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Ontogenetic allometry as a key dimension to understand cranial shape of ?Dolicavia minuscula (Rodentia, Caviidae)
Congreso; 4th International Paleontological Congress; 2014
Institución organizadora:
International Paleontological Association
?Dolicavia minuscula is an extinct member of the family Caviidae. It has an unusually rich record, represented by very complete cranial remains from the Chapadmalal Formation (Chapadmalalan stage, early-late Pliocene), cropping out in the Atlantic cliffs of Buenos Aires province (central Argentina). ?Dolicavia bears a peculiar morphology, partially similar to that of the sister genus Microcavia. Outstanding features involve markedly enlarged orbits and inflated, bowed cranial vault. Here, we propose that these traits would represent a ?juvenilized? morphology. To test this hypothesis, subadult to adult specimens of ?Dolicavia were analyzed within an ontogenetic allometric space including the extant caviine Cavia aperea, Galea musteloides, and Microcavia australis. Patterns of cranial shape variation were examined through geometric morphometric techniques; 22 landmarks + 23 semilandmarks were digitalized onto pictures of crania in lateral view. A Principal Component (PC) analysis was carried out onto shape coordinates in order to accomplish a visual examination of allometric trajectories. Centroid size (CS) was estimated to be used as a proxy of age. Ordinary Least Squares regressions were performed to obtain the slope (shape change rate) and intercept (starting shape) of each trajectory along the first axis of variation. Differences among trajectories were assessed through covariance analyses. In the morphospace defined by PC1 and PC2, the first axis showed the major differentiation among genera. In a regression of PC1 on CS, Cavia and Galea had similar trajectories while Microcavia had the most separate, parallel trajectory. ?Dolicavia located near adults of Microcavia. Covariance analyses supported significant differences among intercepts but not among slopes, suggesting lateral transposition as the pattern of change among trajectories. Ontogenetic pathway of Microcavia is interpreted as post-Displacement by assuming that it is a result of changes occurring in early stages of development, prior to those represented in this study. Although ontogeny of ?Dolicavia is unknown, its position in the allometric space suggests that less shape change from juveniles to adults is expected respect to that of extant species. According to the results, at least part of cranial variation in caviines can be interpreted through an ontogenetic approach as alternative to selective explanations for isolated characters. It remains to be examined whether ?juvenilized? cranial morphology of ?Dolicavia and Microcavia could be related to the occupation of arid environments as proposed for other clades of rodents.