Page 56 - The Restless Earth Fossils

Marking turning points in evolution 55

the paleozoic: shells, creepy craWlers,
and Monster Fish

The first shellfish, including trilobites and brachiopods, evolved
in diverse communities containing corals and the ancestors of
every major group of modern creatures. The first simple plants
invaded the land and were followed quickly by the first land-
loving arthropods. Perhaps 40 or 50 million years later, the first
tetrapods (four-legged vertebrate animals) came ashore. Late in
the Paleozoic, lush first forests composed of lycopods and other
primitive plants sheltered a wealth of amphibians, reptiles, and
giant insects.

important Fossil sites
The western cape of South Africa has produced important marine
fossils. Fossils from Rynie, Scotland, show us what some of the
first land plants and animals looked like. Coal beds near a tribu-
tary of the Illinois River close to Chicago yield fantastic plant and
animal life from some of Earth’s first forests. From the tops of
mountains in the Canadian Rockies, paleontologists have uncov-
ered a rich record of some of our planet’s first animals.

the strange Beasties of the Burgess shale
In the late summer of 1909, Charles Doolittle Walcott (1850–
1927), then the secretary of the Smithsonian Institution in
Washington, D.C., found an amazing collection of creatures
from the earliest Paleozoic high in the Canadian Rockies. The
dark shales in which he hunted had once been oxygen-starved
sand on a Cambrian seafloor at the foot of a deep trench. His
field notebook shows drawings of a creature (Marrella) that he
informally called a “lace crab,” along with sketches of other
arthropods with armored body segments and head shields.
Predators apparently swam in the ocean world these animals
inhabited, forcing them to develop defenses that made them

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