Geometric Morphometric analysis of the Microtus M1 and its application to Early Middle Pleistocene in the UK.

Abstract

Species of the genus Microtus are known to be some of the most rapidly evolving taxa during the Quaternary. Their remains are common in archaeological and palaeontological contexts and are frequently used in palaeoclimatic and habitat reconstructions as well as providing a key component of biostratigraphic dating models.
This study focused on the dental morphology of the lower M1 in 6 species of Microtus found in the British early Middle Pleistocene. The study examined the potential for a new approach to gaining better resolution in biostratigraphic and palaeoclimatic reconstructions in this period, using Geometric Morphometric (GMM) analyses.
GMM analyses of modern samples of known origin found that it was possible to identify M1 teeth to species level with a high degree of statistical significance ( <0.0001). The application of protocols developed on modern samples to those from the early Middle Pleistocene sites at Westbury sub-Mendip and Boxgrove suggested species identification on ancient material was also possible. Taxonomic revision of the extinct species Microtus arvalinus was suggested by their morphological similarity to both modern and ancient M. agrestis samples, not M. arvalis as has previously been suggested. Identification of a large morphological disparity between modern and early Middle Pleistocene examples of M. subterraneus also suggest a complex genetic history, which previously had not been identified.
Additionally, evidence for morphological differences linked to climate was found. Variation in morphology between stratigraphic levels was found to be relatively low in most cases, even when samples were thought to be separated by a significant period of time.
These findings strongly support the use of GMM methods in determining Microtus remains to species level and suggest a strong potential for their use as palaeoclimatic and relative-dating proxies, requiring further research.