Paleozoic Life History - The Changing Earth: Exploring Geology and Evolution - page 581

Dolichosoma

Branchiosaurus

Eryops

◗

Figure 21.26 Carboniferous Coal Swamp The varied amphibian fauna of the time is shown,
including the large labyrinthodont amphibian Eryops , the larval Branchiosaurus , and the serpentlike
Dolichosoma .

a variety of structural adaptations that were fundamental to
the subsequent radiations and diversifi cation that occurred
during the Silurian, Devonian, and later periods (see Geo-
Focus on pages 586 and 587 and Table 21.3). Most experts
agree that the ancestors of land plants fi rst evolved in a ma-
rine environment, then moved into a freshwater environment

before fi nally moving onto land. In this way, the differences
in osmotic pressures between saltwater and freshwater were
overcome while the plant was still in the water.
The higher land plants are divided into two major groups:
nonvascular and vascular. Most land plants are vascular ,
meaning that they have a tissue system of specialized cells for

Shell

Embryo

Yolk sac

Amnion cavity

Therapsids
(Permian-Triassic)

Thecodontians
(Permian-Triassic)

Pelycosaurs
(Pennsylvanian-Permian)

Allantois

Chorion

◗ Figure 21.27 Amniote Egg In an amniote egg, the
embryo is surrounded by a liquid sac (amnion cavity)
and provided with a food source (yolk sac) and waste
sac (allantois). The evolution of the amniote egg
freed reptiles from having to return to the water for
reproduction and let them inhabit all parts of the land.

Protorothyrids
(Pennsylvanian-Permian)

◗ Figure 21.28 Evolutionary Relationship among
the Paleozoic Reptiles