Although Erethizon dorsatum is one of the most morphologically variable species of North American mammals, the few studies addressing this variation are mostly qualitative.
1)--the southwestern United States--in which Erethizon dorsatum has not been well studied and from which sufficient specimens were available.
Sample sizes of Erethizon dorsatum for each known age class and of known sex are, therefore, relatively small.
Even for an animal so large that asymmetry may be readily visible, cranial asymmetry in Erethizon dorsatum is pronounced.
The range of Erethizon dorsatum is vast, encompassing much of North America (Hall, 1981), and recent evidence (Caire et al.
However, the only published attempt to detail geographic variation and the status of porcupine subspecies was that of Anderson and Rand (1943), who synonomized the two existing nominal species (dorsatum and epixanthum) under Erethizon dorsatum, and then proceeded to characterize the five subspecies thought to occur in Canada.
Ahlberg (1969), in a quantitative evaluation of specimens from through-out the range of Erethizon dorsatum, concluded by recognizing only two subspecies: E.