IDENTIFICATION METHODS

Taxonomic identifications of arvicoline m1s from SCC were based on comparisons with the m1s of extant and extinct arvicolines and descriptions of those taxa from the literature. Initial examination and identification of specimens was conducted using 10x magnification. Subsequent verification of the identifications was conducted under a binocular microscope at varying magnification levels.

Dental terminology discussed here and depicted in Figure 2 follows Bell and Jass (2004). The m1 of arvicolines may be rooted or unrooted depending on the taxon. All arvicoline m1s have a posterior loop, a series of enamel-bound triangles, and an anterior cap (Figure 2). Open spaces between triangles are referred to as reentrant angles and may or may not be filled with cementum depending on the taxon. Triangles are numbered sequentially from back to front, and abbreviated references to individual triangles are used in the text below (e.g., T1; see Figure 2). "Primary wings" refers to T4 and T5 whereas "secondary wings" refers to T6 and T7 (Figure 2).

On the illustrations, enamel bands are shown in white, dentine is in black, and cementum is stippled. Broken or missing portions of the teeth are depicted with a series of horizontal lines. The closure of individual triangles relative to each other or the anterior cap was categorized as being open, pinched, exhibiting incipient closure, or closed following Bell and Barnosky (2000). Open or confluent triangles had openings that exceeded three enamel bandwidths. Pinched triangles exhibited openings between two and three enamel bandwidths. Triangles with incipient closure had openings between one and two enamel bandwidths. Closed triangles had openings of less than one bandwidth of enamel.