385 million years ago, the first amphibians evolved
from fish and set foot on land. But what drove them onto land? And how did they
actually learn how to walk?
Land is pretty interesting
The first
amphibians on land, that were also the first animals with a spine on land,
evolved from fish with legs. These fish also needed lungs to survive on land
and many other adaptations. But what drove these fish to start a life on earth?
First of all, most of these fish with legs lived in shallow water. Because of
extreme droughts more than 385 million years ago, the shallow water became more
and more hostile to the fish; it became saltier and warmer. The fish didn’t
like it and fled out of the water, onto the land. Moreover, a lot of bacteria
and viruses made the life for the fish in the water even more unpleasant. But
the land was also attractive to the fish with legs as there weren’t any
competitors, like animals who eat the same food as the fish do, or threats,
like animals that have the fish with legs as prey. This was of course because
there weren’t many animals on land yet, only a couple of simple, insect-like
lifeforms.
 |
| A mudskipper |
Fish hopping around
Swimming
and walking are two wholly different ways of moving, however. On top of that,
soil close to the shallow water where the fish crawled out of isn’t the easiest
to walk on, since it’s usually very muddy and a bit uneven. How did the fish
pull it off to learn how to walk? That’s exactly the question that Benjamin
McInroe and Henry Astley asked themselves. And as it turns out, the tail of
these first amphibians was really important. Stephanie Pierce thought that with
their tails and forelimbs, the fish-like creatures managed to hop around on the
uneven, muddy soil. Much like mudskippers, fish that can also live on land,
still do today. Benjamin McInroe and Henry Astley then made a computer simulation
of the hopping movement, and they found out that it is indeed possible that
these first animals on earth used their tail and arms to move around.
 |
| Ichthyostega |
Seals can’t walk
We know
that these first amphibians didn’t use their hind legs to move around, like
salamanders do, because a discovery made by Stephanie Pierce. She and her team
studied fossils of the extinct Ichthyostega,
one of the first animals on land with complete limbs. And they found out that
it is very unlikely that this animal used its hind legs to move around. As the Ichthyostega had hind legs that pointed
backwards, much like seals have. These legs are excellent for swimming, but
useless for walking. So scientists had to come up with another theory about how
these first amphibians moved; they hopped. And so, the salamander-like way of
moving, with use of the hind legs, evolved at least a bit later.
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