Я что-то упустила: а давно это стало двумя разными животными?

The basilisk is called "king" because it is reputed to have on its head a mitre, or crown-shaped crest. Stories of the basilisk show that it is not completely distinguished from the cockatrice. The basilisk is alleged to be hatched by a cockerel from the egg of a serpent or toad (the reverse of the cockatrice, which was hatched from a cockerel's "egg" incubated by a serpent or toad). In Medieval Europe, the description of the creature began taking on features from cockerels. It has a venomous strike and in some versions of the myth, it has the ability to breathe fire.

The cockatrice became seen as synonymous with the basilisk when the "basiliscus" in Bartholomeus Anglicus' De proprietatibus rerum (ca 1260) was translated by John Trevisa as "cockatrice" (1397).