Three weeks after fertilization and when just over a centimeter long, a dolphin embryo has the first signs of a heartbeat. In a few more days it will begin to grow budding limbs – a genetic nod to the dolphin’s walking ancestors – which will then retract and disappear entirely.
After four weeks, this dolphin embryo will continue to transform. Nostril-looking holes appear, but they move and change, eventually becoming the calf’s blowhole.
By nine weeks of age, this dolphin will have a sleek, distinctive shape with powerful flippers, muscles and a tail. Just past the pregnancy’s halfway point, a dolphin in the womb can move, open and close its eyes independently.
Soon its organs will be fully formed, ears will grow behind the eyes, and it will actually swim in its mother’s womb. But a dolphin will never grow vocal chords, as this species communicates with clicking and whistling sounds made by squeezing air between air-sacs by their blowhole.
At twelve months this dolphin calf will be born underwater, and it must propel to the ocean’s surface to take its first breath of air.
Learn more about how a dolphin embryo develops in the womb – complete with cutting edge 4-D imagery – on In the Womb: Animals premiering Sunday October 17 at 8P et/pt on Nat Geo WILD!