Page 302 - Introduction to Paleobiology and The Fossil Record

THE BASAL METAZOANS: SPONGES AND CORALS 289

(a) (b) (c) (d)

(e) (f)
Figure 11.31 Some typical scleractinian corals: (a) Hydnophora (Recent); (b) Gablonzeria (Triassic);
(c) Montlivaltia (Jurassic); (d) Thecosmilia (Jurassic); (e) Scolymia (Miocene); and (f) Dendrophyllia
(Eocene). All natural size. (From Scrutton & Rosen 1985.)

Box 11.8 Reef building through time

Reefs were not just corals! Throughout geological time, a whole range of mainly modular organisms
have contributed to these calcareous structures (Wood 2001), providing, too, signifi cant carbonate
factories often spalling off the continental shelves into deeper waters. While Early Paleozoic shallow-
marine environments were dominated by various microbes, bryozoans, corals and sponges (including
archaeocyaths and stromatoporoids), the Mesozoic and Cenozoic were characterized by scleractinian
corals (Fig. 11.32). Through time, the more restricted environments were home to stromatolites
during the Paleozoic and early Mesozoic; these too popped up after some extinction events, in for
example the Early Silurian and Early Triassic, as disaster species. The later Mesozoic and Cenozoic
saw the arrival of serpulid and oyster reefs in these more stressed brackish or hypersaline habitats.
Deeper-water environments were the domain of the spicular sponges together with occasional sym-
biotic (ahermatypic) scleractinian corals.

Continued