Brain-body size relations in grasshopper mice

Cranial volumes were measured on museum specimens of two species of grasshopper mice, Onychomys leucogaster brevicaudus and Onychomys torridus pulcher. These were compared with body weights and body lengths, as recorded on the museum tags. On average, females were heavier and slightly longer than males, but they had smaller cranial volumes by about 3%. Statistically, the differences were marginally significant (with no difference in body length for one species), but the pattern of differences was the same in both species, and therefore probably real. This casts suspicion on the common notion that a larger body size requires a larger brain. It also questions the real meaning of encephalization quotients.