Meeting Abstract
The evolution of jointed limbs, flexible axial skeletons, and a reduction in body armor allowed early vertebrates to transition from water to land in the Devonian period, about 370 million years ago. The mangrove rivulus, Kryptolebias marmoratus, is a quasi-amphibious modern teleost with no obvious morphological characteristics that would suggest these fish would be able to efficiently move onto land. We recorded several aspects of their aquatic versus terrestrial behaviors: (1) kinematics of the water-to-land transition and terrestrial excursions, (2) forces generated during terrestrial leaping, and (3) motor patterns of the axial musculature during aquatic escape responses and terrestrial jumps. We compared adult K. marmoratus to size-matched non-amphibious juvenile largemouth bass, Micropterus salmoides, which make extremely rare forays onto land. We found K. marmoratus to use three behaviors when transitioning onto land: launch, squiggle, and pounce. Once on land, K. marmoratus jumps up to 10 body lengths by rotating its head over the long axis of its body and pressing its caudal peduncle against the substrate to launch into ballistic flight. K. marmoratus forces were in the anteroposterior and mediolateral orientations, whereas the bass generated almost all of their forces in the vertical direction with little lateral displacement. Terrestrial motor patterns differed from aquatic escape responses in adult K. marmoratus, whereas juvenile bass showed similar axial motor patterns in both media. K. marmoratus is capable of exploiting different environments without having any obvious morphological adaptations to move on land. We must revisit some of our understanding of the fossil record, as form does not always predict function.
