EVOLUTION Divergent Evolution - Embryology
|Remnant hip bones are present in cetaceans linking them
to their terrestrial ancestors, but there is more evidence visible in embryonic
stages. In early development the fetus has mammalian characteristics that
are lost in later stages of development.
The cetacean fetus in early development displays four bud-shaped limbs, external genitalia and nostrils at the end of the snout. In later stages the forelimbs become flippers and the hindlimb buds disappear. The nostrils eventually move to the top of the head and the genitalia are covered by skin with slits. (Zahn, 1988) The fetus also develops coarse hair which either vanishes before birth or is retained around the front of the head in adults.