Geoscience Reference
In-Depth Information
(
a
)
(
b
)
(
c
)
(
d
)
(
e
)
(
f
)
euryhaline or marine
stenohaline, freshwater
equivocal
Fig. 1. Habitat of early stegocephalians which could be inferred on the basis of parsimony, of the habitat of extant
tetrapods, of extant and extinct sarcopterygians and according to various phylogenies. (a) Hypothesis that prevailed
until the 1980s. Early lungfishes were thought to have lived in freshwater, like extant lungfishes (Romer 1966).
(b) Hypothesis taking into consideration recent data on the habitat tolerance of early lungfishes (Janvier 1996).
(c) Hypothesis reflecting the first phylogenies proposed in a cladistic framework (Panchen & Smithson 1988; Trueb &
Cloutier 1991; Ahlberg & Milner 1994). Computer-assisted phylogenetic analyses (d) suggest a monophyletic origin of
extant amphibians among 'lepospondyls' (Laurin & Reisz 1997; Laurin 1998a), (e) among temnospondyls (Ruta et al.
2003; Ruta & Coates 2007), or (f) a polyphyletic origin (Anderson 2007). Extant taxa are in bold type; paraphyletic
groups are identified by quotation marks and are not capitalized. Reptiliomorpha is euryhaline, as shown by the presence
of amniotes in both freshwater and in saltwater. The trees were drawn using MacClade 4 (Maddison & Maddison 2003).
(1980) and Carroll & Currie (1975), this clade
included all known amphibians (or at least, all tem-
nospondyls and most lepospondyls) (Fig. 1b).
With the advent of cladistics, earlier suggestions
(Bolt 1969; Schultze 1970) that extant amphibians
form a monophyletic group (that excludes all
known Palaeozoic tetrapods) became much more
widely accepted (Trueb & Cloutier 1991). These
ideas should have cast doubts about the environ-
mental
preferences
of
early
(stem)
amphibians,
