Eomyops est un éomiidé assez rare dans le registre fossile. Il apparaît en peu de localités européennes, et, quand il le fait, ce n’est pas l’élément majoritaire de la faune. Le genre Eomyops fut créé par Engesser [10], pour distinguer le matériel européen d’éomiidés jusqu’à ce moment inclu par Hugueney et Mein [18] dans le genre Leptodontomys Shotwell, 1956. La présence de deux rides parallèles dans les incisives inférieures d’Eomyops et quelques autres caractéristiques de la mandibule sont la base pour la distinction entre ces deux genres.

Le genre comprend quatre espèces: E. catalaunicus [17], E. bodvanus [19], E. oppligeri [9] et E. hebeiseni [20]. La distribution temporelle du genre est comprise entre le Miocène moyen et le Pliocène, zones MN 5/6 à MN 17 [11]. Le registre le plus ancien de ce genre qui est connu avec certitude totale en Europe, correspond à la zone MN5 ou MN6 [20]. Le registre le plus récent correspond à celui de la localité de Schernfeld (MN17) [7] and [13]. Il existe, néanmoins, quelques données qui semblent indiquer la présence de ce genre dans les localités de Theobaldof (Allemagne) [22] et de Sankt Gallen (Suisse) [2]. L’âge attribué à ces localités serait compris entre les zones MN2 et MN3.

Dans la coupe de Morteral (bassin du Magro, Valence, Espagne), nous avons découvert le gisement Morteral-20A, où il y a des restes du genre Eomyops. Le tamisage de plusieurs milliers de kilogrammes de sédiment a fourni une des plus importantes collections connues dans le monde de restes fossiles de ce genre.

Eomyops is a rather uncommon eomyid in the fossil record. It appears in some European localities, but never constitutes the main element of the fauna. The genus Eomyops was created by Engesser [10] to distinguish the European material of eomyids that Hugueney and Mein [18] had included in the genus Leptodontomys Shotwell, 1956. The distinctive features in the mandible and the ridges of the lower incisors of Eomyops allowed Engesser to distinguish both taxa. The genus Eomyops comprises four species: E. catalaunicus [17], E. bodvanus [19], E. oppligeri [9] and E. hebeiseni [20]. The temporal range of distribution of the genus extends between the Middle Miocene and the Pliocene (zones MN5/6 to MN17) [7]. Nevertheless, this range could be wider (MN2 or MN3) if we consider the presence of the genus in the localities of Theobaldshof [22] and Sankt Gallen [2].

In this article, the assemblage of Eomyops from the locality of Morteral-20A is described. The material described here shows distinctive features that allow the definition of a new species, E. noeliae.

The section of Morteral, where Morteral-20A is located, is situated in the southeastern part of the Magro Basin (eastern Spain), an intramontane basin established in the Late Cretaceous [25]. All sediments of this basin are continental [25]. In the section of Morteral 12 fossiliferous beds have been found, ranging in age from Lower to Middle Aragonian. The preliminary faunal list of Morteral-20A includes the following taxa: Megacricetodon sp. 2, Fahlbuschia sp., Eumyarion sp. and Glirudinus modestus [24]. Morteral-20A is situated between beds with Megacricetodon primitivus (Freudenthal, 1963) and M. collongensis (Mein, 1958) [25]. The relative position of this locality and the preliminary faunal list allow us to assign Morteral-20A to the Early Aragonian (in the transition between zones MN4/MN5, probably in the MN4 zone).

The nomenclature used in the descriptions of the teeth is that of Fahlbusch [12]. Lengths and widths have been measured as defined by Álvarez-Sierra [1]. Specimens are kept in the “Departamento de Geología” of the University of Valencia, Spain.

Order: Rodentia Bodwich, 1821.

Family: Eomyidae Winge, 1887.

Genus: Eomyops Engesser, 1979.

Eomyops noeliae sp. nov. (Fig. 1).Derivatio nominis: this species is named after Noelia Ruiz.Holotype: MT20A-323, isolated upper molar housed in the Geology Museum of Valencia University.Referred material: 1 Iinf., 3 P₄, 18 M_1,2, 6 M₃, 3 P⁴, 12 M^1,2, 3 M³.Type locality: Morteral-20A (MT-20A), Lower Aragonian, Magro basin, Spain. Coordinates UTM 30SXJ933608.Diagnosis: medium-sized Eomyops, with a medium-sized, generally transverse mesolophid. Anterolophid of M₃ absent or short. Lingual anteroloph absent in about half the M^1,2, very small in the rest. About one third of the M^1,2 have a split mesoloph.Differential diagnosis: E. noeliae differs from the other species of the genus by the poor development of the lingual anteroloph of the upper molars and of the labial anterolophid of the M₃. It is smaller than E. hebeiseni and larger than the other species. It differs from E. hebeiseni by the split mesoloph of the M^1,2. It differs from E. oppligeri by the more reduced mesolophids in the lower molars. It differs from E. catalaunicus by the split mesoloph of the M^1,2 and the lesser development of the mesolophid of M_1,2,3. Finally, it differs from E. bodvanus by the split mesoloph of the M^1,2 and the lesser development of the mesolophids of the lower molars.Measurements: see Table 1.

Iinf: only one specimen is available. The most characteristic feature of this element is the presence of two little ridges along the enamel of the tooth. They are parallel and run from the top to the base of the tooth. Between the two crests a small channel is developed. These crests are slightly displaced toward the right side of the tooth.

D ₄ : this element is much longer than wide, subrectangular. The only tooth shows a very small labial anterolophid. Lingual anterolophid absent. The mesolophid is strongly reduced, nearly absent. Posterolophid very much reduced. It does not reach the entoconid. Hypolophid continuous, connecting the hypoconid and the entoconid.

P ₄ : this element is longer than wide, subquadratic. One out of four specimens shows a very small labial anterolophid. This specimen lacks a lingual anterolophid, whereas the rest lack both the lingual and the labial anterolophid. The mesolophid is very short (1), medium (1) or medium-long (1). The posterolophid is short and thin. It reaches the entoconid in one out of three cases. The crest is partially interrupted near the entoconid in two cases. In one specimen the hypolophid is strongly interrupted and in another two cases it is partially interrupted.

M _1,2 : these teeth are wider than long. Lingual anterolophid strong and well developed, labial anterolophid long (4) or medium sized (12). Mesolophid short (4), medium-sized (11) or moderately long (3). The mesolophid is directed forwards (1), transversally (15) or backwards (2). The posterolophid joins the hypolophid at a sharp (11) or right angle (6).

M ₃ : posterior side strongly or slightly (2) rounded (4). Length and width are more or less equal, so the teeth seem square except for the reduction of the postero-lingual side. The anterolophid is well developed on its lingual side. On its labial side it is very short (3), even absent in three specimens. Mesolophid short or very short (3), medium sized (2) or moderately long (1). The mesolophid is directed forwards (2), transversally (2) or backwards (2). Hypolophid continuous (3) or partially interrupted (3). This causes the extreme reduction of the fourth syncline, which in three cases nearly joins the third syncline.

P ⁴ : this element is much wider than long. The lingual part is shorter than the labial part. Mesoloph short (2) or very short (1), directed forwards (2) or transversally (1). The longitudinal crest is continuous (1), partially interrupted (1) or absent (1). In this last specimen the lingual syncline connects with the second syncline. Mesoloph split into two or more crests, much directed forward. Paracone and metacone slightly displaced to the lingual side, thus forming a small platform in front of the second and third synclines on the labial side.

M ^1,2 : rectangular outline strongly wider than long. Lingual anteroloph absent (7), very weakly developed (5) or well developed (1). The longitudinal crest joins the protocone nearly transverse, so the second syncline is longer than the third syncline. The longitudinal crest is thin and in most cases partially interrupted. Mesoloph short (7), very short (2) or medium sized (5) and directed forward (12) or transversely (2). The mesoloph is slightly forked (5) or simple (9).

M ³ : shape strongly wider than long. Protocone and paracone are the highest cusps. Lingual anteroloph absent (1) or very short (1). First syncline long and narrow. Mesoloph of medium size (1) or medium-long (3) and directed forward. The mesoloph takes up nearly all the space of the second and third synclines. Longitudinal crest nearly transverse. Lingual syncline directed forwards. Second syncline much longer than third syncline. Fourth syncline reduced and open at the postero-labial side.

The dental characters of the genus Eomyops described by Engesser [10] are: “The upper molars show a well-developed lingual anteroloph and the second and fourth synclines extend lingually past the middle of the teeth. The M3/3 are little reduced, M₃ generally having a hypolophid. The fourth syncline of the lower molars is well developed in most species. The mesoloph of the upper molars is mostly short, sometimes bifurcated, and anteriorly directed. The lower incisors are crenulated”.

The length/width scatter diagrams of E. noeliae indicate that all elements have a similar size, except the M³ (Fig. 2). This also happens in E. hebeiseni from Chatzloch, where the M³ is the smallest element of the dentition [20]. Fig. 2 shows the range of measurements of the elements of E. hebeiseni and E. noeliae nov. sp.. The M3/3 are not very much reduced, especially the M₃. The latter is longer than the M³ in E. hebeiseni and in E. noeliae, while both the M³ from Morteral-20A and from Chatzloch [20] are, more or less, as wide as the M₃.

The lingual anteroloph in E. noeliae is not as well developed as described in Engesser's characterization of the genus[10] and [11]. While the lingual anteroloph is mostly well developed in E. hebeiseni, E. oppligeri, E. catalaunicus and E. bodvanus, in E. noeliae the lingual anteroloph is mainly absent.

The development of the second and fourth synclines, extending lingually past the middle of the teeth, is very common in E. noeliae.

The development of the hypolophid of the M₃ is variable. At least in three specimens (50%) this crest is partially interrupted. The rest has a weak and continuous hypolophid.

Engesser figured a fragment of a lower incisor of E. aff. catalaunicus from La Grive that presents two ridges in the underside of the tooth [10]. He distinguished this character as representative of European populations of Eomyops. Among the remains of E. noeliae from Morteral-20A there is a lower incisor with this morphology (Fig. 1R, S, T). The lower incisor from Morteral-20A is complete, so this character can be studied. The two ridges extend throughout the enamel all along the tooth. It consists of two small parallel crests. The highest of these two crests is very small and draws a small channel from the base of the tooth until its apex. This character is not commonly mentioned in the literature, but may be an excellent feature to distinguish the genus Eomyops. After the revision of all the rodent incisors in Morteral-20A, no other incisor with two ridges has been found. Although important in some cases, as can be observed in Eomyops, incisors are usually not studied in fossil collections. Therefore, diagnostic characters based on incisors are seldom utilized for the distinction between taxa at the generic level. Nevertheless, in Eomyops they can be helpful to distinguish the material of this genus from the rest of rodents.

Throughout the chronological range of distribution, the morphology of the teeth of Eomyops is very conservative [8]. The four described species of the genus show great similarities in the morphology. Biometrically, the species of Eomyops are clearly distributed in two groups. A first one is composed by small-sized species: E. catalaunicus, E. bodvanus and E. oppligeri and E. noeliae. The other one comprises only E. hebeiseni, of larger size.

The temporal distribution of E. hebeiseni covers zones MN5 and MN6; E. oppligeri occurs in zones MN7 and probably MN6, MN8 and MN14; E. catalaunicus occurs in zone MN9 and MN10, and probably in MN13 and MN14, and E. bodvanus in MN14 and perhaps MN15. In the German locality of Schernfeld (MN17 a few teeth that represent the youngest record of this genus [8] have been found.

Based on the published literature, we have compared the material of Eomyops from Morteral-20A with that from the type localities of the different species of the genus. For the morphological and biometrical comparison of our material, we follow the chronological order of the different species of the genus Eomyops (E. hebeiseni – E. oppligeri – E. catalaunicus – E. bodvanus).

Fig. 3 and Fig. 4 represent the ranges of several parameters of the dentition of Eomyops species from various European localities. The size of E. noeliae is intermediate between the larger E. hebeiseni and the smaller E. oppligeri, E. catalaunicus and E. bodvanus.

There is no overlap of the measurements with E. hebeiseni, only the maximum length values of the M^1,2 and the M_1,2 of E. noeliae are near the minimum values of E. hebeiseni. This does not happen with lower and upper P4, but those elements are less numerous.

E. oppligeri from Anwil is smaller than E. noeliae, but the biometrical differences are not always evident. The length of lower and upper P4 and width of first and second lower and upper molars do not overlap. In these cases E. noeliae is clearly larger than E. oppligeri. On the contrary, minimum length values of first and second lower and upper molars of E. noeliae overlap with maximum values of first and second lower and upper molars of E. oppligeri, and the values for the width of P₄ come very close. In the case of the upper molars, the values are clearly separated for all the measured parameters, except for the length of the M^1,2. In this case, the extreme length values of the M^1,2 of E. oppligeri match with the minimum ones of E. noeliae from MT-20A.

The material of E. catalaunicus from the type locality, Can Llobateres, is very scarce. So, the comparison of measurements between both populations is difficult. While all parameters of the upper molars in E. noeliae have quite higher values than in E. catalaunicus, the size of the lower molars is more similar. In the M_1,2 the maximum values of E. catalaunicus overlap the minimum values of E. noeliae. In the P₄, the only specimen from Can Llobateres has the same width value as medium-sized specimens from MT-20A.

As in the case of E. catalaunicus, the material of E. bodvanus from its type locality is very scarce. Only the first and second lower and upper molars can be compared biometrically. There is no overlap between the populations of E. bodvanus and E. noeliae. Only the lengths of the first and second lower and upper molars of both species are similar (the maximum values of E. bodvanus are close to the minimum values of E. noeliae).

In the M^1,2 of E. noeliae the lingual anteroloph is absent (54%), very weak (38%) or of short-medium size (8%= 1 specimen). The M³ of E. noeliae is represented by two teeth. One specimen lacks the lingual anteroloph and the other one has a weak anteroloph. On the contrary, in the M^1,2 of E. hebeiseni from Chatzloch predominate morphotypes with well-developed lingual anteroloph (50%) [20]. In Chatzloch, all specimens (4) of M³ have anterolophs [20]. The other species have a well-developed lingual anteroloph in all upper molars.

The mesoloph of the M^1,2 of E. noeliae is short or very short in 64% of the teeth, and of medium size in the rest. The length of mesolophs in the other species of the genus is similar. Only in E. hebeiseni, this crest is moderately long and simple [20]. A remarkable fact is the bifurcation of the mesoloph of M^1,2. While E. noeliae and E. oppligeri have specimens with a clear division of the mesoloph (36% in E. noeliae), in the rest of the species this crest is always single.

Another important morphological difference between E. noeliae and the other species is the development of the labial anterolophid of M₃; in E. noeliae it is weak in three specimens and absent in the other three; this crest it is well developed in E. hebeiseni [20], E. oppligeri, E. catalaunicus and E. bodvanus.

On the another hand, the development of the mesolophid of the lower molars of E. noeliae is clearly different from the other species. In E. noeliae this crest is short or medium sized in 83% of the M_1,2 and in all M₃, E. oppligeri, E. catalaunicus and E. bodvanus have a long or moderately long mesolophid. In the M_1,2 of E. noeliae the mesolophid is directed forwards (1; 6%), transversally (15; 83%) or backwards (2; 11%) and in the M₃ directed forwards, transversally or backwards in the same proportion. In the rest of species of the genus, this crest is directed backwards or transversally.

Kälin [20] lists all localities that have yielded Eomyops in western and central Europe. Four of these localities are located in the Iberian Peninsula (Can Llobateres, Las Planas 5K, Manchones and Arroyo del Val 6). Can Llobateres is the type locality of E. catalaunicus, and the rest of the localities contain a material determined as Eomys sp. [8], Leptodontomys (Eomyops) sp. [13] or L. (Eomyops) aff. catalaunicus [14] in Manchones and Leptodontomys (Eomyops) sp. [13] or L. (Eomyops) aff. catalaunicus [14] in Arroyo del Val 6 [14]. Posteriorly, the material from Las Planas 5K and Manchones is attributed to E. catalaunicus [5] and [6]. Las Planas 5K, Manchones and Arroyo del Val 6 contain M. crusafonti and are assigned to the Aragonian biozone G2 (MN6) [5] and [6]. On the other hand, in Can Llobateres M. ibericus [15] and [16] has been identified, so this site has been assigned to biozone MN9. In spite of the scarcity of material of these localities, the morphological differences of these populations as compared with E. noeliae are based on the same features described before for the type localities of each species. Recently, in the section of “Abocador de Can Mata”, near Can Llobateres (Vallés-Penedés basin), new localities with Eomyops material, provisionally determined as E. cf. oppligeri [4] have been found.

So far, the oldest species of the genus Eomyops was E. hebeiseni from Chatzloch [20] and the youngest E. bodvanus from the Pliocene of central Europe [19]. Nevertheless, there are some data indicating the probable presence of this genus in older deposits of central Europe [2] and [22]. The presence of Eomyops in deposits earlier than zone MN5 is uncertain. The best known Eomyops assemblages correspond to an age range between MN5 and MN17 (Middle Miocene to Late Pliocene).

During many years, the small bunodont eomyids known from some Middle and Upper Miocene localities of Europe had been considered to belong to the North American genus Leptodontomys [18] and [23]. Some differences in morphology lead Engesser [10] to assign the European material of Leptodontomys to the new genus Eomyops. These differences are the presence of two ridges in the lower incisors and other slight differences in the mandible.

Some authors have considered the differences between Eomyops and Leptodontomys not significant enough to justify the existence of two separate genera [3], [7] and [23]. The decision of creating a new genus ultimately depends on the importance assigned to the diagnostic characters distinguishing each genus. The morphological similarities between Leptodontomys and Eomyops are evident. If we accept the fact that the description of the Eomyops material in Europe has been based on the study of each one of the dental elements, including incisors, the difference between Leptodontomys and Eomyops in the lower incisors is also undeniable.

The presence of two ridges in the lower incisor is now known in two assemblages: La Grive [10] and MT-20A (in the other assemblages the lower incisor is not known) and this enforces Engesser's view that Eomyops and Leptodontomys are different genera. So far no crenulation has been described in the lower incisors of Leptodontomys. The North American record of Leptodontomys extends between the Arikareean (Upper Oligocene) [3] and [21] and the Clarendonian (Upper Miocene) [26].

In China, Qiu [23] reports the occurrence of Leptodontomys aff. gansus and Leptodontomys sp. nov. 2 in the Middle Miocene locality of Tunggur, Leptodontomys sp. nov. 1 in the Lufeng site and L. gansus in Harr Obo, Ertemte and Songshan. These last three localities and Lufeng have been attributed to the Upper Miocene. No crenulated incisors have been described in any of the Chinese assemblages studied [23]. According to Qiu, the presence of Eomyops (Leptodontomys selon Qiu) in Europe would be due to the migration of Leptodontomys from North America to Europe through Asia. If this hypothesis is true, Leptodontomys should be present in the basins of the Asiatic migratory route proposed by Qiu in the Lower Miocene or earlier. However, the first record in China of Leptodontomys in the locality of Tunggur is younger than the first Eomyops record in Europe.

The Leptodontomys record in the Chinese continental basins is fragmentary and probably still incomplete [23]. If Eomyops is a descendant of Leptodontomys, and if the latter migrated to Europe through the Asiatic route, new occurrences of Leptodontomys in the Asiatic basins in deposits older than Tunggur are to be expected. If, on the contrary, the Leptodontomys record in China and other possible continental areas connecting Europe and North America were not older than Middle Miocene, the presence of E. noeliae in Lower Miocene deposits in southern Europe would support Engesser's hypothesis about an independent evolution of Eomyops and Leptodontomys in the European and American continent respectively.

The E. noeliae assemblage from the locality of Morteral-20 A contains the greatest collection of fossil remains of the genus Eomyops in the Iberian Peninsula and represents the first true report worldwide of this genus in zone MN4.

The size of this new eomyid species is intermediate between the large E. hebeiseni and the group of small species composed by E. catalaunicus, E. oppligeri and E. bodvanus. Thus, there is no clear trend of size increase or decrease among the species assigned to the genus.

The degree of development of the lingual anteroloph of the upper molars and the lingual anterolophid of the M₃ represents a significant difference with the rest of Eomyops species. The conservative character of the Eomyops morphology made the distinction between species of the group particularly difficult. So far, few or no differences could be established between the representatives of the genus.

The presence of two ridges in the lower incisors of E. noeliae makes this morphological character one of the most important to distinguish between Eomyops and Leptodontomys.

The presence of Eomyops in paleontological sites of zone MN4 adds new information to the analysis of the origin of the genus in Europe and extends the temporal range of the distribution of Eomyops.