Comparação osteológica nas espécies do gênero Sotalia Gray, 1866 no Brasil (Cetacea, elphinidae)

Abstract

Two species have been recently recognized as distinct for the genus Sotalia: S. fluviatilis (Gervais, 1853), occurring in the Amazonian basin, and S. guianensis (van Bénéden, 1864), occurring from Santa Catarina (Florianópolis) (27°35’S and 48°34’W) to Honduras (15°58’ N and 85°42’ W). This study seeks to find information to sustain the separation of distinct species as well as a morphological characterization. A comparative osteological work was performed among marine samples (from the states of AP, PA, CE e SC) and riverine samples (AM) in relation to metric (skull, mandible, scapula, pectoral fin and sternum) and non-metrical characters (skull, mandible and cervical vertebrae). For the non-metrical characters analysis, there was a higher percentage of occurrence of fenestrae in the occipital region (65,9%) and cervical ribs (87,09%) in the fluvial species. The inverted goblet shape of the vomer was more frequent in the fluvial species (56,76%), followed by the intermediate (32,43%) and parallel shape (10,81%). The parallel vomer was more frequent in the marine species (65,79% to 76,19%). In relation to the lacerate anterior foramen, it was observed that an open/elongated shape is more common in the fluvial species (87,80%). Most samples in the marine species present this foramen divided in by a spike shaped projection (72% to 97,67%). The ventrally visible location of the hypoglossal foramen was observed more often in S. guianensis (88% to 97,77%), while in S. fluviatilis, most samples (86,67%) presented this foramen internally displaced to the basioccipital suture, and not visible in ventral view. There was a clear separation of two species in relation to skull and postcranial skeleton in the morphometrical analysis (Canonical Variable Analysis) presented. Proportionally, the marine species presented a wider skull than the fluvial species. The nasals were thinner and there was a bigger distance to the tip of the rostrum to the base of nasal in the fluvial species. The mandible did not present morphologial difference among species. The number of alveoli did not vary among species but did so among samples. The pectoral fin and scapula’s glenoid cavity were proportionally wider in the fluvial species. The sternum, however, was smaller in this species in relation to the maximum width of the manubrium. Nevertheless, this structure still needs to be better studied.