What Was the First Animal to Move from Sea to Land?

For over a decade, scientists believed that a prehistoric millipede was the first creature to have made the transition from sea to land by beginning to breathe air.

A prehistoric ancestor of modern scorpions is thought to be the earliest known creature to venture onto land, thanks to its respiratory apparatus.
A prehistoric ancestor of modern scorpions is thought to be the earliest known creature to venture onto land, thanks to its respiratory apparatus.

Earlier this year, however, researchers studying fossils dug up from a quarry in Wisconsin in the 1980s took a closer look at the remains of two well-preserved scorpions. Measuring just one inch (2.5 cm) in length, Parioscorpio venator was roughly the same size as many modern scorpions. Most notably, these prehistoric scorpions were “likely breathing air” 437 million years ago, presumably after making the transition from life under water to life on terra firma.

The anatomy of these ancient arachnids, the scientists said, shows unmistakable evidence of circulatory, respiratory and digestive systems. The scorpions may not have been fully land-dwelling, though; they could have spent most of their time in the water but briefly emerged on land to mate.

Early landlubbers:

  • The scorpion fossils were among many excavated from the Brandon Bridge Formation, dating back to the Silurian period (443.8 - 419.2 million years ago). They were stored at a museum at the University of Wisconsin, where they were re-examined by paleontologist Andrew Wendruff as part of his PhD project.

  • Unrelated fossilized remains indicate that some scorpion-like creatures grew to a length of 6 feet (1.8 m). Those prehistoric giants were strictly water dwellers and not ancestors of modern scorpions.

  • Paleontologists have observed walking traces in sand that could have been made 560 million years ago, but it’s unclear whether the animals that left those marks were living on land or were sea-dwellers simply making brief forays into the surf.

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    • A prehistoric ancestor of modern scorpions is thought to be the earliest known creature to venture onto land, thanks to its respiratory apparatus.
      A prehistoric ancestor of modern scorpions is thought to be the earliest known creature to venture onto land, thanks to its respiratory apparatus.