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double-LAG pattern, indicating occasional drastic
climatic conditions. At elevations of lower than
550 m, the newt populations do not encounter such
ecological conditions and only hibernate each year.
A similar situation could explain the different
LAG patterns observed in the studied lacustrine
populations of Apateon. It can be assumed that
Niederkirchen (which yielded individuals with a
double-LAG pattern) may have been at a higher
elevation than Erdesbach (which yielded individ-
uals with only occasional double LAGs), which
may have been at a higher elevation than Odernheim
and Rehborn (where no individuals present any
double-LAG patterns).
Such data are consistent with the current model
on the Variscan orogen (Wagner & Lyons 1995)
and the Rotliegend lake systems (Sch¨fer &
Stamm 1989; Stapf 1989), where elevations of up
to 2 km have been calculated in the palaeoaltitudinal
models (e.g. Ziegler & Gibbs 1996).
The crucial point is that these localities also rep-
resent different stratigraphical time intervals
(Fig. 1). When they are ranked according to their
stratigraphical age, Niederkirchen, which is hypoth-
esized to be at the highest altitude, is the oldest
locality (L-O-6). Erdesbach has an intermediate
age (L-O-7) and altitude while Odernheim and
Rehborn are both the youngest localities (L-O-8),
which are also assumed to be at the lowest altitude.
This may indicate that during their existence, the
Saar-Nahe lake systems probably passed from a
higher altitude climatic zone to a lower one, poss-
ibly because of subsidence and/or erosion. Accord-
ing to this scheme, this would have occurred 297
million years ago throughout a period lasting one
million years.
The double-LAG pattern also suggests a signifi-
cant seasonality in the tropical Saar-Nahe Basin.
This palaeoclimatic scenario should of course be
tested with further bone sections of different ver-
tebrates from the Saar-Nahe fauna. However, up to
now, sedimentological (Schneider & Gebhardt
1993; Clausing & Boy 2000) and palaeobotanical
(Ziegler 1990) analyses of this Carboniferous -
Permian European basin have supported the hypoth-
esis of a strong seasonality.
that the palaeoecosystem of the small lake from
Niederkirchen would be more responsive to high
climatic fluctuations (obliging populations of
Apateon to hibernate and aestivate) while the
palaeoecosystems of Erdesbach, and more particu-
larly Odernheim, were more stable (less sensi-
tive
to
seasonal
variations),
because
of
their
respective sizes.
Conclusions
Bone histology and skeletochronology of Apateon,
an abundant Carboniferous and Permian dissoro-
phoid temnospondyl from Europe, have been ana-
lysed for the first time. This analysis is based on
extensive samples of well-preserved growth series
of A. pedestris and A. caducus from the Lower
Permian of the Saar-Nahe Basin, Germany. It com-
pletes previous anatomical data by assessing the
somatic age and the growth rhythms. Moreover,
this analysis also allows a better understanding of
the life-history traits of this key dissorophoid,
often considered to be phylogenetically close to lis-
samphibians. The diaphyseal LAG organization of
Apateon is similar to that of extant urodeles and
shows a double-LAG pattern in some populations,
similar to that of individuals of T. marmoratus
living at relatively high altitudes in the Portuguese
mountains. The latter hibernate and aestivate every
year because of the strongly seasonal climate.
This therefore suggests (1) some populations of
Apateon could probably have hibernated and aesti-
vated every Permian year; (2) the specimens
presume a relatively high palaeoaltitude of the fos-
siliferous localities where they come from
(especially Niederkirchen and Erdesbach); (3) the
probable occurrence of subsidence or erosion 297
million years ago; (4) the confirmation of palaeoe-
cological variations in the different lacustrine
systems; and (5) a strongly seasonal local palaeocli-
mate. (Points 2, 4 and 5 are confirmed by sedimen-
tological and palaeobotanical studies on the
Saar-Nahe Basin.) This is the first time that a bone
palaeohistological analysis has such clear impli-
cations
for
palaeoenvironments,
landscapes
and
palaeoclimates.
Changes in palaeoecological conditions. The
palaeoecology of the lakes from the different
localities has been studied by Boy (1977, 1987)
and Boy et al. (1990) who concluded that the Nie-
derkirchen lake (L-O-6) was rather deep and small
(10 km) while the Odernheim lake was much
larger (70 - 80 km). The Erdesbach lake was prob-
ably intermediate in size and similar to the
(stratigraphically much younger) Kappeln lake
described by Boy (1987). In this context, the
current skeletochronological data would suggest
The authors acknowledge the Museum f¨ r Naturkunde
(Berlin, curator O. Hampe) for providing a part of the
fossil material and allowing the material from the collec-
tions to be sectioned; A. Abourachid (Mus´um national
d'Histoire naturelle and UMR 7179, Paris) for support;
B. Le Dimet and M. Lemoine (Mus
´
um national d'Histoire
naturelle and UMR 5143, Paris) for casting the specimens
and preparing thin sections; P. Loubry (Mus´um national
d'Histoire naturelle and UMR 5143, Paris) for the pictures
of the specimens; T. Schindler (Landesamt f ¨r Denkmalp-
flege,
Mainz)
and
R.
Weitz
(Germany)
for
fruitful
