The 350-million-year-old fossil found near the fishing village of Burnmouth helps reveal how animals transitioned from fins to feet as they evolved to move onto dry land, researchers said.
"This is the earliest and smallest foot ever found with five digits," paleontologist Jennifer Clack of the University of Cambridge in England said. "It tells us that terrestrialization occurred much earlier than we had a hint of before."
Feet with five toes tend to be good at bearing weight and rotating on land, she said.
The specimen is 20 million years older than any known five-toed fossil, measures less than half an inch across and comes from an unknown species, ScienceNews.org reported Monday.
The researchers said they hope to identify which species ultimately gave rise to creatures that walk, crawl and slither around Earth today.