Terrestrial Palaeoecology and Global Change

280 Valentin A. Krassilov. Terrestrial Palaeoecology
Fig. 112. Saccate pollen grains
with zoosporangia of chitrid fungi.
The Early Cretaceous of
Mongolia (Krassilov, 1982).
gal sporangia consume the genetic material of a spore cell nucleus, potentially trunsducing
it with propagation of zoospores.
In the Late Silurian to Early Devonian, the early land plants appeared in the midst
of microbial communities of the rootless soil and were rooted there by way of mutualistic
co-adaptation (VIII.1.1) Mycorrhizal symbiosis had already developed at this
early evolutionary stage. Extant mycorrhizal fungi still induce lignification of host
tissues, a reaction going back to the origin of terrestrial plant habits, with plant lignins
owing to a fungal transduction of genes eliciting a benign plant response (as in the
case of chitinases: Salzer et al., 1997). Lignification then might have evolved as a
defence against arthropod damage eventually acquiring a mechanical function associated
with arboreal habit.
A widespread phenomenon conceivably related to interspecies gene transfer is the
so-called geographic parallelism, a spread of peculiar, selectionally neutral, characters
over a range of not closely related species within a geographic realm (Went, 1970). In
the geological record this phenomenon acquires a time dimension as the chronogeographic
parallelism over a geographic realm/stratigraphic interval. Thus, the Cordaitestype
linear-lanceolate leaves with subparallel venation prevail in the Late Palaeozoic
fossil plant assemblages of Euramerian, Angarian and Cathaysian realms. On evidence
of associated reproductive organs, this leaf morphotype occurred in different gymnosperm
orders, such as the Cordaitales, Vojnovskyales and Peltaspermales. Glossopteris,
a lingulate leaf morphotype with reticulate venation widespread in the Gondwana
continents, appeared not only in the nominate order Glossopteridales but also, simultaneously,
in the co-existing cycadophytes (IV.3). The Permian Gigantopteris and allied
morphotypes, with composite leaf blades of marginally fused segments and areolate
venation, belonged to different gymnosperm and marattialean taxa of the Cathaysian
(Cathamerian) realm. The Mesozoic Taeniopteris-type leaf morphology is shared by at
least three gymnosperm orders, the Cycadales, Bennettitales and Pentoxylales.