Everything Worth Knowing About ... When We Left Water

How our tetrapod ancestors first came ashore.

More than 350 million years ago, our distant fishy ancestors traded in the life aquatic for land. Once ashore, these four-limbed vertebrates, called tetrapods, branched into an impressive range of animals: amphibians, reptiles, dinosaurs, birds and mammals. The fossil record shows that as species evolved to fill particular ecological niches, a few of the tetrapod clan lost limbs (snakes), turned arms into wings (bats, birds and pterosaurs) or decided the heck with dry land and headed back to sea (including whales, seals and some marine reptiles).

The tetrapods’ move to land has long been one of the great evolutionary puzzles. Fossil finds from this transitional period are too few to explain why or how it occurred, or exactly when the first fully terrestrial tetrapods evolved. Even so, researchers are getting closer to piecing it all together.

The tetrapod story starts with lobe-finned fishes nearly 400 million years ago. Unlike ray-finned fishes, which make up the majority of fish species today, the lobe-finned varieties evolved with bony limb-like fins, a handy adaptation (no pun intended).

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