Coringasuchus anisodontis, Kellner, Alexander W. A., Pinheiro, André E. P., Azevedo, Sergio A. K., R, Deise D., Carvalho, Luciana Barbosa De & Oliveira, Gustavo R., 2009

Kellner, Alexander W. A., Pinheiro, André E. P., Azevedo, Sergio A. K., R, Deise D., Carvalho, Luciana Barbosa De & Oliveira, Gustavo R., 2009, A new crocodyliform from the Alcântara Formation (Cenomanian), Cajual Island, Brazil, Zootaxa 2030, pp. 49-58 : 50-51

Coringasuchus anisodontis sp. nov.

Holotype: MN 7128-V ( Figs. 3-5 ), partial right lower jaw (dentary) housed at the Department of Geology and Paleontology of the Museu Nacional/Universidade Federal do Rio de Janeiro.

Etymology: The specific name is derived from the Greek anisos (unequal, irregular) and odontos (tooth), in allusion to the odd variation of alveolar morphology that indicates a strongly heterodont dentition in the new taxon.

Locality: Laje do Coringa, on the most eastern beach of Cajual Island, Maranhão State, Northeast Brazil, about 25 km west of São Luís. The specimen was found as surface float (UTM coordinates 2070559882 / 9726080).

Horizon and age: Alcântara Formation, Itapecuru Group, São Luís Basin, earliest Late Cretaceous (early Cenomanian).

Diagnosis: Mesoeucrocodylian with the following combination of characters that distinguish it from other members of this group: strong size variation of dentary teeth; comparatively small anterior rounded alveoli followed by larger elliptical alveoli; main axis of elliptical alveoli directed anterolingually-toposterolabially; some, but not all, alveoli distinctively raised above the level of the dorsal margin of the dentary.

Description. The holotype of Coringasuchus anisodontis consists of an incomplete right mandibular ramus. Based on general morphology the preserved part appears to be from close to the posterior end of the mandibular symphysis ( Figs. 3–5 ). The preserved part of the alveolar margin is 29.6 mm long, the maximum preserved height is approximately 23 mm, and the maximum transverse width (at the anterior end) is approximately 10.5 mm. The specimen has a dark brownish color, which is typical of fossils from the Laje do Coringa site. Despite having the margins and teeth broken, there are no signs of deformation that could have altered the shapes of the alveoli. Some parts of the element have been abraded and the external bone surface is slightly damaged, suggesting that this specimen was freed from the matrix and laid exposed as surface float for some time prior to collection, an interpretation supported by the presence of encrusting bivalves (removed from the specimen). Based on the nature of the broken edges, MN 7128-V was likely more complete before being exposed and broken by wave action.

The dentary is the sole bone preserved. The lateral surface ( Fig. 3 A–B) is smooth and lacks strong ornamentation. Some occlusal scars, made by the contact of the upper dentition with the lower jaw, are present. At the posterior preserved end the lateral surface is flat or slightly concave and becomes gradually more convex towards the anterior end. Neurovascular foramina are not visible on the lateral surface, which is possibly a taphonomic artefact. The medial surface ( Fig. 3 C–D) is gently convex and shows scars (weakly preserved) and fractured areas. The splenial is not preserved and the position of the dentary-splenial suture could not be identified with certainty. Several small neurovascular foramina are found scattered on the medial surface ( Fig. 3 D).

The occlusal view ( Figs. 4–5 ) provides the most important anatomical information. No complete teeth are preserved, but the position of the alveoli demonstrates that the teeth were located close to the medial margin. At the preserved anterior end, the lateral border is quite broad and slightly concave, indicating that some of the teeth were slightly displaced medially.

Five alveoli (four of which contain part of the tooth root in place) are preserved and the remnant of a possible sixth alveolus is also present ( Fig. 3 ). The specimen is broken at the first preserved alveolus, exposing a thin layer of the dentine of the root. The second alveolus is sub-circular (diameter of approximately 4.3 mm) and is raised above the level of the dorsal margin of the dentary. The third alveolus ( Fig. 5 ) is also subcircular (diameter of approximately 3 mm) but much smaller than the more anterior ones. In alveoli two and three a cross-section through the tooth exposes the enamel, dentine and the pulp cavity. The fourth alveolus ( Fig. 5 ), the only one that lacks part of the root, is larger than the preceding ones, and has an elliptical shape with the long axis directed lingually at approximately 60 degrees to the long axis of the dentary. The fifth alveolus is also elliptical and raised above the level of the dorsal margin of the dentary. It is the largest of all those preserved and possesses the same general inclination of its long axis as alveolus four but at a much lower angle (approximately 10 degrees to the long axis of the dentary). The medial portion of the fifth alveolus is broken exposing part of the enamel and dentine of the tooth. The root of this tooth is quite long relative to the height of the lower jaw, a common feature in crocodylomorphs. A small concavity at the posterior preserved end of the jaw indicates the presence of another alveolus.

Figures

FIGURE 3. Photographs and drawings of the lower jaw of Coringasuchus anisodontis gen. et. sp. nov. (MN 7128 - V) in lateral (A, B) and medial (C, D) views. Scale bars = 10 mm. Anatomical abbreviations: a 1 - a 5, alveoli; a 6?, alveolus?; d, dentary; fa, fractured area. Neurovascular foramina are indicated in the circles.

FIGURE 4. Photographs and drawings of the lower jaw of Coringasuchus anisodontis gen. et. sp. nov. (MN 7128 - V) in occlusal view (A, B). Scale bars = 10 mm. Anatomical abbreviations: a 1 - a 5, alveoli; a 6?, alveolus?; e, enamel; lab, labial dentary process; os, occlusal scar.

FIGURE 5. Photograph of the lower jaw of Coringasuchus anisodontis gen. et. sp. nov. (MN 7128 - V) showing occlusal view of the third and fourth preserved alveoli. Scale bar = 5 mm.