Offshore and coastal common bottlenose dolphins of the western South Atlantic face‐to‐face: What the skull and the spine can tell us

Abstract

The taxonomy of Tursiops truncatus in the western South Atlantic is not resolved. Two different hypotheses have been proposed: (1) offshore and coastal ecotypes with a parapatric distribution, and (2) two species, T. truncatus and T. gephyreus, living in sympatry. To test these hypotheses, we examined a total of 100 physically mature skulls and 35 vertebral columns from the suggested overlap zone in southern Brazil. In all skulls, 24 measurements, four alveoli counts and two categorical variables were analyzed. Vertebral formula was determined and five measurements were taken from selected vertebrae. Multivariate analyses were conducted for skull and vertebral data. Results revealed the presence of two well‐separated groups. Specimens of Group1 had smaller skulls and shorter body lengths, but more vertebrae, than Group2. The morphological characteristics of each group corresponded well with two ecotypes of common bottlenose dolphins reported in other ocean basins. Therefore, we assigned the specimens of Group1 to the offshore ecotype, and Group2 to the coastal ecotype. Differences in the geographic locations and ratio of strandings supported the parapatric hypothesis. The significant morphological differentiation observed suggests the presence of different subspecies, but an additional independent line of evidence is needed to hypothesize whether they represent different species.

Can habitat characteristics shape vertebral morphology in dolphins? An example of two phylogenetically related species from southern South America

“…Costa et al . () studied both coastal and offshore forms of bottlenose dolphins in the southwestern Atlantic and found significant differences in vertebral morphology that coincide with some of our findings. The offshore form showed vertebrae shorter ( i.e ., disk‐shaped) and higher total counts than the coastal form.…”

“…A similar pattern has been observed in the caudal area of the bottlenose dolphin (MCM, personal observation), a species with coastal and off‐shore forms that have been found to have differences in vertebral morphology (Costa et al . ), suggesting that fluke morphology might be highly preserved among delphinid taxa.…”

Variations and anomalies in the vertebral column of the bottlenose dolphin (Tursiops truncatus) from southern Brazil

“…Rommel, 1990;Crovetto, 1991). According to Costa et al (2016), coastal and offshore bottlenose dolphins from the western South Atlantic Ocean have different vertebral formula and total number of vertebrae.…”

“…Specimens of Tursiops truncatus analyzed in this study. Ecotype classification according to Costa et al (2016). SC = state of Santa Catarina.…”

“…This paper describes cases of morphological variation and bone anomalies in the axial skeleton of the bottlenose dolphin, with emphasis on the vertebral column and considering the physical maturity of those specimens. Ecotype classification of the data set followed Costa et al (2016) and it was used to check for frequency differentiation of anomalies between the groups. We analyzed the vertebral columns of 28 individuals of bottlenose dolphins collected along the southern coast of Brazil (Table 1; Figure 1).…”