Approximately 375 million years ago, our ancestors made their way from the sea to the land, evolving from swimming fish to vertebrates that hunt and live outside of the ocean. Although scientists are still unsure exactly how this transition took place, a new examination of a blind fish that walks in the same way vertebrates do might shed light on the mystery.
The waterfall-climbing cave fish (Cryptotora thamicola) was discovered in Thailand in 1985 and possesses many of the adaptations and skeletal features that allowed our ancestors to walk, including a pelvis.
"It's really weird," said John Hutchinson, a biologist from the University of London who was not involved in the new study. "It's a good example of how much fish diversity there's left to be discovered."
The unique fish is two inches long and feasts on microbes and organic matter that grows on the cave walls. Although it was discovered back in 1985, the recent study is the first to attempt a close examination of the species and look for parallels with our ancestors.
After a recent expedition to the caves, Apinun Suvarnaraksha, a co-author of the study, took videos of the unique fish and showed them to biomedics expert Brooke Flammang, another co-author of the study.
"I was completely blown away," Flammang said, noting their ability to utilize a tetrapod gait as opposed to flopping or crutching.
"These guys seemed to be very leisurely walking up the rock face," she added.
In order to study the species more closely, the team took one of the few preserved specimens of the fish and examined it in a high-resolution computerized tomography (CT) scanner. The pictures showed a skeleton that resembled that seen in a tetrapod.
"I literally thought someone was playing a trick on me," Flammang said.
The images confirmed the team's hunch that the fish were using their tetrapod-like skeletons to walk with a similar gait, one that closely resembles that of a salamander.
Flamming believes that it is possible that the findings could solve the mystery of the trackways in Poland dating back 400 million years, which predate all known tetrapod fossils.
"We see these footprints in a fish today, doing something very unfishlike," she said.
The team hopes that their results will eventually help scientists discover how fish arrived on land.
The findings were published in the March 24 issue of Scientific Reports.
