Amphicynodon sp. 1

(Fig. 1A)

DESCRIPTION

Less complete than the former, another left hemi-mandible (UP VAL1) retains only p3-p4, m2 and alveoli of p1-2, m1, m3 (Fig. 1A). It is slightly larger than UP VAL2. The dentition is unworn, p1 and m3 are single rooted, and p3 is slender and asymmetric. The p4 is less asymmetric and includes a pacd, the crown terminating distally in a small upturn. Based on the alveoli the length of m1 is estimated to 8 mm. The structure of m2 is unusual with a large mesial fovea limited mesially by a cristid and, distally by the cristids of protoconid and metaconid, two pyramidal cuspids of similar size, with convex buccal and lingual and lingual faces respectively. There is a very long basin bordered by the hypocristid and entocristid, terminating in the hypoconid and entoconid respectively, followed by cristids distally closing the basin. An m2 that long is unusual in Amphicynodon . Without taking into account forms with an especially short m2 (A. velaunus and A teilhardi), the index (length m2/ length m1) × 100 is 75 (the length of m1 measured from the alveoli). In the sample from the locality Itardies (MP 23), the same index is 44-62, mean 52. It is 54 for the type specimen of A. crassirostris (Filhol, 1876), 56 for A. typicus (Schlosser, 1888), 48 for A. rossignoli (Filhol, 1882) but 75 for A. gracilis (Filhol, 1874). Thus, the latter has the same proportions as UP VAL1 and we may place this specimen near A. gracilis. Nevertheless, there are some differences insofar as A. gracilis is smaller, there is no pacd in p4 and all the premolars have a marked cingulid. Thus, this identification is inappropriate and UP VAL1 remains Amphicynodon sp.