Taucanamo grandaevum ( Fraas, 1870 )

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 : 705-706

Taucanamo grandaevum ( Fraas, 1870) (Figs 8: 5-10; 9: 1)

MATERIAL EXAMINED. — From the same individual: p4 (l), MHNT Béon AR SN 9 ; p4 (r), MHNT Béon AR SN 8 ; mandibular fragment with m1 (r), MHNT Béon AR SN 12 ; m1(l), MHNT Béon AR SN 11, mandibular fragment with m2-m3 (l), MHNT Béon AR SN 7 ; isolated cranio-dental elements: mandibular fragment with p1 (r), MHNT Béon F2 627 ; p2 (r), MHNT Béon AR SN 10 ; mandibular fragment with p3 (r), MHNT Béon E3 37 ; Cm (r), MHNT Béon E 3 86 ; M2 (l), MHNT Béon AR SN 15 associated with M3 (l), MHNT Béon AR SN 17 ; cm (r), MHNT Béon SN 201 ; m2 (l), MHNT Béon AR SN 14 ; m3, MHNT Béon AR SN 13 (l) ; postcranial elements: astragalus (l), MHNT Béon 321 ; Béon 1, Montréal-du-Gers ( MN4 , SW France) .

STRATIGRAPHICAL AND GEOGRAPHICAL RANGE. — Late early to late middle Miocene ( MN 4 to MN 7-8) of Western Europe ( Germany, France). T. grandaevum is not documented during the MN 5 and MN 6 zones.

COMPARATIVE DESCRIPTION

Upper dentition (Fig. 8: 9, 10)

The upper canine (MHNT Béon E3 86, Fig. 8: 9) is highly compressed, with slight torsion from the root to the tip and it only presents two enamel bands (i.e. the ventral one is lacking). The anterior edge is sharp, and its dorsal part does not present the groove that is present in Hyotheriinae . The posterior edge bears a sharps crest of enamel.

The occlusal outline of M2 is rectangular whereas it is more quadrate in Chicochoerus n. gen. (Fig. 8: 10a); the lingual wall of the tooth is not sloping laterally but is straight as in other species of Taucanamo . The associated M3 displays a reduced third lobe and a very small metacone. The lingual roots being absent, it is impossible to determine whether they were fused or not. However, considering the vertical orientation of the lingual roots and the vertical lingual wall of the crown (Fig. 8: 10b), it is likely that the lingual roots where also vertical and fused (suid roots in contrast flare outward and are separated, Fig. 8: 4b). The upper molars are smaller than in T. sansaniense and the M2 is slightly wider than that of T. grandaevum from Steinheim ( Fig. 10E, F ).

Lower dentition (Fig. 8: 5-8)

A partial mandible, split into several fragments, contains p4-m3 (MHNT Béon AR SN 9, MHNT Béon AR SN 8, MHNT Béon AR SN 12, MHNT Béon AR SN 11, MHNT Béon AR SN 7). The tooth enamel is smooth. The p1 is uniradiculate and caniniform, high and narrow-crowned (Fig. 8: 6). The p2 is a very simple tooth with a high straight cuspid sloping lingually, a short precristid and a low simple postcristid without differentiated accessory cusps (Fig. 8: 7). The posterior cingulum forms a small bud. The p4 is also very simple, with one major cuspid and a reduced incipient metaconid, erased after slight wear (Fig. 8: 8). There is no paraconid, the postcristid is short and low, and the posterior accessory cuspid is reduced compared to that of Taucanamo sansaniense . Anterior, posterior, and buccal cingula are weakly developed. The lower molar dimensions overlap the size range of T. sansaniense from Sansan ( Fig. 10 B-D), while the premolars are smaller and correspond to the size of T. grandaevum from Steinheim (type locality, MN7; Fig. 4A ; Chen 1984). The cuspids are pointed and present sharp angles (Fig. 8: 5). On each lobe, the cuspids are well separated, with wide intermediate grooves. The lingual and buccal roots of each lobe are fused (Fig. 8: 5b). Buccal and lingual walls are continuously convex and there is no demarcation at the cervix. The preprotocristid is reduced in comparison to Aureliachoerus .

Postcranial elements

Astragalus (Fig. 9: 1): the astragalus MHNT Béon 321 is here referred to T. grandaevum by comparison with specimens from Sansan referred to T. sansaniense (specimens Sa 4632-38; 4640-44; 7802; 9319, 10749). Even if MHNT Béon 321 is wider (transverse diameter) than MHNT SN 4541 and MHNT SN 4540 (here attributed to Chicochoerus minus n. comb.), which recalls Hyotherium , the crest lining the medial border of the sustentacular facet is oblique in contrast to Hyotherium , and the sustentacular facet is convex in its dorsal part. The cuboid facet represents a small portion

A B

of the distal trochlea. The P index ( Dehm 1934) equals 30.6, i.e. less than in Taucanamo sansaniense from Béon 1 (P = 33.9) and from the type locality, Sansan (15 specimens, with values ranging from 32.7 to 36.5).

DISCUSSION

Colobus grandaevum from Steinheim (MN7, Germany) was named by Fraas (1870) and misidentified as a small primate. Subsequently, Stehlin (1899 - 1900) recognised that the specimens belong rather to Suidae and placed the material in Choerotherium pygmaeum ( Depéret, 1892) ; Simpson (1945) moved Choerotherium Lartet, 1851 into the Tayassuidae and changed the generic name to Taucanamo . However, as noticed by Van der Made (1996a), the generic name Choeromorus Gervais, 1852 has priority over Taucanamo , but as Taucanamo has been widely used since 1945 ( Ginsburg 1974; Pickford 1976; Pickford & Ertürk 1979; Chen 1984; Fortelius & Bernor 1990; Van der Made 1997a; Liu 2003), it will be applied here to promote nomenclatural stability as recommended by the International Code of Zoological Nomenclature ( ICZN 1999: Art. 23). Depéret (1892) named the species Choerotherium pygmaeum for a small suoid from La Grive Saint-Alban (MN7-8; Isère, France), but Van der Made (1996a) demonstrated that the holotype belongs to the small suid genus Albanohyus erected by Ginsburg (1974) for the same material. However, the material from Steinheim as a whole can be referred to Taucanamo as a species different from the type species Taucanamo sansaniense ( Chen 1984; Fortelius & Bernor 1990). The size difference between T. sansaniense from Sansan and the Taucanamo from Béon 1 is clear in the premolars and upper molars and slight in the lower molars ( Fig. 10 ). Chen (1984) detailed the major differences between the material from Steinheim and Sansan, considered as two different species: the Taucanamo from Steinheim is slightly smaller; the P4 is less molariform; the upper molars are rectangular whereas in T. sansaniense they are quadrate; the Cm-P1 and P1-P2 diastemata are small; the talonid of p3 and p4 consist of an elevated cuspid with a clear elevated cingulum on the postero-external side; the talonid of m3 is shorter and simpler in Taucanamo from Steinheim. Later, Fortelius & Bernor (1990) suggested that Taucanamo grandaevum should be the valid name for the Steinheim material. In his revision of Taucanamo, Van der Made (1997a) agrees and extends the hypodigm of T. grandaevum to the material from La Grive and Anwill (MN7-8); he named T. primum for early material originating from MN4 localities (Artenay, Bézian, and Els Casots).

There is no question about T. primum being clearly different from T. grandaevum . On the one hand, the Taucanamo from Béon 1 and T. primum are not only coeval but also morphologically distinct: some clear morphological differences exist between the holotype from Artenay and comparable material from Béon 1: the lower molars are simpler in Béon 1, the cusps are smaller and more rounded in T. primum , the buccal cingulum is absent in Béon 1, and the pentaconid on m2-m3 is reduced in T. primum ( Fig. 11 ). On the other hand, the Taucanamo from Béon 1 and T. grandaevum are distinct from a stratigraphical point of view, but very similar morphologically, thus justifying referring the Béon 1 material to T. grandaevum , and extending its stratigraphical range down to the middle Orleanian ELMA (MN4).

Figures

FIG. 10. — Scatter plots of the dental dimensions of Taucanamo primum from Artenay (type locality;�), T. grandaevum from Steinheim (type locality; ×), Bézian (□), Els Casots (▲), and Béon 1 (○), and Taucanamo sansaniense from the type locality of Sansan (■). Abbreviations: B, maximum tooth breadth; L, tooth length.

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. 11. — Comparison of the lower molars of: A, Taucanamo primum (holotype MNHN Ar 5); B, Taucanamo grandaevum from Béon 1 (Montréal-du-Gers, Gers, France) (MHNT Béon1 AR SN 7, SN 11). Abbreviations: bc, buccal cingulum; td, talonid. Scale bar: 2 cm.