Abstract

The traditional notion of a gap between fishes and amphibians has been
closed by a wealth of fish-like fossil tetrapods, many discovered since the
mid 1980s. This review summarizes these discoveries and explores their
significance relative to changing ideas about early tetrapod phylogeny, biogeography,
and ecology. Research emphasis can now shift to broader-based
questions, including the whole of the early tetrapod radiation, from the
divergence from other lobed-finned fishes to the origins of modern amphibians
and amniotes. The fish-to-tetrapod morphological transition occurred
within the Upper Devonian; the divergence of modern tetrapod groups is an
Early Carboniferous event. Modern tetrapods emerged in the aftermath of
one of the five major extinction episodes in the fossil record, but the earlier
Devonian tetrapod radiation is not well understood. Tetrapod limbs, paired
fins, and comparative developmental data are reviewed; again, research emphasis
needs to change to explore the origins of tetrapod diversity.