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1985). The expression of this double-LAG pattern
leads to the assessment of the somatic age on the
basis of accounting two LAGs per year.
add complementary suggestions to the current
knowledge on the palaeoecological, palaeoaltitudi-
nal and palaeoclimatic reconstructions of the basin.
A. pedestris from Odernheim. The skeletochronolo-
gical analysis shows that the number of growth
marks in this set of A. pedestris varies between four
and seven (Fig. 3a). This indicates that the youngest
specimen (SMNS 54963) was at least four years old
whereas the oldest one (SMNS 54988) was at least
seven years old when it died.
Palaeoecological influence on bone growth
of studied populations
The current histological data show some variations
in the diaphyseal bone-growth rate that could par-
tially explain the body size differences between
the studied taxa; the specimens of A. caducus from
Erdesbach are on average larger than those of
A. pedestris from Odernheim and Niederkirchen.
Moreover, it seems that these bone-growth differ-
ences could also be correlated with the different
palaeoecological living conditions of the sampled
populations. Indeed, Boy (1977, 1987) and Boy
et al. (1990) concluded that the Niederkirchen lake
(L-O-6) and the Erdesbach lake (L-O-7) were prob-
ably rich in planktonic nutrients. However, the Nie-
derkirchen lake was dominated by large sharks
while the Odernheim lake (L-O-8) (even if large
and dominated by small temnospondyls) offered
poorer living conditions. Hence, the differences in
bone-growth rate might also reveal differences in
overall living conditions of the freshwater lakes,
especially regarding food supply and trophic chain.
A. caducus from Erdesbach. According to the skele-
tochronological analysis, the number of growth
marks varies from three to eight (Fig. 3b), sug-
gesting that the youngest specimen (GPIM-N
1589) was three years old whereas the oldest one
(GPIM-N 1602) was eight years old when it died.
A. pedestris from Niederkirchen. The earliest indi-
vidual was two years old when it died (GPIM-N
1471)
and
the
oldest
one
was
nine
years
old
(SMNS 55017).
Palaeoecological and palaeoclimatic
implications
Most authors agree with the fact that the Saar-Nahe
and adjacent basins held intermountainous positions
within the vast Variscan Orogen, at an altitude of at
least several hundred metres (Ziegler & Gibbs
1996). Schultze & Soler-Gij ´n (2004) suggested a
marine influence on the sediments of the Saar-Nahe
Basin, inferred largely from the ecological prefer-
ences of modern sharks. However, as the fossil
amphibians could have lived in various water
environments (from freshwater to marine environ-
ments; Steyer 2002), we prefer to leave this question
of the marine influence unanswered. From a geo-
logical perspective, there is little doubt that the Saar-
Nahe Basin was levelled at high altitude and was
indeed lacustrine (Sch¨fer & Stamm 1989; Boy
and Sues 2000), but we do not exclude any episodic
marine influence by storms, tsunamis, winds, etc.
(as this would depend on various factors such as
topography, distance from the coast, climate, etc.).
As the Saar-Nahe Basin was situated in the
tropics during the Late Carboniferous and Early
Permian (Poplin 1994; Fluteau 2003; Roscher &
Schneider 2006), the studied branchiosaurid
samples represent populations that inhabited the
same large-scale climatic zone. These populations
fall in three different time slices (L-O-6, L-O-7,
L-O-8 of Meisenheim Formation) that might have
spanned a total time interval of around one million
years (Fig. 1).
Bone microstructures and LAG patterns, which
differ between the studied samples (Fig. 3d), may
Palaeoclimatic influence on biological
cycles of Apateon individuals
All the specimens from Odernheim (A. pedestris)
show a simple-LAG pattern whereas the specimens
from Erdesbach (A. caducus and A. pedestris) some-
times show double LAGs. The sampled set of
A. pedestris from Niederkirchen throughout pre-
serves a double-LAG pattern. Finally, the popu-
lations from Rehborn (A. pedestris), even if
represented by a very tiny sample, seem to express
a simple LAG pattern (Fig. 3d).
Different hypotheses (described below), or their
combination, could explain the observed locality-
specific variation in LAG patterns.
Clines of palaeoenvironmental conditions through
geological time. A skeletochronological study has
been conducted on low- and high-elevation popu-
lations of the extant newt T. marmoratus from the
Northern Mountains (National Park of Peneda
Gerˆs) of Portugal (Caetano et al. 1985; Caetano
& Castanet 1993). This skeletochronological analy-
sis showed that populations living at elevations of
1.5 km hibernate during winters because of the
very low local temperature and aestivate during
summers because of high temperature and
drought. However, populations living at elevations
between 650 m and 1 km only sometimes show a
