Heterodactyly is like zygodactyly, except that digits three and four point forward and digits one and two point back.
2.
Zygodactyly occurs in the parrots, woodpeckers ( including Ma ( early Cretaceous ), 50 million years before the first identified zygodactyl fossils.
3.
The zygodactyly ( from Greek ?????, a yoke ) is an arrangement of digits in birds, with two toes facing forward ( digits two and three ) and two back ( digits one and four ).