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siderable distance before finding another suitable home. It breathes with prim-
itive nostrils and lungs as well as with gills, placing it midway on the line of evo-
lution from fish to land-living vertebrates.Air breathing is also important for fish
striving to survive in warm, shallow, stagnant waters with a low oxygen content.
The descendants of the lobe-finned fish and lungfish were the first
advanced animals to populate the land some 370 million years ago. By the late
Devonian, the descendants of the crossopterygians evolved into the earliest
amphibians.Their legacy is well documented in the fossil record. At no other
time in geologic history were so many varied and unusual creatures inhabit-
ing the surface of Earth.
Animal tracks tell of the earliest land invasion.Tracks of primitive Devon-
ian fish that first ventured onto dry land and gave rise to the four-legged
amphibians exist in formations of late Devonian age onward. Amphibian foot-
prints became abundant in the Carboniferous beginning about 350 million
years ago and to a lesser extent in the Permian, owing to the amphibians’ pref-
erence for a life in water and to the rise of the reptiles.The fossil remains of the
amphibians are largely fragmentary, however, because of the manner by which
vertebrate skeletons are constructed. Their large number of bones that are eas-
ily scattered by surface erosion leave a scant record of their existence.
THE OLD RED SANDSTONE
Beginning in the late Silurian and continuing into the Devonian, from about
400 million to 350 million years ago, a collision between present eastern
North America and northwestern Europe raised the Acadian Mountains (Fig.
103).The terrestrial red beds of the Catskills in the Appalachian Mountains of
southwestern New York State to Virginia are composed of sandstones and
shales cemented by r ed iron oxide and are the main expression of the Acadian
orogeny in North America. Extensive igneous activity and metamorphism
accompanied the mountain building at its climax.
The Devonian Antler orogeny was another mountain-building episode,
resulting from a collision of island arcs with the western margin of North Amer-
ica.The island arcs appear to have formed approximately 470 million years ago
off the west coast of North America.The orogeny intensely deformed rocks in
the Great Basin region from the California-Nevada border to Idaho.
The Innuitian orogeny, from the Devonian through the Carboniferous,
deformed the northern margin of the present North American continent.The
mountain building episode raised the Innuitian Mountains on Ellesmere
Island in the Canadian Arctic.It resulted from a collision with another crustal
plate, possibly the eastern Siberian continental mass. Block faulting and basin
filling succeeded the mountain building in the region.
137DEVONIAN FISH