To find out exactly what might have happened when aquatic animals first moved to land, Standen and her colleagues took 111 juvenile Polypterus senegalus — a fish species that goes by the common name Senegal bichir, or “dinosaur eel” — and raised them for eight months in a terrestrial environment. This environment consisted of mesh flooring covered in pebbles and just 3 millimeters of water — a precaution that, combined with water misters, prevented the fish from drying out. The researchers also formed a control group using 38 fish growing up in their usual aquatic environment.
“These fish have functional lungs and can breathe air,” explains Standen. Dinosaur eels also have gills, but they breathe at the surface regularly to increase their oxygen supply. They also occasionally use their fins to walk on land. “There’s anecdotal evidence that they move on land from ephemeral pond to ephemeral pond [when they dry up],” Standen says, “but they don’t do it voluntarily.” Still, that was more than enough to attempt to raise these young fish on land.
“We used high-speed video to analyze their movements at the end of the eight-month period,” Standen says. Because of time restraints, this part of the analysis was carried out in 20 of the terrestrial fish and 10 of the aquatic fish. The researchers also killed and scanned individuals from both groups to look at how living on land had affected their skeletons.
As it turns out, growing up on land really does change how a fish walks.