Page 226 - Introduction to Paleobiology and The Fossil Record

PROTISTS 213

Box 9.3 Modeling of foram tests

David Raup’s theoretical work on the modeling of mollusk morphospace created a paradigm shift
in our understanding of shell ontogeny (see p. 332). The skeletons of many groups of organisms can
now be generated, mathematically, according to a simple set of equations in each case. The shapes
of microfossils can also be modeled in this way, with a set of rules based on the angle of deviation,
a translation factor and a growth factor (Tyszka 2006). By varying these, a huge range of possible
and impossible tests can be homegrown on the computer (Fig. 9.6). The forms illustrated here are
only a subset of the total number of possibilities. Interestingly, these sorts of computer models always
generate some bizarre forms. The dysfunctional forms, for example, are geometrically possible but
the shapes and volumes of the chambers could simply not function; vacant ranges on the other hand
contain fully functional morphologies but these forms have not yet been found in the fossil record.
Why not?

Δφ
0° 30° 60° 90° 120° 150° 179.99°
1.3
0.9 GF
1.2
TF
0.6 1.1

0.3 0.9 TF

0.001 0.6

–0.3 0.3

–0.6 0.001 0

–0.9 –0.3
1.3 –0.6

1.2
GF –0.9
1.1
0° 30° 60° 90° 120° 150° 179.99°
Δφ

Figure 9.6 Modeling foraminiferan tests: part of a theoretical three-dimensional morphospace for
foraminiferans. GF, growth factor; TF, translation factor; Δφ, deviation factor. (From Tyszka
2006.)