Oxyaenoides lindgreni, (RICH, 1971), 2014

Solé, Floréal, Falconnet, Jocelyn & Yves, Laurent, 2014, New proviverrines (Hyaenodontida) from the early Eocene of Europe; phylogeny and ecological evolution of the Proviverrinae, Zoological Journal of the Linnean Society 171 (4), pp. 878-917 : 882-885

OXYAENOIDES LINDGRENI ( RICH, 1971) COMB. NOV.

( FIG. 2 )

Emended diagnosis (modified from Rich, 1971) Oxyaenoides lindgreni is characterized by premolars that are compressed labiolingually and elongated mesiodistally with low and poorly individualized paraconid on P 3 and P 4, entoconid on P 4, M 1 smaller than M 2 and M 3, absence of metaconid, elongated molars, short and narrow talonid with no distinction between the cusps, labial part of talonid taller than lingual part, paracone reduced compared with metacone, and an elongated and distally shifted postmetacrista. Oxyaenoides lindgreni differs from Oxyaenoides bicuspidens by a smaller size and numerous plesiomorphic features such as a shallower mandible, lower hypoconid on P 4, less individualized paraconid on P 4 and larger paracone on M 1.

Chresonymy

1971: Francotherium lindgreni in Rich, pp, 20–23, fig. 6.

Holotype

MNHN.F.L-49-Ma, right mandible with P 4, M 1, and M 3, and alveoli of P 1, P 2, P 3, and M 1.

Referred specimens

MNHN.F.Ma14826, right mandible with P 3 and P 4, posterior alveolus of P 2, and anterior root of M 1;

MNHN.F.Ma14833, RM 2; MNHN.F.L-23-Cuis, LM 1.

Type locality

MP10, Mancy ( France).

Additional distribution

MP10, Cuis ( France).

Measurements

See Table 1.

Description

The enamel is crenulated. The paracone and metacone, which are connate, are high and pointed. The base of the metacone is larger than that of the paracone; metacone and paracone of similar height on MNHN.F.L- 23-Cuis, but because the apex of the metacone is worn, the latter was probably taller than the paracone. The postmetacrista is aligned mesiodistally and is as long as the paracone and metacone together. The parastyle is very reduced and short, suggesting that MNHN.F.L- 23-Cuis corresponds to an M 1. The stylar shelf is also very reduced. The protocone, which is missing on MNHN.F.L-23-Cuis, was probably very small and shifted mesially, as in Oxyaenoides bicuspidens .

*Estimated on the basis of the roots.

†Weight estimated after Morlo (1999).

N, number of specimens; OR, observed range. Diastemata are present between the canine, P 1, P 2, and P 3. P 3 and P 4 are close. The mandible is deep and its depth is constant. Foramina are present below P 1 and P 3. The symphysis reaches the distal root of P 2.

P 1 and P 2 are only known by their alveoli. The two teeth are two-rooted. The premolars lengthen mesiodistally from P 1 to P 4. The preserved premolars are mesiodistally elongated and are symmetrical in lateral view. The enamel is crenulated on P 3 and P 4. On P 3, a paraconid is present mesially, but is low and poorly individualized. The protoconid is high, with a rather blunt apex. The talonid is low and short, being wider than long. It is as wide as the protoconid. The hypoconid is high and located labially. The entocristid is low and bears no cusp. Only a poorly developed postcingulid is present. The P 4 is similar in morphology to the P 3. In comparison, the paraconid is slightly more individualized, but is as low as on P 3. The talonid is short, although as wide as the protoconid. As on P 3, the talonid is wider than long. The hypoconid is labially located as on P 3, but is taller. A very small and low entoconid is present. A small postcingulid is visible. There is no precingulid.

The M 1 is presently unknown. However, the holotype MNHN.F.L-49-Ma shows that the M 1 is clearly smaller than the two other molars. The specimen MNHN.F.Ma14833 is identified as an M 2 based on a comparison with the holotype MNHN.F.L-49-Ma. The molars are sharpened and simplified compared with those of earlier hyaenodontidans. There is no metaconid on the M 2 and M 3. The paraconid is shifted mesially. The protoconid is distinctly taller than the paraconid. The talonid is shorter and narrower than the trigonid. The talonid cusps are poorly individualized except for the hypoconid, which is clearly visible. There is no entocristid; the postfossid is thus fully opened lingually. The labial part of the talonid is distinctly taller than the lingual part.

Discussion

As the teeth on the holotype ( Fig. 2C–E ) are very worn, the new specimens described here provide new information concerning one of the largest hyaenodontidans from the Early Eocene of Europe – only Matthodon menui ( Rich, 1971) is larger than Oxyaenoides lindgreni (see below). The new lower teeth described here all agree with the holotype described by Rich (1971): the P 4 of MNHN.F.L-49-Ma and MNHN.F.Ma14826 are almost equal in size. MNHN.F.Ma14833 perfectly fits in size and morphology with the M 2 of MNHN.F.L-49-Ma.

The presence of a two-rooted P 1 and a developed entoconid on P 4 supports the referral of the Mancy specimens to the Proviverrinae . They display numerous features that are plesiomorphic for Proviverrinae , such as diastemata separating premolars and a narrow talonid on the molars. By contrast, they show apomorphic characters such as a mesially located paraconid, absence of a metaconid, and a simplified talonid. These features represent specializations towards a sectorial dentition.

Rich (1971) noted the morphological similarity between O. lindgreni and Propterodon irdinensis Matthew & Granger, 1925 , from the Middle Eocene of Mongolia. He also noted that O. lindgreni might represent an ancestor of the Hyaenodon − Pterodon complex. Morlo & Habersetzer (1999) referred O. lindgreni to Hyaenodontinae s.l. However, as demonstrated by Polly (1996), the development of a sectorial dentition occurred several times amongst the Hyaenodontida. The similarities between O. lindgreni and the other hypercarnivorous hyaenodontidans could therefore result from convergent evolution. Oxyaenoides lindgreni has recently been referred to the Proviverrinae (Solé, 2013) ; this referral is here supported. The European species is distinguished from Propterodon by the presence of an entoconid on P 4 and the development of the paraconid on premolars, which are characteristic features of Proviverrinae . Thus, Propterodon and O. lindgreni evolved independently towards hypercarnivory.

The remains of O. bicuspidens from MP11 of Geiseltal are closest to the species from Mancy. The two species share the absence of a metaconid and entoconid, as well as the presence of mesiodistally elongated premolars and molars, a mesially well-projecting paraconid on molars, a narrow and short talonid, a high labial part of the talonid, a lingually open postfossid, a metacone larger than the paracone, and a long and distally shifted postmetacrista. The morphology of the P 3 and P 4 are very similar to what is known in O. bicuspidens : the P 3 and P 4 are mesiodistally elongated and have a low and mesially elongated paraconid. Finally, the Mancy specimens and O. bicuspidens share a constant depth along the mandible; this is an apomorphic feature compared with the hyaenodontidans Prototomus (Sinopinae) and Parvagula (Proviverrinae) . The P 4 (MNHN.F.Ma14826) found in Mancy differs from that of O. bicuspidens in having a wider talonid, a lower and narrower hypoconid, and a lower and less individualized paraconid. The talonid of MNHN.F.Ma14826 is less sectorial than that of O. bicuspidens . The paracone on M 1 is larger in O. lindgreni than in O. bicuspidens . By comparison, all the features of the Mancy P 4 and Cuis M 1 can be regarded as plesiomorphic. The Mancy mandibles are slightly shallower than the mandible of O. bicuspidens ; this is a plesiomorphic feature. Finally, O. bicuspidens is larger than the fossils from the MP10 localities.

Despite the several differences between the fossils from MP10 and those of O. bicuspidens , they clearly share a common pattern characterized by hypercarnivorous adaptations (e.g. loss of entoconid and metaconid, reduced paracone). We see no reason for referring the MP10 material to a genus distinct from Oxyaenoides . The features that distinguish the former from the latter are plesiomorphic and only justify a specific distinction. We thus propose a new combination for the taxon because Francotherium appears to be a junior synonym of Oxyaenoides .

Consequently, the hypercarnivorous hyaenodontidan Oxyaenoides was present in Europe during the Early Eocene. Oxyaenoides is clearly more specialized than the other proviverrines from the Early to earliest Middle Eocene (M7−MP13). Only Matthodon displays similar hypercarnivorous features (e.g. loss of metaconid), but differs in having enlarged premolars (see below). Finally, together with Matthodon menui , O. lindgreni represents the largest carnivorous mammal of MP10, with a mass of about 10 kg.

Figures

Figure 2. Oxyaenoides lindgreni (Rich, 1971) comb. nov. A, B, MNHN.F.L-23-Cuis, LM1. A, occlusal view; B, labial view. C−E, MNHN.F.L-49-Ma (holotype), right dentary bearing P4, M2, and M3, and alveoli of C1−P3 and M1. C, labial view; D, lingual view; E, occlusal view. F−H, MNHN.F.Ma14826, right dentary bearing P3 and P4 and alveoli of P2 and M1. F, occlusal view; G, labial view; H, lingual view. Scale bar = 10 mm.