Type species: Eurolagus fontannesi (Depéret, 1887), by monotypy; La Grive Saint-Alban (Isère, France), Astaracian.

Diagnosis.—Large semihypsodont lagomorph, smaller than Megalagus and larger than Amphilagus antiquus, Desmatolagus, most species of Gobiolagus, Gripholagomys, Mytonolagus, Piezodus, and Titanomys, and all species of Palaeolagus, except the larger P. intermedius. More strongly hypsodont than most of the primitive stem lagomorphs, with a tooth crown height comparable to that of Megalagus and advanced Mytonolagus (M. wyomingensis), slightly lower than that of Amphilagus, and markedly lower than that of the semihypsodont species of Palaeolagus. Curvature of the upper teeth is definitely larger than in Palaeolagus, less than in the rootless Titanomys calmensis, and similar to that in Amphilagus, Desmatolagus, Megalagus, Mytonolagus, Titanomys visenoviensis, and Piezodus branssatensis. A trilobate P2 distinguishes Eurolagus from the basically bilobate tooth of Palaeolagus. P3 is not molarized, unlike that of Palaeolagus; the lingual lobe of P3 is longer than in Amphilagus, Desmatolagus, Gobiolagus, and most of Mytonolagus, and more compressed anterodistally than in those genera and in Megalagus. P4 molarized unlike that of Gobiolagus and Lushilagus. Persistency of the enamel pattern on the upper cheek teeth separates Eurolagus from Lushilagus, Shamolagus, and Gobiolagus, in all of which the hypostriae are weak and the occlusal pattern wears relatively quickly. The hypostria is deeper than in Desmatolagus, and comparable to that of Mytonolagus and Megalagus; it is relatively shallow on P3 and P4 (shallower than in Palaeolagus) and cuts across one-third of the occlusal surface on M1 and M2. Hypostrial lakes are absent in Eurolagus, unlike in Palaeolagus, Megalagus, Mytonolagus, Gripholagomys, and Desmatolagus. The p3 is single-rooted, unlike the double-rooted tooth of Mytonolagus, Megalagus, and Strenulagus. The crown of p3 is bilobate and compact, with a short and relatively large trigonid, and a slightly concave anterolingual side in younger individuals, resembling in outline and proportions the p3 of Amphilagus antiquus, Megalagus, and Gripholagomys at most wear stages. This tooth further differs from that of Desmatolagus, which has a smaller trigonid, Mytonolagus, which has an enlarged trigonid, and Gobiolagus, Lushilagus, and Shamolagus, which have a trilobate p3. The lingual reentrant of p3 is much less persistent than in Titanomys, Palaeolagus, and some species of Mytonolagus. Together with the absence of an isolated anteroconid, this distinguishes Eurolagus from Piezodus. Differs from all genera (apart from Mytonolagus) in having more persistent reentrants on the buccal instead of the lingual side of the talonids of the lower cheek teeth. The m2 has fused roots as in Amphilagus and Palaeolagus, unlike the condition in Megalagus and Mytonolagus. The m3 is reduced in comparison to that in Lushilagus, Shamolagus, and Gobiolagus and marked by two conids, unlike the m3 in Amphilagus, Titanomys, and Piezodus (m3 with single conid). Both conids become fused late during ontogeny as in Desmatolagus, but unlike the condition seen in Megalagus and Palaeolagus. Eurolagus further differs from Gobiolagus, Lushilagus, Mytonolagus, and Shamolagus in having no trace of an additional lobe on m3.

Holotype: ML LGr 169, maxilla with P4 and M2. Figured in Depéret 1887: pl. 13: figs. 19–19b.

Material.—P2 (MF/5065, MF/5066, MF/5067, MF/5068, MF/5069); P3 (MF/5070, MF/5071, MF/5072 juv., MF/5075); P4 (MF/5074, MF/5101/a, MF/5077); M1 (MF/5076, MF/5101/b, MF/5080); M2 (MF/5078, MF/5079, MF/5081, MF/5073 juv., MF/5088); p3 (MF/5082, MF/5083); m1 or m2 (MF/5084, MF/5085, MF/5086); m3 (MF/5087); trigonids of lower premolars or molars (MF/5089–95, MF/5099); talonids of lower premolars or molars (MF/5096–98); other tooth fragments (MF/5101).

Diagnosis.—As for the genus.

Description

The studied material consists of isolated teeth representing all loci except the incisors (dI2/di2) and M3 (Table 2).

P2.—Five specimens at different stages of wear are represented in the Bełchatów sample. The tooth is oval, trilobate, and compressed anterodistally. Generally, the morphology of P2 is very conservative in Lagomorpha, and the same trilobate pattern is shared by most species known from the Eocene to the Miocene, with the teeth differing only in their level of hypsodonty (Dawson 1958; Tobien 1974, 1975; Topachevsky 1987; Meng et al. 2005; Fostowicz-Frelik and Tabrum 2009).

The lobes are separated by two anterior reentrants, of which the buccal one is less persistent (Figs. 4A, B, 5A, B). The lingual lobe is the largest, convex lingually, and in juvenile specimens sometimes gently flattened or concave buccally. The central lobe is more symmetrical; in juvenile specimens, it is elongated, tear-shaped, and connected to the posterior base of the tooth through a narrow isthmus. The latter broadens during ontogeny, and in older specimens nearly equals the width of the lobe at mid-length (Fig. 5A₂). Both lobes have a thickened enamel layer, the lingual lobe mainly on the lingual side and the central lobe along the anterior wall. The buccal lobe appears last during ontogeny. It forms a small separate cusp, initially placed much more dorsally on the tooth shaft than the other two cusps (Figs. 4A, 5A₂). As wear progresses, this cusp eventually becomes nearly equal in dorsoventral dimension to the other two cusps (Fig. 5A₁). At this stage, it is connected to the central lobe by a long, low ridge (Fig. 5A₂). While the occlusal surface of the buccal lobe is generally round, it sometimes develops a shallow buccal groove in older specimens (Fig. 5B). The enamel layer of the buccal lobe is sometimes thickened along the anterior and buccal surfaces. The P2 has a single root (Figs. 4A₁, 5A₁), and a moderately high crown broadening near the base. The latter is of uneven height, being highest on the lingual side, at the base of the lingual reentrant, and lowest on the buccal side dorsal to the buccal lobe.

P3.—The P3 is represented by two strongly damaged and two worn teeth (Fig. 4C, D), one (MF/5071) classified as a senile stage (sensu Tobien 1974). The early ontogenetic stages of this locus can therefore not be ascertained. In both specimens, the lingual lobe is markedly long, surrounding the central lobe almost completely. At this stage of wear, it is more extended buccally than in Amphilagus antiquus (Tobien 1974), the P3 of Eurolagus fontannesi from La Grive (Tobien 1974), and the strongly worn teeth of “Amphilagus” sarmaticus (Topachevsky 1987: fig. 9), a contemporaneous species from Ukraine (listed as Eurolagus sarmaticus in Nesin and Nadachowski 2001). The crescentic valley is open (Fig. 4C, D) and there is no anterobuccal connection between the lingual and central lobes, contrary to the condition observed in some specimens of E. fontannesi from La Grive (see Tobien 1974: fig. 36). In the less worn specimen (MF/5075, Fig. 4C), the central lobe resembles an irregular triangle with a convex buccal margin featuring a shallow buccal basin. In the senile specimen (Fig. 4D), the central lobe is larger and oval, and the buccal valley is completely missing. The remnants of the buccal lobe are obliterated in MF/5075 and absent in MF/5071 (Fig. 4D). The hypostria is very shallow, cutting across ca. 10% or less of the occlusal surface. The occlusal surface of the senile specimen displays a morphology typical of semihypsodont teeth; there is marked slope relief, with an elevated, less worn buccal side and a depressed lingual part (Fig. 4D₁).

P4.—The P4 is only represented by fragments, some of them juvenile (Figs. 5D, E, 6). The best-preserved specimen, MF/5074, has a very shallow but still persistent hypostria, which extends almost to the base of the crown, and a clearly visible crescent-like central lobe. The lingual lobe is connected to the buccal side of the tooth, virtually closing the crescentic valley, even though the valley shallows rapidly buccally toward the anterior buccal cusp (Fig. 5D₂). The buccal side of the tooth is missing and the internal structure of the crescent can be observed. Its dorsoventral dimension equals ca. two-thirds of the total height of the tooth. The two arms of the crescent are marked throughout all of its height, resulting in this structure retaining its crescent-like shape at the occlusal surface until late during ontogeny. This feature seems to characterize the European lineages of the semihypsodont lagomorphs and differentiates them from the North American stem lagomorphs, such as Mytonolagus or Palaeolagus, in which the occlusal shape of the crescent rather quickly turns into a rounded islet (Dawson 1958, Fostowicz-Frelik and Tabrum 2009).

The other specimens tentatively classified as P4 share a characteristic shallow hypostria and a generally centrally placed central lobe with an eminent and thickly enameled lingual margin, forming the buccal part of the crescent structure late during ontogeny.

M1 and M2.—These teeth are similar in structure, differing mainly in size (M2 is smaller), lobe structure and position of the crescent. The hypostriae are visibly deeper than on P4 (cutting across ca. 35% of the occlusal surface) and filled partly with cement (Figs. 4E₂, 5I, J₁). In M2, the hypostria is directed slightly anteriorly (Fig. 5I, J₁). The anteroposterior length of the anteroloph is larger than that of the posteroloph in M2 (Fig. 5I, J₁), whereas this asymmetry is only weakly expressed in M1 (Fig. 5G₁). Nevertheless, the crescent is placed mainly within area of the posteroloph. In the ontogenetically younger specimens, such as MF/5078 (Fig. 4E₂), two buccal cusps and the buccal basin are well-preserved, as are the remains of two buccal roots.

p3.—There are two p3s (left and right) in our sample (Figs. 4F, 5K). One (MF/5083) is from a slightly younger individual than the other, but both represent adult specimens. Their outline is rounded, with a deep external reentrant (hypoflexid; López Martínez 1977), crossing about half of the total width of the tooth. While the slender talonid remains wider than the trigonid throughout ontogeny, the trigonid becomes more rounded and enlarges with wear, as seen in the ontogenetically older specimen. Unlike in “Amphilagus” ulmensis and Piezodus, there are no additional anteroconids or cingula at the anterior margin of the trigonid (López Martínez 1974; Tobien 1974).

The enamel layer surrounding the tooth is generally thick, being thickest in the region of the trigonid and thinnest on the talonid side of the reentrant, which is also crenulated (Fig. 4F₃). The anterolingual side of the trigonid is gently concave in both specimens. Specimen MF/5082 resembles the specimens of Eurolagus fontannesi from La Grive in having a shallow concavity on the lingual margin (Fig. 4F₁; Tobien 1974: figs. 39, 43, 45; López Martínez 1989: fig. 50). However, this concavity is much less marked than in “Amphilagus” sarmaticus, and there is no pronounced buttress situated anterior to the concavity as found in both the latter species (Topachevsky 1987: figs. 4–7) and Titanomys visenoviensis (Tobien 1974: figs. 54, 68).

p4, m1, and m2.—The lower molariform teeth all have a similar structure and differ mainly in the degree of curvature of the trigonid and talonid, as is typical for lagomorphs. The later increases anteroposteriorly, with p4 being almost straight, m1 being slightly curved distally, and m2 being strongly bent distally (Figs. 4D, 5L). The material referred to the lower cheek teeth consists mostly of isolated trigonids and talonids (Figs. 7E, 8A), although one ml (MF/5085) and two complete m2 (Figs. 4G, 5L) are present. The trigonid is not completely surrounded by enamel and shows an enamel-free hiatus in the central part of its anterior wall (Fig. 5L₂).

In younger individuals, there is an additional fold on the talonid (hypoconulid sensu López Martínez 1989 or “additional talonid” sensu Sych 1977), which disappears during ontogeny. In juvenile specimens, it forms a separate, small, and anteroposteriorly compressed conid, which later connects to the talonid halfway along its width. This results in the formation of two posterior (lingual and buccal) reentrants of the talonid, which then finally close. As a rule, in Eurolagus fontannesi, the lingual one closes first (Fig. 8A) (Tobien 1974; López Martínez 1989), although specimen MF/5084 shows the opposite sequence (Fig. 4G₁). Thus, this character is variable for Eurolagus at least in the case of m2. Nevertheless, the longer persistence of the buccal posterior reentrant of the talonid is a very rare feature among the Lagomorpha and distinguishes E. fontannesi from all the late Oligocene and Miocene European species, including Amphilagus, Titanomys, and the Piezodus—Prolagus lineages (Tobien 1974, 1975; Topachevsky 1987; Angelone 2009), as well as the majority of Asian semihypsodont lagomorphs, such as Desmatolagus or Gobiolagus (Erbajeva 1988; Lopatin 1998; Meng et al. 2005), and the North American Palaeolagus (Dawson 1958). The only lagomorphs retaining buccal reentrants longer than the lingual ones are representatives of Mytonolagus petersoni Burke, 1934 from Utah and specimens assigned to Mytonolagus near petersoni (sensu Dawson 1970) from the Badwater area in Wyoming (USA).

The lower cheek teeth of Eurolagus fontannesi are rooted, with m2 having fused roots with a single pulp cavity. The crown is significantly heightened, with the trigonid and talonid connected by cement for most of the crown height. Because the connection between the trigonid and talonid is located near the base of the crown (Fig. 5L₃, L₄), the formation of the lingual enamel bridge does not occur until the senile stage.

m3.—The m3 is the smallest of the lower teeth, although it is not reduced to just one conid as seen in Amphilagus, Titanomys, and other genera usually assigned to Ochotonidae (sensu Tobien 1974; López Martínez 1977, 1989). Instead, it is marked by two conids joined by a very thin central isthmus (Fig. 5N). The trigonid is large, wide and oval, whereas the talonid is more triangular. The enamel layer is thickened particularly along the buccal and lingual sides of the trigonid, and there is an enamel hiatus in the anterior wall of the trigonid (Fig. 5N₃). A bilobate structure of the m3 as observed in Eurolagus fontannesi has not been reported for any ochotonid species, but is typical for all leporids and stem groups such as “Palaeolaginae” and “Mytonolaginae” (Wood 1940; Dawson 1958, Fostowicz-Frelik and Tabrum 2009), as well as Procaprolagus and Agispelagus (Gureev 1960), and was also found in Desmatologinae (Tobien 1974; McKenna 1982; Lopatin 1998).

Enamel microstructure.—Previous work on the enamel structure of lagomorphs focused on their incisors (see Koenigswald 1995; Martin 2004), with their premolars and molars, especially those of their primitive semihypsodont representatives, generally not attracting much attention (but see Mazza and Zafonte (1987) for Prolagus and Koenigswald (1996) for some extant taxa). For the purpose of this study, we sectioned the upper (Fig. 6) and lower (Figs. 7, 8) cheek teeth of Eurolagus fontannesi and studied the enamel structure in vertical (longitudinal sensu Koenigswald 1995) and transverse sections; the longitudinal section of P4 gave an insight into the tangential view as well, as a part of the crescent was cut along this plane (Fig. 6C).

The enamel shows some variability in thickness (Table 3) and level of complexity owing to its position at the occlusal surface of the tooth and the biomechanical requirements resulting from the orthogonal shearing and transverse grinding movements characteristic for lagomorphs (Meng et al. 2003). In the upper molarized teeth, the thickest and most complex enamel is found along the anterior margin of the anteroloph and in the central part of the crescent (Figs. 5, 6). In the lower molarized dentition, this type of enamel is located on the distal, buccal, and lingual margins of the trigonid (Fig. 7, Table 3) and along the talonid rim, except for the anterobuccal margin and the internal areas of the folds (Fig. 8). The anterior part of the trigonid displays a hiatus, which completely lacks enamel (Fig. 7B, E).

The enamel of the cheek teeth is mainly two-layered (internal and external layers), with either a strongly or weakly pronounced transition. The internal layer is composed of radial enamel showing a noticeable degree of inclination towards the external surface, which varies from 45° in the upper premolars (Fig. 6A, B) to almost 90° in the lower molars (Figs. 7C, 8C). The angle of the inclination is frequently not constant within the layer, and increases towards the outer surface, changing the direction of the prisms from tangential (internally) to radial sensu stricto (externally), i.e., perpendicular to the enamel-dentine junction (Martin 1999). The interprismatic matrix is parallel to the prisms, thus expressing a condition primitive for Glires (Martin 1999; Meng et al. 2003).

The external zone is formed by decussating bundles of prisms forming Hunter-Schreger bands (HSB). In Eurolagus, the HSB bands, consisting of 4–6 prisms, are best expressed in longitudinal section (Fig. 6A, B), whereas in cross-sections the margins of the decussating bundles and the general pattern are obscured (Figs. 7A, C, D, 8C). The decussating external enamel occupies 35–50% of the total enamel layer (Table 3), and is least developed along the talonid. While the anterolingual (Fig. 8C) and the most pronounced buccal parts of the talonid clearly show the decussating external layer of enamel, the prisms in the external layer along its distal edge only display a slight degree of lateral undulation, indicating very weakly developed HSB (Fig. 8F). In addition, an even more simplified enamel structure is present in the internal parts of the folds (Figs. 8B, D, E).

The most external segment of the enamel, varying from 5 to 15 um in thickness (Table 3), forms prismless enamel (PLEX), as commonly observed in Glires (Martin 1999, 2004).

Dental microwear.—Tooth microwear was only observed in some of the best preserved upper premolars and molars (Fig. 9). Fine scratches and small pits dominate the microwear pattern, and are most strongly developed on the main enamel shearing blades, the anterior enamel layer of the anteroloph, and on the distal surface of the crescent (Fig. 9A₁, A₂, B). By contrast, the dentine seems to be unaffected, and the buccal cusps show only very fine microwear consisting mainly of small pits and cross-scratches (Fig. 9A₃). The upper M1 (MF/5101/b; Figs. 5G, 9A) was chosen for a more detailed study. However, the results should be treated as preliminary, as microwear has not been studied in lagomorphs previously, thus the comparisons are limited to rodents and ungulates.

The striae on the grinding surfaces are generally shallow and delicate compared to those found in most ungulates (Solounias and Semprebon 2002) and some rodent groups, such as Caviidae or Muridae (Townsend and Croft 2008; Gomes Rodrigues et al. 2009).

The main shearing blade shows an average of 34 pits and 20 scratches per 0.09 mm². There is a great predominance of small pits (19–40) over large pits (2–3), and fine scratches (13–20) over coarse scratches (0–4) or cross-scratches (0–4). The scratches are parallel or subparallel and inclined 20–30° in a buccolingual direction, indicating the main chewing movements. The two gouges present on the main shearing blade may be artifacts caused by transport and sedimentation, and thus their presence needs to be treated with caution. Towards the lingual edge of the shearing blade, the fine parallel scratches become less noticeable and occur less frequently (5–9 per 0.09 mm²), whereas the cross-scratches are more common (8–9 per 0.09 mm²). The count of small pits increases in the lingual area (up to 70 per 0.09 mm² along the edge), but the count of large pits remains low (1–2 per 0.09 mm²) and no gouges are present. The microwear on the buccal cusps consists mainly of small pits (56 per 0.09 mm²) and cross-scratches (14 per 0.09 mm²); the number of large pits is similar to that on the main shearing blade (4 per 0.09 mm²) and no gouges were observed (Fig. 9A₃).

Discussion.—Eurolagus fontannesi has previously been placed within Lagodus, Titanomys, or Amphilagus (Depéret 1887, 1892; Major 1899 and Wegner 1913; Gureev 1964 and Tobien 1974, respectively). López Martínez (1977) placed Amphilagus fontannesi in a new genus, Eurolagus on the basis of two sets of characters: first, the relative primitive features found in Eurolagus in comparison with Amphilagus antiquus, such as the less developed hypsodonty and bilobate m3; and secondly, the development of an occlusal pattern on p3 indicating a Titanomys-like stage with two symmetrically placed reentrants (lingual and buccal) present in juvenile specimens (López Martínez 1977, 1989). Moreover, there is no trace of the minute separate anteroconid characteristic of “Amphilagus” ulmensis and Piezodus. These characters clearly differentiate Eurolagus from Amphilagus and Piezodus, as well as from Titanomys (besides the basic p3 pattern in juveniles). A. antiquus displays only a single buccal (external) reentrant during ontogeny. This difference in the development of the p3 reflects the formation of an enamel lake present in both genera in subadult and young adult specimens. According to López Martínez (1977), the enamel lake in Eurolagus was formed as a result of the closure of the lingual reentrant, as can also be observed in many North American taxa—including Mytonolagus, Palaeolagus, and Chadrolagus (Dawson 1958; Gawne 1978; Fostowicz-Frelik and Tabrum 2009), as well as the European Titanomys (Tobien 1974). By contrast, the enamel lake in Amphilagus antiquus was formed from the internalmost part of the buccal reentrant, cut off buccally by a dentine bridge (López Martínez 1977, 1989: fig. 50). Furthermore, Eurolagus differs from most other lagomorphs in the formation of the posterior reentrants of the talonid on p4–m2 (Wood 1940; Dawson 1958; Gureev 1960; López Martínez 1989; Lopatin 1998; Meng et al. 2005; Angelone 2009; Fostowicz-Frelik and Tabrum 2009).

Despite the overall morphological similarity of the cheek teeth of Eurolagus and Amphilagus, the presence of the bilobate m3 casts doubt upon the assignment of Eurolagus fontannesi to the Ochotonidae. This character is recognized as typical of the Leporidae (unlike the Ochotonidae, which have a single column m3), and outside this group is found only in the Desmatolaginae (McKenna 1982), which, although they share some typically ochotonid characters (e.g., the premolar foramen), also display a leporid type of incisor enamel (Martin 2004) and have been suggested to form a clade separate from the ochotonids (Lopatin 1998).

Tobien (1974) proposed Eurolagus fontannesi as the final link in the Amphilagus antiquus—“Amphilagus” ulmensis lineage. By contrast, López Martínez (1977) linked the latter to the Piezodus lineage and instead suggested E. fontannesi to be a representative of a primitive lineage of Asian descent, which arrived in Europe a few million years after “Amphilagus” ulmensis had disappeared. However, López Martínez (1977) still placed Eurolagus within the Ochotonidae. The Asian origin of Eurolagus is to some extent supported by the presence of some scarce findings attributed to “Amphilagus” cf. fontannesi from the Late Oligocene and/or Early Miocene of Kazakhstan, the Baikal region (Russia), and Japan (Erbajeva 1988; Tomida and Goda 1993; Erbajeva and Filipov 1997; Erbajeva and Tyutkova 1997; McKenna and Bell 1997), as well as specimens from the Middle Miocene of the Caucasus area reported as Eurolagus aff. fontannesi (Pickford et al. 2000). Some of these findings stratigraphically precede the earliest European records of Eurolagus from Subpiatră (Hír and Venczel 2005), as well as the material from Rothenstein 1 (Sen in Bernor et al. 2004). Remains of a large lagomorph from Sandelzhausen (MN 5, Germany), although regarded as “Amphilagus” sp. by Angelone (2009) on the basis of stratigraphy, also resemble Eurolagus in size and morphology.

We consider Eurolagus fontannesi to be a stem lagomorph (sensu Asher et al. 2005; see López Martínez 2008 for the contents of this group), which most probably originated independently from “Amphilaginae” and Ochotonidae, and follow López Martínez (1977) in proposing that it represents a lineage descended from some immediate Asian ancestors, probably more closely related to Desmatolaginae. Until a comprehensive phylogenetic analysis is conducted, we thus place Eurolagus in Palaeolagidae Dice, 1929, along with other stem lagomorph taxa.

Stratigraphic and geographic range.—Late Middle to Late Miocene of western and central Europe (Fig. 1)