Protopterus annectens, also known as the African lungfish, appears to be an unlikely candidate for a feat such as self-propulsion across land; however, studies on the eel-like body of this freshwater fish may prove otherwise. The African lungfish is capable of living for several months without water, due to its ability to obtain oxygen through the use of 2 lungs, rather than gills. (Gills are still present in the lungfish, but they are atrophied and unable to supply enough oxygen for survival.) The question has been, however, is the lungfish actually able to propel itself through fin-based locomotion?
Lungfish In Action
Only the hind limbs of a lungfish are used to propel its body forward. It moves by using two types of movement.
- In some cases, both pelvic appendages are used simultaneously to produce forward momentum with a lunging action.
- In other cases, the lungfish’s pelvic appendages are alternated to achieve more of a “walking” motion.
Researchers think that the lungfish increases buoyancy underwater by filling both lungs with air, to reduce the amount of work required for the pelvic limbs to aid in locomotion.
A study published today in the Proceedings of the National Academy of Sciences analyzes extensive video of the lungfish in action. Due to this in-depth analysis of the lungfish’s movements, researchers found that fossil tracks previously thought to have been produced by early tetrapods could actually have been made by an ancestor of the lungfish. Decoded Science had the opportunity to ask Heather King, lead author of the study, a few questions about this research.
Decoded Science: When did you first suspect that a lungfish had the capability to create prints like the fossil prints previously thought to have been created by tetrapods?
King: Actually, we don’t necessarily think that lungfish created those tracks, but it is possible that animals that share some important functional features with the lungfish (such as lack of feet, lack of digits, lack of a sacrum, having lungs and lobe-fins) might have. It is very challenging to identify trackmakers of fossil trackways. One way scientists have identified possible trackmakers in the past was by comparing the patterns of the tracks to the patterns of limb movement (ie gaits) used by living animals. Before this study, we didn’t have good evidence for what kinds of gaits lungfish used, but we now know that they can use bipedal gaits, that range from walking (alternating of fins) to bounding (both pelvic fins moving together). These patterns are very similar to some patterns we see in fossil trackways. While we can’t say for sure that fish made these fossil trackways, we can say that it might have been possible for lobe-finned fishes to have made them, in addition to tetrapods. The new evidence from our study widens the pool of possible track-makers.