Page 65 - Prehistoric Animals

Ik-tay-Ost-Ega

Ichthyostega

Ichthyostega (Fish roof) is an extinct genus of
limbed tetrapodomorphs. Fossils found in
late (Geologic period) Devonian in Green-
land indicated it roamed the planet some 370 million
years ago. It measured around 1.5 metres long. Fossil
records have also revealed that Ichthyostega was one
of the first vertebrates with forelegs and hindlegs in-
stead of fins and among the first to venture onto land.
However, if it did walk on dry land it was only for
short periods, its legs at that stage were suited more
for wading or swimming in the watery marshland
which was the key feature of its environment.

Since being named by Gunnar Säve-
Söderbergh in 1932, many fossils have been un-
earthed; most in Greenland. This has made compari-
son with other species of vertebrates more detailed.
This detail comparison has shown that Ichthyoste-
ga probably used its lungs as its primary means of
breathing. Most vertebrate of the time still used their
gills. Ichthyostega also had a much more robust and
load bearing skeletal structure, than its less robust
counterparts. This would have allowed it more time
out of the water ‘walking’ and safely out-of-reach
from any predators like large fish. Being one of the
first amphibians to venture onto land, it probably had
no natural land predators and was therefore, able to
roam and feed safely.

Although most primitive vertebrates, used
their ‘legs’’ for balance and their body and tail to cre-
ate movement, Ichthyostega, used the more advanced
method; using its tail for balance and its ‘legs’ for
movement. Ichthyostega however, was still very prim-
itive, so-much-so that it was once described as, ‘A fish
on legs’; it still had to return to the water to lay its soft
spongy eggs. Its reproductive process still required
water, both for fertilization and the wellbeing of its
soft eggs. It would be another 30 million years, before
the first truly land living vertebrates appeared. They
would lay their eggs on land.