Chicochoerus minus ( Golpe Posse, 1972 ) Orliac & Antoine & Duranthon, 2006

Orliac, Maeva J., Antoine, Pierre-Olivier & Duranthon, Francis, 2006, The Suoidea (Mammalia, Artiodactyla), exclusive of Listriodontinae, from the early Miocene of Béon 1 (Montréal-du-Gers, SW France, MN 4), Geodiversitas 28 (4), pp. 685-718 : 698-705

Chicochoerus minus ( Golpe Posse, 1972) n. comb. ( Figs 7 ; 8: 1-4; 9: 2, 4, 5)

Palaeochoerus minus Golpe Posse, 1972: 117 , pl. IV, fig. 4b, pl. V, fig. 5a.

Aureliachoerus minus – Van der Made 1998: 244, pl. 1. — Van der Made & Morales 1999: fig. 3.

HOLOTYPE. — Fragment of left maxilla with P4-M2 ( IPS 1417) figured by Golpe Posse (1972: pl. V, fig. 5a) from El Canyet ( Spain, Burdigalian; Golpe Posse 1972).

GEOGRAPHICAL RANGE. — Europe ( Spain, France, Austria).

STRATIGRAPHICAL RANGE. — Middle part of the Orleanian European Land Mammal Age (MN4), late early Miocene.

LOCALITIES. — El Canyet ( Spain), Can Canals ( Spain), Oberdorf (Styria, Austria), Seegraben (Styria, Austria), Béon 1 (Montréal-du-Gers, Gers, France), Pellecahus (Gers, France), La Romieu (Gers, France). The material from Wintershof West has also been referred to this species by Van der Made (1989-1990b, 1998; Van der Made & Morales 1999) and might well belong to C. minus .

MATERIAL EXAMINED. — Béon 1 (Montréal-du-Gers, MN4 , SW France), dental remains: from the same individual: M1 (r), MHNT Béon AR SN 19 ; M2 (r), MHNT Béon E3 95 ; M3 (r), MHNT Béon AR SN 16 ; portion of mandible with m2-m3 (r), MHNT Béon E3 67 ; isolated remains: Cm (l), MHNT Béon E 3 894 ; P4 (r), MHNT Béon AR SN 21 ; M2 (r), MHNT Béon AR SN 18 ; m3 (l), MHNT Béon E3 818 ; postcranial elements: astragalus (l), MHNT Béon F3 238 ; astragalus (r), MHNT Béon SN 4540 ; calcaneum (l), MHNT Béon E3 48 ; Mc III (r), MHNT Béon SN 4509 ; Mc III (r), MHNT Béon E 3 103 .

Pellecahus ( MN 4, Gers, SW France; Antoine et al. 2000b): left hemimandible with cm, p2-m3, MHNT Pel. 1 (Philippe Olivier collection, Toulouse; cast available at the MHNT).

DIAGNOSIS. — Small suid with simple lower premolars with sharp postcristids; p2 strongly asymmetrical with a convex precristid; size of p2 greatly reduced when compared to p3 and p4; p4 simple without a metaconid; lower molars with clear prefossids between the two anterior cusps, forming an internal basin; endocristids of both anterior cusps oriented posteriorly; endometacristid narrow without incipient endometaconulid; upper canine without incipient ventral enamel band, and slender compared to other Hyotheriinae .

DIFFERENTIAL DIAGNOSIS. — Small Hyotheriinae which differs from Aureliachoerus , Hyotherium and Xenohyus by its simpler lower molars with sharper postcristids; p2 strongly asymmetrical and without anterior enamel bud; p4 lacking a metaconid; lower molars with an internal basin in the anterior lophid and without an incipient endometaconulid; slender upper canine without incipient ventral enamel band.

1a 5a COMPARATIVE DESCRIPTION

Upper dentition (Figs 8: 2)

The upper cheek teeth are represented by an upper canine, a P4, and a complete molar row from Béon 1. The upper canine (MHNT Béon E3 894, Fig. 8: 2) has a shallow antero-dorsal groove (illustrated in Appendix 5: 2e); it is straight and slightly inflated on the lingual side; it is, however, strikingly slender for a hyotheriine suid. In Taucanamo Simpson, 1945 , there is no antero-dorsal groove, the upper canine is slightly twisted from the root to the apex, and the lingual side is flat. The P4 (MHNT Béon AR SN 21, Fig. 8: 3) was attributed to C. minus on the basis of the rectangular occlusal outline of the tooth, which is rounded in Taucanamo ( T. sansaniense MNHN Sa 4662 and T. grandaevum ; Chen 1984: pl. 3, figs 2, 3a). The tooth presents only one buccal cusp and the protocone lies in an anterior position, even anterior to the paracone. The P4 from El Canyet (IPS 1417) presents a well developed metacone, and the specimen (IPS 1416) from Can Canal has a more reduced one. A complete row of right upper molars is associated with a portion of right mandible bearing m2-m3. The quadratic occlusal outline of the teeth (Fig. 8: 4a) and the separated buccal roots indicate a suid condition. The separation of buccal roots is correlated with divergent anterior roots (Fig. 8: 4b, 10b); this character is interesting as a lot of specimens have lost their buccal roots so that it is impossible to say if they were fused or not. The anterior position of the preprotoconulid, which is fused to the anterior cingulum and is not included in the preprotocrista is also characteristic of suids ( Van der Made 1996a, b). The M3 MHNT Béon AR SN 16 presents a well developed talon with its own root.

Mandible and lower dentition ( Figs 7 ; 8: 1)

In the Béon 1 material, the lower dentition of Chicochoerus minus n. comb. is represented by an m2-m3 series (MHNT Béon E3 67, Fig. 8: 1) and an isolated m3 (MHNT Béon E3 818). A left hemimandible with cm and p2-m3 ( Fig. 7 ) from Pellecahus (MN4 according to Antoine et al. 2000b) greatly improves our knowledge of this species. The horizontal ramus is broken in front of the lower canine and the ascending ramus is miss- ing. The horizontal ramus is slender, but its height increases backwards. There is no trace of the vascular incisura; in Taucanamo and Palaeochoerus Pomel, 1847 , the height of the horizontal ramus does not increase backwards and even decreases at the level of the vascular incisura. On the buccal side, there is a deep masseteric fossa, which is shallower in Taucanamo ( T. sansaniense from Sansan MNHN Sa 4661; T. primum from Artenay, type specimen MNHN Ar 5). On the lingual side, the bone bulges under m3 (flat in Taucanamo ) whereas the ventral part bears a deep concavity and the ventral edge is recurved lingually.

The large and robust lower canine (MHNT Béon E3 894) is typical of a male. It is compressed labiolingually, as in Taucanamo , but the posterior face is less developed. The p1 is lacking, but its alveolus is preserved and it further indicates that there was neither postcanine diastema nor p1-p2 diastema. The lower cheek tooth row is shown in Figure 4C, D . The p2 is small when compared to p3 and p4 for all its measurements; this recalls Tetraconodontinae , but the latter present only low crowned p1-p2, whereas the length of the tooth remains consistent with p3-p4. The p2 of Chicochoerus minus n. comb. is strongly asymmetric with a short convex precristid and a long concave postcristid ( Fig. 4D ). There is no anterior enamel bud. The morphology of p2 differs markedly from that of A. aurelianensis from Artenay (MNHN Ar 2662): in A. aurelianensis , p2 is more symmetrical, the precristid is straight and there is a small anterior enamel bud. The p4 presents hyotheriine morphology, with a high precristid and no paraconid; the posterior accessory cusp is well developed but the metaconid only consists of a small bulge on the lingual part of the protoconid; this structure would disappear with wear. In A. aurelianensis , the metaconid is more developed.

The lower molars present high angular cusps ( Fig. 4C, D ); the internal crests are not developed, but the global aspect of the teeth is more sublophodont than in A. aurelianensis , in which the cuspids are more rounded. The endometacristid is slender and does not bear an incipient endometaconulid (secondary cusp originating from an important development of the endometacristid), in contrast to other Hyotheriinae which present a large en-

1a 1b

1c 1d dometacristid (see H. lacaillei n. sp., Fig. 3 : 4a). The two cusps of each lobe are, however, close to each other, whereas in Taucanamo and Doliochoerus they are well separated. The endoprotocristid is inflated, which reduces the space between the two anterior cusps and separates the prefossids from the groove at the junction of the preprotoconulid. In Taucanamo , the endoprotocristid is not inflated and the space between the anterior cuspids is wider. The anterior cusps of the lower molars are closer to each other in Chicochoerus minus n. comb. than in Taucanamo ; this determines a slight inflection in the buccal and lingual walls of the lower molars, separating the cusps from the base of the crown. In Taucanamo and Palaeochoerus , the lingual and buccal walls are straight. The prehypoconulid of Chicochoerus minus n. comb. is clearly separated from the hypoconid by a deep groove, still present with considerable wear; this groove is found in all other Hyotheriinae . The roots of the lower molars are clearly separated from cervix to apex (Fig. 8: 1c), as in hyotheriines in general ( Ginsburg 1974; Hellmund 1992) and even suids ( Van der Made 1996a). The enamel is slightly wrinkled horizontally, while it is vertically wrinkled in Taucanamo in unworn teeth or smooth when worn. The endoprotocristid and endometacristid of m2-m3 are low and well developed; they meet in the sagittal plane of the teeth. Anterior to the two endocristids, the two prefossids form a small internal basin. Such morphology of the anterior lophid differs from what is observed in Hyotheriinae (endometacristid much more developed than the endoprotocristid; no internal basin; this internal basin can also be weakly developed in some Taucanamo sansaniense ). The representatives of Taucanamo also differ from the small suid from Béon 1 both by the absence of deep prefossids and the presence of high endocristids in the anterior lophid. The prehypoconulid is transversely stretched, and clearly separated from the hypoconid by a deep groove, still visible on worn teeth, whilst the prehypocristid is strong and fused to the prehypoconulid in Taucanamo . On the buccal side of the teeth, there is a clear demarcation between the cusps and the inflated base of the crown, which increases the tooth width. In Taucanamo , the lingual wall is straight and the tooth therefore appears slender.

Postcranial skeleton

Forelimb. Mc III (Fig. 9: 4, 5): two Mc III fragments are attributed to Chicochoerus minus n. comb. on the basis of their small size and of the presence of a well developed median crest on the anterior surface of the distal trochlea which is lacking in palaeochoerids ( Van der Made 1996a, 1997a, 1998). The specimen MHNT Béon SN 4509 lacks the proximal end, but the shape of the diaphysis is congruent with that of a third metacarpal. The distal part of the diaphysis is not inflated as is the case in T. sansaniense (MNHN Sa 10895 from Sansan). MHNT Béon E3 103 corresponds to the proximal two thirds of the diaphysis of Mc III. The proximal surface slopes latero-posteriorly to a higher degree than in T. sansaniense . On the posterior side, the proximal facet and the posterolateral facet are separated by a small tuberosity, which confers a rounded shape to the posterior extension of the proximal facet. In T. sansaniense , the proximal facet and the postero-lateral facet contact each other and the posterior extension of the proximal facet is sharp.

Hindlimb. Astragalus (Fig. 9: 2): three small suoid astragali are known from Béon 1. Two of them are attributed to C. minus (MHNT Béon F3 238, SN 4540) notably on the basis of: 1) the orientation of the crest lining the medial border of the sustentacular facet, which is straight as in Hyotherium ; and 2) the large concavo-convex facet corresponding to the coracoid process of the calcaneum on the lateral side. In Taucanamo sansaniense , the medial crest is more oblique, restricting the distal surface of the facet and the contact with the coracoid process of the calcaneum is more simple (comparative sample of 15 astragali, specimens Sa 4632-38; 4640-44; 7802; 9319; 10749 from the type locality Sansan). The cuboid-facet represents a small portion of the distal trochlea: the P index ( Dehm 1934) is superior to that of the specimen attributed to the small Taucanamo grandaevum , the value for both specimens of C. minus is P = 33.9. This value is within the 33.0-36.5 range measured on the three specimens of A. aurelianensis from Artenay (MNHN Ar 2789, 2790, 2791) and within the 32.7-36.5 range measured on a 15-specimen sample from Sansan.

Calcaneum (Fig. 9: 3): the shape of the sustentaculum tali posterior face of MNHN Béon E3 348, which slopes laterally, clearly indicates that it is a suoid and not a small ruminant. It is allocated to the genus Chicochoerus n. gen., on the basis of its small size and because of the complex concavoconvex contact with the astragalus on the coracoid process. This contact appears to be simpler in Taucanamo (astragalus from Sansan) and Palaeochoerus (MNHN SG 133390, 9862). The lateral edge of the sustentaculum tali is thin; there is no thickening to guide the tendon of the peroneus longus muscle. The extension of the bone from the sustentacular facet to the distal end is reduced when compared to A. aurelianensis (MNHN Ar 2792, Artenay) and to Sus scrofa . The posterior extremity of the tuber calcanei is sub-circular in dorsal view, whereas in H. lacaillei n. sp. the antero-posterior breadth exceeds the medio-lateral breadth.

DISCUSSION

At Béon 1, small-sized suoid specimens can clearly be assigned to two distinct taxa: one is related to the Palaeochoeridae and the other to the Suidae . If some features can clearly differentiate suids from palaeochoerids, such as the anterior development of the median crest on the distal part of the metapodials, it is, however, more difficult to assign isolated and fragmentary elements to a given group.

Until this study, two species were included in Aureliachoerus , A. aurelianensis and “ A. ” minus , the former being the type species. Here, “ A. ” minus is removed from Aureliachoerus and considered to be the type species of Chicochoerus n. gen. The smaller suid from Béon 1 presents the same lower cheek tooth morphology as that from Oberdorf, previously referred to “ Aureliachoerus ” minus ( Van der Made 1998: pl. 1, figs 1-5). Tooth measurements are also congruent, even if the specimen from Pellecahus is somewhat larger. Comparison to the type material of “ Palaeochoerus minus ” from El Canyet (MN4, Spain) is more difficult because the type specimen is considerably worn. However, morphology of the material from the type locality and from Can Canals (IPS 1415) is also congruent. Van der Made (1989-1990b, 1998; Van der Made & Morales 1999) differentiated “ A. ” minus from A. aurelianensis on the basis of the smaller size of the former and of the absence of a posteriorly elongated talonid on m3. Golpe Posse (1972, 1981) referred the species to the genus Palaeochoerus . Later, the material from El Canyet and Can Canals was included in Aureliachoerus aurelianensis by Hellmund (1992: 23). Indeed, dental and postcranial characters indicate without doubt that this taxon is a suid. Yet the lower cheek tooth morphology is markedly different from that of the type species Aureliachoerus aurelianensis and resembles the palaeochoerid condition: the lower male canine is slender; the morphology of the lower premolars is simpler than in A. aurelianensis , with no metaconid in the p4, no posterior accessory cusps in the p3, and asymmetrical p2 without anterior enamel bud. The buccal and lingual cusps of lower molars are not as closely apposed as in A. aurelianensis and the endometacristid is more reduced, without incipient endometaconulid. However, the small size of the second premolar in respect to the third one is a hyotheriine character (see part “Results and systematic implications”).

The smallest Miocene European suids are usually referred either to Albanohyus Ginsburg, 1974 or to Aureliachoerus . A third genus, Barberahyus Golpe Posse, 1977 , is considered to be a junior synonym of Albanohyus by Van der Made (1996a). The small suid from Béon 1 differs from Albanohyus by the following characters: 1) the male upper canine of C. minus presents only two enamel bands and has no trace of the ventral one, whereas in Albanohyus the morphology is derived with a fully developed ventral enamel band (MHNL LGr 6003, La Grive-Saint-Alban, MN7-8; Van der Made 1996a: fig. 3E); 2) the lower canine of C. minus is slender whereas in Al. castellensis (Golpe Posse, 1977) , it is wide; 3) p2 is much smaller than p3 and p4, in contrast to what occurs in Al. castellensis ; 4) the p4 of C. minus lacks a metaconid whereas it is developed in Al. castellensis ; and 5) in m2-3, the two prefossids of the first lobe form a basin which is lacking in both Albanohyus pygmaeus ( Deperet, 1892) and Al. castellensis .

The material from Béon 1 is similar to the small suid found in Can Canals and El Canyet but it cannot be referred to Aureliachoerus neither to Albanohyus . This statement, together with the results of the phylogenetic analysis (see part “Results and systematic implications” of the phylogenetic analysis), lead to the creation of a new genus.

Family PALAEOCHOERIDAE Matthew, 1924 Subfamily SCHIZOCHOERINAE Golpe Posse, 1972 Genus Taucanamo Simpson, 1945

Figures

FIG. 7. — Mandible of Chicochoerus minus n. comb., MHNT Pel. 1 (cast) from Pellecahus (Gers, France, MN4): A, buccal view; B, occlusal view; C, lingual view. Scale bar: 2 cm.

FIG. 4. — A, B, lower cheek tooth row of the type specimen of Hyotherium lacaillei n. sp. (MHNT Béon 2003 H5-4) from Béon 1 (Montréal-du-Gers, Gers, France, MN4); A, occlusal view; B, buccal view; C, D, lower cheek tooth row of Chicochoerus minus n. comb. (MHNT Pel. 1) from Pellecahus (Gers, France, MN4); C, occlusal view; D, buccal view. Scale bars: 2 cm.

FIG. 3. — Isolated dental remains of Hyotherium lacaillei n. sp. from Béon 1 (Montréal-du-Gers, Gers, France, MN4): 1, left p1, MHNT Béon G4 537 (a, buccal; b, posterior; c, lingual; d, anterior); 2, left i1, MHNT Béon 92 G3 1170 (a, lingual; b, mesial); 3, right i2, MHNT Béon 93 G4 468 (a, lingual; b, mesial); 4, left m2-m3, MHNT Béon AR SN 6, MHNT Béon AR SN 4 (a, occlusal; b, lingual); 5, left I1, MHNT Béon 92 G3 111 (a, lingual; b, distal); 6, left I2, MHNT Béon AR SN 2 (a, mesial; b, lingual; c, distal; d, labial); 7, right I3, MHNT Béon AR SN 3 (a, mesial; b, lingual; c, distal; d, labial); 8, right Cm, MHNT Béon AR SN 1 (a, lingual; b, anterior). Scale bars: 1-5, 8, 2 cm; 6, 7, 1 cm.