Hyracotherium leporinum Owen, 1841

Bronnert, Constance & Métais, Grégoire, 2023, Early Eocene hippomorph perissodactyls (Mammalia) from the Paris Basin, Geodiversitas 45 (9), pp. 277-326 : 288-289

Hyracotherium leporinum Owen, 1841

( Fig. 7 )

Hyracotherium leporinum Owen, 1841: 203-206 ; 1865: 340 (partim), pl. 10, fig. 2. — Depéret 1901: 200-201 (partim), pl. 4, fig. 1. — Savage et al. 1965: 6-8, fig. 2h. — Lydekker 1886: 11.

Hyracotherium aff. leporinum – Hooker 1994: 53-57, fig. 20.

HOLOTYPE. — BMNH M16336 , skull with right P2-M3 and left P4-M2 .

MATERIAL. — Herne Bay (see Hooker 1980, 1994).

Mutigny: P4 (R: MNHN-MU5919); M1/2 (R: MNHN-MU220-L, MU12329 [broken]; L: MNHN-MU222-L, MU17167, MU12375 [worn]); M3? (L: MNHN-MU192-L); dp3 (L: MNHN-MU200-L); p3 (R: MNHN-MU5640), dp4 (R: MNHN-MU12300, MU12385 [broken]); p4 (L: MNHN-MU6574); m1/2 (R: MNHN-MU12292 [broken]); m3 (R: MNHN-MU12378; L: MNHN-MU1210 [broken], MU6567 [broken]) .

Avenay: dP3 (L: MNHN-AV4664, AV14684); P4 (R: MNHN-AV42-Ph; L: MNHN-AV4789); M1 (L: MNHN-AV65514); M1/2 (L: MNHN-AV1012-L); dp4 (R: MNHN-AV15815); p3 (R: MNHN-AV4634); m3 (L: MNHN-AV14685) .

Prémontré: m3 (R: MNHN-SLP-29-PR1906) .

TYPE LOCALITY. — Herne Bay (Kent, United-Kingdom), MP8-9.

DISTRIBUTION. — Mutigny, Avenay (MP8-9), Prémontré (MP10) ( France).

EMENDED DIAGNOSIS. — Lower molar hypoconulid linked to the hypoconid. High cristid obliqua oriented toward the center of the protolophid. P2 without labial cusp. Mesostyle or mesostylar crest on upper molars. Developed paraconule.

DIFFERENTIAL DIAGNOSIS. — Differs from Pliolophus and Cymbalophus by the presence of a mesostyle on upper molars, and by a more flexed centrocrista.

DESCRIPTION

Teeth

The parastyle of P4 is low ( Fig. 7B, G ). The paraconule is developed, it is half the size of the protocone. The metaconule is large but smaller than the paraconule. The protoloph is interrupted before joining the preparacrista. A small postprotocrista is present, as well as a small endoprotocrista. The cingulum is continuous.The upper molars parastyle is developed ( Fig.7 C-E, H-I). The paraconule and the metaconule are well developed. The centrocrista is labially flexed. A small mesostyle is usually present, often as a ridge starting from the centrocrista but it can be absent ( Fig.7E ). The cingulum is continuous, but sometimes interrupted around the hypocone.The protoloph joins the preparacrista, and is sometimes interrupted just before the connection. The metaloph is interrupted at the base of the metacone. The slightly more labially situated hypocone on Fig. 7I could indicate that the tooth is a M3.

The protoconid and metaconid of p3 are quite apart ( Fig. 7J, K ). A small paraconid is present.The hypoconid is developed and low. The entoconid is absent. The cristid obliqua connects the center of the protolophid to the hypoconid. The p4 metaconid is twinned ( Fig. 7M ).The entoconid is absent.The hypoconid is low and well developed.The protolophid is notched. The cristid obliqua connects the hypoconid to the protolophid towards its center, slightly labially.The m3 metaconid is twinned ( Fig.7P ). The cristid obliqua is oriented towards the center of the protolophid ( Fig. 7O, P ). The hypoconulid lobe is well developed. A postcristid links the hypoconid to the hypoconulid. The protolophid is notched. The hypolophid is poorly developed.

Deciduous teeth

The parastyle of DP3 is large and anteriorly projected. The centrocrista is almost straight. The hypocone is larger than the protocone. The paraconule and the metaconule are small. The protoloph joins the paracone.The cingulum is almost continuous, slightly interrupted at the level of the hypocone.

The dp3 is very worn. The paraconid is well developed. The heavy wear seems to indicate that the hypoconulid is linked to hypoconid and entoconid.The dp4 is molariform and the talonid is wider than the trigonid.The metaconid is twinned.The cristid obliqua is oriented toward the center of the protolophid. The hypoconulid is low.It is linked to the hypoconid by a postcristid. The protolophid is notched. The hypolophid is low.

COMPARISONS

The morphology of the P2, with no protocone, is not found in other European hippomorph species but can be observed on some American equids, such as Orohippus and ‘ Hyracotherium’ craspedotum. The upper molar centrocrista is more flexed than in Pliolophus and Cymbalophus . A mesostyle is present while it is absent in Pliolophus and Cymbalophus . The m3 postcristid links the hypoconid in a more lingual position than in Pliolophus and Cymbalophus , but more labially than in Orolophus and Propalaeotherium gaudryi in which the hypoconulid is connected to the hypolophid. Hyracotherium is larger than Sifrhippus sandrae . The upper molar centrocrista is more flexed than in S. sandrae , and the mesostyle is always absent in S. sandrae . The upper premolar metaconule is larger in Hyracotherium than in S. sandrae .

COMMENT

The upper molars of the Mutigny specimens resemble those of the type-specimen and specimens found in the London Clay in England. In contrast, the lower molars show some differences with the Sheppey mandible ( Hooker 1994). The metaconid is twinned and the hypoconulid lobe of m3 is wider in the Paris Basin, but this may result from intra-specific variation.

Figures

FIG. 7. — Teeth of Hyracotherium leporinum Owen, 1841 from Mutigny and Avenay in occlusal view: A, left DP3 (MNHN-AV14684); B, right P4 (MNHN-MU5919 [reversed]); C, left M1/2 (MNHN-MU17167); D, right M1/2 (MNHN-MU220-L [reversed]); E, left M1/2 (MNHN-MU222-L); F, right dp3 (MNHN-MU200-L); G, right P4 (AV-42-Ph [reversed]); H, left M1/2 (MNHN-AV1012-L); I, left M1/2 (MNHN-MU192-L); J, right p3 (MNHN-AV4634); K, right p3 (MNHN-MU5640); L, right dp4 (MNHN-AV15815); M, left p4 (MNHN-MU6574 [reversed]); N, right dp4 (MNHN-MU12300); O, left m3 (MNHN-MU1210 [reversed]); P, right m3 (MNHN-SLP-29- PR1906). Coated with magnesium. Scale bar: 5 mm.