Page 299 - Introduction to Paleobiology and The Fossil Record

286 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box 11.6 Computer reconstruction of colonies

The colonial tabulate Aulopora had a long geological history and mainly occupied an encrusting
niche, coating brachiopods, stromatoporoids and other, larger corals. Aulopora grew by dichoto-

mous branching, pursuing a creeping or reptant life mode, efficiently siting its corallites adjacent to
potential sources of food at, for example, the inhalant currents through brachiopod commissures.
Colin Scrutton (University of Durham) has reconstructed colonies of the free-living animals in three
dimensions using a computer-based technique (Fig. 11.28). Serial sections of the colony were digitized
and assembled on a micro-VAX mainframe with software routinely used for building up three-
dimensional views of diseased kidneys. Both the ontogeny of the procorallites and the astogeny of
the colony as a whole were established in considerable detail by these techniques. With the develop-
ment of desk and laptop microcomputers such modeling is now, more or less, routine.
Halysitids were tabulate corals that dominated some Ordovician and Silurian assemblages. As
each colony grew, budding chains were able to find their way back to the colony, instead of heading

off in random directions. Perhaps they could sense the gradient of a diffusive fi eld of “pheromones”,
their waste products or the depletion of nutrients set up by the colony. In a simulation by Hammer
(1998), new protocorallites are introduced into random positions, simulating “polyplanulate” asto-
genesis and the diffusive zones are established by numerically solving the differential equation for
diffusion and decay.
Other fossil simulations are available at http://www.blackwellpublishing.com/paleobiology/.

(b)

(c)

(a)

(d)
Figure 11.28 Aulopora morphology: computer-generated reconstructions of (a) the plan, (b) the
lower side, and (c) the direction of the procorallite; (d) reconstruction of the colony. (Courtesy of
Colin Scrutton.)