Brain size/body length relations among myomorph rodents

The relation between cranial volume and body length was examined in 45 species of myomorph rodents to determine how accurately the former can be estimated from the latter. On average within species, cranial capacity was directly proportional to body length (proportional to the cube root of body weight). On average across species, cranial capacity was directly proportional to the square of body length (proportional to the two-thirds power of body weight). Geometric similarity held within species, but the differences in habitus among species within the same genus generated genus slopes that differed from those defined by strict geometric similarity. It was found that cranial capacity could be estimated as accurately from body length as from body weight, and that body length was better if any differences in habitus were involved (because body length is relatively insensitive to habitus). Therefore, body length (or some strong correlate thereof) may serve well as the primary variable in brain paleoallometry.