, respectively, in China, and I. bakalovi Kovachev, 1988 , from Kalimantsi in Bulgaria. The recently described I. zdanskyi Qiu and Tedford, 2003 , from Baode, China, is similar, but is more derived in several features. All these localities are also of MN12/13−equivalent age. Indarctos arctoides ( Depéret, 1895) is best known from Montredon ( MN 10; Depéret and Gomez−Llueca 1928; Beaumont 1988), Westhofen ( MN 9?; Tobien 1955), Pfaffstetten ( MN 11?; Thenius 1959), and Küçükçekmece ( Petter and Thomas 1986), while I. vireti Villalta and Crusafont, 1943 , is mostly known from the Vallesian of Spain, chiefly from Can Llobateres ( MN 9; Crusafont and Kurtén 1976), but has also been reported from Sinap ( Viranta and Werdelin 2003). The status of I. anthracitis Weithofer, 1888 , from Monte Bamboli, is disputed.

The dentary from Yulafli compares best with a dentary of I. atticus from Samos in the NHMW ( Thenius 1959: fig. 7), except that the depth of the latter, as in all I. atticus , increases caudally. Robustness is variable in other specimens of I. atticus but some of them, such as those from Crevillente−2 ( Montoya et al. 2001: pl. 2: 1) and Kalimantsi ( NMNHA) have an extremely convex lower border of the corpus, and an anterior border of the ramus which is slightly inclined forwards. This is of course a consequence of the shortening of the cranial basis in this species. The dentaries from the Vallesian of Spain seem to have a much less upright ramus that is, however, largely reconstructed. The dentary from Küçükçekmece ( Petter and Thomas 1986: fig. 5) is extremely slender, and perhaps even pathological.

The lower canine is poorly known. The description of those of I. vireti by Crusafont and Kurtén (1976) perfectly matches that of our specimen, except that they are smaller.

The relatively large p2 and p3, which are both doublerooted, contrast with the sharp reduction of these teeth in typical I. atticus (and still more with the loss of these teeth in I. zdanskyi ). On the contrary, p4 is enlarged in I. atticus , so that there is a sharp difference between p3 and p4, whereas size harmoniously increases from p2 to p 4 in our specimen. Molar morphology does not provide many discriminating features. The m1 of I. atticus often has a labial tubercle behind the protoconid; it is absent in TTMEU−CY−46.

Discussion.—The specific distinction between the middle and late Turolian I. atticus and the early Vallesian form (whether it is called I. vireti or I. arctoides vireti ) is widely acknowledged. The former differs from the latter by (1) its larger size; (2) its shortened dentary, and cranial base; (3) its much smaller p2 and p3, with only one root; (4) its enlarged and broadened p4. Other features of the molars do not prove very discriminant. The trigonid/talonid ratio of m2, used by Petter and Thomas (1986), although potentially meaningful, is too hard to estimate precisely.

It is nonetheless clear that species demarcation is blurred when chronologically intermediate forms, many of them called I. arctoides , are taken into consideration. The size of m1, taken as an indicator of overall size, forms an almost perfect continuum ( Fig. 3 ; the apparent gap in Montoya et al. 2001: fig. 4 results from the non−inclusion of two intermediate specimens, the type of I. lagrelii and the Samos specimen in NHMW). The Lm2/Lm1 ratio, stated by Montoya et al. (2001) to be smaller in I. arctoides than in both other species, is in fact variable. It is always large in I. atticus , but may be small (Küçükçekmece) or large (Pfaffstetten) in I. arctoides , as well as in I. vireti (respectively, Can Purull and Can Llobateres). Morphological characters are also intermediate. For instance, at Montredon, the lower border of the dentary is strongly curved, as in several I. atticus , and the p3 has its roots “étroitement soudées” (Depéret and Gomez−Llueca 1928).

At two localities, both usually included in biozone MN11, Dorn−Dürkheim ( Roth and Morlo 1997) and Crevillente 2 ( Montoya et al. 2001), I. atticus has been reported to coexist with a more primitive form, I. arctoides in the former site, and with I. cf. vireti in the second. In both cases, this second species is documented by rather poor or fragmentary material. At Crevillente−2, the identification of two species rests mostly upon size, but the differences certainly do not exceed what can be expected in a single population. Even the “ I. atticus ” there has primitive features: it is rather small, its p2 and p3 are bi−radiculated, the parastyle of its P4 is stronger than in I. vireti , but clearly smaller than in typical I. atticus ( Montoya et al. 2001: fig. 5). At Dorn−Dürkheim, an M2 referred to I. atticus is almost identical in size to a tooth from Montredon, type−locality of I. arctoides . Two M3s, each referred to a different species, are little different in size (18.8 × 15.2 and 21.4 × 17.85).

It is far more likely that, in both localities, we are dealing with a single species, intermediate between the Vallesian and middle Turolian forms. This is not unexpected in early Turolian sites. Features of these taxa appear to have evolved mosaically, with intermediate forms displaying a mixture of primitive and derived traits. On the whole, not a single trait forbids hypothesising an anagenetic evolution from I. vireti to I. atticus , through I. arctoides .

The Indarctos from Yulafli clearly belongs to this intermediate stage. Its m1 is smaller than those of all I. atticus , and close in size to I. arctoides from Montredon, but its m2 is large, near the lower range of I. atticus (however, an m2 from Can Llobateres is almost as large). It has no cuspid between protoconid and hypoconid on m1, in contrast to I. atticus . The clearest primitive features of the Yulafli specimen are found in the premolars. The harmonious increase in size from p2 to p4 is quite unlike I. atticus , where p4 is much enlarged in respect to the reduced p3. Correlatively, p2 and p3 are still two−rooted, while the former is already one−rooted at Pfaffstetten and Küçükçekmece, and the latter may also be one−rooted in I. atticus .

Typical I. atticus (large size, much reduced and one−rooted p2 and p3, enlarged p4) are known only in MN12–13 or equivalent age. Records of earlier age are either doubtful in age, or display more primitive features. Besides those mentioned above, I. atticus is present in Mecquenem’s collection from Maragha ( Mecquenem 1925), but the dating of this collection, which may well not be homogeneous, is unknown. According to Bernor (1986: 83), Indarctos “was collected by Mecquenem presumably from somewhere within the middle Maragheh sequence”. At Terrassa, at site referred to MN10, the record of I. atticus ( Pons−Moyà 1990) is based upon a fragment of m1, not a sound basis for specific identification. The identification of I. atticus at Aubignas I ( Petter and Thomas 1986) looks reasonable but, pending detailed analysis of the fauna, the age of the site, given as MN 11 ( Azanza et al. 1993), is debatable, all the more as the site underlies a basalt dated to 6.4 Ma. Reciprocally, primitive forms are absent from MN12–13 sites, except three isolated teeth at Hatvan in Hungary ( Bernor et al. 2003) that are so small that their identification is not fully certain. Indarctos arctoides occurs only in the late Vallesian–early Turolian, while I. atticus occurs only in the middle–late Turolian.

Figures

Fig. 2. Indarctos arctoides, TTMEU−CY−46, Yulafli, Turkey, Vallesian, late Miocene. Left mandibular ramus, lateral (A) and occlusal (B) views of p2–m2 (stereo).

Fig. 3. Length versus width plot of m1 in the genus Indarctos, showing continuous variation.