416-359 million years ago


Over millions of years, the bones of the arms (the first two illustrations) and legs (above) of the ancestors of amphibians became more robust and articulated with each other. These would have helped the animals move across the bottom an aquatic habitat and navigate through marshes and flooded regions. At least one fish which was not in the lineage directly ancestral to amphians seems to have evolved multijointed bony digits in its fins as well. Sauripteris was a fish not closely related to amphibians which developed such fins. (It belonged to a group of sarcopterygian fish called the rhizodonts; some rhizodonts measured up to 7 meters long with teeth approaching the size of those of Tyrannosaurus; Clack, 2002).

fin with digits