Page 98 - Introduction to Paleobiology and The Fossil Record

PALEOECOLOGY AND PALEOCLIMATES 85

Box 4.1 The terebratulide brachiopod Dielasma from the Permian of the
Tunstall Hills

The smooth terebratulide brachiopod Dielasma is common in the limestones and dolomites associ-
ated with the Permian reefs of the Sunderland area in northeast England. Is it possible to use data
from simple length measurements of the brachiopod shell to determine the growth strategies of these
animals? One sample shows a bimodal pattern suggesting two successive cohorts are present in the
population; overall the survivorship curve suggests increasing mortality with age, in possibly a stable,
equilibrium environment (Fig. 4.6). But this was not the only environment around these Permian
reefs; other samples show different-shaped curves, some demonstrating high infant mortality in pos-
sibly less stable environments, whereas a population with a bell-shaped curve suggests that the shells
have been transported and sorted prior to burial. A selection of datasets is available by following
this link, http://www.blackwellpublishing.com/paleobiology/.

30 30

Frequency Frequency

0 0
0 25 0 25
Length (mm) Length (mm)
(a) (b)
100 100
Cumulative frequency (%) Survivors (%)

0.1 0.1
0 25 0 25
Length (mm) Length (mm)
(c) (d)
Figure 4.6 Size–frequency histogram (a), polygon (b), cumulative frequency polygon (c) and
survivorship curve (d) for a sample of 102 conjoined valves of Dielasma from the Permian reef
base deposit of the Tunstall Hills, Sunderland. (From Hammer & Harper 2005.)

(their address) or with reference to their niche, of physical, chemical and biological factors
their lifestyle (their occupation). Modern may characterize an organism’s environment;
organisms occupy a range of environments unfortunately, few can be recognized in the
from the top of Mount Everest at heights of fossil record.
nearly 9 km to depths of over 10 km in the Some of the most abundant and diverse
Marianas Trench in the Pacifi c Ocean. Recog- communities inhabit the littoral zone, where
nition of extremophiles (see p. 205), living in rocky shores hold some of the most varied
even more bizarre habitats, has considerably and extensively studied faunas. For example,
extended our understanding of the environ- nearly 2000 individual organisms have been
2
mental range of life on Earth. A large number recorded from a 250 mm quadrat on an