An African lungfish can leave trackways on sand or mud akin to that of footprints made by walking animals, according to research by Liverpool John Moores University and California State University, San Bernardino.
Peter Falkingham, a senior lecturer in vertebrate biology at LJMU, and Angela Horner, an assistant professor of biology at CSUSB, published their findings this week in Scientific Reports after analysing the traces left behind when an ancient fish species — lungfish — moves over a soft substrate.
Lungfish breathe air, an evolutionary adaptation that allows them to move between bodies of water, such as when the pond they are living in dries up. When they move over land, they do so by planting the head into the mud, and then “flicking” the rest of the body forward.
The researchers found that as the lungfish moved in this way, the head would create relatively deep impressions while the body made only small disturbances to the sediment. The resulting trackway consisted of alternating left-right impressions, which share similarities with trackways made by animals with feet.
The study also found that sometimes, if the mouth of the fish was open, the upper and lower jaws would leave separate impressions.
“This study could have much broader implications for palaeontologists and biologists alike,” Falkingham said. “Lungfish as a group have been around since the Devonian, some 400-plus million years ago, and yet there are no reports of fossil lungfish trackways. This is a little surprising, because we have body fossils of lungfish spanning from the Devonian to the present day, and we also have fossil lungfish burrows, but there are no reports of lungfish trackways. It could be because no one has ever thought to look for them, or really known what they would look like.”
More significantly, the authors contentiously suggest that the similarities between lungfish trackways and those made by animals with feet — tetrapods — might mean that, if found in the fossil record, lungfish traces might be assumed to be made by tetrapods.
“There are currently a wealth of studies focusing on the movements modern ‘tetrapod analogue’ fishes use during terrestrial locomotion, such as the walking catfish and mudskipper,” said Horner. “We hope that researchers might add trackway studies to their repertoire to enhance the fossil trackway search image.”
The findings are online at “Trackways Produced by Lungfish During Terrestrial Locomotion.” Two video links are at the bottom of the webpage, under “Supplementary information,” that show how the lungfish move over land.
One of the videos may also be viewed on YouTube at “Lungfish terrestrial locomotion.”
For more information the African lungfish research, call CSUSB Assistant Professor Angela Horner at (909) 537-5597.
For more information on Cal State San Bernardino, contact the university’s Office of Strategic Communication at (909) 537-5007 and visit news.csusb.edu.