Cymbalophus cuniculus ( Owen, 1842 )

Bronnert, Constance & Métais, Grégoire, 2023, Early Eocene hippomorph perissodactyls (Mammalia) from the Paris Basin, Geodiversitas 45 (9), pp. 277-326 : 286-287

Cymbalophus cuniculus ( Owen, 1842)

( Fig. 6 )

Hyracotherium cuniculus Owen, 1842: 1-2 , figs 2, 5. — Forster-Cooper 1932b: 438-441, figs 1A, C, 2B, E, F, 6, 9, pl. 51. — Simpson 1952: 196-204, fig. 4B. — Hooker 1980: 104-108, fig. 1.

Macacus [sic] – Wood 1839: 444-445, fig. 57.

Macacidae [sic] – Owen 1839: 446-448, fig. 58.

Macacus eocaenus Owen, 1846: 1-10 , figs 1, 3.

Hyracotherium sp. – Teilhard de Chardin 1927: 27, 28, figs 28c, 22, pl. 5.

Hyracotherium [sic] – Quinet & Verlinden 1970: 1-10, pls 2-3.

Cymbalophus cuniculus – Hooker 1984: 230-237, figs 1-12.

LECTOTYPE. — BMNH-36569 , M3 .

MATERIEL. — see Hooker 1980, 1984 .

TYPE LOCALITY. — Kyson, United-Kingdom.

DISTRIBUTION. — Kyson (United-Kingdom); Erquelinnes, ( Belgium), MP7.

EMENDED DIAGNOSIS. — Lower molar cristid obliqua joining the protolophid, slightly labially. Straight upper molar centrocrista. Short p1-p2 diastema.

DIFFERENTIAL DIAGNOSIS. — Larger than C. hookeri . More labially oriented cristid obliqua, less developed and straighter centrocrista than C. hookeri . Reduced m1-2 hypoconulid that is closely appressed to the hypolophid, whereas it is linked to the hypoconid in Pliolophus .

DESCRIPTION

Erquelinnes mandible

The alveoli indicate that three incisors are present on each hemimandible. The alveoli indicate that the canines are large and anteriorly oriented ( Fig. 6A ). The left hemimandible shows a reduced alveolus of p1 (less than 1 mm). The right hemimandible is broken at the level of the p1 alveolus, but this alveolus seems larger than that of the left hemi-mandible. The symphysis is long and narrow. The post-canine diastema is long (9 mm), and the post-p1 diastema is shorter (4 mm on the right hemi-mandible). The p3 displays a small paraconid ( Fig. 6F ). The protoconid is larger than the metaconid. The hypoconid is developed. The cingulum extends lingually toward the hypoconid. The protoconid and metaconid of p4 are well-separated. Two crests extend lingually from the hypoconid. One is transversal (possibly the posthypocristid), and the second is oriented posteriorly toward a small cingular bulge, located at the position of the hypoconulid. A small entoconid is present. The cristid obliqua ends on the lingual side of the protoconid. The m1-2 have a twinned metaconid ( Fig. 6F ). The metaconid and the entoconid are higher than the protoconid and the hypoconid. The cristid obliqua ends on the lingual side of the protoconid. The paralophid is short. The protolophid is slightly notched. The hypolophid is more deeply notched than the protolophid. The hypoconulid is closely appressed to the hypolophid, but slightly more lingually placed. The labial part of the hypolophid joins the lingual part anterior to the hypoconulid. The cingulum is continuous.

Fossils from Kyson

The P3 is nonmolariform ( Fig. 6D ). The paraconule is small but well defined. A very small metaconule is present and linked to the metacone by a small crest. The postprotocrista runs from the protocone to the lingual side of the metaconule. The cingulum is continuous and posteriorly elongated. The parastyle of upper molars is small ( Fig. 6E ). The centrocrista is straight and low. The paraconule is small and the metaconule is absent or very weak. The cingulum is well developed and continuous. The metaloph is interrupted close to the metacone. A small crest is present between the metaloph and the metacone. The m3 lophids are well developed ( Fig. 6C, G ). The cristid obliqua is oriented labially. The metaconid can be twinned or not. A small pre-entocristid is present. The hypoconulid lobe is small and narrow. The hypoconulid is linked to the hypoconid by a postcristid.

COMPARISONS

The lower canine of C. cuniculus is anteriorly oriented, whereas it is more lateral in Pliolophus quesnoyensis and P. barnesi . The symphysis is long and narrower than in Pliolophus . The m3 cusps are more obliquely aligned in C. cuniculus than in P. quesnoyensis , and a pre-entocristid is present. The upper molar cingulum is continuous, whereas it is interrupted close to the hypocone in Pliolophus , but the intraspecific variability of Cymbalophus is unknown. The lower molar hypoconulid-hypolophid junction (hypoconulid closely appressed to the hypolophid) in C. cuniculus is similar to that of Sifrhippus sandrae ( Gingerich, 1989) , but differs from the hypoconulid-hypoconid junction observed in Pliolophus (hypoconulid linked to the hypoconid by a postcristid). The cusps of p3 are spaced and transversally aligned, whereas they are closely appressed and obliquely aligned in Cymbalophus aff. cuniculus from Rians ( Godinot 1981). The p4 trigonid is larger than in C. aff. cuniculus from Rians.

COMMENT The mandible from Erquelinnes possesses a reduced p1 alveolus on the left ramus. The right ramus is broken at the level of the p1 alveolus, which seems much larger in posterior view than on the left ramus. We hypothesize that the p1 was about as large as in Pliolophus . Thus, the left p1 was probably broken during the animal’s life, and the corresponding alveolus was probably reabsorbed (Thierry Smith pers. com.).

On the mandible from Erquelinnes, m1-2 display a twinned metaconid, but the m3 is missing. The same character is observed on a m3 (1951.28.25) housed in the collection of the Ipswich museum and referred to C. cuniculus by Hooker (1984). The rest of the m3 referred to this species display predominantly a unicuspid metaconid according to Hooker (1984). Whether a twinned metaconid is present on the m1-2 is not clear on the few specimens collected in Kyson because those molars are generally heavily worn.

Figures

FIG. 6. — Teeth of Cymbalophus cuniculus (Owen, 1842) from Erquelinnes and Kyson, and C. aff. cuniculus from Condé-en-Brie in occlusal view; A, mandibular symphysis (IRSNB-M-167); B, right m3 (MNHN-CB1597); C, right m3 (BMNH-14113); D, left P3 (BMNH-36572); E, left M3 (lectotype, BMNH-36569); F, left p3- m2 (IRSNB-M-167); G, right m3 (BMNH-29710). B, coated with magnesium. Scale bar: 5 mm. Photo credits A, C-G, C. Bronnert.