Source : Webster's Revised Unabridged Dictionary (1913)

Heterocercal \Het`er*o*cer"cal\, a. [Hetero- + Gr. ? tail.]
   (Anat.)
   Having the vertebral column evidently continued into the
   upper lobe of the tail, which is usually longer than the
   lower one, as in sharks.

Source : WordNet®

heterocercal
     adj : possessing a tail with the upper lobe larger than the lower
           and with the vertebral column prolonged into the upper
           lobe [ant: {homocercal}]