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Origins of the Frog-Kick? Alternate-Leg Swimming in Primitive Frogs, Families Leiopelmatidae and Ascaphidae

Anick Abourachid and David M. Green
Journal of Herpetology
Vol. 33, No. 4 (Dec., 1999), pp. 657-663
DOI: 10.2307/1565583
Stable URL: http://www.jstor.org/stable/1565583
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Origins of the Frog-Kick? Alternate-Leg Swimming in Primitive Frogs, Families Leiopelmatidae and Ascaphidae
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Abstract

When swimming, as when jumping, frogs typically kick synchronously and symmetrically with both hind legs. This is an evolutionarily derived, drag-based mechanism employing the feet as paddles and the hind limbs as thrusters. But morphologically archaic frogs of the genera Leiopelma and Ascaphus, although they jump when on land, obligately swim using alternating leg movements. We video-recorded swimming Leiopelma hochstetteri, L. archeyi, and Ascaphus truei, and other frogs. Leiopelma spp. and Ascaphus always swam with alternating movements of their hind limbs, holding their forelimbs forward and outstretched. One leg always trailed the body acting as a rudder reducing yaw. The frogs swam with near constant velocity and, like swimming tadpoles, the body swung from side to side, pivoting at the level of the otic region. All other species swam with simultaneous and symmetrical movements of the hind limbs, without lateral movement, and with forelimbs pulled back to lie alongside the body; asynchronous leg movements were associated only with mid-water directional changes. The locomotor behavior of Leiopelma and Ascaphus demonstrates that frog jumping and frog swimming are independent locomotor modes with separate evolutionary derivations and neural controls. Therefore, even though the earliest known anurans may have jumped like frogs it does not follow that they swam like frogs.

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