Phosphatosaurus, Bergounioux, 1955

Hill, Robert V., Mccartney, Jacob A., Roberts, Eric, Bouaré, Mohamed, Sissoko, Famory & O'leary, Maureen A., 2008, Dyrosaurid (Crocodyliformes: Mesoeucrocodylia) Fossils from the Upper Cretaceous and Paleogene of Mali: Implications for Phylogeny and Survivorship across the K / T Boundary, American Museum Novitates 3631 (1), pp. 1-20 : 7-9

PHOSPHATOSAURUS Bergounioux, 1955

PHOSPHATOSAURUS GAVIALOIDES Bergounioux, 1955

HOLOTYPE: MM D15 .

NEW REFERRED SPECIMENS: CNRST SUNY 275, articulated dentaries and splenials with one replacement tooth.

LOCALITY: Mali-20; Eocene phosphate conglomerate.

DESCRIPTION: CNRST SUNY 275 (fig. 4) is recognized as a dyrosaurid on the basis of a relatively small alveolus for the seventh dentary tooth. It is referred to Phosphatosaurus gavialoides on the basis of several characters, including large size, nonhomodont dentition, robust teeth with straight carinae and longitudinally striated enamel, and a spoon-shaped lateral expansion of the rostral portion of the mandible. In addition, CNRST SUNY 275 possesses a splenial symphysis that reaches the level of the ninth alveolus, and a mandibular symphysis that is inclined caudodorsally when viewed from the lateral side. Both of these features have been described in a specimen referred to Phosphatosaurus sp. ( Buffetaut, 1979b) .

Examination of the specimen allows the interpretation of certain character states that could not be identified in previously known specimens of Phosphatosaurus . Jouve et al. (2005b) coded the character describing the seventh mandibular tooth as unknown for Phosphatosaurus in their analysis. Buffetaut (1979b), however, described a fragment of the mandibular symphysis of Phosphatosaurus sp. from the Paleocene of Niger that preserves the seventh through tenth alveoli. The specimen shows the presence of a small seventh dentary alveolus in Phosphatosaurus . CNRST SUNY 275 further corroborates this interpretation, as its seventh alveolus is comparatively small on both sides. The specimen shows an unusual variation of this character, however. In CNRST SUNY 275, both the sixth and seventh dentary teeth are small in size, and are closer to one another than to the fifth or eighth tooth. Although this character has not been reported in dyrosaurids before, such ‘‘alveolar couplets’’ occur in certain

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tooth. Inset: detail of tooth showing features of enamel. Scale bars equal 2 cm. other longirostrine crocodyliforms, notably Eosuchus minor ( Brochu, 2006) . The diastemata on either side of the alveolar couplets presumably served to receive comparatively larger maxillary teeth.

CNRST SUNY 275 also allows interpretation of Jouve et al.’ s (2005b) character describing the relative width of the mandibular symphysis. It is clearly wider mediolaterally than it is high dorsoventrally, giving the symphysis a wide, oval cross section along its entire length. Nothing is preserved of the external mandibular fenestra, if one existed in this taxon.

DYROSAURIDAE de Stefano, 1903

cf. PHOSPHATOSAURINAE Buffetaut, 1979a

NEW REFERRED SPECIMENS: CNRST SUNY 279, caudal region of skull roof and occiput.

LOCALITY: Mali-18; Paleocene phosphate conglomerate.

DESCRIPTION: CNRST SUNY 279 preserves the caudal region of the skull roof of a large dyrosaurid (fig. 5). The specimen is recognized as a dyrosaurid on the basis of a dorsoventrally high occipital region, pronounced medial expansion and midline contact of the otic capsules, and large supratemporal fenestrae separated by a relatively narrow interfenestral bar. Although occipital tuberosities were present, their extent cannot be determined due to breakage at the bases of both processes. The specimen preserves most of the parietal and paired squamosals, along with the supraoccipital and portions of the exoccipital elements. The dorsal surface of the skull roof is robustly ornamented with deep pits. The dorsal surface of the interfenestral bar is broken, however, and the extent of ornamentation on this structure cannot be assessed. The caudal margin of the skull roof is not straight, but moderately invaginated, forming a wide V-shape. This differs from the deep, U-shaped concavity seen in Rhabdognathus keiniensis , which may extend rostrally beyond the caudal border of the supratemporal fenestra. Based on its large size, this specimen probably represents a member of Phosphatosaurinae , the taxon that includes Phosphatosaurus and Sokotosuchus ( Buffetaut, 1979a; but see Jouve et al., 2005b). The gently invaginated caudal parietal margin compares more closely with that of Sokotosuchus than with the straight parietal margin of Phosphatosaurus (e.g., Halstead, 1975; Buffetaut, 1979a; Jouve et al., 2005a).