Morphological Variation in the Cranium of Lagostomus maximus Along Its Geographic Distribution

Abstract

Three subspecies of Lagostomus maximus have been traditionally recognized (L. maximus maximus, L. maximus immollis, and L. maximus petilidens), but their distributional ranges are uncertain and, although there are brief descriptions of the skull morphology of each subspecies, they are not clearly differentiated. We examined the cranial material of Lagostomus maximus from localities encompassing the ranges of the recognized subspecies, grouping them into three regions based on the involved phytogeographic provinces: North (Chaco+Northern Espinal), Pampas (Pampas), and South (Monte+Southern Espinal). Using morphometric variables and different methodological approaches (exploratory methods, between-group Principal Component Analysis, and Discriminant Analysis), we explored and evaluated the presence of morphological variation of the cranium along these three main regions and its possible correspondence with already proposed traits with systematic value. Our analyses do not show remarkable differences between vizcachas of the North, Pampas, and South regions, but some subtle yet statistically significant differences could help to characterize vizcachas from each region. Specimens from the North region have slightly wider heads, wider palates, and longer cheek teeth series than the South and the Pampas regions. Specimens from the South region have narrow palates, shorter cheek teeth series, and smaller skulls. Specimens from the Pampas region have narrow heads and palates, and larger skulls. Some of these differences are in line with already proposed traits that characterize subspecies, and eventually related to environmental factors, but there is a need for larger samples of many of the studied localities for further studies.