Calcaneus secundarius: an osteo-archaeological note.

Calcaneus secundarius, a minor anatomical variant in the foot, is subclinical and its true prevalence in modern populations is uncertain. The trait is clearly visible in dry bones, and osteo-archeological evidence suggests that it may be a more frequent occurrence than was formerly thought. The etiology of the trait is outlined, and its possible value is assessing "biological distance" in past populations is considered.