Plesiomeryx, GERVAIS, 1873

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 : 150-151

GENUS PLESIOMERYX GERVAIS, 1873 PLESIOMERYX CADURCENSIS GERVAIS, 1873

Holotype: Right mandibular P/2-M/3 ( MNHN-QU 1772 ). Mouillac locality, Quercy Phosphorites. Age and precise locality are unknown (Old Quercy collections).

Diagnosis: Protocone and protoconule present (stage B, Hürzeler, 1936: 8). Long diastema between P1/ and C and between P/1 and P/2. P1/, P2/, P/2 and P/3 are short, P3/ with a strong lingual cone, P2/ with a weak lingual cone. The premaxilla reaches the frontal. The nasal is long, narrow and straight. The ethmoidal slit is falciform. The choanae are large. The horizontal portion of the lower jaw is slender ( Hürzeler, 1936).

Referred material: Aubrelong 1: left maxillary fragment with P2/-M3/ ( ABL 1 1452), right maxillary fragment with P3/-M3/ ( ABL 1 1453); isolated left P3/ ( ABL 1 1559); 12 mandibular fragments, one with left P/1-P/2 ( ABL 1 1457), one with left P/2-M/2 ( ABL 1 1458), one with right P/2-M/1 ( ABL 1 1459), one with left P/2-P/4 ( ABL 1 1461), one with right P/2-P/3 ( ABL 1 1463), one with right P/3-M/2 ( ABL 1 1465), one with left P/2-P/3 ( ABL 1 1487), one with broken right P/2-M/ 2 ( ABL 1 1492), one with broken right P/2-M/1 ( ABL 1 1497), one with left P/1-P/3 ( ABL 1 1780), one with right P/3-P/4 ( ABL 1 1786), one with right P/2-P/4 ( ABL 1 1787); three isolated left P/2 ( ABL 1 1488, ABL1 1492¢, ABL1 1668), three isolated right P/3 ( ABL 1 1462, ABL1 1777, ABL1 1794). Ravet: two isolated right P2/ ( RAV 597, RAV 973), an isolated left P2/ ( RAV 598), an isolated left P3/ ( RAV 840); five mandibular fragments: with left P/2-M/2 ( RAV 1017), one with left P/1-M/1 ( RAV 1024), one with right P/3-M/1 ( RAV 1025), two with left P/2-M/2 ( RAV 1026, RAV 1027); an isolated left P/2 ( RAV 853), three isolated right P/2 ( RAV 739, RAV 740, RAV 892), four isolated right P/3 ( RAV 732, RAV 889, RAV 895, RAV 1037), four isolated left P/3 ( RAV 849, RAV 887, RAV 898, RAV 901). Mas de Got: 13 mandibular fragments, one with right P/1-M/3 ( MGT 104), one with left P/2-P/4 ( MGT 129), one with left P/2-M/2 ( MGT 135), one with right P/2-P/4 ( MGT 151), one with left P/3-M/3 ( MGT 154), one with left P/2-P/4 ( MGT 190), one with left P/ 2-P/3 ( MGT 195), one with right P/3-M/1 ( MGT 3185), one with right P/3-P/4 ( MGT 3196), one with right P/1- P/2 ( MGT 3199), one with left P/2-P/3 ( MGT 3200), one with right P/2-P/3 ( MGT 3202), one with right P/2-P/4 ( MGT 3203). La Plante 2: five maxillary fragments, two with left P3/-M2/ ( PL 2 1180, PL 2 1191), one with left P1/-P2/ ( PL 2 1201), two with left P2/-P3/ ( PL 2 1211, PL 2 1213), 10 mandibular fragments, one with right P/2-M/3 ( PL 2 1168), three with left P/3-M/3 ( PL 2 1169, PL 2 1242, PL 2 1275), one with right P/4-M/3 ( PL 2 1173), one with left P/2-M/3 ( PL 2 1174), two with left P/3-M/3 ( PL 2 1175, PL 2 1176), one with left P/2-P/ 4 ( PL 2 1177), one with right P/2-P/3 ( PL 2 1250). Pech Crabit: three right mandibular fragments with P/3-M/ 1 ( PCT 366) and one with P/2-P/3 ( PCT 367, PCT 385). Mounayne: two left mandibular fragments, one with P/2-M/2 ( MOU 209) and one with P/2-P/4 ( MOU 148), a right maxillary fragment with P2/-P3/ ( MOU 187). Itardies: a right mandibular fragment with P/2-M/3 ( ITD 941).

Measurements: See Table 3. For P. cadurcensis , the Kolmogorov- Smirnov and Shapiro- Wilk tests confirm normality for L P/3 from Aubrelong 1 (N = 12, K–S, d = 0.163, P> 0.20, W = 0.955, P = 0.721), Ravet (N = 12, K–S, d = 0.135, P> 0.20, W = 0.949, P = 0.629), La Plante 2 (N = 9, K–S, d = 0.244, P> 0.20, W = 0.903, P = 0.269) and Mas de Got (N = 12, K–S, d = 0.104, P> 0.20, W = 0.968, P = 0.887).

The weakness of variation coefficients (4 < V <10) confirms the homogeneity of samples of P. cadurcensis from localities of the same reference level. For the length of P/3 from Aubrelong 1 and Ravet ( MP 21): N = 24, M = 3.40, s = 0.23, K–S, d = 0.897, P> 0.20, W = 0.96, P = 0.438, V = 6.87. P/3 from Mas de Got and La Plante 2 ( MP 22): N = 21, M = 3.02, s = 0.21, K–S, d = 0.084, P> 0.20, W = 0.97, P = 0.672, V = 6.93. P/3 from Pech Crabit, Mounayne, Itardies ( MP 23): N = 6, M = 3.21, s = 0.16, K–S, d = 0.19, P> 0.20, W = 0.97, P = 0.897, V = 5.05.

Description

Upper dentition: A maxillary fragment from Aubrelong 1 ( Fig. 3A ) bears a premolariform P1/ that is short and biradicular. The elongate P2/ has a weakly developed distolingual tubercle. The triangular P3/ has a well developed mediolingual cusp from which two crests extend to the prominently strong parastyle and metastyle. The labial and lingual cusps of P4/ are median, the parastyle and the metastyle are strong. The same characters are evident in specimens ( PL 2 1180) from La Plante 2 ( MP 22).

Lower dentition: On the mandibular fragment ( MGT 104), the single-rooted P/1 is caniniform and the anterior stylid is not clearly marked ( Fig. 3B ). The diastema that separates P/1 from P/2 varies between 0.5 and 1.9 mm in length. The double-rooted P/2 bears a well developed paraconid, while the main cusp is directed backward and reaches the distolingual angle. On P/3, the paraconid is situated lingually and P/4 has a well developed style. The protoconid and the metaconid form large tubercles separated by a deep notch (e.g. ABL1 1458). There are no differences between the material from Aubrelong 1 and that from La Plante 2 or Pech Crabit.

Comparison: The presence of a single-rooted caniniform P/1, a diastema between this premolar and P/2, the presence of a well developed mediolingual cusp and a short anterior lobe on P/3 indicate that this small cainotherine from Aubrelong 1 ( MP 21) belongs to Plesiomeryx . In specimens from the localities of Aubrelong 1, La Plante 2, and Pech Crabit, the dimensions of teeth in the lower dental rows ( Table 3), and the features of the lower premolars agree with the description of P. cadurcensis . The same is also true for the upper tooth rows, which correspond in their morphology and dimensions to material of P. cadurcensis described by Hürzeler (1936) and Berger (1959). The general similarity of the morphological patterns and dimensions of the material reflect a degree of homogeneity despite the different ages of the studied material.

Figures

Figure 3. Plesiomeryx cadurcensis. A & B, occlusal view. A, left P2/-M3/ (ABL1 1452). B, right C-M/3 (MGT 104). P. huerzeleri. C & D, occlusal view. C, right P2/-M3/ (MGT 3209). D, left P/2-M/3 (MGT 3187). Scale bar = 1 mm.