age” in the sense that little is known about the soft bodies of animals that
inhabited the seas. Soft-bodied marine animals living in the Silurian some 430
million years ago included a host of worms and bizarre arthropods.Among the
odd animals were a half-inch-long bristly worm and a tiny shrimplike crea-
ture with a tentacled head, a segmented body, and a triangular tail. More enig-
matic yet was a half-inch-long creature that might be an unknown relative of
a group of small stubby-legged worms called lobopods. A large variety of
wormlike creatures had their beginning in the Cambrian and apparently
evolved into higher forms of animal life.
Coral reef formation during the Silurian was widespread, indicating the
presence of warm shallow seas with little seasonal temperature variation.
Corals began constructing extensive reefs in the Ordovician, forming barrier
islands and island chains.They also built atolls atop extinct submerged volca-Figure 80Marine flora
and fauna of the middle
Silurian.
(Courtesy Field Museum
ofNatural History)
Historical Geology