Dahutherium, Montenat, 1968

Moreau, Jean-David, Vullo, Romain, Bichr, Elsie, Thomas, Jérôme, Gand, Georges, Gagnaison, Cyril, Barrier, Pascal & Néraudeau, Didier, 2024, Crocodylomorph and dinosaur tracks from the lowermost Jurassic of Le Veillon (western France): ichnotaxonomic revision of the type material (Lapparent collection), Geodiversitas 46 (8), pp. 343-366 : 356

“ Dahutherium ” isp. (nomen nudum)

( Fig. 8 )

Dahutherium sp. – Lapparent & Montenat 1967: 13-14, pl. II, figs 5-5bis. — Montenat 1968: 373-35, pl. 1.4, 2.2-9. — Demathieu & Haubold 1972: 805, 818, 820, fig. 5.8. — Gand 1974a: 9-10, pl. 8A-D; 1974b: fig. 2G. — Haubold 1984: 150, 152, fig. 102.7.

EXAMINED MATERIAL. — ULB-04C15_A , ULB-04C18_B .

DESCRIPTION

Lapparent & Montenat (1967) described two isolated tracks including a tetradactyl pes track (ULB-04C18_B; Fig. 8 A-C) and a tridactyl manus track (ULB-04C15_A; Fig. 8 D-F) that were collected ex-situ. Our interpretation is that the track ULB-04C18_B described as a tetradactyl pes track byLapparent & Montenat (1967) actually represents two superimposed tridactyl grallatorid footprints ( Fig. 8 A-C). The smallest of the two superimposed tracks is longer than wide (L/W = 1.7), 12.2 cm long and 7.2 cm wide. The trace of digit III shows a long free part (L/D = 2.4). Impressions of digits are very well-defined, thin and elongated. The impression of digit III is longer than traces of digits II and IV. The trace of digits II is the shorter. At the base of the trace of digit IV, the position of the digito-metatarsal pad is more proximal than that of digit II. The divarication angle II-IV is 40°. Round to oval phalangeal pads and pointed marks of claws are well marked. The largest of the two superimposed tridactyl tracks is ≈ 14 cm long (value measured on a partial length of track, the apex of the trace of III being not well-marked), 12 cm wide. Impressions of digits are thin, elongated and separated. The divarication angle II-IV is 41°. The impression of digit III is the longest. ULB-04C15_A ( Fig. 8 D-F) is tetradactyl, not tridactyl as proposed by Lapparent & Montenat (1967). This track is quite wider than long, 3.0 cm long and 3.9 cm wide ( Table 1 ). Impressions of digits are short and their apices are rounded. Traces of digit I are poorly impressed whereas those of II-IV are well marked. Impression of digit III is the longest, and impression of digit I the smallest. The divarication angle of digits I-IV is 83°.

REMARKS

The ichnogenus “ Dahutherium ” was formally erected by Montenat (1968) based on material from the Middle Triassic of the Daüs Plateau (Ardèche, southern France). However, Lapparent & Montenat (1967) used this ichnotaxon (erroneously mentioned as “ Dahutherium Montenat, 1967 ”), which was not yet available at that time, for the assignment of two isolated tracks from Le Veillon (as “ Dahutherium ” sp.). Adding to the confusion, they also provided the main features characterising the ichnogenus “ Dahutherium ”: “ Medium-sized quadrupedal tracks; footprint dimensions = 120 × 80 mm. The difference in size and shape between manus and pes is very marked. The manus track is small, probably tetradactyl, although there are often only three digits observable. The pes is tetradactyl. The digit development order is the same as that of Batrachopus . The digit I, very reduced, let an inconspicuous imprint. The digits are oriented medially, little divergent, without differentiated claws (translated from French)”. Dahutherium has been reported from several Middle Triassic to Early Jurassic tracksites from France ( Montenat 1968; Haubold 1971; Gand 1974a, b). The smallest and the largest of the two superimposed tridactyl tracks (initially interpreted as a tetradactyl “ Dahutherium ” pes by Lapparent & Montenat (1967); ULB-04C18_B) can be ascribed to G. variabilis and Grallator isp., respectively. Although Lapparent & Montenat (1967) interpreted ULB-04C15_A as a tridactyl manus track of “ Dahutherium ”, the morphology and the dimensions of this specimen match with Batrachopus . Following Klein & Lucas (2021), “ Dahutherium ” is considered as a nomen nudum.

Figures

FIG. 8. — Tracks ascribed to Dahutherium sp. by Lapparent & Montenat (1967) and that are here reinterpreted: A-C, two superimposed tridactyl grallatorid footprints, ULB-04C18_B, photograph (A), interpretative sketch of Lapparent & Montenat (1967) (B), and our interpretation (C), showing a small footprint (dark grey) and larger footprint (light grey); D-F, Batrachopus isp., ULB-04C15_A, photograph (D), interpretative sketch of Lapparent & Montenat (1967) (E), and our interpretation (F). Scale bars: A-C, 5 cm; D-F, 2 cm.