LAUSR

We provide the first documentation of morphological variation in the lower first molar (m1) of Lemmiscus curtatus from southern Canada. A total of 370 specimens were obtained from owl pellets taken from 4 localities in southern Saskatchewan. The 4 most common morphotypes are, in order of descending relative abundance, molars with 5 closed triangles and a well-developed but widely open sixth triangle, molars with 5 closed triangles and a sixth triangle that is pinched at the confluence of the anterior cap, molars with 5 closed triangles and incipient closure of the sixth triangle from the anterior cap, and specimens with 6 closed triangles. As is true of other modern populations of L. curtatus, the samples from Saskatchewan include no morphotypes with only 4 closed triangles. This collection is notable for the relatively high proportion of specimens with pinched, incipient, or full closure of a sixth triangle on the m1, and it also highlights the complex dynamics of dental evolution in arvicoline rodents.