A new species of Caiman (Alligatoridae, Caimaninae) from the Upper Miocene of Paraná, Argentina

BONA, P; PAULINA CARABAJAL, A.; GASPARINI, Z.

San Juan

Congreso; IV Congreso Latinoamericano de paleontología de vertebrados; 2011

Museo de Ciencias Naturales, Universidad Nacional de San Juan

Paleontological research on Mio-Pliocene South American taxa have provided information that allowed supporting taxonomical and biogeographical hypotheses, many of them erected since the middle of XIX century. The richest and most diverse record of Crocodyliformes in South America Cenozoic correspond to Neogene localities related to basins that surround the areas of Urumaco (Venezuela), La Venta (Colombia), Acre (Northwestern Brazil), Fitzcarrald (Peru) and Paraná (Northeast Argentina). Fossils from Upper Miocene in Paraná area were recovered from the “Conglomerado Osífero” (Ituzaingó Formation) and assigned to several taxa of Caimaninae (Alligatoroidea) and one Gavialoidea. Rovereto (1912) was the first author to perform a more detailed study of the vertebrate fauna there recordered providing clear illustrations and descriptions of several crocodilian taxa. Alligator? ameghinoi (Rovereto, 1912) was based on several isolated big sized cranial and postcranial materials posteriorly assigned by Rusconi (1933) to the genus Xenosuchus. Among the type material of Rovereto´s species we recognize a fragment of premaxilla with morphological features that fix with the rostral morphology of specimen MLP MLP-73-IV-15-1, represented by premaxillae, maxillae, nasals and left lacrimal and a skull table with parts of the occipital region and braincase Both specimens belongs to a same taxa. A big sized Caimaninae alligatorid with parietal exclude from posterior edge of table (Brochu, 1999 character 82-3; modified from Norell 1988, character 11) and exoccipital sending slender processes ventrally to basioccipital tubera (Brochu, 1999: 151-2). This species present a “Caiman like” general morphology and differs from other big sized as Purussaurus species by the outline, size and morphology of the narial openings, premaxillar lowed in lateral view and the general morphology of the skull table. These several snout features, related to narial position, bones proportions and sculpturing differentiates this taxon from other extant Caiman species. Particularly it differs from C. latirostris in not having conspicuous maxillary crests, in the kind of ornamentation with practically absence of cells and the different proportion of the snout bones. Although this species belonged to a broad snouted caimanin it presents relative narrowed nasal, differing from the broad snouted C. latirostris, in which nasals are proportionally wider with lateral convex margins (and not parallel and straight as in this Caiman species). The posterior skull sector of this taxa of Caiman sp. also shows peculiar morphological conditions as the position of the opening of internal carotids, which are laterally situates and did not opens at the occipital table, as generally occur in caimanins. This taxon, for the Upper Miocene of Argentina represents one of the largest known Caiman species, which they could have belonged numerous huge mandibular and postcranial remains founded in the area of Paraná.