Source : Webster's Revised Unabridged Dictionary (1913)

Heterodactyl \Het`er*o*dac"tyl\, a. (Zo["o]l.)
   Heterodactylous. -- n. One of the Heterodactyl[ae].

Source : WordNet®

heterodactyl
     adj : (of bird feet) having the first and second toes directed
           backward the third and fourth forward [ant: {zygodactyl}]