Leptolophus, Remy, 1965

Badiola, Ainara, Astibia, Humberto, Suberbiola, Xabier Pereda & Murelaga, Xabier, 2002, First record of the genus Leptolophus Remy, 1965 (Mammalia, Perissodactyla) in the late Eocene (Priabonian) of Europe, Geodiversitas 24 (4), pp. 841-848 : 842-846

Leptolophus sp. ( Figs 1-3 )

MATERIAL EXAMINED. — Right M1 ( MCNA 9947); right M2 ( MCNA 9948); right upper (P4?) tooth ( MCNA 9963); fragment of upper tooth ( MCNA 9964); left mandible with the m1-2 molar series ( MCNA 9002).

LOCALITY AND AGE. — Zambrana, Alava; late Eocene (Priabonian, MP 18) (see Astibia et al. 2000).

REMARKS

The classical systematic nomenclature considers Plagiolophus Pomel, 1847 and Palaeotherium Cuvier, 1804 as members of either the Equidae or the Palaeotheridae ( Savage et al. 1965; Franzen 1968; Remy 1976). Here we follow the systematic proposition of Cuesta (1993, 1994) who classified Plagiolophus and closer relatives as Pachynolophidae .

DESCRIPTION

The upper tooth remains which we described were found at the same level and in close proximity to each other. They probably belong to the same species and even to the same individual.

The molar series exhibits a strong height gradient ( Fig. 1 ). The size of the M1 is much smaller than that of the M2. The crown of M1 is very worn and less high (17.5 mm) than that of the M2 (31 mm). The M1 is very molariform and it has a trapezoidal outline, with the lingual wall being shorter than the labial one ( Fig. 1 A-C). Morphologically, the M1 is similar to the M2, but its cingula are more developed. The labial cingulum is W-shaped, quite thick and prominent. The anterolingual cingulum is also well developed and it ascends up to the occlusal surface. Moreover, the development of the parastyle and metastyle is decreasing in the molar series. These styles are less developed in M1 than in the M2.

The M2 ( Fig. 1 D-F) is moderately worn. It is very hypsodont, with its internal wall being as high as the external one. The crown is trapezoidal, with the basal part being narrower than the occlusal surface. The ectoloph is anteroposteriorly flat, showing an external wall that is lingually inclined and slightly concave on both sides of the mesostyle. The latter is very sharp and prominent. The ribs of the paracone and metacone are absent. In contrast, the parastyle and metastyle are well developed. The parastyle protrudes notably on the labial side, while the metastyle extends more posteriorly. Protoloph and metaloph are quite slender and oblique relative to the ectoloph. The latter is incomplete but it seems that the metaloph is connected to it, so that the two transversal valleys are separate. Owing to the oblique metaloph, a short and slend- er crista (hypoloph?) is present between the ectoloph and metaloph; it is sligtly convex and closes the posterior fossa. The labial cingulum is quite incomplete, but it continues and ascends up to the occlusal surface. The basal part of the internal surface is also incomplete, but it seems that the internal cingulum is not present.

MCNA 9963 and 9964 look like the M1 and M2 described above, but they are much smaller and less hypsodont than these teeth ( Fig. 2 ). The best preserved tooth (MCNA 9963) is quite molariform ( Fig. 2 A-C). The protoloph is slender, arches anteriorly and posteriorly; it is connected to the ectoloph and exhibits a U shape. The development of the styles is very similar to that of the M1. The ribs of the paracone and metacone are absent. These teeth are reminiscent of the premolars (probably the P4) of Leptolophus ( Remy 1998) .

The mandible MCNA 9002 preserves only the m1 and m2 ( Fig. 3 ). These teeth are hypsodont, narrow and exhibit a strong height gradient: the size of the m2 is much larger and longer than the m1. The crowns are trapezoidal and the internal wall is as high as the external one. In lateral view, the lophids are rounded and have a U shape, with a concave aspect in the internal wall. The paralophid is well developed and it protrudes notably on the lingual side. The m2 has a small hypoconulid, but does not ascend up to the occlusal surface; in m1 it is absent.

COMPARISONS

The M1 and M2 of Zambrana are typical of the genus Leptolophus and differ from those of Plagiolophus by the following characteristics:

1) trapezoidal outline, with the basal part being more narrower than the occlusal surface; 2) proto- and metaloph much longer and more slender, very lophodont and oriented more obliquely to the ectoloph; 3) less developed intermediate conules; 4) much higher internal cusp, with the hypsodonty of the labial and lingual surfaces being almost equal; 5) ectoloph anteroposteriorly flat; and 6) absence of ribs of the paracone and metacone.

The mandible MCNA 9002, previously referred to as Plagiolophus aff. mazateronensis Cuesta, 1994 by Astibia et al. (2000), differs from that of Plagiolophus by the following characters: 1) the height gradient of the m1-2 series is well developed; 2) the teeth have a trapezoidal outline; 3) the internal wall is as high as the external one; and 4) m1 without hypoconulid, m2 with a small one which does not ascend up to the occlusal surface.

The Zambrana upper teeth are larger and more hypsodont than those of the Leptolophus species from the late middle Eocene of southern France and Switzerland ( L. stehlini and L. nouleti Stehlin, 1904 ; see Remy 1998) ( Fig. 4 ). Morphologically, the teeth are comparable to those of Leptolophus sp. from Mazaterón, but the Zambrana teeth are clearly larger and more hypsodont. The large size and the more accentuated hypsodonty are considered as derived characters compared to Leptolophus from Mazaterón. This interpretation is coherent with the younger age of the Zambrana locality (MP 18) relatively to Mazaterón (MP 15-16) (see Antunes et al. 1997). On the basis of these differences, the Zambrana specimens may belong to a new species of Leptolophus . By pending a revision of all the material of Leptolophus , the Zambrana teeth are referred to Leptolophus sp.

A

Figures

FIG. 1. — Upper series M1 and M2 of Leptolophus sp. from Zambrana (Alava, Basque Country); A-C, right M1 (MCNA 9947); A, labial view; B, occlusal view; C, lingual view; D-F, right M2 (MCNA 9948); D, labial view; E, occlusal view; F, lingual view. Scale bar: 5 cm.

FIG. 2. — Upper teeth of Leptolophus sp. from Zambrana (Alava, Basque Country); A-C, right P4? (MCNA 9963); A, labial view; B, occlusal view; C, lingual view; D, E, left fragment of upper tooth (MCNA 9964); D, labial view; E, occlusal view. Scale bar: 5 cm.

FIG. 3. — Left mandible (MCNA 9002) showing the m1-2 series of Leptolophus sp. from Zambrana (Alava, Basque Country); A, occlusal view; B, labial view (modified from Astibia et al. 2000). Scale bar: 5 cm.

FIG. 4. — A, diagram d/D (in mm) of the M1 of several Pachynolophidae from the Eocene of Europe, D, largest diagonal (from the parastyle to the hypocone) of the upper teeth, d, diagonal perpendicular to D; B, diagram l/L (in mm) of the M2 of several Pachynolophidae from the Eocene of Europe, l, maximum width, L, average length of the external wall of the ectoloph. Measurements from Casanovas 1975 and Casanovas et al. 1998 for Plagiolophus annectens (Owen, 1848); Cuesta 1994 for Plagiolophus mazateronensis Cuesta, 1994 and Leptolophus sp.; Remy 1998 for Leptolophus stehlini Remy, 1965 and Leptolophus nouleti Stehlin, 1904.