OFR 151.pdf - CRC LEME

2.1.3 Palaeoecology
Palaeoecology is the study of the interactions of organisms with one another and with their
environment in the past. It differs from the ecology of living organisms in that incomplete
preservation usually prevents direct observation of many aspects of the biota.
2.2 Plant macrofossils
Plant macrofossil assemblages (macrofloras) constitute a highly detailed record of past
vegetation that is strongly biased towards plants growing close to water, e.g. on the banks of
sluggish rivers or around lakes (Burnham 1989, Christophel and Greenwood 1987a,
Greenwood 1992, 1994, Alexander et al. 1999).
2.2.1 Taphonomic constraints
Plant remains are subjected to a number of processes between the time of abscission and their
burial in sediments where conditions may or may not lead to long-term preservation. For
example, cellulose and lignin, which are the major compounds making up cell walls, are the
food source for many fungi and soil invertebrates. Similarly, the size of many plant remains
makes them susceptible to physical attrition during transport and deposition, especially by
water and wind. Accordingly, except under anoxic conditions, only the more robust plant
parts such as roots, stems, twigs and leaves are preserved in an unaltered state. The most
commonly found remains are leaves, particularly those of species with naturally dehiscent
foliage such as deciduous trees.
2.2.2 Taxonomic constraints
The taxonomic level to which plant macrofossils can be identified using foliage or wood is
high, often to genus or species level, since many of the taxonomic characters are the same as
the characters used to identify modern plant species or genera. For example, leaf cuticle is
chemically stable, and microscopic features such as the distribution of stomata and presence
of trichomes (plant hairs) allow small fragments to be compared with those of living species
with great accuracy, even when primary taxonomic evidence such as flowers and fruits are
absent. Similarly the arrangement of the various types of cells making up wood (xylem)
allows some stem remains to be assigned to modern genera. If such characters are not
preserved, e.g. in impressions and casts, it can be difficult or impossible to determine
phylogenetic affinities accurately (Jordan and Hill 1999).
The resistance to decay of wood and leaf cuticle is similar to that of fossil spores and pollen
and both are major components of the finely disseminated (acid-resistant) detritus (kerogen)
preserved in sedimentary rocks (cf. Rowett 1993a).
2.3 Plant microfossils
Fossil pollen and spores (miospores) together with phytoliths and algal cysts are by far the
most abundant and widespread of all plant remains. Although dispersed by much the same
transport processes, the distinction between spores and pollen is an important one in plant
migration, and therefore how the palaeobotanical record mirrors past climates:
• Spores are produced by fungi, mosses, liverworts, fern allies and ferns (collectively
termed cryptogams) and are functionally equivalent to the seeds of flowering plants in
that they germinate to produce the next generation of plants. Dispersal is by wind
and/or water, less commonly by foraging insects.
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