Page 170 - Introduction to Paleobiology and The Fossil Record

FOSSIL FORM AND FUNCTION 157

stance phase swing phase

(a)
early stance mid-stance late stance

muscle
moment

GRF {
knee
moment
arm
(b) (c) (d)

(e) (f) (g)

Figure 6.13 The running stride of Tyrannosaurus rex. (a) The main components of a stride, showing
the stance phase when the foot touches the ground, and the swing phase. (b–d) Three positions of the
limb in early stance, mid-stance and late stance, as the body moves forward, and showing the main
forces, including the ground reaction force (GRF). (e–g) Three alternative postures for the limb, with
the body held high or low. Read more, and see the movies at http://www.rvc.ac.uk/AboutUs/Staff/
jhutchinson/ResearchInterests/beyond/Index.cfm. (Courtesy of John Hutchinson.)

example, fossil reefs may be killed off in There are some rare examples of arthro-
a particular crisis, and all the organisms pods preserved at the ends of their trails.
that lived together are found in life posi- The link between trace fossil and producer
tion; some corals, bryozoans and crinoids is usually a little less clear: dinosaur foot-
may be fixed to the substrate in their prints may be found at certain levels within

normal growth position, and mobile a particular geological formation, and the
organisms like gastropods or trilobites skeletons of likely producers at other
may be preserved among the thickets of levels. The bones of fishes and marine rep-

benthic sessile organisms. Similarly, a tiles may be found associated with phos-
paleosol (see p. 518) may preserve roots phatic coprolites (fossil dung) in certain
and stems of dozens of plants in life posi- marine beds – it is likely that the copro-
tion, together with burrows of insects and lites were dropped by one or other of the
worms that lived among them. Associa- associated animals. If a link can be made
tions of fossils can also be more intimate, between a trace fossil and its maker, then
where for example parasites may be found a great deal of additional paleobiologi-
attached to their hosts, or fossils of one cal information can be established (see
species may be found in the stomach Chapter 19).
region of another. 4 Close study of the body fossils themselves
3 Associated trace fossils can sometimes be is also warranted. Skeletal fossils regularly
linked to their producers, but not always. preserve evidence of soft tissues and other