Morphology of the skull of Inia geoffrensis humboldtiana Pilleri & Gihr, 1977 (Cetacea: Iniidae): a morphometric and taxonomic analysis.
DOI:
https://doi.org/10.3989/graellsia.2020.v76.253Keywords:
Cranial, dolphin, multivariate analysis, Orinoco, VenezuelaAbstract
The morphology and anatomy of the two current subspecies of Inia geoffrensis (Blainville, 1817) are very similar. For this reason, the taxonomic validity of these has been the subject of discussion among different researchers. To provide additional information to clarify this situation, the analysis of the shape, external appearance and proportions in 20 skulls of Orinoco river dolphin, Inia geoffrensis humboldtiana Pilleri & Gihr, 1977, was carried out. For the morphometric analysis, 28 anatomical characters plus the count of the number of dental alveoli were selected. All values obtained in this study were analyzed and compared using univariate and multivariate statistics with published data from Inia geoffrensis geoffrensis (Blainville, 1817). Both skull ‘shape’ and ‘size’ are important components of the morphological differentiation between I. g. humboldtiana and I. g. geoffrensis. The analysis of the cranial morphology allowed the identification of 10 characters that differentiate I. g. humboldtiana from the other subspecies and species of the genus. Univariate and multivariate analyses demonstrated clear differences in cranial morphometry. The facial region concentrates 45.46% off this variation and the cranium region presents 54.54%. 60.00% of skulls variables, directly associated with the feeding function, in I. g. humboldtiana are smaller than I. g. geoffrensis. In contrast, 24.00% of variables associated with the setting of the skull showed higher average values. Discriminant analysis was used to examine how well each subspecies can be differentiated. The percentage of correct classification by discriminant functions was 62.16%. The variation obtained in this study allows suggesting that in I. g. humboldtiana the cranial variables have been modified possibly as a response to selective pressures of the type environmental and ecological. Despite some overlap, the results reveal sufficient evidence to affirm that the subspecies geoffrensis and humboldtiana are manifestly different. Therefore, and based on the morphological and genetic differences that exist between these taxa, it is recommended that the Inia of the Orinoco be considered a distinct or independent species.
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