Devonian
Life and Fossils
 The
Devonian period brought significant diversification of terrestrial
life, including the first vertebrates, the amphibians, and the
first forests of trees appeared; this completed a land colonization
process that likely started in the late Cambrian. So too did marine
life increase in diversity and complexity. The lobe-finned (Sarcopterygii)
and ray-finned (Actinopterygii)
fish appear. Among the Sarcopterygii,
the first fish evolved legs to
walk on land as tetrapods some 365 mya. Class Chondrichthyes
fishes (Sharks, Rays and Skates) become more common, larger, and
fiercer. Among invertebrates, the ammonite mollusks appeared,
and crinoids, coral, and brachiopods remained common and thriving.
The first seed-bearing plants spread across dry land, ultimately
forming huge forests. Early Devonian plants lacked roots and leaves
and mostly lacked vascular tissue, and where tiny. They probably
spread largely by vegetative growth, and did not grow much more
than a few centimeters tall. However, by the late Devonian, primitive
plants such as the lycophytes, sphenophytes, ferns, and progymnosperms
had formed widespread forests. The Late Devonian extinction severely
affected marine life, particularly brachiopods, trilobites, ammonites,
conodonts, and acritarchs, jawless fish, and placoderms.
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