Page 285 - Introduction to Paleobiology and The Fossil Record

272 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Box 11.2 Plugging the leaks: experimental morphology of archaeocyaths

It is often extremely difficult to reconstruct the life modes of long-extinct organisms that apparently

lack modern analogs (see p. 150), particularly when the entire phylum is extinct. In an innovative
experimental biomechanical study Michael Savarese (then at Indiana University) constructed models
of the three main archaeocyathan morphotypes (aseptate, porous septate and aporous septate), and
subjected each to currents of colored liquid in a fl ume (Fig. 11.12). The fi rst morphotype, a theoreti-

cal reconstruction, performed badly with fluid escaping through the intervallum while also leaking
through the outer wall. The porous septate form, however, suffered some slight leakage through the
outer wall but no fluid passed through the intervallum. The aporous septate form was most effi cient

with no leakage through the outer walls and no flow through the intervallum. Signifi cantly, ontoge-

netic series of the fossils show that an initially porous septate morphotype become aporous in later
life, perhaps to avoid leakage through the outer wall (Savarese 1992). This was clearly a
great advantage to an organism that survived by pumping huge volumes of seawater through its
system!

current flow
aseptate porous septate aporous septate
condition condition condition

Figure 11.12 Modeling the functional morphology of the archaeocyaths. (From Savarese 1992.)

varied forms, and brilliant colours. . . . In glowing accounts I had ever read of the
and out among [the rocks and living wonders of a coral sea.
corals] moved numbers of blue and red

and yellow fishes, spotted and banded Alfred R. Wallace (1869)
and striped in the most striking manner, The Malay Archipelago
while great orange or rosy transparent
medusæ [jellyfi sh] floated along near the

surface. It was a sight to gaze at for The cnidarians (or “nettle-bearers”) include
hours, and no description can do justice the sea anemones, jellyfish and corals and are

to its surpassing beauty and interest. For the least complex of the true metazoans
once, the reality exceeded the most (eumetazoans), having cells organized into a