Morphological integration of native South american ungulate mandibles based on 3D landmarks.

CASSINI G. H.; MUÑOZ, N. A.; HERNANDEZ DEL PINO, S.; VIZCAÍNO S. F.

Congreso; 4th International Palaeontological Congress; 2014

SouthAmerican native ungulates include several extinct lineages that evolved withinthe context of the South American Cenozoic geographic isolation. By the lateEarly Miocene Santacrucian Age, the three orders Notoungulata, Litopterna, andAstrapotheria were clearly differentiated. Recent studies, in an ecomorphologicalframework, highlighted a complex functional pattern related to habitat/diet andhypsodonty. In order to understand these complex relationships in anevolutionary context we used geometric morphometrics methods to evaluate themorphological integration of two of the primary functional units of themandible: the alveolar region, and the ascending ramus. Twenty seven mandibularthree-dimensional landmarks were digitized. Principal component analyses (PCA),and Partial Least Squared (PLS) were used to explore the patterns ofcovariation between these two modules. The PCA of tangent space coordinatesresulted in the six PCs accounting for nearly 85% with the three first PCsaccounting for most of the 70% cumulative variance. The shape changesassociated to the first eigenvector goes from a robust curved mandibular corpusand expanded coronoid and angular process on the negative end to a gracile straightmandibular corpus and shrink coronoid and angular process on the positive end.The PLS analyses shows a very high RV coefficient (~0.73) and only the firstpair of PLS were significant explaining the 88% of covariation. The shapechanges associated to PLS1 was very similar to those of PC1 (angle between vectors:5°). These results were consistent when the PLS was repeated on the independentcontrast. These results indicate a strong morphological integration in thesethree orders. In the Astrapotheria and Litorpterna we found a common pattern ofcovariation, which might be due to similar constraints (developmental,functional and/or biomechanical). Conversely, in the Notoungulata thedimensions displayed a clear distinction between species suggesting a slightydifferent pattern of covariation in the different families of the order. The PLSinside the litopterns and notoungulates indicate that only the PLS1 weresignificant explaining a ~93% and 87% of covariation and showing a higher RVcoefficient 0.91 and 0.66 respectively. The fact that the three orders differsin their hypsodonty could shaped the morphological covariation between the twomodules. In addition the different covariation patterns in notoungulates withrespect to litopterns, are in concordance with both the taxonomical andmorphological diversity of the clade, particularly in the typotheres.