Terrestrial capture of prey by the reedfish, a model species for stem tetrapods.

ABSTRACT

Due to morphological resemblance, polypterid fishes are used as extant analogues of Late Devonian lobe-finned sarcopterygians to identify the features that allowed the evolution of a terrestrial lifestyle in early tetrapods. Previous studies using polypterids showed how terrestrial locomotion capacity can develop, and how air ventilation for breathing was possible in extinct tetrapodomorphs. Interestingly, one polypterid species, the reedfish Erpetoichthys calabaricus, has been noted being capable of capturing prey on land. We now identified the mechanism of terrestrial prey-capture in reedfish. We showed that this species uses a lifted trunk and downward inclined head to capture ground-based prey, remarkably similar to the mechanism described earlier for eel-catfish. Reedfish similarly use the ground support and flexibility of their elongated body to realize the trunk elevation and dorsoventral flexion of the anterior trunk region, without a role for the pectoral fins. However, curving of the body to lift the trunk may not have been an option for the Devonian tetrapodomorphs as they are significantly less elongated than reedfish and eel-catfish. This would imply that, in contrast to the eel-like extant species, evolution of the capacity to capture prey on land in early tetrapods may be linked to the evolution of the pectoral system to lift the anterior part of the body.