Part 3
Many older palaeobotanical textbooks distinguish a clear floral break within
the Permian. This is the so-called
Palaeophytic-Mesophytic boundary (e.g., Gothan & Weyland 1954). The Late
Permian Zechstein floras of northwest and central Europe indeed show
considerable differences compared to the Rotliegend floras. However, in
later years it has become clear that the Zechstein represents only a rather
limited amount of time, and that the northwest and central European Permian
is very incomplete. Moreover, many sediments are unfossiliferous. A few
years ago conifer-dominated floras including taxa which can be considered as
direct descendants of Rotliegend conifers have been described from the Upper
Permian of the Italian Alps. Moreover, palynological investigations have
shown that the succession is much more continuous than was assumed until
recently. The more complete classical succession in Russia shows a very
gradual development of the flora that does not support the assumption of a
Palaeophytic-Mesophytic floral break in the Permian. The differences that
have been emphasised in the earlier literature thus rather refer to the
incompleteness of the fossil record and our knowledge than to hard facts.
Although within Europe certain differentiations can be noted, the floras of
the Upper Permian generally have a very low diversity and are dominated by
conifers. Many of these forms have thick and fleshy leaves, usually with
thick cuticles covered by many hairs. This suggests a warm and dry climate.
An arid climate is also indicated by the presence of thick evaporite
deposits. Also pteridosperms partly show such adaptations to an arid
climate.
Fig. 6: An Early Permian landscape in the Saar-Nahe Basin.
According to recent estimations, about 95% of all plant and
animal species and 50% of all genera became extinct at the end
of the Permian (Erwin 1993). This is the largest mass extinction
in Earth's history. However, macropalaeobotanical data are not
available because the uppermost Permian and lowermost Triassic
are virtually always developed in a marine facies. Therefore, the
floral record exclusively relies on palynological data. The causes of
this mass extinction are still being discussed and a generally
accepted scenario has not yet been put forward. Although many plant
species and genera became extinct, the larger
groups of plants mostly persisted. Many genera of conifers which
were dominant in the Late Permian disappeared, but were replaced
by others and also in the Triassic conifers were often predominant.
This is in strong contrast to the fauna; several groups of
animals became completely extinct like the trilobites.
Fig. 7: The stratigraphy of
the Upper Palaeozoic with the most important floral developments.
For further literature on Palaeozoic forests please refer to the above
mentioned publications.
U = lake margin vegetation with calamites, ferns and a few seed ferns; Si =
Sigillaria stand in a deltaic environment;
P =
pteridosperm-dominated vegetation; K =
conifer-dominated hinterland vegetation.