According to evolutionary theory, something must have crawled from the sea onto land hundreds of millions of years ago—but what? How about a blind fish called Cryptotora thamicola, which uses four fins like crutches to wriggle up waterfalls and across slimy rocks, the Smithsonian reports. Discovered in northern Thailand more than 30 years ago, Cryptotora thamicola came to the attention of US biomechanics researcher Brooke Flammang when a colleague showed her video of the cave dweller crawling along surfaces, Wired reports. "I was like, 'Fish can’t do that,'" says Flammang. "That’s ridiculous." So she teamed up with Thai scientist Apinun Suvarnaraksha, who shot video of the endangered species and had a museum specimen CT-scanned at a dental school.
Published in Scientific Reports, their results show that Cryptotora thamicola has a skeletal structure made for walking. The pelvis is bound by long ribs to the spine, and overlapping vertebrae keep the spine stiff—unlike modern fish but much like ancient four-limbed tetrapods that once crawled around like salamanders, the New York Times reports. "Functionally, it makes perfect sense, but to see it in a fish is incredibly wild," says Flammang. Scientists have identified possible tetrapod tracks dating back nearly 400 million years, Nature reported in 2009, but could it have been Cryptotora thamicola? "We see these footprints in a fish today, doing something very unfishlike," says Flammang, who believes the Thai fish may show how creatures first reached land. (Evolutionary theory could explain why we can't find alien life.)