Massaliasuchus affuvelensis (Matheron, 1869)

Martin, Jeremy E. & Buffetaut, Eric, 2008, Crocodilus affuvelensis Matheron, 1869 from the Late Cretaceous of southern France: a reassessment, Zoological Journal of the Linnean Society 152 (3), pp. 567-580 : 576-577

AFFINITIES OF MASSALIASUCHUS AFFUVELENSIS

In Massaliasuchus affuvelensis , the choanae are completely surrounded by the pterygoids and the palatines are therefore excluded from their margin. This condition is typical for eusuchians ( Huxley, 1875; von Huene, 1933; Benton & Clark, 1988; Norell & Clark, 1990; Clark & Norell, 1992; Brochu, 1999; Buscalioni et al., 2001; Salisbury et al., 2006).

Massaliasuchus displays synapomorphies that make it more derived than the basalmost eusuchians ( Isisfordia duncani , Allodaposuchus precedens and Hylaeochampsa vectiana ). These are the lacrimal making broad contact with the nasal and the absence of caudal process of the maxilla between them (93-0 of Brochu, 1999).

Given the poor preservation of the specimens, it is difficult to go further down the taxonomy. A few alligatoroid synapomorphies are observable in Massaliasuchus affuvelensis . The occlusion is typically alligatoroid. The maxillary teeth occlude laterally to the mandible, the dentary teeth occluding lingually as in derived alligatoroids. A second character reminiscent of that group is the absence of a notch between the premaxilla and maxilla. A dentary tooth occludes in a pit at this level (77-1 of Brochu, 1999). As stated by Brochu (1997), at least one neosuchian possesses a pit rather than a notch, i.e. Shamosuchus ( Efimov, 1983) , but most close relatives to Eusuchia show a notch. Basal alligatoroids such as the Diplocynodontinae are considered to have a pit between the premaxilla and maxilla, at least early in ontogeny ( Norell, Clark & Hutchison, 1994; Brochu, 1997). While the basal eusuchian Isisfordia also displays maxillary teeth that occlude labially as in alligatoroids ( Salisbury et al., 2006), the posterior maxillary and mandibular teeth of Massaliasuchus affuvelensis are bulbous as in alligatoroids but unlike the condition seen in Isisfordia . In Massaliasuchus , the fourth maxillary tooth is the largest (89-2) as in the globidontan Stangerochampsa mccabei (contrasting with Acynodon and Brachychampsa ) and Alligatoridae ( Salisbury et al., 2006) . This character would support derived alligatoroid affinities, but other characters suggest a more basal position within alligatoroids. The lacrimal is longer than the prefrontal (117-0 of Salisbury et al., 2006) as in most neosuchians such as Bernissartia , Goniopholis or more derived eusuchians such as basal alligatoroids ( Leidyosuchus, Diplocynodontinae , basal globidontans), Caimaninae and crocodyloids, but unlike Hylaeochampsa and derived alligatorids ( Alligator , Arambourgia , Procaimanoidea ) in which the prefrontal is longer. The fact that the palatine–pterygoid suture does not stop near the posterior angle of the suborbital fenestra (85 of Brochu, 1999) is not supportive of a globidontan affinity for Massaliasuchus . Instead, the palatine suture is placed cranially to the posterior angle of this fenestra. The relatively long and slender snout of Massaliasuchus is reminiscent of that of the basal alligatoroid Leidyosuchus and the outgroup taxon to alligatoroids: Borealosuchus . In Massaliasuchus affuvelensis , the nasals are dorsally excluded from the external naris (95-2 of Brochu, 1999). This character, although present in Diplocynodontinae, is ambiguous because it is also shared with Borealosuchus and the basal Caimaninae Orthogenysuchus and Mourasuchus . The absence of a premaxillary–maxillary notch makes it less basal than Leidyosuchus . No other synapomorphies relating Massaliasuchus to Diplocynodontinae could be detected and it would be reasonable to place this taxon either as an outgroup to the clade Diplocynodontinae + Globidonta or as a sister taxon of Diplocynodontinae. The nature of the available material does not allow us to clarify this point ( Fig. 5 ). The lack of resolution in the tree topology results from a lack of information. However, the presence of specific shared derived character states with alligatoroids leads to the prediction that more complete material, if and when found, will support a position within that particular clade.

The presence of isolated procoelous vertebrae is indicative of a eusuchian. Their size corresponds to that of the skull remains. Therefore, it seems reasonable to associate these vertebrae with the cranial remains, as proposed by Matheron. The several fragmentary specimens indicate size variation of the snout width (measured at the level of the premaxillary–maxillary suture) ranging from 66 to 122 mm. A rough estimate would give a skull length of 400 mm for the largest specimen.

In conclusion, Massaliasuchus affuvelensis seems to be a basal alligatoroid as suggested by Brochu (1997), but its affinities within that clade remain obscure mainly because of the lack of information regarding the braincase or the posterior skull table. Regardless, the information gathered from the hitherto unpublished specimens refutes the attribution of this crocodylian to the genus Crocodilus .

CAN THE FUVEAU MATERIAL BE ATTRIBUTED

Figures

Figure 5. Phylogenetic position of Massaliasuchus affuvelensis. Strict consensus of 484 trees recovered in a maximumparsimony analysis.