The Baculum in the Chipmunks of Western North America

This work dives into an unexpected but telling feature of western North American chipmunks – the tiny bony structure at the base of the male reproductive organ. By examining the shape, size, and ridge patterns of the baculum, the author shows how these details can serve as reliable clues for distinguishing species and subspecies. The study balances clear anatomical description with broader questions about how such a minute organ reflects evolutionary relationships.

Drawing on almost two hundred specimens gathered from museums across the United States, the researcher measures each bone with precision and compares the findings to traditional skull‑based classifications. Readers will follow a systematic exploration of individual variation, age‑related changes, and occasional oddities, all illustrated with meticulous drawings. A concise identification key rounds out the text, offering a practical tool for anyone interested in the subtle anatomy that helps map chipmunk diversity.