Indarctos arctoides (Depéret, 1895)

Peigné, Stéphane, 2016, Carnivora, Geodiversitas 38 (2), pp. 197-224 : 199-200

Indarctos arctoides (Depéret, 1895)

( Fig. 1A, B )

Ursavus sp. – Malik & Nafiz 1933: 109, pl. 12, fig. 6.

Indarctos arctoides – Petter & Thomas 1986: 579, figs 1-5.

REFERRED MATERIAL FROM KÜÇÜKÇEKMECE. — MNHN.F.TRQ947, subcomplete left hemimandible with the root of the canine, the root of p1, the alveolus of p2, the fused roots of p3, p4-m2, and the root of m3.

DESCRIPTION

Mandible ( Fig. 1A, B )

The hemimandible is slender and low compared to other specimens of I. arctoides (for example, the holotype from Montredon, Depéret & Llueca 1928: pl. 9, figs 3, 4; the hemimandible from Yulaflı, Geraads et al. 2005: fig. 2). However, it does not display any obvious pathology. The depth of the mandibular body is rather constant below p1-p4 (DMp2-3 = 39.3; DMp3-4 = 40; DMp4-m1 = 41), then increases slightly from m1 and posteriorly (DMm1-2 = 43.8; DMm2-3 = 46). Thickness of the dentary across p3 and m1 is 17.6 mm. The coronoid process is not preserved; the masseteric fossa has its dorsal part missing, is approximately 75-mm long and shallow. The anterior margin of the fossa is situated below the distal border of m3. The ventral margin of the fossa is marked by a crest, which continues posteriorly to the tip of the angular process. The latter is short and extends medially by a small, dorsoventrally flat process. The process displays an additional, ventral crest marking the lateral extension of the internal pterygoid muscle insertion.This insertion is particularly visible in the lingual face of the mandible, where it occupies a dorsally curved, oval-shaped area of 35-mm length. The anterior limit of this area is marked by a conspicuous tubercle located ventrolingually on the mandibular body.

Dentition ( Fig. 1A, B )

The p1, p2, p3 and m3 are not preserved. The p1, p2 and m3 are single-rooted, with alveolar length of 9, 8.6 and 13 mm, respectively; the p3 has two roots that are mostly fused, for a total alveolar length of 12 mm. The tooth row is 125.5- mm long, from the mesial margin of the alveolus of p1 to the distal margin of the alveolus of m3. There is no distinct diastema between cheek teeth but a small one between p2 and p3 (L = 3 mm). The premolar row (L = 52 mm, measured at alveolar level) is much shorter than the molar row (L = 74 mm, measured at alveolar level). The teeth are lightly worn.

*, type specimen; 1, from Pickford (2007); 2, cast of GSI D 156. See Material and methods for abbreviations.

The main cuspid of the p4 (L = 17.7; W = 9.4) is broken off and a small, mesiolingual fragment of the crown is missing. Distal and mesial accessory cuspids are vestigial; the talonid is long, narrow, and marked by a central, longitudinal crest; it is bordered distally by a distinct cingulid. The m1 (L = 33; W = 15.7;TLim1 = 22.4) is elongated and low, especially the trigonid cuspids. The protoconid is the tallest trigonid cuspid, the paraconid and metaconid being approximately of equal height. The paraconid and protoconid have an orientation parallel to that of the long axis of the body of the mandible. The metaconid is located distolingually to the protoconid and is visible in labial view. The labial face of the tooth is marked by a pronounced concavity at the trigonid/talonid junction. The talonid is much wider than the trigonid and the labial cingulid is particularly developed; its lingual (and not labial, contra Petter & Thomas 1986: 575) crest bears two low cuspids, an entoconid distally, and a slightly larger and mesially located entoconulid. The crista obliqua is low and diverges distad to the hypoconid, which is the only labial cuspid. The talonid basin is shallow. The m2 (L = 25.3; W = 17.6; TWm1 = 16.6) is rectangular in outline, with a trigonid slightly longer and, especially labially, wider than the talonid. The trigonid is composed of a horseshoe-shaped basin outlined mesially by a circular crest and distally by a transverse crest connecting protoconid and metaconid. The lingual margin of the talonid bears two vestigial cuspids, the entoconulid being the most developed one. The hypoconid is partly broken and/or worn. The m3 is not preserved but its root is long and narrow.

COMPARISONS AND DISCUSSION

The genus Indarctos is a typical member of the late Miocene Holarctic faunas. In Eurasia, its species content is still disputed, with 2 to 5 species (see, for example, Hunt 1998; Baryshnikov 2002; Geraads et al. 2005). In Europe, three species are generally recognized, with evolution from MN9, Indarctos vireti Villalta & Crusafont, 1943 , to MN12-13, Indarctos atticus (Weithofer, 1888) , through the intermediate species I. arctoides (MN9-MN11). The first description and detailed comparison of the dentition of MNHN.F.TRQ947 were made by Petter & Thomas (1986), who assigned TRQ947 (KUC 1 in their paper) to Indarctos arctoides . The main difference from their description that is worth noting here is the alveolar length of p1, 0.4 mm in Petter & Thomas (1986), a value difficult to reconcile with my measurement, 9 mm. The specific assignment of Petter & Thomas (1986) is based on the overall size of teeth (compared with the Turolian Indarctos atticus ), and the single-rooted p2, especially compared with Indarctos vireti from Can Llobateres. In their study of Indarctos arctoides from the site of Yulaflı (9.3-9.4 Ma, late Miocene, Thrace, Turkey) Geraads et al. (2005) also assigned the specimen from Küçükçekmece to Indarctos arctoides . In their discussion, they underline how difficult species demarcation is in this genus, but they conclude that Indarctos arctoides occurs only in the late Vallesian-early Turolian, while I. atticus is known from later Turolian sites. There is little I can add here to support this assignment. A major contribution to the knowledge of I. arctoides will certainly come when the extraordinary sample from the Vallesian site of Batallones-3, Spain, which yield- ed approximately 2000 bones of this species representing a minimum of 16 individuals ( Abella et al. 2013) is published.

The M2 assigned to Ursavus sp. figured by Malik & Nafiz (1933: fig. 6) probably belongs to the same species (see discussion in Petter & Thomas 1986). This specimen was part of the collection stored at the Geology Institute of Istanbul University and was probably destroyed by the fire of 1942.

Figures

FIG. 1. — A, B, Indarctos arctoides (Depéret, 1895): MNHN.F.TRQ947, subcomplete left hemimandible with p4-m2 in labial (A) and occlusal (B) views; C-E, Sivaonyx hessicus (Lydekker, 1890): KÇ 83, fragment of right hemimandible with m1 in lingual (C), occlusal (D), and labial (E) views; F-H, Cryptophoca sp.: KÇ 101, fragment of left hemimandible in occlusal (F), lingual (G), and labial (H) views. Scale bars: 10 mm.