Armantomys cf. bijmai (Lacomba & Martínez-Salanova, 1988)

Ruiz-Sánchez, Francisco J., Murelaga, Xabier, Larrasoaña, Juan C., Freudenthal, Matthijs & Garcés, Miguel, 2012, Hypsodont Myomiminae (Gliridae, Rodentia) from five new localities in the Lower Miocene Tudela Formation (Bardenas Reales, Ebro Basin, Spain) and their bearing on the age of the Agenian-Ramblian boundary, Geodiversitas 34 (3), pp. 645-663 : 652-654

Armantomys cf. bijmai (Lacomba & Martínez-Salanova, 1988) ( Fig. 4 A-E)

HOLOTYPE. — QU1-165, left M1 (Lacomba & Martínez- Salanova 1988: pl. 1, fig. 8).

TYPE LOCALITY. — Quel 1, Ebro Basin, Spain.

LOCALITY AND AGE. — Cabezo Hermoso 1 ( CH 1), province of Navarre, Spain. Agenian (Local subzone Y1, MN 2).

MATERIAL AND MEASUREMENTS (L × W). — CH 1-3 (13.04 ×), incomplete right m1; CH 1-5 (6.83 × 7.56), right D4; CH 1-4 (7.96 × 9.61), right P4; CH 1-6 (12.84 × 17.11), left M2; CH 1-7 (14.50 ×), incomplete right M1,2; CH 1-8 (8.77 × 13.32), incomplete right M3.

DESCRIPTION

m1

Anterolophid separated from the protoconid by a deep furrow.Metalophid short and oblique, separated from the metaconid. Centrolophid short. Between metalophid and mesolophid there is a short isolated accessory ridge. Mesolophid and posterolophid separated at the entoconid by a deep furrow and without other connections among the ridges.

D4

Anteroloph reaching the labial tooth border and connected to the paracone. Protoloph long and continuous. Precentroloph absent. The metaloph is a transverse ridge, directed to the protoloph, with a posterior connection to the posteroloph. Postcentroloph short. The posteroloph has a narrow furrow halfway its length. Posteroloph not connected to protocone.

P4

Anteroloph reaching the labial tooth border and connected to the paracone. The lingual end does not reach the protocone. Protoloph and metaloph continuous and connected to the protocone, forming a composite Y-shaped ridge. Posteroloph lingually and labially elongated, connected to protocone and metacone.

M1

Tooth labially broken. The metaloph joins the protoloph. The posteroloph joins the protocone lingually.

M2

The anteroloph is labially separated from the paracone. Protoloph continuous. A medium-sized precentroloph is connected to the protoloph. A tiny postcentroloph is present. The metaloph is a continuous ridge, connected with the short postcentroloph. Posteroloph labially separated from the metacone and lingually connected to protocone.

M3

Anteroloph labially connected to the paracone at medium height and lingually high connected to the protocone. Protoloph and metaloph continuous and connected to the protocone, forming a composite Y-shaped ridge. No centrolophs. Posteroloph continuous, not connected to metacone and with a narrow furrow just in front of the protocone.

REMARKS

The morphology of the material of Armantomys from CH 1 is similar to A. bijmai and A. daamsi . A. bijmai is characterized by its hypsodonty, medium size, the constant presence in M1,2 of a metaloph-protoloph connection and the variable presence of centrolophs and centrolophids. On the other hand, the M1,2 of A. daamsi may have one or two short centrolophs and the m1,2 may have a short centrolophid.

The hypsodonty of the material from CH 1 is very similar to what Lacomba & Martínez-Salanova (1988: 116, fig.5) described for A. bijmai , and much weaker than that of the large species of Armantomys ( A. aragonensis from the Ramblian-Lower and Middle Aragonian, and A. tricristatus from Middle- Upper Aragonian), and of the contemporary genera Praearmantomys and Pseudodryomys .

The development of a connection between protoloph and precentroloph in A. bijmai is variable. This connection looks like a shepherd’s crook (see Lacomba & Martínez-Salanova [1988: fig. 2, morphotype C]) or a Greek “Tau” (op. cit., morphotype T), but other morphologies exist too. A shepherd’s crook shape is common in Santa Cilia (29%) and Quel 1 (52%). A Greek letter “Tau” shape appears in 53% of the specimens from Santa Cilia, 48% from Quel 1 and 20% from Fuenmayor 2. The only M2 recovered in CH 1 ( CH 1-6) presents a precentroloph of medium length with an intermediate morphology between these two morphotypes ( Fig. 4A ) and a tiny postcentroloph. The presence of precentroloph and postcentroloph is known in the M2 of A. bijmai from Quel 1 (QU1-164; Lacomba & Martínez-Salanova 1988: pls 1, 10) and in some specimens of A. daamsi from San Juan (Álvarez- Sierra et al. 1991).

The constant metaloph-protoloph connection is characteristic for A. bijmai . It is the exclusive morphology in the upper molars from CH 1. It also appears in A. daamsi , although not exclusively like in A. bijmai .

Among the remains from CH 1 there is a m1 ( CH 1-3; Fig.4E ) with the postero-labial side broken off. This specimen shows a metalophid disconnected from the metaconid, a short centrolophid, a short accessory ridge between metalophid and mesolophid and a mesolophid-posterolophid not connected at the lingual border. The first two morphologies appear in A. bijmai and a few specimens of A. daamsi and A. parsani , but the accessory ridge between metalophid and mesolophid has only been found in A. bijmai from Santa Cilia (STC-56) (Lacomba & Martínez-Salanova 1988). According to size and morphology the material of CH 1 can be assigned to A. bijmai . We call it A. cf. bijmai because of the scarcity of material.

Figures

FIG. 4. — A-E, Armantomys cf. bijmai from Cabezo Hermoso 1 (CH1): A, left M2,CH1-6;B, right M3,CH1-8; C, right P4,CH1-4;D, right D4, CH1-5; E, right m1, CH1-3; F-M, Armantomys daamsi from Cuesta Agujeros 2 (CA2): F, left M1, CA2/1-6; G, right M2, CA2/1-5; H, right M2, CA2/2-6; I, right M3, CA2/1-15; J, right P4, CA2/1-12; K, left m1, CA2/1-8; L, left m1, CA2/1-10; M, right m3, CA2/2-5; N, Armantomys cf. jasperi from Cuesta Agujeros 4 (CA4), fragmentary right m2, CA4/1-27; O, P, Armantomys cf. parsani from Cuesta Agujeros 3 (CA3): O, left M2, CA3-1; P, left P4, CA3-2; Q, R, Armantomys cf. daamsi from Cabezo Carboneras 1 (CC1): Q, right M1, CC1-31; R, left M2, CC1-38; S, cf. Praearmantomys crusafonti from Cabezo Carboneras 1 (CC1), right m3, CC1-22. Scale bar:1 mm.