You're viewing this item in the new Europeana website. View this item in the original Europeana.

Paleoecology of carboniferous arboreous Lycopsids from order Lepidodendrales with special consideration of region of Balkan peninsula

During the Carboniferous period, 320-306 million years ago, swamp forests
with tree-like lycopsids named Lepidodendrales as edificatory species have
developed in the region of tropical belt (paleoequator). The lycopsids belong
to the general division of Lycopodiophyta, representing one of the oldest
plant groups, and their evolution continues to this day. The oldest lycopsids
have appeared about 400 million years ago and their representatives from
genera Asteroxylon, Drepanophycus and Baragwanathia belong to the group of
first land plants. Lycopodiophyta were also the first land plants to form the
phanerophyte life form (genera Cyclostigma and Archaeosigillaria in Upper
Devonian, 370 million years ago). During the Carboniferous period, the
arboreous lycopsids have reached their maximal development. At that time
there were large areas of paleotropical belt covered in swamp forests, where
the edificatory species were Lycopodiophyta over 40 m tall. The Carboniferous
arboreous lycopsids belonged to order Lepidodendrales and genera
Lepidodendron, Synchysidendron, Diaphorodendron, Lepidophloios and
Sigillaria. By the end of Carboniferous (about 300 million years ago) all the
arboreous lycopsids became extinct, and according to present knowledge the
tree-like life forms never appeared again in this group. Today the
representatives of Lycopodiophyta are a marginal group of plants, with a
minor role and importance in various vegetation lists. Their representatives
(Lycopodium, Selaginella, Isoetes etc.) have almost no morphological
similarities with the arboreous lycopsids of order Lepidodendrales. The
comparative analysis of Lepidodendrales and the recent dendroflora was mostly
based on principles of actualism and rules of plant fossilization. The
actualistic methods were applied as some basic similarities were noted in
development of vegetation in Upper Carboniferous and Neogene/Quaternary. It
is particularly important to mention certain factors/events that led to
formation and differentiation of different vegetation belts. They include
appearance of Carboniferous and Pleistocene Ice Ages, appearance of intensive
orogeny (Hercynian/Variscan and Alpine), formation of similar wetland
habitats, presence of a tropical vegetation belt, as well as the fact that
Carboniferous and Neogene swamp forests have both left behind prominent large
amounts of coal. The paleotropical forests dominated by tree-like lycopsids
of order Lepidodendrales are representative of particularly important forest
vegetation, well-documented by fossils. Its complex ecological importance may
be summed in a following way: 1. Unsustainable energetic resources of
enormous amounts of Carboniferous coal, mostly originating from stems of
Lepidodendrales. 2. Morpho-anatomic characteristics convergent with those of
phylogenetically distant land (vascular) seed plants (tree-like habit,
branching types, seed-like structures, appearance of monocarpy). This
indicates that many of the plant characteristics and life forms (in this case
phanerophytes) have appeared independently several times in phylogenetically
distant evolutionary lines. 3. The accelerated development of land animals
took place only after the formation and development of lush paleotropical
forests and appearance of favorable forest microclimates, suitable habitats
and almost infinite sources of food. In order to explain development and
dynamics of these forests, paleoecological characteristics of certain
edificatory genera were analyzed. The reference genera were chosen by number
of fossil and literature data and by being previously determined as
morphotypes, for example Lepidodendron, Synchysidendron, Diaphorodendron,
Lepidophloios and Sigillaria. These genera were compared with structural
characteristics of recent representatives of dendroflora, primarily trees and
woody seed plants, regarding the general habit, type of branching, height of
habit/stem and characteristics of root system. Appearance and role of similar
or different morpho-anatomical characteristics in studied fossil
Lepidodendrales and referenced representatives of recent dendroflora were
used to determine numerous convergent structural characteristics explaining
the paleoecological character and importance of extinct Lepidodendrales
During the analysis of general habit and height of trees, it was determined
that the monocarpous species, particularly the genus Lepidodendron, could
reach over 40 m in height (that is the greatest determined height of this
genus so far), indicating that certain representatives of Lepidodendrales
could reach the height of recent conifers and were taller than many
present-day arboreous flowering plants. Analogous heteroblastic and
monocarpous characteristics of vegetative and reproductive adult stages were
recorded in representatives of ancient genera Lepidodendron, Synchysidendron
and Lepidophloios and in recent monocarpous species from families Agavaceae,
Bromelidaceae and Asteraceae. The monocarpous Lepidodendrales are showing
certain similarities with some giant rosette-bearing (herbaceous) monocarpous
plants of genus Agave, which have a pronounced heteroblastic change in
habitus during the reproductive stage. As monocarpous representatives of
Lepidodendrales remain in the habitat after the reproductive phase, they may
also be compared with arboreous monocarpous species of genus Tachigali, which
lack the heteroblastic changes but also remain in the habitat for some time
after the reproductive phase, providing shelter for young individuals of its
species with its stem. Also noted was similarity of heteroblastic changes
during the shift from the vegetative to the reproductive stage in
Lepidodendrales and shift from the juvenile to the adult stage in recent
polycarpous species of genus Pseudopanax. The comparative analyses based on
structure and role of leaves and leaf cushions led to conclusion that leaves
of Lepidodendrales, periodically excised while leaving leaf bases (cushions)
on the stem, are a unique characteristic of order Lepidodendrales and may not
be definitively compared with recent plants. On the other hand, there are
certain analogous morphological characteristics of main flower parts,
primarily the leaf plate and ligula in Lepidodendrales and certain recent
plants. The transversal cut of leaf plate of Lepidodendrales is similar to
that of certain species of Pinus from Diploxylon group or species from
Haploxylon group. The ligula of Lepidodendrales may be compared to some
extent to ligula in family Poaceae, primarily due to the similar position –
between the leaf and the stem, at the transition between the leaf sheath and
blade. The rhizomorph or root system of Lepidodendrales named stigmaria
(genus Stigmaria) may be compared with roots of certain recent woody plants
from wetland and marsh habitats. It may be assumed that the lateral root
shoots of stigmaria had a role in aeration, similar to pneumatophores in
roots of present-day species from genera Taxodium, Nyssa, or mangrove
vegetation (Rhizophora spp.). In relation to the large number of fossil
remains it was concluded that stigmaria were aerial organs or aerial parts of
root system, while the underground part, like many other underground plant
organs, was not preserved in fossil form. The Ph.D. thesis also includes a
comparative analysis of paleotropical forests of Lepidodendrales and
corresponding recent forest associations. It was determined that the
paleotropical forests show most similarities with the subtropical swamp
forests dominated by swamp conifer Taxodium spp. Both these associations,
although very distant from each other in time, are characterized by similar
swamp soil and similar random distribution and general habitus of edificatory
species – the greatest part of phytomass is situated in the bole while the
canopy size is negligible. The paleotropical swamp forests may also be
compared to the recent tropical rainforests, as both associations develop in
conditions of humid tropical climate. However, it must be considered that the
structure of recent tropical forest is far more complex due to diverse life
forms developed by various species of flowering plants. Also discussed was
certain analogy between the paleotropical forests of Lepidodendrales and
boreal conifer forest (taiga), expressed in low taxonomic diversity and a
small number of edificatory species. This dissertation is the first paper
with detailed analysis of all studies on Lepidodendrales performed at Balkan
Peninsula. The available data in floristic lists and paleophytocoenological
data on a larger number of different paleotropical associations of
Lepidodendrales in western and central parts of Balkans (the territories of
present-day Slovenia, Bosnia-Herzegovina and Serbia) were used for
reconstruction of possible/assumed habitat of appropriate paleophytocoenoses.