Terrestrial Palaeoecology and Global Change

Chapter 5. Tectonic factors of global changes
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convergence in the western part of it and to divergence in the east. It is virtually impossible
to reconcile the reconstructions for the Permian/Triassic with those for the Late
Triassic without invoking a megashear that is not there (Weil et al., 2001).
Despite such geological inconsistencies, the Gondwanaland concept is immensely
popular among biogeographers and evolutionists relating phylogenetic divergence to continental
separations. In particular, it encouraged separate phylogenies for the “northern”
and “southern” plant orders, such as conifers (Florin, 1954; Meyen, 1987). There are
also proponents of a pre-Cretaceous divergence of the “Laurasian” and “Gondwanic”
angiosperms.
The following considerations seem pertinent to the Gondwanaland concept as it stands
today:
(1) All terrestrial plants are able to surmount water barriers. Some terrestrial plants,
such as the coconut palm, are adapted to dispersal by sea currents. If terrestrial
plants do not disperse over seaways (as, for instance, the redwood species that
are lacking on the offshore Californian islands), an explanation can be more
readily related to habitat limitations rather than water barriers.
(2) Floristic differentiation, even of the highest phytogeographic rank, as between
the African Sahel and Cape provinces, can develop even in the absence of
water barriers. The continuity of Glossopteris flora does not prove a continuous
landmass.
(3) Landmass separation in the Early Carboniferous did not interfere with, even
seemed promoting a floristic homogeneity, whereas the floristic divergence of
Gondwana and Laurasia developed at the time of landmass aggregation on the
way to “Pangea”.
(4) The major groups of the present-day “southern” conifers, the Araucariaceae
and Podocarpaceae, were widely spread over the northern continents during the
Mesozoic and early Tertiary (Krassilov, 1967a, 1976a). Extinct angiosperms related
to the presently typically “southern” Proteaceae and Nothofagus have
been also found on Laurasian lands (e.g. Ushia: Krassilov et al., 1996b). Their
present-day southern distribution is owing to their persistence there rather than
the Gondwanaland origins.
In much the same way, the “Angaraland” has preserved its climatic and vegetational
identity far beyond its supposed isolation as a landmass by the Uralian and Mongolo-
Okhotskian seaways. The ecotonal Eurangarian (“Subangarian”) and Cathangarian provinces
over the boundaries of “Angaraland” are evidence of climatic differentiation rather
than landmass separation.
As discussed in (IV.3.1), the Permian phytogeography reflects a system of cooltemperate
to tropical biomes that concur with the present-day latitudinal zones, thus
scarcely compatible with the palaeogeographic reconstructions in which Laurasia is placed