Terrestrial Palaeoecology and Global Change

Chapter 4. Palaeoecogeography
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the Permian coniferoid xeromorphs, often preserved as scattered scale-leaves (e.g., in
the Nedubrovo locality: II.7.2). Mesozoic brachyphylls of a highly variable shoot morphologies
(Fig. 39), often show basally constricted or obliterate branchlets. Accumulations
of detached coriaceous scale-leaves of pro-gnetophytic Dinophyton (Ash, 1970;
Krassilov & Ash, 1988) and hirmerellids are examples of the Ephedra-type microphyll
deciduousness.
In bennettites of Ptilophyllum–Otozamites morphotypes, the swollen petioles of pinnate
macrophylls might have been due to insect galling that inflicted leaf shedding that
developed into seasonal deciduousness as an adaptation to the wet/dry climate. High
frequencies of galled, mined or cut leaves in early angiosperms (Krassilov & Baccia,
2000) suggest a low level of biochemical defense. This invites consideration that angiosperm
deciduousness arose in response to herbivory or, with insect pollination, for
redirecting insects from leaves to flowers (VIII.1.2).
IV.2.3. Conifer forests
The Palaeozoic coniferoids have appeared as sclerophyllous wetland plants derived
from helophytic pteridosperms. Ecologically they were perhaps comparable with swamp
cypresses of the presently relict coniferous wetlands. The prehistory of the modern-type
conifer forests commenced in the mid-Triassic with differentiation of the modern families
Araucariaceae, Podocarpaceae, Taxodiaceae and Pinaceae the latter two families
linked to the ancestral voltziaceaous stock via the transitional Swedenborgia
(Podozamites), Elatides and Schizolepis (Pityophyllum). On taphonomic evidence, all
these were riparian trees or shrubs. Both Podozamites and Pityophyllum shed leaves
and leafy short-shoots frequently preserved as leaf-mats. Elatides and derived scaleleaved
taxodiaceous morphotypes are abundant in fluvial facies. Their germinate seeds
and seedlings were found in situ in flood-plain alluvium (Krassilov, 1987, Fig. 24).
At the communal level, the Podozamitetum was cosmopolitan as a streem-side community,
while the Pityophylletum occurred over a wide range of peatland facies, with
the needle-leaved pinaceous conifers forming pure stands or co-dominant in the Pityo–
Pseudotorellietum, Pityo–Baieretum, etc., the edaphic variants of temperate wetland
forests. The Elatidion formed a distinct catenic belt of riparian vegetation next to fernmarshes
(III.3.3) attesting to evolutionary continuity of the arboreal wetland line.
At the Cretaceous stage of adaptive radiation, these scale-leaved and needle-leaved
wetland communities gave rise to mesic varieties, with morphological innovations in their
dominant conifers. The Athrotaxites–Geinitzia–Parasequoia component of Cretaceous
shrublands (below) might have derived from the Elatidion, with Sphenolepis or related
transitional forms. The mesic derivatives of Pityophyllion were dominant over the highlands
of Mongolo-Okhotskian fold-belt, with their wind-borne cone-scales, samaras and
occasional leafy spur-shoots reaching deposition sites in rift lakes of Transbaikalia and