- THE GREAT STEP IN EVOLUTION
- From fishes to land animals
Vertebrate evolution’s greatest step is undoubtedly
the transition from aqueous gill-respiring fishes to air-breathing,
walking, land animals. Despite the numerous complex changes that
this requires, the transition from osteolepiform fishes to primitive
amphibians was no great deal, as already the prerequisites were
inherent in the group. The limbs, shoulder and hip girdles of
these fishes were strong. Their arms and legs (as fins) already
had the same bone pattern that all land animals would retain.
Lungs were already present as swim-bladders, and the pattern
of skull and cheek bones did not have to change at all.
The greatest single advancement in the evolution of vertebrates
from fish to human was, in John Long's opinion, the advent of
the hard-shelled egg, or amniote egg (containing the embryonic
amnion). This enabled the early tetrapods to venture away from
seas, rivers and lakes to seek new inland habitats. Ancestral
ties with water was finally broken. The invasion of continents
by vertebrates was beginning. The rest is history. (See Chapter
10.)
Summary by Dr. Irwin Haydock of the book entitled The Rise
of Fishes, 500 million years of evolution, by John A. Long, Johns
Hopkins University Press, 1995. (See Chapter 10)
If you would like to learn more about the evolution
of fishes, we recommend Long's excellent book. It's loaded with
information, well written and easy to understand.
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