CASSINI Guillermo Hernan
congresos y reuniones científicas
Morphological integration of native South American ungulate mandibles based on 3d landmarks
Congreso; 4th International Palaeontological Congress The history of life: A view from the Southern Hemisphere; 2014
Institución organizadora:
International Palaentological association
South American native ungulates include several extinct lineages that evolved within the context of South American Cenozoic geographic isolation. By the late Early Miocene Santacrucian Age, the three orders Notoungulata, Litopterna, and Astrapotheria were clearly differentiated. Recent studies, in an ecomorphological framework, highlighted a complex functional pattern related to habitat/diet and hypsodonty. In order to understand these complex relationships in an evolutionary context we used geometric morphometrics methods to evaluate the morphological integration of two of the primary functional units of the mandible: the alveolar region and the ascending ramus. Twenty seven mandibular three-dimensional landmarks were digitized. Principal component analyses (PCA), and two blocks Partial Least Squared analyses (PLS) were used to explore the patterns of covariation between these two modules. The PCA of tangent space coordinates resulted in the six PCs accounting for nearly 85% of variance with the three first PCs accounting for most of the 70% cumulative variance. The shape changes associated with the first eigenvector go from a robust, curved mandibular corpus and expanded coronoid and angular process on the negative end to a gracile, straight mandibular corpus and shrunken coronoid and angular process on the positive end. The PLS analyses show a very high RV coefficient (~0.73) and only the first pair of PLS were significant, explaining 88% of covariation. The shape changes associated with PLS1 were very similar to those of PC1 (angle between vectors: 5°). These results were consistent when the PLS was repeated on the independent contrast. These results indicate a strong morphological integration in these three orders. In the Astrapotheria and Litopterna we found a common pattern of covariation, which might be due to similar constraints (developmental, functional and/or biomechanical). Conversely, in the Notoungulata the dimensions displayed a clear distinction among species suggesting a slighty different pattern of covariation in the different families of the order. The PLS within the litopterns and notoungulates indicate that only PLS1 was significant, explaining ~93% and 87% of covariation and showing higher RV coefficients, 0.91 and 0.66, respectively. The fact that the three orders differ in their hypsodonty could shape the morphological covariation between the two modules. In addition, the different covariation patterns in notoungulates with respect to litopterns are in concordance with both the taxonomic and morphological diversity of the clade, particularly in the typotheres.