Matthodon menui, (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 : 885-889

MATTHODON MENUI ( RICH, 1971) COMB. NOV.

( FIGS 3–4 , 13A–B )

Emended diagnosis (modified from Rich, 1971) Matthodon menui is smaller than Ma. tritens by 12%. It differs from Ma. tritens in retaining plesiomorphic Chresonymy

1971: Oxyaena menui in Rich, pp. 25–29, fig. 9; 1971: Oxyaenoidea or Hyaenodontoidea in Rich, pp. 30–33, fig. 11.

Holotype

MNHN.F.1939-586, left mandible with M 3 and roots of M 2 and distal root of M 1.

Referred specimens

MNHN.F.Cui14838, LP 4; MNHN.F.CHO14799, right mandible with canine, P 2 to M 2, and alveolus of P 1; T.S. 914, right maxillary with P 3 and P 4; T.S. 374, right mandible with complete P 2 -P 4, and M 3, fragmentary M 1 and M 2, and alveolus of P 1; MNHN.F.Ma 14832, RP 4; MNHN.F.L-68-GR, left mandible with M 1 and alveoli of P 2 to P 4 and M 2; MNHN.F.L-58-Ma, RM 2.

Type locality

MP10, Cuis ( France).

Additional distribution

MP10, Chavot, Monthelon, Mancy, and Grauves ( France).

Measurements

See Table 2.

Description

The P 3 is two-rooted and very robust. Its enamel is crenulated. The parastyle is very low and poorly

*Estimated on the basis of the roots.

†Weight estimated after Morlo (1999).

M = mean; N, number of specimens; OR, observed range.

individualized, the paracone is wide, and the postmetacrista is short and low. The P 4 is threerooted. The parastyle is as small as on P 3, the paracone is robust, and the postmetacrista is longer and taller than on P 3. The protocone, which is slightly shifted mesially, is individualized and elongated transversally. A small cingulum is present labially.

The parastyle is large on MNHN.F.L-58-Ma. A notch is present between the paracone and parastyle. The postmetacrista is longer than the preparacrista, but it is aligned transversally. The paracone and metacone are partially fused. The metacone is taller than the paracone. The protocone, which is short and narrow, is slightly shifted mesially. The parastyle, paraconule, and protocone are aligned. No metaconule is visible. The ectoflexus is pronounced, and the stylar shelf is wide. We think that MNHN.F.L-58-MA is an M 2 because of the presence of a strong parastyle.

What is known of the mandible shows that it is very deep, wide, and robust, and that it was apparently short. The depth of the mandible is constant. The symphysis is high and extends under the P 3. Mental foramina are present below P 2 and the anterior root of P 4.

The premolars are very close together. The P 1 is unknown, but based on MNHN.F.CHO14799, this tooth is single-rooted. The three other premolars are tworooted. The P 2 is shorter and smaller than P 3 and P 4. The mesial part of the tooth is wide, but there is no individualized paraconid. The protoconid is asymmetric in lateral view. The talonid is shallow and bears no individualized cusp. However, the distal part of the tooth is distally elongated and is only slightly narrower than the mesial part. The P 3 is less asymmetric than the P 2. The mesial part is more developed than on P 2, but no real paraconid is visible. The protoconid is robust. The talonid is short. The lingual part of the talonid is broken, but is larger than the mesial part. A very small cusp (hypoconid?) is present labially. The P 4 is more symmetrical than the P 2 and P 3. The protoconid is high and pointed. It is developed but the paraconid is small, low, and poorly individualized. The talonid is wide. A large and high hypoconid is present labially. An entoconid is present lingually. A lingual wear facet is visible on the entoconid.

Thanks to the several specimens housed in European museums, the three molars of the taxon are known. The M 1 is only slightly shorter than the M 2. The M 3 is almost the same size as the M 2. The trigonid of the M 1 is worn, as usually observed in hyaenodontidans. The metaconid and paraconid are fully separated. The paraconid is taller than the metaconid. The latter is very reduced. The paraconid is project- ed mesially, and the paracristid is more elongated mesiodistally than transversally. The metaconid is more distal than the protoconid. The protoconid is distinctly taller than the paraconid. The talonid is short but as wide as the trigonid. The postfossid is narrow (the hypoconid is weakly located labially), deep, and closed both labially and lingually. The different cusps are weakly individualized. The distal part of the talonid is taller than the lingual part. The hypoconid is strongly truncated by wear facet 3. Only a short precingulid is present. The less worn M 2 trigonid still presents distinct and pronounced wear facets 1 and 2. The metaconid is taller than on M 1, but remains small. The paraconid is sectorial and projected mesially. The M 2 talonid is shorter than on M 1, but similar in morphology: the postfossid is narrow and closed, the talonid is wide, and the cusps are not individualized. The wear facet 3 is large. The M 3 is known thanks to the holotype (MNHN.F.1939-586) and a referred specimen from Monthelon (T.S. 374). The paracristid is more sectorial than on M 2. The wear facets are similar. The metaconid is more reduced than on M 2. The talonid is more reduced (length and width) than on M 2. The talonid cusps are not separated.

Discussion

Rich (1971) described MNHN.F.1939-586 as an Oxyaenidae because he considered that only two molars were present. He referred it to a new species of the genus Oxyaena , as Oxyaena menui , founded on the peculiar morphology of its M 2. In the same study, Rich (1971) also referred MNHN.F.L-68-Gr to either an Oxyaenoidea or a Hyaenodontoidea. Gunnell & Gingerich (1991) established the similarity of these two specimens and proposed to refer them to the hyaenodontine Propterodon . This genus is only known from the?Middle Eocene of northern China. It is similar to Matthodon in several features, such as the reduction of the metaconid, but differs in having less robust premolars and less developed paraconid and entoconid on the premolars. Thus, the similarities shared by the two genera (e.g. absence of a metaconid) probably result from adaptations to the consumption of vertebrate flesh. Few proviverrines from the Early Eocene and earliest Middle Eocene display molars characterized by reduced metaconids and entoconids. This condition is present in Oxyaenoides and Matthodon from Geiseltal (Middle Eocene, MP11) and the ‘ Francotherium ’ – here synonymized with Oxyaenoides (see above) – from the Paris Basin (Early Eocene, MP10). Matthodon differs from Oxyaenoides in having premolars that are robust and tightly packed and molars on which the postfossid is closed lingually by the entocristid. The material collected from Cuis, Chavot, Monthelon, Mancy, and Grauves (MP10) is clearly reminiscent of that of Ma. tritens (Middle Eocene) . Matthodon menui shares with Ma. tritens the presence of a compressed lower dentition (no diastema between the premolars), a large canine, a single-rooted P 1, wide premolars, and a reduced metaconid and talonid on molars. Moreover, the mental foramina in both Matthodon species are more distal than in other proviverrines: they are below the anterior root of P 2 and anterior root of P 4. Finally, the dentary symphysis of the MP 10 specimens extends to the level of the P 3, as in Ma. tritens .

Matthodon menui possesses the typically robust premolars of the genus Matthodon , although they are less robust and narrower than in Ma. tritens . In the lower molars, the metaconid is less reduced than in Ma. tritens . Matthodon menui therefore represents a new species that is close to, but less specialized than Ma. tritens .

Matthodon tritens is only known from its lower dentition ( Lange-Badré & Haubold, 1990). A maxillary fragment with roots of I 2 to P 3 from Geiseltal has been referred to cf. Matthodon sp. by Lange-Badré & Haubold (1990); the upper dentition of Matthodon has thus remained poorly known. Nevertheless, amongst the material that we examined during the course of this study, we were able to refer one P 3, two P 4 (T.S. 914, MNHN.F.Ma14832), and one M 2 (MNHN.F.L-58-Ma) to Ma. menui , as they fit in size and morphology with the P 3, P 4, and M 2 that are available for this species.

As indicated above, Matthodon displays features that are also known in the hypercarnivorous genus Oxyaenoides : a reduced metaconid and cusps and a mesially projecting paraconid. These apomorphic features are adaptations towards a sectorial dentition. Interestingly, the postfossid of Matthodon is closed lingually by the entocristid, a plesiomorphic feature compared with what is seen in Oxyaenoides . Moreover, Matthodon also differs from Oxyaenoides by the posterior location of the mental foramina, the tightly packed, wider, and more robust premolars, the single root of the P 1, and a postmetacrista on M 2 that is less distally shifted. To us, the numerous differences between Matthodon and the hypercarnivorous Oxyaenoides suggest a possible convergence in hypercarnivorous specialization. The enlargement of the premolars in Matthodon indicates that it probably had a durophagous diet. This feature is combined with a specialization of the molars (e.g. strong reduction of the metaconid). As a result, the dentition of Matthodon species reminds one of that of extant scavengers such as the striped hyena.

The discovery of Ma. menui is crucial because it supports a close relationship between the Early Eocene MP10 of the Paris Basin and the Middle Eocene MP11 of Geiseltal where Ma. tritens was found. It is now clear that there was a continuity between Early and Middle Eocene proviverrine faunas.

Figures

Figure 3. Matthodon menui (Rich, 1971) comb. nov. A−C, MNHN.F.L-68-GR, left dentary with M1 and roots of P2 to P4 and M2. A, occlusal view; B, lingual view; C, labial view. D, E, MNHN.F.CHO14799, right dentary with canine, P2 to M2, and root of P1. D, labial view; E, lingual view; F, occlusal view. G−I, T.S. 374, right dentary with complete P2−P4, and M3, fragmentary M1 and M2, and root of P1. G, labial view; H, lingual view; I, occlusal view. Scale bar = 10 mm.

Figure 4. Matthodon menui (Rich, 1971) comb. nov. A, B, TS 914, right maxillary with P3 and P4. A, labial view; B, occlusal view. C, D, MNHN.F.Ma14832, RP4. C, labial view; D, occlusal view. E, F, MNHN.F.L-58-Ma, RM2. E, labial view; F, occlusal view. Scale bar = 10 mm.

Figure 13. Comparison of two bone-cracking proviverrines. A, B, Matthodon menui, MNHN.F.CHO14799 (holotype), right dentary bearing canine, P2−M2, and root of P1. A, labial view; B, occlusal view. C, D, Quercytherium tenebrosum, MNHN.F.Qu8644 (holotype), left dentary bearing P2 to M3 and alveoli for C and P1. Mirrored views. C, occlusal view; D, labial view. Note the depth of the dentaries and the robustness of the premolars in both genera. Scale bar = 10 mm.