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(Luksevics 1992; Clack 2006). As mentioned above,
Tulerpeton was probably marine.
One of the first to question the freshwater, steno-
haline tolerance of all Permo-Carboniferous stego-
cephalians was Parrish (1978). His thorough
sedimentological, faunal and taphonomic study of
the Thrift bonebed in Wichita county (Texas) led
him to propose that
by recognizing 'crossopterygians', Diplocaulus,
Seymouria and Dimetrodon as 'truly deltaic
markers', but he did not comment on water salinity.
Several other recent studies raise doubts about
the interpretation of most Permo-Carboniferous
localities yielding stegocephalians as freshwater
environments (Table 2). This applies particularly
to North American localities such as Garnett,
Hamilton and Robinson (Kansas, USA) and Las
Cruces (Robledo Mountains, New Mexico, USA),
and suggests that many groups of early stegocepha-
lians inhabited marginal marine environments (at
least occasionally). Thus, they may have been eury-
haline (Schultze & Maples 1992; Schult 1994;
Schultze et al. 1994; Schultze 1995, 1999).
If the results of these studies are accepted, there
is actual evidence that the widespread (but not uni-
versal) intolerance of lissamphibians to the marine
environment is a relatively recent feature (it prob-
ably arose in the Late Carboniferous or in the
Permian) because their closest known relatives
have been found in coastal environments. This con-
clusion can be drawn whether a traditional phylo-
geny (Fig. 2a) such as Panchen & Smithson (1988)
or Lombard & Sumida (1992) or a more recent phy-
logeny such as Laurin (1998a) or Anderson (2001)
is used (Fig. 2b), since both presumed sister
groups of lissamphibians (lysorophids, among
lepospondyls and various dissorophoids, among
temnospondyls) appear to have tolerated saltwater
(Schultze 1995). This is supported not only by
body fossils, which could conceivably have been
transported into deltas and lagoons by rivers and
streams, but also by trace fossils such as burrows
and trackways (Schult 1994, 1995a, b).
In his studies of the Lower Permian Speiser
Shale fauna from Kansas, Schultze (1985, 1999)
...the strong possibility exists that the fauna [which
inhabited a former mudflat pond located only about
3 km from the sea and included abundant Trimerorha-
chis insignis, as well as less numerous remains of
Xenacanthus, Eryops, Zatrachys, Archeria, Diplocau-
lus, Ophiacodon and Dimetrodon] was capable of tol-
erating brackish, if not marine, salinities.
Earlier studies which suggested that Permo-
Carboniferous stegocephalians were freshwater
inhabitants led him to suggest that a storm had
caused a massive influx of saltwater into the pond,
and that 'Fresh-water species intolerant of marine
salinities would have been placed in double jeo-
pardy.' This hypothesis of the origin of at least
some of the stegocephalian fossils is plausible
because sudden and important variations in salinity
can be lethal, even for euryhaline species such as
Fejervarya cancrivora (Gordon et al. 1961,
p. 662) or Bufo viridis (Gordon 1962). However,
perhaps a massive influx of freshwater (quite
likely to occur in a coastal pond during or after a
storm) into a brackish to hypersaline pond might
have nearly as deleterious effects on the fauna. In
any case, Parrish (1978) suggested that some early
stegocephalians probably tolerated brackish to
saltwater. Among earlier studies, only Vaughn
(1969, p. 403) came close to suggesting brackish
water
tolerance
in
some
early
stegocephalians
(
a
)
(
b
)
euryhaline or marine
stenohaline, freshwater
equivocal
Fig. 2. Habitat of early stegocephalians inferred on the basis of parsimony and a review of the literature on their habitat.
Whether lissamphibians are part of (a) temnospondyls (Panchen & Smithson 1988; Lombard & Sumida 1992) or of (b)
'lepospondyls' (Laurin 1998a; Vallin & Laurin 2004), a freshwater (or terrestrial) habitat is an autapomorphy of
Lissamphibia. Under both phylogenies, the limited evidence of salt- or brackish water tolerance in early stegocephalians
suggests that this taxon retained the saltwater tolerance inherited from their finned ancestors.
