Caryonosuchus pricei, Kellner & Campos & Riff & Andrade, 2011

Kellner, Alexander W. A., Campos, Diogenes A., Riff, Douglas & Andrade, Marco Brandalise De, 2011, A new crocodylomorph (Sphagesauridae, Notosuchia) with horn-like tubercles from Brazil, Zoological Journal of the Linnean Society 163 (5), pp. 644-645 : 644-645

CARYONOSUCHUS PRICEI GEN. ET SP. NOV.

Holotype: Anterior portion of the skull and lower jaw housed at the Earth Science Museum of the Departamento Nacional da Produção Mineral under the number DGM 1411 - R (cast at the Museu Nacional/ UFRJ) ( Figs 1–4 ).

Etymology: The specific name honours Llewellyn Ivor Price, a palaeontologist who described the genus Sphagesaurus and also had a partial (unpublished) manuscript on the specimen DGM 1411- R ( Kellner et al., 1995).

Type locality: Vicinity of Presidente Prudente City, south-west São Paulo State, Brazil.

Type horizon: Adamantina Formation, Bauru Group; Campanian to Maastrichtian ( Gobbo-Rodrigues, Petri & Bertini, 1999, Batezelli et al., 2003).

Diagnosis: Sphagesaurid that can be separated from all other members of this clade based on the following combination of characters (autapomorphies are indicated with an asterisk): rostrum with horn-like tubercles on the premaxilla* and on the maxilla*; rostrum showing rough ornamentation with grooves and bony ridges*; first tooth posterior to the premaxillary hypercaniniform is supported exclusively by the premaxilla; palatine ramus of maxilla covered by low crests and shallow wrinkles; shallow fossa present at symphysis, medial to the first three teeth.

Remarks: Kellner & Campos (1999) briefly mentioned the specimen DGM 1411- R and tentatively assigned it to Sphagesaurus sp. , but in the light of new sphagesaurid material recently described in the literature, we regard this specimen as representing a new genus and species.

Description

The holotype of Caryonosuchus pricei ( DGM 1411 - R) consists of the anterior portion of the rostrum, whose bone surface is extremely well preserved ( Fig. 1 ). The upper jaw shows both premaxillae and maxillae, with opposite elements unfused. The nasal is missing, exposing the internal region of the external naris. The tip of the dentary that was originally preserved in close contact with the upper jaw was separated during mechanical preparation. The upper teeth are in their natural position whereas several teeth of the lower jaw were displaced anteriorly during the fossilization process .

Premaxilla: The right premaxilla is more complete than the left and includes the palatine ramus ( Fig. 1 ). This bone has an anterodorsal flange partially covering the external naris that forms a lateral notch. This flange is strongly ornamented, as is the dorsal part of the premaxilla. Two well-developed and ornamented horn-like tubercles are present. On the area of the tubercles, the ornamentation is composed of semicircular well-delimited deep pits and differs from the remaining part of the rostrum. Dorsally, near the suture with the nasal, the pits become shallower, less defined, and elongated, turning into an area covered by elongated sulci and crests that are orientated diagonally in respect to the sagittal plane.

Part of the internal surface of the right nasal cavity is preserved, more extensively than its left counterpart. Although the bone surface is smooth, there is a small area that is lightly ornamented.

The alveolar margins lack ornamentation. The left premaxilla shows one neurovascular foramen located laterally, in an area above the middle point between the first and the second premaxillary teeth. A second and smaller foramen is located posterodorsally, close to the suture with the maxilla.

The right palatine ramus of the premaxilla also shows light ornamentation, with a small foramen medial to the second tooth.

Premaxillary dentition: Two teeth are present in both premaxillae, all incomplete, showing oblique implantation as a result of paramesial rotation ( Fig. 2 ). The first tooth on the left side shows a partial crown and the root, and most probably was a hypertrophied caniniform. The second tooth is entirely supported by the premaxilla.

Maxilla: Both maxillae are incomplete, with the right one better preserved than the left ( Fig. 1 ). This bone partially overlies the premaxilla, a common feature in notosuchids (including other sphagesaurids). As in the premaxilla, the maxilla has the dorsal side heavily ornamented and the lateral side smooth, particularly close to the alveolar margin. At least two tubercles can be identified, which are smaller than the ones found in the premaxilla. The first is horizontally aligned with the two first ones whereas the second is located dorsally and medially in respect to those.

On the left maxilla there are five neurovascular foramina positioned above the alveolar margin, forming an anterodorsally arched line. The two anterior-most foramina are located dorsal to the first maxillary tooth and the following are dorsal to the second maxillary tooth. On the right maxilla, the neurovascular foramina are arranged in a more irregular way. The palatine ramus is laterodorsally displaced, and has light but evident ornamentation composed of low crests and shallow wrinkles. Another series of six neurovascular foramina can be identified next to the teeth, on the right maxilla. These foramina are located medially to the teeth, in couples.

Maxillary dentition: There are three teeth preserved in each maxilla, but the third on the left side was damaged during the fossilization process ( Fig. 2 ). All are obliquely implanted with each tooth having the posterolingual portion of the crown ending in a carina and the anteriolabial margin rounded, resulting in a teardrop cross-section. None of the roots are exposed.

The first maxillary tooth on the left side is better preserved than the one on the right side. The apex and part of the lingual portion are not complete. On the labial face, seven undivided ridges that reach the apex of the tooth are present. Smaller ridges, restricted to the base of the crown can also be observed. On the lingual face there are remnants of only five ridges in the mesial-most section, whereas the remaining surface is destroyed. On both faces, the ridges are smooth, but the enamel is clearly ornamented in a pebbled pattern. Part of the root is dorsally exposed, showing an elliptic cross-section and oblique orientation, supporting the idea that this tooth has undergone paramesial rotation rather than a simple rearrangement of the crown.

Part of the enamel on the second maxillary tooth of the left side has been lost, exposing the dentine. The folded pattern shows that the ridges observed on the teeth express a structural characteristic of the crown, rather than a superficial ornamentation restricted to the enamel. As in the preceding tooth, seven main ridges are present in the labial face and five occur on the lingual side, again complemented by smaller ridges that do not reach the apex. The distance between ridges increases from the posterolingual to the anterolabial edges of the crown. The apex has a rounded shape. A wear surface is present, extending from the apex to the mid-length of the carina. No denticles or pebbled ornamentation can be identified on this surface. This worn down surface is neither a preservation artefact nor created during the collecting or preparation processes, but was produced in vivo, as the animal processed food. A similar wear surface is observed on the second maxillary tooth of the right side. This tooth has up to nine basiapical ridges on the labial surface of the crown.

On the third maxillary tooth of the right side, six labial and up to three lingual ridges can be identified. This crown shows a posterior carina, with an undulated basal section that lacks denticles, and an apical section that displays three denticles. No wear surface is observed.

Mandibular symphysis: Only the anterior end of the mandibular symphysis is preserved ( Fig. 3 ). The ventral surface is eroded, suggesting that this portion of the specimen was exposed before collection. The anterior-most section is narrow and widens posterior to the third tooth. A concavity is present close to the anterior tip of the symphysis, positioned medial to the first three teeth. It is shallow, longer than wide, and unknown in other sphagesaurid specimens (including RCL 100).

Mandibular dentition: The right side of the symphysis holds three conical teeth and part of one crown ( Figs 3 , 4 ). The first three pairs are mostly procumbent, as in other sphagesaurids and notosuchids. They are very inclined, which is attributed to the taphonomic compression suffered by the specimen during the fossilization process. All teeth bear isomorphic, smooth, and nonserrated basiapical ridges and an apical wear facet, which is small and inclined.

Only the apical section of the fourth tooth of the right side is preserved, displaced from its original anatomical position ( Fig. 4C ). The apex is clearly compressed, consistent with the reversed teardrop morphology typical of sphagesaurids. Additionally, this tooth bears at least three lateral ridges and a carina. Although the medial and basal portions of the carina are not preserved, it is possible to identify three conspicuous denticles in the preserved section. These are proportionally large when compared with the denticles of other ziphosuchian crocodylians, and correspond to what Prasad & Broin (2002) classify as true denticles. However, these denticles are tuberous and do not correspond to the typical cuneiform morphology found in theropodomorph dentitions of highly predacious crocodylomorphs (e.g. Baurusuchus, Stratiotosuchus, Sebecus ). They are rather similar to the denticles of Mariliasuchus , corresponding to the ziphomorph pattern sensu Andrade & Bertini (2008c).

Figures

Figure 1. Caryonosuchus pricei gen. et sp. nov. (DGM 1411-R), rostrum in lateral (top), medial (middle), and ventral (bottom) views. Note that the right side of the specimen (A) is better preserved than the left side (B). Scale bar = 20 mm.

Figure 2. Ventral view of the right (A) and left (B) sections of the upper jaw of Caryonosuchus pricei gen. et sp. nov. (DGM 1411-R), showing the oblique disposition of posterior crowns. Scale bar = 20 mm.

Figure 3. Symphysis of Caryonosuchus pricei gen. et sp. nov. (DGM 1411-R), in ventral (A) and dorsal (B) views, in comparative view with the symphysis of Sphagesaurus huenei (RCL-100) (C). Note the concave area on the anterior section of the symphysis of C. pricei and its wedge-like profile in ventral view. Scale bars = 10 mm.

Figure 4. Dentition of Caryonosuchus pricei gen. et sp. nov. (DGM 1411-R), in detail. A, ventrolateral view of teeth of the left side, showing the labial face of the crowns with basiapical ridges; B, lingual face of the same teeth, where the pebbled ornamentation and a wear facet are evident. C, apex of symphyseal crown showing tuberous denticles. D, maxillary tooth of the right side, showing the denticulated carina and wear facet. E, symphysis of Sphagesaurus huenei (RCL-100) with the first four mandibular pairs of teeth, the last showing extensive wear. F, palate of S. huenei (RCL-100) showing the premaxillary hypertrophied caniniforms and the first maxillary teeth. In comparison, RCL-100 shows the same general features, but its ridges seem to be more numerous when compared with the dentition of C. pricei. Note that in (A) that the basiapical ridges are evident even in areas where the enamel was not preserved and the dentine is exposed; in (F) the crowns of the fifth dentary teeth are preserved, attached to the palate. White pointers indicate wear facets. Scale bars = 10 mm.