Paroxacron undetermined

Blondel, Cecile, 2005, New data on the Cainotheriidae (Mammalia, Artiodactyla) from the early Oligocene of south-western France, Zoological Journal of the Linnean Society 144 (2), pp. 145-166 : 147-149

PAROXACRON SP. (FIG. 2A- D)

Material: Escamps ( Legendre, 1980). Aubrelong 1: a right maxillary fragment with P2/-P4/ ( ABL 1 1455), a left maxillary fragment with P3/-M1/ ( ABL 1 1454); two isolated right P3/ ( ABL 1 1558, ABL1 1565), an isolated left P3/ ( ABL 1 1557), two left mandibular fragments with P/2-P/3 ( ABL 1 1479, ABL1 1485); an isolated left P/3 ( ABL 1 1792). Ravet: a left maxillary fragment with P4/-M3/ ( RAV 1055); five isolated upper teeth, a right P2/ ( RAV 595), three left P3/ ( RAV 599, RAV 602, RAV 604), a right P3/ ( RAV 771); three left mandibular fragments, one with P/2-M/1 ( RAV 1022), one with P/1-P/3 ( RAV 1019), and one with P/3-P/4 ( RAV 1023); an isolated left P/2 ( RAV 595), and an isolated right P/3 ( RAV 902). La Plante 2: two left maxillary fragments, one with P2/-M1/ ( PL 2 1202) and one with P2/-P3/ ( PL 2 1203).

Measurements: See Table 1.

Description

Upper dentition: The premolariform P2/ (Fig. 2A) is more elongate than that of P. cadurcensis . A cingulum occurs on the lingual side of the crown. The triangular P3/ (Fig. 2B) bears a very elongate anterior lobe similar to that of the P3/ of P. cadurcensis , and the parastyle is well pronounced. The lingual cusp is developed distally. M1/ possesses a lingual paraconule which gives this molar a quadrangular lingual outline. Hür-

A B

Figure 2. Paroxacron sp. A- D, occlusal view. A, right P2/-P4/ ( ABL 1 1455). B, left P3/-M1/ ( ABL 1 1454). C, left P/1-P/3 ( RAV 1019). D, left P/2-M/1 ( RAV 1022). P. cf. bergeri . E, left P1/-M3/, MGT 3210, occlusal view. Scale bar = 1 mm.

zeler (1936) indicates that the mesostyle of Paroxacron is split, although this feature, which only can be observed on unworn teeth, is variable.

Lower dentition: The double-rooted P/1 is premolariform, elongate and narrow on the mandible from Ravet (Fig. 2C). This premolar possesses a sharp median cusp and a faint paraconid. The double-rooted and elongate P/2 is separated from P/1 by a diastema which varies from 0.8 to 1.4 mm in length. The paraconid is lingual and more developed than on P/1. A diastema varying from 0.5 to 1.1 mm long separates P/ 2 from P/3. The elongate P/3 is wider distally than P/ 2, its paraconid is more pronounced than that of P/2 and a crest extends from a median cusp to the distolingual part of the tooth. The stocky P/4 is less elongate than the first premolars. The paraconid is strongly pronounced and the protoconid and the metaconid are also developed. The latter are separated by a notch, although the metaconid is situated distally (Fig. 2D).

Comparison: The presence of a premolariform P/1, the very elongate premolars and the occurrence of a diastema between P/1-P/2 and P/2-P/3 enables the form described above to be attributed to Paroxacron , although the dimensions of this specimen are more comparable to those of Plesiomeryx cadurcensis ( Tables 1–3). The Paroxacron material from Ravet, Aubrelong ( MP 21) and from La Plante 2 ( MP 22) differs from that from Escamps ( Legendre, 1980) in that the P/2-P/4 row is a little shorter. Material is rare, however, so it is difficult to determine whether these differences are simply due to variation or whether they represent a trend toward premolar reduction in the evolution of this lineage. In any case, it is the first record of a small species of Paroxacron that has been found in early Oligocene levels.