Peridyromys murinus (Pomel, 1853)

Crespo, Vicente Daniel, Ríos, María, Marquina-Blasco, Rafael & Montoya, Plini, 2023, They are all over the place! The exceptional high biodiversity of dormice in the Early Miocene of the Ribesalbes-Alcora Basin (Spain), Geodiversitas 45 (20), pp. 589-641 : 600-603

Peridyromys murinus (Pomel, 1853)

( Figs 5 H-AE; 6A-Z)

LOCALITIES. — MCX1, MCX3, MCX7, MTR1, MTR2, BC1, BC2, FS1, MAB0A, MAB0B, MAB0C, MAB3, MAB5, MAB10, MAB11, MAB13, and CBR0B.

MATERIAL. — MCX1: 1 M1/M2; MCX3 : 2 p4, 1 m1, 1 D4, 2 P4, 5 M1/M2; MCX7 : 1 p4, 1 m1, 1 m2, 2 P4, 2 M1/M2; MTR1 : 1 m1; MTR2 : 1 p4, 6 m1, 6 m2, 6 m3, 5 D4, 8 P4, 21 M1/M2; BC1: 4 p4, 4 m1, 4 m2, 3 m3, 2 D4, 3 P4, 5 M1/M2; BC2: 1 m2, 1 M3; FS1: 2 m2; MAB 0A: 1 m1, 1 M1/M2 ; MAB 0B: 1 p4, 1 M1/M2; MAB 0C; 1 d4; MAB3 : 2 p4, 4 m1, 4 m2, 2 m3, 1 P4, 15 M1/M2, 2 M3 ; MAB5 : 2 p4, 4 m1, 2 m2, 3 m3, 1 D4, 2 P4, 9 M1/M2 ; MAB10 : 1 M1/M2 ; MAB11 : 1 p4, 1 m1, 3 m2, 1 m3, 1 P4, 3 M1/M2, 1 M3 ; MAB13 : 1 p4 ; CBR 0B: 1 M1/M2.

MEASUREMENTS. — Appendix 8

DESCRIPTION

d4 (MAB0C)

The tooth has a subtriangular outline. The anterolophid is long and semicircular. The metalophid is delicate, short and surrounds a well-developed central cuspid. There is a long centrolophid. The mesolophid and the posterolophid are long and developed; they show a low interconnection forming an ellipse.

p4 (BC1)

The tooth has a subtriangular outline. The anterolophid is long and semicircular. The metalophid may be a spur of the anterolophid (2 out of 3), or form an ellipse with the anterolophid but without making contact with it (1 out of 3). The mesolophid may be long and labially connected to the anterolophid (1 out of 3) or long and isolated (2 out of 3). The posterolophid may be long and connected to the mesolophid lingually (2 out of 3) or labially (1 out of 3). The specimens found in MCX3 are similar to those just described. In MCX7 the anterolophid is short and the posterolophid is isolated. In the specimens found in MTR2, MAB 0B and MAB 11 the metalophid is a posterior spur of the anterolophid (and in MTR2 and MAB 0B the posterolophid may be isolated). In MAB 3 the endolophid is a spur of the mesolophid. In MAB 5, the anterolophid and metalophid are short. In MAB 13, the posterolophid and the mesolophid are isolated.

m1 (MTR2)

The tooth is rectangular with high crestids and wide valleys. The anterolophid is short. The metaconid is connected to the anteroconid. The metalophid is curved and long. The centrolophid is well developed and exceeds half of the tooth width, one specimen it isolated labially and perpendicularly connected to the endolophid. The endolophid may be a spur of the centrolophid (4 out of 5) or be absent (1 out of 5). The mesolophid and the posterolophid may be long and show a low (4 out of 6) or a high (2 out of 6) connection. The labial cuspids are better developed than the lingual cuspids. The posterior valley is the widest one. There are no accessory crestids. The enamel is rough. The specimens found in MAB 11 are similar to the ones just described. In MCX3 and MAB 5 the anterolophid is generally shorter. In MCX7 and MTR1 the mesolophid and the posterolophid are not connected and in BC1 the centrolophids may be shorter than in the MTR2 material (2 out of 3). In MAB 0A there is a small centrotrophid. In MAB 3 the length of the anterolophid is more variable than in the material here described; in one specimen there is a small centrotrophid with a cuspid as high as the extra crestid.

m2 (MTR2)

The outline is sub-rectangular with high crestids. The anterolophid may be long (2 out of 6) or of medium length (4 out of 6). The metaconid is connected to the anteroconid. The metalophid is either complete (3 out of 6) or it is curved, long and with a narrowing that almost separates it from the metaconid (3 out of 6). The centrolophid may be well developed up to the middle of the tooth (2 out of 6) or it may not reach this point (4 out of 6). The endolophid may be a spur of the entoconid (5 out of 6) or be absent (1 out of 6). The mesolophid and the posterolophid are long and they may show a low (2 out of 5) or a high (2 out of 5) connection, or they may end together but without connection (1 out of 5). The labial cuspids are more developed than the lingual cuspids. The posterior valley is the widest one. No accessory crestids. The specimens found in MCX7, BC2, MAB 3 and MAB 5 fit in this description. In one specimen from BC1 the centrolophid is isolated and the mesolophid and the posterolophid have a low connection. In one individual from FS1 there is a very short posterotrophid, barely discernible. In another specimen from MAB 11 the mesolophid is divided in two.

m3 (MTR2)

The tooth has a D-shaped outline, lacking a reduced posterior part. The anterolophid is long; in one individual the lingual connection is low. The metalophid is curved and attached to the anteroconid and the metaconid; in one specimen the anteroconid is isolated from the metaconid. The centrolophid is of medium size and does not exceed half of the tooth width; in one specimen it is absent. The endolophid may either be well developed (1 out of 5), be merely a spur (4 out of 5) or be absent (1 out of 5). The mesolophid and the posterolophid may be long and connected in a low connection (3 out of 6) or not connected at all (3 out of 6). In one specimen the metaconid is separate from the mesolophid. The posterior valley is the widest one. There are no accessory crestids. In BC1, MAB 3, MAB 5 and MAB 11 the centrolophids are longer than in MTR2; in one individual from MAB 3 there is a spur behind the posterolophid and another specimen has a short anterolophid; in a specimen from MAB 5 the spur is located behind the mesolophid. Also, in MAB 5 there is a specimen with an anterotropid and another one with a posterotropid.

D4 (MTR2)

The outline is subtriangular, with fine crests and wide valleys. The anteroloph may be short (4 out of 5) or long (1 out of 5) and labially connected to the paracone. The protocone is poorly developed. The protoloph and the metaloph form a Y. The centroloph may be short and isolated (1 out of 5) or attached to the metacone (4 out of 5). The posteroloph is long (longer than the anteroloph, except in one specimen) and it may be labially attached (3 out of 5) or independent (2 out of 5). In MCX3, BC1 and MAB 5 there is no centroloph. In BC1 there is one specimen with an isolated protoloph.

P4 (MTR2)

The tooth has a subrounded outline, with fine crests and wide valleys. The anteroloph may be short (6 out of 8) or long (2 out of 8) and isolated. The protocone is poorly developed. The protoloph and the metaloph may form a Y-shape (6 out of 8) or a V-shape (2 out of 8). There is a short, independent centroloph, which is absent in two specimens. The posteroloph is longer than the anteroloph and it may be either isolated (6 out of 8) or connected with the protoloph-protocone (2 out of 8). The specimens found in MCX3, MCX7 and MAB-11are similar to those just described. In BC1 and MAB 5 the posteroloph may be connected on both sides. In MAB 3 the metaloph is short and isolated. In one specimen from MAB 5 the metaloph is divided in two.

M1/M2 (MTR2)

The tooth has a square outline, with narrow valleys and broad crests. The anteroloph may be long (7 out of 18) or medium (11 out of 18) and it may be isolated (12 out of 17) or with a low and labial connection (5 out of 17). In one specimen the protoloph shows an anterior spur, in another specimen this spur connects with the anteroloph and in another one it is labially isolated. The protoloph and the metaloph form the typical Y-shape, and they may join near the lingual side (10 out of 21), or form a V-shape, joining at the lingual side (8 out of 21), or form a U-shape (3 out of 21). The precentroloph is longer than the postcentroloph, although in one individual they are of equal size; they may join in the center of the tooth forming a Y (8 out of 21), or a V (1 out of 21) or be disconnected (12 out of 21). In five specimens there is a metatrope. In two specimens the precentroloph connects with the metaloph. The postcentroloph may be intermediate (11 out of 21), short (7 out of 21) or very short (3 out of 21); in five individuals it is isolated labially and in one it is divided in two. In one specimen the metaloph has an anterior spur. The posteroloph may be long but shorter than the anteroloph (7 out of 21), or short (14 out of 21); it may be either isolated (7 out of 20), connected on the lingual side and isolated on the labial side (9 out of 20), or connected on both sides (4 out of 20). The enamel tends to be rough. The specimens found in MCX1, BC1, MAB 0A, MAB 0B, MAB 10, MAB 11 and CBR 0B fit in the description above. In one individual from MCX3 there is a small metatrope; in another specimen the precentroloph is short and the posterior is long and unconnected; in another one the postcentroloph is long. In MCX7 the postcentrolophs are longer than in MTR2. In MAB 3 there are three specimens with metatropes. In one individual from MAB 5 the paracone has an anterior spur and the metacone a posterior one.

M3 ( MAB 3)

The tooth is of sub-rectangular outline. The anteroloph is long and forms a closed ellipse with the protoloph. The endoloph is continuous. The precentroloph may be short (1 out of 2) or absent (1 out of 2). The postcentroloph is labially isolated and it may be lingually connected to the metaloph (1 out of 2) or not (1 out of 2). The protoloph and the metaloph meet forming an X-shape near the lingual part. The metaloph and the posteroloph do not contact on the labial side. The posteroloph is short. In BC2 the protoloph and the metaloph contact each other in a U-shape. In MAB 11 the centrolophs differ from MTR 2 in that the precentroloph is longer, while the posterior one is delicate and shorter, and connected on both sides. The two centrolophs are connected forming an X-shape.

REMARKS

Peridyromys murinus from the upper Oligocene (MP28a) of France (Pech Desse; Vianey-Liaud 2003) is the oldest species of the genus. An unspecified representative of this genus has been recorded at the Iberian site of Canales, which belongs to the same stratigraphic zone (MP28a) as the French site ( Álvarez-Sierra et al. 1999). Peridyromys probably became extinct at the end of the Aragonian. As previously mentioned, its validity is under discussion; according to Daams & De Bruijn (1995), it could be the ancestor of several Miocene genera. Probably, the species P. murinus is a wastebasket taxon that may include several species with similar morphologies, due to its lasting presence spaning from the late Oligocene (MP28) to the end of the Middle Miocene (MN7-8), for a total of almost 14 m. y.

Following this controversy, Álvarez-Sierra et al. (1990) assigned to Pseudodryomys the larger species with broad, robust crests and deep valleys, while the relatively small species with broad crests and hypsodont teeth were ascribed to Peridyromys . Some authors such as Hordijk et al. (2015) suggest that both genera are synonyms, and Bilgin et al. (2021) include the genus Myomimus . This shows that a thorough revision of the three genera is necessary.

Peridyromys murinus is the most abundant taxon in the Ribesalbes-Alcora Basin and was already cited in the classic locality of Araya ( Agustí et al. 1988). It is present in all the sites with a representative sample. The metric values and morphology are very similar among the different sites, with no clear trend in the variation of their biometry. This is already noted by Daams (1981), who did not observe any variation from the late Oligocene to the Middle Miocene in different European sites. Furthermore, it has been decided not to separate the M1 from the M2, since in some cases their morphology is very similar, and they cannot be distinguished. Nevertheless, other authors such as Freudenthal & Martín-Suárez (2019) propose two lineages in this long-range species.

In some sites it is difficult to distinguish P. murinus from Ps. ibericus , as for example in Montalvos 2. In this site, Hordijk et al. (2015) ascribed these two species to a single group Ps. aff. ibericus , based on their simple morphology like in P. murinus , and their large size, as in Ps. ibericus . In our material P. murinus is smaller and simpler than Ps. ibericus , so they can be easily distinguished, with only some difficulties in ascribing the premolars and third molars.

According to the classification of Daams (1981), the lower molars would all belong to category 1, as in the rest of the sites, where they are in the majority of this dormouse, except in the locality of Buñol. As expected in this species, the upper molars belong mainly to morphotype C, with a few specimens ascribed to morphotype D, like in the rest of the European sites. The measurements fit within the variability expected and described by Daams (1981).

Figures

FIG. 5. — Gliridae from the Ribesalbes-Alcora Basin. Bransatoglis cf. infralactorensis: A, right p4 (MAB3-382); B, right m1 (MAB3-399); C, right m1 (MAB11-78); D, left m2 (MAB5-258); E, right m2 (MAB0A-75); F, left m3 (MAB0A-74); G, left M3 (MAB3-295). Peridyromys murinus: H, right d4 (MAB0C-1); I, right p4 (BC1- 15); J, right p4 (BC1-113); K, right p4 (MAB3-380); L, left p4 (MAB13-2); M, right p4 (MTR2-130); N, right m1 (MTR2-133); O, left m1 (MTR2-132); P, right m1 (MTR2-131); Q, left m1 (MCX7-3); R, left m1 (MAB5-608); S, left m1 (MAB3-418); T, left m2 (MTR2-141); U, right m2 (MTR2-139); V, left m2 (MTR2-15); W, right m2 (MAB11-79); X, right m2 (FS1-44); Y, right m2 (BC1-120);Z, left m3 (MTR2-147); AA, right m3 (MTR2-146); AB, left m3 (MTR2-145);AC, right m3 (MAB3-468); AD, left m3 (MAB5-856); AE, right m3 (BC1-140). Scale bar: 1 mm.