Propalaeotherium cf. gaudryi (Lemoine, 1878), 2019

Remy, Jean A., Krasovec, Gabriel, Lopez, Éric, Marandat, Bernard & Lihoreau, Fabrice, 2019, The Palaeotheriidae (Equoidea, Perissodactyla, Mammalia) from the Eocene fauna of Aumelas (Hérault department, France), Geodiversitas 41 (13), pp. 525-585 : 534-537

Propalaeotherium cf. gaudryi (Lemoine, 1878)

( Fig. 7 )

MATERIAL. — AUM 47, right M3/; AUM 164, right maxillary fragment with M3/; AUM 168, right maxillary with canine and P1/ alveoli, P2/- P3/-(P4/-M2/)-M3/; AUM 192, right P4/; AUM 209, right maxillary fragment with M1/-M3/; AUM 1583, palate with right P1/-M2/ and left P2/-M3/; AUM 1584, left maxilla with P2/-M3/; AUM 1585, left maxilla with (P2/)-(P3/)-P4/-M1/; AUM 1587, right M2/-M3/; AUM 1590, left M3/; AUM 1592, left M2/; AUM 1593, left M3/; AUM 1594, right P4/; AUM 1595, left M2/; AUM 1658, 1659, left M3/. AUM 206, right mandible with (alv.P/1-alv.P/2)-P/3-M/3 ( Pr. sudrei in Remy & al. 2016 , fig. 3 E-F); AUM 236, right P/3; AUM 1560, right P/3; AUM 1561, right P/2; AUM 1601, right mandible with (P/4)-M/1- M/3; AUM 1603, right mandible with (P/3)-P/4-M/3; AUM 1604, right mandible fragment with M/1-M/2; AUM 1606, left mandible with P/4-M/3; AUM 1607, right (M/1)-M/2; AUM 1608, left M/2.

DESCRIPTION

We gather some maxillaries or maxillary fragments of Propalaeotherium , which display differences with Propalaeotherium sudrei and that present larger measurements ( Table 2). Indeed the upper cheek teeth row is on average 13% longer (60- 62 mm instead of 54 mm), and the upper molar row is 16% longer (36-38 mm instead of 32 mm). All cheek teeth are on average 10% larger in linear measures. On lower cheek teeth, the length mean difference is of 8% (Appendices 16; 17). Upper teeth areas are about 30% larger (Appendix 10). Lower teeth areas (Appendix 11) show less mean size difference (14%). Most of these differences are significant (p: <0.1 to <0.001). These measures support a body mass estimation of 34 kg (Appendix 8).

The upper molars are brachyodont with an average IH of 0.39 (0.34 to 0.45) (Appendix 12; Fig. 4 ). The size gradient from M1/ to M3/ is important, but M2/ can be the largest molar in some specimens (AUM 209; Fig. 7E ). On these molars, which are trapezoidal, tapering distally, the hypocone is labially shifted. The ectoloph becomes increasingly oblique from M1/ to M3/. It is fairly flat, despite the presence of ribs on the cusps (especially on the paracone), and the centrocrista appears deeply notched on unworn specimens (AUM 209). The parastyle is moderately developed on M1/ and becomes prominent outward on M2/ and even more on M3/. The ectocingulum is continuous and thick. The metastyle is only well-marked on M3/. The mesostyle is rather narrow and protruding. It is not continuous with the ectocingulum like on Pr. sudrei , and it may lack at least on M3/ (AUM 209, AUM 1583). On protoloph, the groove between protocone and paraconule varies in depth. It is deep on the M2/ and M3/ on AUM 209, but it is shallower on other specimens (e.g. AUM 1583). The metaloph, which lacks discernible metaconule, runs first toward the distal side of the paracone, and turns to reach the mesio-lingual side of the metacone. The lingual cingulum is well developed on these molars. Although thin and disrupted in front of the cusps, the cingulum is continuous on some M1/ (AUM 209) and M2/ (AUM 1592), but limited to the medivallum on the M3/ (AUM 168). The distal outline of M3/ is convex, with a strong distal cingulum, which eventually bears small knobs (hypostyle) (AUM 168, AUM 1583).

The mean PMI is estimated to 70 (ranging from 68 to 71) and the mean SP / SM surface ratio is 44 (ranging from 41 to 50; Appendix 9). P4/ is transversely elongated (L/ W 0.73 on average). The labial cusps of P4/ are bunodont and close to each other, separated by a groove. The centrocrista is slightly notched and lacks mesostyle. The ectocingulum is continuous, not salient and its external outline is strongly concave. The styles are rather low and variably protruding. The protocone is mesio-distally centered. The paraconule is well defined even if the groove between protocone and paraconule is not deeply notched. The lingual outline is variable, narrow on AUM 192, wider on AUM 1583 with a large posterior basin. On AUM 192 and AUM 1594, there is a small metaconule connected to a curved postprotocrista, a somewhat starry feature. A cingulum encircles the whole internal part of the tooth on most specimens (AUM 192 and AUM 1594), but it is interrupted at the protocone on AUM 1592, AUM 1584, and AUM 168 (very worn).

P3/ offers a similar shape but is less transversely elongated; AUM 1584 is almost quadratic. The bunodont labial cusps are slightly tighter than on P4/. They display a labial continuous and concave cingulum. The parastyle is stronger and protrudes outward and forward. It appears weaker on AUM 168 with a metastyle as marked as parastyle. The lingual shape is wider than on P4/. It is even much enlarged on AUM 1584, which is nearly rectangular, with a slightly forwardly shifted protocone. Conversely on AUM 168, the internal contour remains narrow and the protocone is centered. The protoloph is not deeply notched and the paraconule is almost indistinct on AUM 1584 (more individualized on AUM 168). We note the presence of a postprotocrista that lacks a well-defined metaconule. Conversely, the metaconule is well marked on AUM 168, it is low and sinuous on AUM 1584. The lingual cingulum is always interrupted facing the protocone.

P2/ seems rather variable. On AUM 168 and AUM 1584, it is a triangular tooth, barely enlarged transversely and tapering forward. On the distal crest of the prominent paracone, which is remote forward, we note the presence of a small but rather individualized low metacone. The ectocingulum is continuous, rather weak, and less thick than on P3/ and P4/. Likewise the styles are weak. The internal part of the tooth is surrounded by a continuous cingulum. A rise of this cingulum, at the widest level of the tooth, evokes a small protocone. On AUM 1584, a tiny knob is present at the place of the metaconule. AUM 1583 shows on the right P2/ a structure according to this description, but the left P2/ is transversely broader, with a well marked protocone and a rather wide posterior basin.

P1/, partly preserved on the right side on AUM 1583, is a simple elongated tooth, surrounded by a circular cingulum, its prominent cusp is barely shifted oralwards. The two alveoli of P1/ are also to be seen on AUM 168. On both specimens, there was not any diastema between P1/ and P2/.

Ten lower jaw fragments or isolated teeth are related to this taxon ( Fig. 7 ). The teeth are first characterized by their dimensions larger than those of Pr. sudrei (see above). Mor- phologically, this material offers little information to differentiate the taxon compared to other Propalaeotherium , because of the weak characterization of the lower cheek teeth and of individual variations. One can only observe that the crescents of the molars are fairly rounded, and their metaconid are generally well splitted. The labial cristid of the M/3 hypoconulid is connected halfway to the hypolophid. The ectocingulum is quite variably developed.

Moreover, P/4 is rather bulbous; its talonid, a bit wider than on Pr. sudrei , is slightly lower than the trigonid; it does not show any hypolophid, but a tiny entoconid is present. P/3 is narrowed mesially and the crescent of the trigonid is very flat. The anterior cingulum lacks paraconid. The protoconid is linked to the metaconid through a very oblique protolophid. The talonid is short and the metalophid is low and oblique disto-labially, free of a well-developed hypoconid. Anterior teeth are not known.

Only few observations are available concerning the skull morphology. The alveolus of a rather large and mesio-distally elongated canine is preserved on AUM 168, which was likely pertaining to a male. This allows evaluating relative length of the DPC. It was 21 mm long with a LRDJ of 62 mm, and the % DPC is estimated at 33.9 (Appendix 20A). The obliquity of the nasal opening edge suggests that the notch did not likely exceed the level of P1/. The anterior opening of the infraorbital canal (FIO) is open 9 mm above the alveolar margin, its distal edge is very rostrally located, above the limit P2/-P3/.

The morphology of the mandible is also only partly known. The mandibular body is not very high (26 mm under M/3; AUM 1601, AUM 1603) and it seems not to be much lowered under the premolar row. A mental foramen opens under the limit P/3-P/4, and a smaller one under P/1 (AUM 206). The angular process is broad and is not ventrally protruding. The vertical ramus seems to have been high (AUM 1606).

COMMENTS

As already noticed, this material is significantly larger than that of Pr. sudrei . It is also greater than Pr. voigti (oUK to MK) with differences averaging about +8% in linear measures and about +24% in surfaces (p: <0.1 to <0.001 for most parameters; Appendices 10; 18). Conversely, these Aumelas specimens are significantly smaller than those of Pr. hassiacum and Pr. isselanum.

As a result, their measures are only compatible with Pr. gaudryi from the Paris Basin or with the specimens of the Geiseltal uUK usually referred to Pr. voigti . The specimens from Rouzilhac (molassic beds of Issel, Aude, France), recently assigned to the taxon ( Godinot et al. 2018) also seem to be about the same size. Actually, with the available material of Aumelas, differences of upper cheek teeth size relative to Pr. gaudryi are negligible. Likewise, as regards lower cheek teeth, the dimensions fall within variation ranges of that taxon (Appendices 16; 17).

Great morphological similarities are also observed at Aumelas with Pr. gaudryi . Like in Pr. gaudryi , a mesostyle is not always present on upper molars. The degree of brachyodonty is identical, more marked than on Pr. sudrei ( Fig. 4 ). The enamel appears rather thick.

Besides, we find as in Pr. gaudryi the great development of the parastyle of upper molars, the usually moderate splitting of the protoloph. The shape of the premolars P3/ and P4/ is similar, they are more transversally elongated than on Pr. sudrei . Moreover we may observe on P4/ a metaconule distally connected to the postprotocrista as on some specimens of Pr. gaudryi (NMB TS-83). Like in Pr. gaudryi , P2/ bears two distinct labial cusps. Its shape is rather variable, from triangular, anteriorly tapering, to almost quadratic. The material of the Geiseltal uUK up to now referred to as “ Pr. voigti ” (see above), which presents great similarities with these specimens, might also be close to Pr. gaudryi .

Nevertheless, the Aumelas material differs from Pr. gaudryi by several features that prevent a complete assimilation to this species, in the current state of knowledge. First, the relative surface of upper premolar area seems slightly greater (although the difference be not significant, failing sufficient documentation, and due to the variability of P2/). Thus the SP 4/ SM3 ratio reaches 54 (50 to 61) instead of 51 (49 to 54) for Pr. gaudryi ). The material of Rouzilhac presents values close to those of Aumelas: the same ratio is 56 on the maxillary RZ-221 ( Godinot et al. 2018: fig. 40-a). Then the lingual cingula are slightly less marked than with typical Pr. gaudryi , notably on premolars, and finally there is no P1/-P2/ diastema. These observations would attest to the slightly more progressive nature of the form of Aumelas (as well as that of Rouzilhac material, also recognized by the authors of the monograph) compared with Propalaeotherium gaudryi from the Paris basin.

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Finally, the Aumelas material could be closer to the taxon of Rouzilhac than to that latter. However, the name of Propalaeotherium cf. gaudryi is retained because of the meager fossil register

Figures

FIG. 7. — Propalaeotherium cf.gaudryi (Lemoine,1878) from Aumelas:A, AUM 1584,left maxillary with (P1/ roots)-P2/-M3/,occlusal view (reversed); B, AUM 1583, maxillary with left P2/-M3/ and right P1/-M2/, occlusal view (reversed); C, AUM 168, right maxillary with (alv. C/)-(alv. P1/)-P2/-M3/; C1, labial view, C2, occlusal view; D, AUM 192, right P4/, occlusal view; E, AUM 209, right maxillary with M1/-M3/, occlusal view; F, AUM 206, right mandible with (alv. P/1-P/2)-P/3-M/3; F1, occlusal view; F2, labial view; G, AUM 1603, right mandible with (P/3)-P/4-M/3; G1, occlusal view; G2, labial view; H, AUM 1601, right mandible with (P/4)- M/1-M/3, occlusal view. Scale bar: 2 cm.

FIG. 4. — Hypsodonty indexes of upper cheek teeth (IH) for various propalaeotheres.Symbols:large squares, mean;heavy lines, mean ±s; thin lines, mean ±2s. Data from Appendices 12 and 13.