Heterochronic evolution in a Late Pliocene–Early Pleistocene lineage of western European voles (Arvicolinae, Rodentia, Mammalia)

In this paper, the evolution of the lineage of western European populations of the genus <i>Kislangia</i> (Arvicolinae) is analysed, including the species <i>Kislangia cappettai</i> from Balaruc 2, <i>Kislangia ischus</i> from Zújar 11, and <i>Kislangia gusii</i> from Galera 2 and Almenara-Casablanca 1. The range of this lineage covers the Late Pliocene and the Early Pleistocene. Our analysis has been focused on the m1. Measurements of size, hypsodonty, perimeter, and area of the teeth have been recorded. An increase in size is observed from <i>K. cappettai</i> to <i>K. gusii</i>, while hypsodonty also increases in a punctuated manner. The functional fitness of the m1 is calculated on the basis of the structural density. It is observed that at the individual level, as wear advances, there is an increase in the structural density of the teeth. Consequently, the adult tooth is functionally more efficient than at younger stages of wear. When considering the structural density across the evolution of the lineage, higher structural density values are found for the same ontogenetic stages. This indicates that older ontogenetic stages of the more archaic populations appear earlier in the descendant species. It is concluded that this evolutionary process corresponds to the heterochronic change known as acceleration.