Charruodon tetracuspidatus, Abdala & Ribeiro, 2000

Abdala, Fernando & Ribeiro, Ana Maria, 2000, A new therioherpetid cynodont from the Santa Maria Formation (middle Late Triassic), southern Brazil, Geodiversitas 22 (4), pp. 589-596 : 590-592

Charruodon tetracuspidatus n. sp. ( Figs 2 ; 3 ; Tables 1; 2)

HOLOTYPE. — Fragment of the left dentary horizontal ramus, with alveoli for three incisors, roots of the canine and three postcanines, and a fifth tooth with a well-preserved crown ( Figs 2 ; 3 ) (MCP-3934 PV).

ETYMOLOGY. — tetracuspidatus , in reference to the four-cusped crown morphology.

LOCALITY. — 29°42’07.44’’S, 52°51’43.95’’W, approximately 8 km West of the city of Candelaria in the State of Rio Grande do Sul, southern Brazil.

HORIZON. — Santa Maria Formation. The presence of Exaeretodon and Proterochampsa here is strongly suggestive of a Carnian age for this stratum of the formation (Rogers et al. 1993).

DIAGNOSIS. — Lower jaw with a high horizontal ramus when compared with the postcanine size, approximately 0.31 with respect to the anteroposterior length of the crown of the fifth postcanine; four welldeveloped cusps on the crown of the postcanine; second cusp “a” is the largest, followed closely in size by the third (“c”); the three posterior cusps (“a”, “c” and “d”) are directed posteriorly; a sharp constriction distinguishes the crown from the root; roots undivided.

DESCRIPTION

The dentary fragment extends from an open and high symphysis to the level of the third postcanine ( Fig. 2A, B ). There are three alveoli for the incisors. The root of the canine is larger than those of the incisors and postcanines, but has undergone some transverse compression during fossilization. The mental foramen is located at the level of the second postcanine, and closer to the symphysis are some nutritive foramina ( Fig. 2B ). Three postcanines are represented only by their roots. All ap- pear relatively small compared with the anterior height of the jaw. Originally, the region preserved extended as far posteriorly as the fifth alveolus, which contained a replacing tooth that preserved a complete crown. This tooth was isolated and prepared in order to examine its crown morphology ( Fig. 3 ). Four aligned cusps are present and there is no indication of a cingulum. The main cusp “a” is slightly larger than the first posterior accessory cusp “c” from which it is separated by a notch. Both of these cusps are slightly recurved posteriorly. The second posterior accessory cusp “d” is the lowest. It is posteriorly directed and wellseparated from cusp “c” by a notch. The anterior accessory cusp “b” is relatively small and closely united with the main cusp by a high crest. In occlusal view, the crown is bulbous, with convex labial and lingual sides, the latter being particulary rounded. The root is undivided and distinguished from the crown by a prominent constriction.

Total length of specimen 23.5 Height at the level of the first postcanine 15.2 Anteroposterior length of the root of the canine 5.0 Anteroposterior length of the root of postcanine 1 2.8 Anteroposterior length of the root of postcanine 2 3.0 Anteroposterior length of the root of postcanine 3 3.0 Crown length 4.8 Crown height 3.0 Crown width 1.8

Figures

FIG. 2. — Stereo pair and line drawing of the mandibular ramus of Charruodon tetracuspidatus n. sp. (MCP-3934 PV); A, labial view; B, lingual view. Scale bar: 10 mm.

FIG. 3. — Fifth tooth of Charruodon tetracuspidatus n. sp. (MCP-3934 PV); A, labial view; B, lingual view; C, crown view. Scale bars: 10 mm.