Le gisement de Córcoles (Guadalajara, Espagne) a livré une faune abondante et diversifiée de mammifères [1] datée du Miocène inférieur (Zone C ; MN 4a). Cette faune inclut deux espèces de rhinocérotidés, dont un élasmothériiné, initialement décrit sous le nom d'Hispanotherium matritense [19] and [21]. Toutefois, les 700 spécimens dentaires et postcrâniens concernés présentaient certaines différences morphologiques avec l'hypodigme d'H. matritense sensu stricto. De ce fait, « H. matritense de Córcoles » et H. matritense s. s. ont été traitées séparément dans l'analyse cladistique des Elasmotheriina [3]. Cette analyse, détaillée ci-dessous, confirme la particularité de l'élasmothériiné de Córcoles et permet de lui conférer un statut spécifique au sein du genre Hispanotherium.

The Elasmotheriina are fossil Rhinocerotidae known from the Early Miocene to the Late Pleistocene in Eurasia [3]. Among them, the genus Hispanotherium is widely spread in Spain, Portugal and France during the late Early Miocene [3], [7] and [8] and during the Middle Miocene in Anatolia [16] and [17]. The type species H. matritense (Lartet in Prado, 1864) has the best representation. It has been recognized in about 30 localities, mainly from Iberia [6], [7] and [8], but also in France [3] and [14].

The locality of Córcoles (Guadalajara, Spain) has yielded a diversified mammal fauna [1] and [21], which allows to place it within the Lower Aragonian (zone C; MN 4a). The rhinocerotid fauna was supposed to associate ‘Plesiaceratherium’ platyodon (Mermier, 1895) and H. matritense [19], [20] and [21]. Nevertheless, the latter appeared to bear some distinctive features, once compared with the whole hypodigm of H. matritense sensu stricto [3] and [21].

A cladistic analysis has been performed recently in order to recover the phylogenetic relationships of Elasmotheriina within Rhinocerotidae [3]. This analysis included an exhaustive list of Elasmotheriina, among which H. matritense and ‘H. matritense from Córcoles’ were treated as two distinct series. The results, developed in Section 3 and illustrated in Fig. 1 lead us to consider ‘H. matritense from Córcoles’ as distinct from H. matritense sensu stricto and from other Elasmotheriina. Thus, we propose to name a new species for the former.

Order Perissodactyla Owen, 1848

Family Rhinocerotidae Owen, 1845

Tribe Elasmotheriini Bonaparte, 1845

Subtribe Elasmotheriina Bonaparte, 1845

Hispanotherium Crusafont and Villalta, 1947

Type species. H. matritense (Lartet in Prado, 1864).

Other species. H. grimmi Heissig, 1974; H. beonense (Antoine, 1997); H. corcolense n. sp.

Diagnosis. Elasmotheriine rhinocerotid more evolved than Kenyatherium, Bugtirhinus and Caementodon in having an isolated hypocone on M1, a protocone constriction on P3–4, a straight medial border on the radius diaphysis, proximal radio-ulna facets generally isolated, a small trapezium-facet on the scaphoid, a straight posterior tuberosity on the magnum, a calcaneus-facet 1 generally wide and low on the astragalus and low intermediate relieves on central metapodials. Procoelodonta, Huaqingtherium, Iranotherium, Sinotherium and Elasmotherium are more evolved in possessing an always-simple crochet on P2–4, a continuous posterior cingulum on M1–2, a lingual wall on D2 and a constricted entoconid on lower milk teeth.

The phylogenetic relationships of H. corcolense n. sp. are assessed by a cladistic analysis, based on 282 anatomical characters [3] and checked in 26 terminal taxa. The outgroups are Tapirus terrestris (Linnaeus, 1758), Hyrachyus eximius Leidy, 1871, Trigonias osborni Lucas, 1900 and Ronzotherium filholi (Osborn, 1900). Other non-Elasmotheriina rhinocerotids included in the analysis are the Western European Protaceratherium minutum (Cuvier, 1822) and Plesiaceratherium mirallesi (Crusafont, Villalta and Truyols, 1955) and the North-American Diceratherium armatum Marsh, 1875 and Menoceras arikarense (Barbour, 1906). H. matritense and H. corcolense n. sp. are separately checked as distinct series.

The elasmotheriines included in the analysis are Elasmotherium sibiricum Fischer, 1809, Hispanotherium matritense (Lartet in Prado, 1864), Iranotherium morgani (Mecquenem, 1908), Elasmotherium caucasicum Borissiak, 1914, Sinotherium lagrelii Ringström, 1923, Parelasmotherium schansiense Killgus, 1923 (= Ninxiatherium longirhinus Chen, 1977), Procoelodonta mongoliense (Osborn, 1924), Beliajevina caucasica (Borissiak, 1935), Begertherium borissiaki Beliajeva, 1971, Caementodon oettingenae Heissig, 1972, Beliajevina tekkayai Heissig, 1974, Hispanotherium grimmi Heissig, 1974, Kenyatherium bishopi Aguirre and Guérin, 1974, Huaqingtherium lintungense (Zhai, 1978) (= Hispanotherium tungurense Cerdeño, 1996, = Caementodon tongxinensis Guan, 1993), Tesselodon fangxianense Yan, 1979, ‘Aegyrcitherium’ beonense Antoine, 1997 (here H. beonense), Bugtirhinus praecursor Antoine and Welcomme, 2000 and Hispanotherium corcolense n. sp.

Two equally parsimonious trees are obtained by means of Hennig86, version 1.5 [11]. The trees are 746 steps long, with an average consistency index (0.47) and a rather good retention index (0.64). In both trees, the Elasmotheriina are monophyletic, with Menoceras arikarense as a sister-group (Fig. 1). The only uncertainty concerns the relative positions of Hispanotherium matritense and H. corcolense: in the first tree (Fig. 1A), H. matritense and H. corcolense form a monophyletic group, whereas H. matritense is the sister-group of the (H. corcolense (‘A.’ beonense (more evolved Elasmotheriina) clade in the second tree (Fig. 1B). The former topology, with a (H. matritense, H. corcolense) clade, is selected by successive weighting.

The detailed branching sequence of the Elasmotheriina is (K. bishopi (B. praecursor (C. oettingenae ((B. caucasica, T. fangxianense) (H. grimmi ((H. matritense, H. corcolense) (‘A.’ beonense (B. tekkayai (B. borissiaki (P. mongoliense (H. lintungense (I. morgani (P. schansiense (S. lagrelii (Elasmotherium))))))))))))))). The exhaustive distribution of characters is detailed in Antoine (in press), but discussing the distribution of characters from the nodes A to E (Fig. 1A) is sufficient in order to express the phylogenetic relationships of H. corcolense n. sp.

The node A excludes the most primitive Elasmotheriina (i.e. K. bishopi, B. praecursor, C. oettingenae, B. caucasica and T. fangxianense). It defines the (H. grimmi (Node B)) clade. This node is strongly supported by three non-homoplastic synapomorphies (CI = RI = 1), thus justifying a generic distinction: an isolated hypocone on M1, a straight medial border on the radius diaphysis and low intermediate relieves on central metapodials. The protocone constriction on P3–4 (RI = 0.83) is further supporting the node A, together with four postcranial characters: proximal radio-ulna facets generally isolated, small trapezium-facet on the scaphoid, posterior tuberosity straight on the magnum, calcaneus-facet 1 generally wide and low on the astragalus.

The node B sets H. grimmi as the sister-group of the ((H. matritense, H. corcolense) (‘A.’ beonense (Node E)) clade. It is feebly supported by five homoplastic apomorphies: a sagittal lingual groove is present on the mandible, the foramen mandibulare is located above the neck line, the paracone fold is strong on M1–2, the metaconid constriction is absent on lower milk teeth and the proximal radio-ulna facets are always fused.

The node C isolates the (H. matritense, H. corcolense) clade, owing to two characters: the crista is generally absent on the upper molars and the anterior indentation on the medial side of the magnum is generally shallow.

The node D sets ‘A.’ beonense together with more evolved Elasmotheriina (i.e. node E). Three characters appear: the protocone and the hypocone are equally developed on P2, the calcaneus-facet 1 is always high and narrow on the astragalus and the calcaneus always bears a fibula-facet. This node is not very well supported.

At last, the node E is robustly setting apart B. tekkayai and more evolved Elasmotheriina (from Middle Miocene and later) from Hispanotherium. These taxa (i.e. B. tekkayai, B. borissiaki, P. mongoliense, H. lintungense, I. morgani, P. schansiense, S. lagrelii and Elasmotherium) share at least four dental synapomorphies: the crochet is always simple on P2–4, the posterior cingulum is continuous on M1–2, a lingual wall is present on D2, as a constricted entoconid on lower milk teeth (non-homoplastic synapomorphy: CI = RI = 1).

Apart from the cladistic analysis, which sets the phylogenetic relationships of H. corcolense as shown in Fig. 1, we have made a character-by-character comparison between H. corcolense and the closest Elasmotheriina, which are H. grimmi, H. matritense and ‘A.’ beonense. This comparison, restricted to the characters checked in the four taxa, is synthesized in Table 1 (split into seven subtables).

Eight features, shared by H. corcolense, H. matritense and ‘A.’ beonense, differ in H. grimmi (subtable a): the lingual groove present on the corpus mandibulae, the strong paracone fold on M1–2, the metaconid constriction on lower milk teeth and the proximal radio-ulna facets always fused are four synapomorphies located at node B (Fig. 1A). The presence of i2, the lacking of a medifossette on P3–4, the reduction of the posterior cingulum on M1–2 and the trigonid determining an acute dihedron on the lower cheek teeth further distinguish these three taxa from H. grimmi.

Eight characters rally H. corcolense, H. grimmi and ‘A.’ beonense, but exclude H. matritense (subtable b): the crochet generally simple on P2–4, the lingual wall absent on D2, the double paralophid on d3, the acute distal border of the semi-lunate, the straight posterior tuberosity of the magnum, and three characters on the MtIII (sigmoid proximal border, distally widened diaphysis and cuboid-facet present). Alternative character states define the autapomorphies of H. matritense (column 3).

Eight characters put H. corcolense, H. grimmi and H. matritense together in contrast with ‘A.’ beonense (subtable c): the protocone weaker than the hypocone and the continuous protoloph on P2, the protoloph–ectoloph connection on P3, the independence of the pyramidal- and McV-facets on the unciform, the posterior McII-facet always absent on the McIII, the TD/H ratio lower than 1.2 and the expansion of the calcaneus-facet 1, generally wide and low on the astragalus, and the weak development of the postero-lateral process on the ectocuneiform. Alternative character states correspond to the autapomorphies of ‘A.’ beonense (column 3).

Three features separate H. corcolense and ‘A.’ beonense from H. grimmi and H. matritense (subtable d): the lingual cingulum generally present on P2–4, the crista always absent on P3 (always present in H. grimmi and generally absent in H. matritense) and the fibula-facet concave on the astragalus.

Three characters bring together H. corcolense and H. matritense, with respect to H. grimmi and ‘A.’ beonense (subtable e): the crista generally absent on the upper molars, which is a synapomorphy of the node C (Fig. 1A), the posterior part of the ectoloph straight on M1–2 and the fibula-facet generally absent on the calcaneus (always absent in H. grimmi and always present in ‘A.’ beonense).

The absence of a lingual groove on the protocone of M2 is jointly characterizing H. corcolense and H. grimmi (subtable f), contrary to H. matritense (generally absent) and ‘A.’ beonense (always present).

At last, six characters define only H. corcolense, as autapomorphies (subtable g): the labial cingulum generally present on the upper premolars (while generally absent in other species); the antecrochet generally present on P4 (always absent in other species); the posterior valley sometimes closed on d2 (always open in other species); the glenoid fossa bearing a straight medial border on the scapula (oval otherwise); the generally shallow medial indentation on the magnum (the parsimony of which is interpreted as a synapomorphy acquired at the node C; Fig. 1A). This indentation is always shallow in H. matritense and always deep in both H. grimmi and ‘A.’ beonense; the expansion of the pyramidal-facet generally absent on the unciform (generally present in ‘A.’ beonense, always absent in both H. grimmi and H. matritense).

Various authors [6], [7], [8], [9], [10], [21] and [24] do consider that Early and Middle Miocene Elasmotheriina from Eurasia (i.e. Caementodon oettingenae Heissig, 1972, Beliajevina caucasica (Borissiak, 1935), Tesselodon fangxianense (Yan, 1979), Hispanotherium grimmi Heissig, 1974, Beliajevina tekkayai Heissig, 1974) should be included within the genus Hispanotherium. Meanwhile, other authors [2], [3], [4], [5], [12], [13], [15], [16], [17] and [18] assume that these taxa correspond to different species and/or genera.

The present work confirms the second opinion (Fig. 1): not only C. oettingenae, Beliajevina caucasica and Tesselodon fangxianense are excluded from Hispanotherium (Fig. 1A; node A), but Kenyatherium bishopi Aguirre and Guérin, 1974 and Bugtirhinus praecursor Antoine and Welcomme, 2000 are also much more primitive than Hispanotherium matritense, type species of the genus, and its closest relative (Fig. 1A). Still, the phylogenetic relationships within Elasmotheriina between the nodes B–D are not solved, but H. corcolense does represent a distinct species. At last, other Elasmotheriina from the Middle Miocene and later (i.e. B. tekkayai, B. borissiaki, P. mongoliense, H. lintungense, I. morgani, P. schansiense, S. lagrelii and Elasmotherium) are definitely more evolved than H. matritense and its closest relatives, as shown in Fig. 1A (node E).

All this leads us to put H. matritense, H. grimmi, ‘A.’ beonense Antoine, 1997 and H. corcolense n. sp. together within the genus Hispanotherium, in agreement with Antoine [3], but not with Antoine [2] and Antoine and Welcomme [4]. As noticed in Section 3 , the nodes B to D (Fig. 1A) are not supported enough to justify any generic distinction between the involved species. Thus, the genus Hispanotherium is paraphyletic, representing a grade within Elasmotheriina. Still the monophyly of (H. corcolense, H. matritense) cannot be excluded.

The earliest elasmotheriine, Bugtirhinus praecursor, is reported in the basal Miocene of Balochistan [3] and [4]. The following branches in the parsimonious trees successively lead to elasmotheriines restricted to Asia, Caucasus and Minor Asia (Anatolia). Thus, the group may have differentiated in Asia and dispersed westward throughout the Early Miocene. Hispanotherium or a close relative has probably joined Western Europe through Anatolian plate, as a consequence of the Eurasian and Arabo-African plates collision, also responsible for the major dispersal event named ‘Proboscidean Datum Event’ [22].

H. corcolense is so far restricted to the locality of Córcoles, which represents the oldest occurrence of an elasmotheriine in Iberia (MN 4a, zone C). So far, H. matritense only occurs in younger deposits (MN 4b and MN 5, zones DE) [3] and [21]. On the other hand, H. beonense occurs also during the MN 4a zone, in the French locality of Pellecahus, almost contemporaneous of Córcoles [5]. Its time range is extending up to the MN 4b and the MN 5 zones in the Aquitaine and Loire basins [2] and [3]. H. grimmi is so far restricted to the Middle Miocene of Anatolia [16], [17] and [18].

Thus, three distinct elasmotheriines have been recorded in Western Europe during the MN 4–5 zones: H. corcolense and H. beonense during the MN 4a zone; H. beonense and H. matritense during the MN 4b–MN 5 zones). H. beonense and H. matritense have been sympatric in the Loire Basin [3] and [14].