Urodeles

Abstract

The modern Amphibia are quite different from their remote Paleozoic ancestors. The modern forms are generally considered to be a single monophyletic group (Szarski 1962; Parsons and Williams 1963; Thomson 1967; Schmalhausen 1968; Carroll and Holmes 1980; Gardiner 1983; Carroll 1988; but see Jarvik 1960, 1980). Jarvik (1960, 1980) is an outspoken proponent of the polyphyletic origin of modern amphibians from at least two, and probably even three, different crossopterygian groups: urodeles are hypothesised to be derived from porolepiform fishes, while anurans and amniotes are thought to be derived from populations of osteolepiform fishes. Embryological data also suggest a possible polyphyletic origin of recent amphibians (Nieuwkoop and Sutasurya 1976). Gymnophionans are thought to be derived from some other, unknown group. When the land vertebrates arose, whether from the crossopterygian rhipidistians (e.g. Schaeffer 1965; Schmalhausen 1968; Edwards 1977, 1989; Szarski 1977; Holmes 1985; Schultze 1987) or from the lungfishes (see Rosen et al. 1981; Bemis et al. 1987), the lateral paired fins were converted into organs of locomotion on the ground (Gregory and Raven 1942).