80 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD
PALEOECOLOGY
Pebbles and shells on the beach give us clues
about their sources. Paleontologists can recon-
struct ancient lifestyles and ancient scenes
based on such limited information, and this is
the basis of paleoecology. Paleoecology is the
study of the life and times of fossil organisms,
the lifestyles of individual animals and plants
together with their relationships to each other
and their surrounding environment. We know
a great deal about the evolution of life on our
planet but relatively little about the ways
organisms behaved and interacted. Paleoecol-
ogy is undoubtedly one of the more exciting
disciplines in paleontology; reconstructing
past ecosystems and their inhabitants can be
great fun. But can we really discover how
extinct animals such as the dinosaurs or the
graptolites really lived? How did the bizarre
animals of the Burgess Shale live together and
how did such communities adapt to environ-
mental change?
It is impossible to journey back in time to
observe extraordinary ancient communities,
so we must rely on many lines of indirect
evidence to reconstruct the past and, of course,
some speculation. This element of speculation
has prompted some paleontologists to exclude
paleoecology from mainstream science, sug-
gesting that such topics are better discussed
at parties than in the lecture theatre. Emerg-
ing numerical and statistical techniques,
however, can help us frame and test hypothe-
ses – paleoecology is actually not very differ-
ent from other sciences.
More recently, too, paleoecology has devel-
oped much wider and more serious signifi -
cance in investigations of long-term planetary
change; ecological data through time now
form the basis for models of the planet’s
evolving ecosystem. The infl uential writings
of James Lovelock have extravagantly echoed
the suspicions of James Hutton over two cen-
turies ago, that Earth itself can be modeled as
a superorganism. The concept of Gaia
describes the planet as a living organism
capable of regulating its environment through
a careful balance of biological, chemical and
physical processes. Ecological changes and
processes through time have been every bit as
important as biodiversity changes; these
studies form part of the relatively new disci-
pline of evolutionary paleoecology.
Paleoecological investigations require a
great deal of detective work. It is relatively
easy to work out what is going on in a living
community (Fig. 4.1). Ecologists are very
interested in the adaptations of animals and
plants to their habitats, the interactions
between organisms with each other and their
environment, as well as the fl ow of energy and
matter through a community. Ecologists also
study the planet’s life at a variety of levels
ranging through populations, communities,
ecosystems and the biosphere as a whole. By
sampling a living community, ecologists can
derive accurate estimates of the abundance
and biomass of groups of organisms, the
diversity of a community and its trophic struc-
ture. But fossil animals and plants commonly
are not preserved in their life environments.
Soft parts and soft-bodied organisms are
usually removed by scavengers, whereas hard
parts may have been transported elsewhere or
eroded during exposure (see Chapter 3). In a
living nearshore community (Fig. 4.1) the
soft-bodied organisms, such as worms, would
rapidly disappear together with the soft parts
of the bony and shelly animals, for example
the fi shes and the clams; the multiskeletal
organisms such as the bony fi shes would dis-
aggregate and animals with two or more shells
would disarticulate. Fairly quickly there
would only be a layer of bones and shells left
with possibly some burrows and tracks in the
sediment. Moreover, some environments are
more likely to be preserved than others;
marine environments survive more commonly
than terrestrial ones.
Although fossil assemblages suffer from
this information loss, paleoecological studies
must, nevertheless, have a reliable and sound
taxonomic basis – fossils must be properly
identifi ed. And although much paleoecologi-
cal deduction is based on actualism or unifor-
mitarianism, direct comparisons with living
analogs, some environments have changed
through geological time as have the lifestyles
and habitats of many organisms. For example,
some ecosystems such as the “stromatolite
world” – sheets of carbonate precipitated by
cyanobacteria (see p. 189) – existed through-
out much of the Late Precambrian, returning
during the Phanerozoic only after some major
extinction events and only for a short time
(Bottjer 1998). Nevertheless, a few basic prin-
ciples hold true. Organisms are adapted for,