RESUMO
For almost 90 years, the cetacean vertebral column has puzzled scientists. This is the first 3D geometric morphometric study on the vertebral column of such a numerous group of small odontocetes (24 species). It uses a functional subdivision of the cetacean vertebral column and three landmark configurations to describe and compare vertebral morphology in Delphinidae, relating particular morphologies with the biomechanical requirements of each species. To this end, I assess the effect of size, and that of size and subfamily on vertebral morphology. I also analyzed the statistical differences in shape between species. Phylomorphospaces were created to assess similarities or differences in shape between closely related species with similar/dissimilar habitats. The allometric effect was low in all regions, and there were subfamily-specific allometric effects. Differences between species were greater in the mid-column but this was only partially confirmed statistically, presumably due to low n for some species. The percentage of variance explained by the first two PCs was higher than 58% in all regions, with the torso and the tail stock showing the greatest percentages of explained variance. The results suggest that the common ancestor of dolphins would have be a non-fast-swimming oceanic species. Coastal habitats seem to have evolved secondarily by means of a reduction in vertebral count, and vertebral morphology associated with greater flexibility (i. e., longer centra, smaller faces). On the contrary, an increased total count and disk-shaped vertebrae were observed to varying degrees in non-coastal species, with the most extreme modifications being found in species with particular habitat specializations. My results support the hypothesis that diversification in vertebral morphology in association to particular habitats was a key factor in delphinid explosive radiation, and provides descriptive basis for analysis of the phylogenetic constrains in vertebral morphology needed to elucidate dolphin diversification and the factors behind it.
RESUMO
PURPOSE: To investigate the spinopelvic alignment and vertebral shape in children, and associations with body composition and structural spinal abnormalities on magnetic resonance imaging (MRI). METHODS: We performed a cross-sectional study embedded in the Generation R Study, a prospective population-based birth cohort. Pelvic incidence and vertebral concavity ratios for each lumbar level were determined on sagittal MRI images in 9-year-old children, and structural spinal abnormalities were scored semi-quantitatively. The BMI-SD score was calculated, and body composition was assessed using DXA scans. Associations of pelvic incidence and vertebral concavity ratios with structural abnormalities and body composition measures were assessed using (multilevel) regression analyses. RESULTS: This study included 522 participants (47.7% boys), aged 9.9 years (IQR 9.7-10.0). The mean pelvic incidence was 36.6° (SD 8.0). Vertebral concavity ratios ranged from 0.87 to 0.90, with significantly lower ratios for boys compared to girls. Associations were found for a larger pelvic incidence with decreased disc height [OR 1.03 (95% CI 1.02-1.05)], and a pelvic incidence in the lowest tertile with less disc bulging [OR 0.73 (95% CI 0.56-0.95)]. Increased vertebral concavity ratio was associated with decreased disc height [OR 14.16 (95% CI 1.28-157.13)]. Finally, increased fat-free mass index was associated with a smaller pelvic incidence [adjusted OR 0.85 (95% CI 0.07-1.63)]. CONCLUSION: The mean pelvic incidence of 9-year-old children is 36.6° on supine MRI images, and a slightly concave shape of the lumbar vertebrae is seen. Spinopelvic alignment is associated with structural spinal abnormalities, and might itself be influenced by the children's body composition.
