7 - Trends in rodent assemblages from the Aragonian (early–middle Miocene) of the Calatayud-Daroca Basin, Aragon, Spain

Summary

Introduction

Previous studies on rodent faunas from the Calatayud-Daroca Basin are numerous. An extensive enumeration of these papers is given by Daams et al. (in press). In this paper we will limit ourselves to the ones on paleoecology and paleoclimatology.

The latest rodent databases used in paleoecological analysis of this basin are from Daams & Freudenthal (1988) and van der Meulen & Daams (1992). In the 1990s, many more faunas have been sampled and are included in the present study. Faunas with less than 100 rodent M1–2 are excluded from the present analysis since they are considered not to be representative enough. The faunal succession covers the latest Ramblian, Aragonian and the early Vallesian (MN3–MN9; 16.8–10 Ma). Stratigraphic control and dense magnetostratigraphic sampling allowed correlation to the chronostratigraphic and numerical time scales (Krijgsman et al., 1994, 1996). In this paper some corrections are introduced as far as the correlation of the lower part of our succession to the numerical time scale is concerned. Numerical ages are assigned to the individual faunas using the paleomagnetic data in combination with average sedimentation rates of the predominantly lacustrine sediments.

Association structure

In order to describe the association structure, and more precisely its variation through time, we calculated the reciprocal of Simpson's index (Peet, 1974) since it depends only slightly on the number and frequency of rare species. Thus, the effect of a possible sampling bias is minimized.

We decomposed the changing diversity of the mainly Aragonian rodent faunas into two components: equitability (Fig. 7.2) and species richness (Fig. 7.5). The results are discussed in the following paragraphs.