TERMINOLOGY AND MATERIAL
An international common standard is used to describe the new material referred to M. hordijki. The terminology used to describe the occlusal pattern of the arvicoline molars is after
van der Meulen (1973). Terminology of the dentine tracts follows the system proposed by
Rabeder (1981) in which HH-index is the square root of the sum of heights of dentine tracts of hypoconid and hypoconulid in lower molars; PA-index is the square root of the sum of heights of dentine tracts of protocone and anterocone in upper molars; ASD is anterosinuid; HSD hyposinuid; HSLD hyposinulid; MSD mimosinuid; PRS protosinus; AS anterosinus; and DS distosinus. Lower case m designates lower molars, and upper case M designates upper molars. L = length, W = width, A/L = index of anteroconid, H = labial crown height, Lbas = basal crown length, EL = elevation of Mimomys ridge above crown base of m1, P/L = index of posterior loop of M3 (includes T4), AL = anterior loop, and PL = posterior loop. All measurements are in mm.
The global stratigraphic terminology of the Pliocene-Pleistocene follows the new usage of the International
Commission on Stratigraphy (2009) with the Late Pliocene (Piacenzian) ranging from 3.6 to 2.588 Ma, and Early Pleistocene including Gelasian (2.588 to 1.81 Ma) and 'Calabrian' (1.806 to 0.781 Ma). The Zuurland materials are stored in the Local Museum of Brielle (LMB), The Netherlands. The investigated material comes from 11 different parallel boreholes (Z1 – Z11) located very close to each other.