Page 150 - Introduction to Paleobiology and The Fossil Record

Chapter 6

Fossil form and function

Key points

• Fossil species are identifi ed according to their external form; this is termed the morpho-
logical species concept.
• Variations in form include normal levels of individual variation between members of a
species, as well as variation that results from geographic distribution, sexual dimor-
phism (different males and females), different growth stages, or ecophenotypic variation
(changes in form occurring within the lifetime of an organism as a result of the
environment).
• Fossil species may show allometry, or changes in relative proportions during growth;
specific organs may show positive (grow faster) or negative (grow slower) allometry.

• The development of an organism may give some evidence about phylogeny.
• Changes in developmental rates and timing (heterochrony) may affect evolution.
• The new “evo-devo” perspective shows how certain developmental genes control fun-
damental aspects of form, such as symmetry, front–back orientation, segmentation and
limb form.
• Inferring function from ancient organisms is diffi cult. There are various methods of
doing this: comparison with modern analogs, biomechanical testing and circumstantial
evidence.
• Modern analogs may provide exact parallels with some fossil organisms, but more often
they provide only principles or rules.
• Biomechanical models may be used to assess how the design of an ancient organism

matches the hypothetical forces acting on it; an example is finite element analysis, a
standard engineering technique.
• Biomechanical models of locomotion are easy to produce, but it is important to check
that all possible gaits have been considered.
• Circumstantial evidence, such as the enclosing rocks, associated fossils, trace fossils and
close study of the fossils themselves, can add considerable information on fossil func-
tion. Many such observations are the result of chance preservation.

There is grandeur in this view of life that, whilst this planet has gone cycling on

according to the fixed law of gravity, from so simple a beginning endless forms most
beautiful and most wonderful have been, and are being evolved.

Charles Darwin (1859) On the Origin of Species