Stratigraphic and taxonomic revision of the fossil vole remains (Rodentia, Microtinae) from the Lower Pleistocene deposits of eastern England

Abstract

We review the fossil microtine rodent assemblages from the Lower Pleistocene deposits in eastern England, consisting mainly of marine sediments of the Norwich Crag and Cromer Forest-bed Formations. Material from 17 localities, including the ‘Weybourne Crag’ of the Norfolk Coast, the inland ‘Norwich Crag’, and the Crag of the north Suffolk coast has been studied. The taxaMimomys pliocaenicus, M.rex, M.blanci, M.newtoni, M.pitymyoides, M .altenburgensisandClethrionomysare recognized.Mimomys pitymyoidesandM.altenburgensisare described for the first time from Britain. The type material ofMimomys reidiandM.newtoniis redescribed, and we show thatM.newtoniMajor 1902 is a senior synonym ofM.hungaricus(Kormos), thus resolving confusion that has existed in the literature. The prior name for the species described by M. A. C. Hinton (Monograph of the voles and lemmings (Microtnae) living and extinct. London: British Museum (Natural History) 1926) asMimomys newtoniappears to beMimomys blancivan der Meulen 1973. No evidence has been found for mixing of faunas of different age at a single horizon or locality. Differences in crown height are demonstrated between samples ofMimomys pliocaenicusfrom different localities, and differences between localities in the presence and absence of various species are tabulated. This evidence combined with current interpretations of the stratigraphy leads us to recognize three faunal groups. Group 1 faunas containMimomys pliocaenicus, M.reidi(type level),M.newtoni(type level),M.pitymyoides, M.blanciandClethrionomys. They come from coastal deposits previously termed ‘Weybourne Crag’ and currently considered to date from Pre-Pastonianato Pastonian. The faunas are clearly later than group 2 faunas, which containMimomys pliocaenicus, M.reidi, M.newtoni(these three species less advanced than in group 1 faunas),M.rexandM.altenburgensis(these two species lacking in group 1 faunas). Group 2 faunas come from inland ‘Norwich Crag’ localities and crags in Suffolk yielding a Chillesford type pollen assemblage, which are currently considered to date from the Bramertonian stage. Group 3 faunas containMimomys pliocaenicus, M.reidiandM.blanciand are from coastal deposits at Covehithe and Easton Bavents associated with Baventian stage clays. The evidence from the microtine rodents confirms the relative position of the Bramertonian and Pre-Pastonianastages, but does not yet allow conclusions to be drawn on the relative age of group 3 faunas or the deposits in which they occur. The fauna of the Pastonian stage still requires clarification, since it is not possible to allocate unambiguously to this stage any of the material described here. The British Lower Pleistocene assemblages are broadly similar to material from Tegelen, The Netherlands (Tiglian TC4-6) and to material from superimposed loess levels at Stranzendorf, Austria. The British assemblages are characterized by the presence ofMimomys pliocaenicusand the absence of species with unrooted teeth, indicating that they belong to theMimomyssuperzone of the biostratigraphic system of A. J. van der Meulen (Quaternaria17, 1-144, 1973) corresponding to the Villanyian stage. On the basis of microtine evidence we suggest limits to the correlation of the Pre-Pastonian and Bramertonian stages with the Netherlands chronostratigraphy. These limits are earlier than suggested by other lines of evidence. Correlation of the Pre-Pastonian with part of the Eburonian and the Bramertonian with part of the Tiglian is thought to merit consideration.