Heterochronic evolution in the late pliocene-early pleistocene arvicolids of the mediterranean area

Abstract

In this paper, three cases of heterochronic evolution in Plio-Pleistocene arvicolids of the Mediterranean area are reviewed. A first heterochronic process is described in Kislangia. Two different lineages have been recognized in this genus, one leading to Kislangia rex from Central Europe, the second one leading to K. gusii from the Iberian peninsula. The latter is characterized by a significant increase in size and hypsodonty. The ontogenetic trajectories of the first lower molar can be interpreted in terms of a peramorphic process (acceleration) in which the features of the adult ancestor tend to appear as juvenile characters in the descendant. On the other hand, the apparent loss of roots in the molars of some arvicolid lineages at the Plio-Pleistocene boundary can be also described as a heterochronic process, although of a different kind. Therefore, the origin of the first rootless arvicolids ( Allophaiomys) can be regarded as a paedomorphic process (neoteny). The analysis of the arvicolid samples from the sites of Gilena-2 and Barranco Conejos in southem Spain indicates that this process took place at least twice in the late Pliocene. The new species Mimomys oswaldoreigi is created for these almost rootless Mimomys populations. A second paedomorphic process is described in the case of middle Pleistocene Terricola species, whose origin can be traced back to Allophaiomys chalinei. Thus, the molars of young individuals of this species show complicated morphotypes that are almost identical to the adult stages of Terricola gregaloides. Finally, an explaination based in the Red Queen hypothesis is proposed to explain the evolutionary pattern of arvicolids during the Plio-Pleistocene.