PHYLOGENY AND SIZE AND SHAPE CHANGES IN THE SKULL OF THE SOUTH-AMERICAN RODENT PROECHIMYS

The rodent genus Proechimys has undergone rapid chromosomal speciation during late Pleistocene, resulting in several species and subspecies occurring in Venezuela. Here we present hypotheses for patterns of mor phometric change in the skull based upon genetic relationships between two species of the ''guairae'' complex (P. guairae and Proechimys sp. ) and P. trinitatis. Morphometrics of these species was studied using a geometric approach, and shape changes were visualised with respect t o the branching in the allozymes tree. There is a consistency between morphometric change in the dorsal side of the skull and genetic variat ion, suggesting a phylogenetic explanation; however, there is incongru ency between genetics and morphometrics of the ventral side of the sku ll. Incongruity may result from mutation rates which vary for both all ozymes and morphometry and from the evolutionary forces which may act differently on the functional units (auditory, feeding, respiratory, o lfactory) of the ventral side of the skull.