Meeting Abstract
Amphibious fishes are surprisingly diverse and can serve as excellent models for understanding locomotor challenges of relevance to early tetrapods and basal amphibians. While studies of amphibious fishes moving across flat surfaces have revealed diverse behaviors and techniques enabling terrestrial locomotion, still little is known about how they move across complex terrain. The bichir is an elongate fish that moves on land using a combination of stepping with the pectoral fins and lateral body undulations, and proposed to be similar to how early tetrapods moved on land. In this study, we quantified how Senegalese bichirs (Polypterus senegalus) co-opt basic lateral bending for more complicated tasks, such as obstacle crossing. We filmed individuals with high-speed cameras (Photron SA-3) at 250 fps as they moved over obstacles of different heights (1-5mm), and quantified pectoral fin placement and head and body posture and elevation. Several key characteristics were identified that facilitated successful obstacle crossing: (1) bichirs adjusted nose elevation to match the obstacle height; (2) fish appeared to use a combination of skull pitch and roll to increase head elevation, rather than pure dorsal flexion; and (3) pectoral fin placement relative to the obstacle was of critical importance. When the fins were planted more than 3cm from the obstacle, the bichirs failed to cross, regardless of the amount of head elevation. The fact that pectoral fin placement was such an important determinant of obstacle crossing demonstrates how being able to coordinate axial and appendicular movements for moving across complex terrain may have been a critical step in the evolution of terrestriality among early tetrapods.
