Eastern Musk Turtles (Sternotherus odoratus) in a few populations exhibit megacephaly, including those from a population in Arkansas herein described. I initiated a growth experiment in the laboratory with hatchlings from a megacephalic population and those from a nearby normocephalic population in Arkansas, both fed on fish chow for 22 yrs. The experiment, although compromised, suggested that megacephaly in the Eastern Musk Turtle is a plastic, environmental response to diet rather than a genetically based adaptation.