Relation between climatic fluctuation and morphological variability in Microtus (Terricola) grafi (Arvicolinae, Rodentia) from Bacho Kiro (Bulgaria, Upper Pleistocene)

Morphological variability within the species Microtus (Terricola) grafi is investigated in relation to the parameters of time and climate. Microtus (Terricola) grafi has been described from the Upper Pleistocene cave of Bacho Kiro (Bulgaria), which has yielded numerous teeth from several levels reflecting climatic fluctuations. The first lower molars are analyzed by 23 biometric variables so as to quantify tooth shape and its variation with time and climate. This morphological analysis reveals a number of shape indexes reflecting whether an individual lived in warm or cold conditions. The most significant result is that individuals living in warm conditions exhibit the more primitive feature of having a less tilted pitymyan rhombus.