Page 166 - Introduction to Paleobiology and The Fossil Record

FOSSIL FORM AND FUNCTION 153

Wind-driven float
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Depth (m) 4 5

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Plankton
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(b)

(a) (c)

Figure 6.10 The use of a modern analog to interpret a mysterious fossil. (a) A colony of the
pseudoplanktonic crinoid Traumatocrinus attached to a fossil piece of driftwood, from the Late
Triassic of China. (b) Reconstruction of the crinoids in life, showing how the wind pulled the log
to the left, and the dangling crinoids captured plankton like a net. (c) A tow-net used to
maximize catches of fish, a possible modern analog that explains the feeding mode of the fossil

colony. (Courtesy of Wang Xiaofeng.)

tures, while other modeling methods seek to near enough right, but that the animators
establish how ancient organisms moved. chose only one out of many possible positions
A number of attempts have been made to for the limbs.
understand how dinosaurs ran, and of course In the most likely running gait (Fig. 6.13a)
everyone focuses on Tyrannosaurus rex. At the backbone is horizontal and the legs rela-
one level, we all know how T. rex ran – we tively straight and long. Whatever happens,
have seen it on Jurassic Park and Walking the animal must not fall over, so the fi rst thing
with Dinosaurs, so what is the problem? The in reconstructing locomotion is to determine
locomotion in those movies was based on the center of mass, the central point in the
study of the limb bones, calculation of their core of the body. This can be found crudely
ranges of movement, observation of modern by dangling a plastic model from a string and

ostriches at speed, and computer animations finding the three-dimensional central point of
that rendered a reasonable swing of the leg, balance – or a more elaborate set of calcula-
and that prevented the animal from falling tions can be done in the computer. In T. rex
over. But Hutchinson and Gatesy (2006) have the center of mass lay just in front of the hips,
urged caution. They argue that the style of and the tail balanced the body over the hips
locomotion shown in those fi lms is probably that acted as a fulcrum.