It is easy to imagine a fish wiggling its way through wetlands to eat
the vegetation. It is not so easy to find a living example of such a
fish that is particularly convincing at all. The fact is that they
needed another reason to do this and make the major changes needed.
I suggest that what drove the move was security. A fish able to get
up even briefly onto land was away from his enemies and survived.
Once the adaptation was made to allow this behavior the rest
followed.
Fish even today can throw themselves onto the bank and then throw
themselves back of into the water. Likely such a clever fish adapted
its fins to make better use of this skill and it all developed from
there. A thrusting rear set of legs would be naturally acquired.
One presumes that in the primeval world that the rewards were ample
and the environment was quickly adopted.
Ancient walking
mystery deepens
By Helen BriggsBBC
News
23 May 2012 Last
updated at 14:48 ET
Reconstruction of the
body of Ichthyostega
One of the first creatures to step on land could not have walked
on four legs, 3D computer models show.
Textbook pictures of
the 360-million-year-old animal moving like a salamander are
incorrect, say scientists.
Instead, it would have
hauled itself from the water using its front limbs as crutches,
research in Nature suggests.
The move from living
in water to life on land - a pivotal moment in evolution - must have
been a gradual one.
Ichthyostega is
something of an icon in the fossil world. Living during the Upper
Devonian period, it was dubbed a "fishapod", with its
mixture of fish-like and amphibious features.
Although it probably spent much of its time under water, at times
it was thought to have crawled halfway up onto land on limb-like
flippers.
Exactly how it moved
on land has been a matter of much debate, however.
Now, a team from The
Royal Veterinary College, London and the University of Cambridge, has
spent three years reconstructing the first 3D computer model
of Ichthyostega from fossils.
It enabled them to
study how ancient vertebrates made the "monumental transition"
from swimming to walking.
Study author Dr
Stephanie Pierce, of The Royal Veterinary College, said the 3D
skeleton allowed them to calculate the range of movement in the
joints of its limbs for the first time.
The research suggests
the animal shuffled on land using hind limb movements similar to that
seen in seals rather than moving its limbs in the familiar walking
pattern seen today.
Dr Pierce told BBC
News: "We're almost bringing the animal back to life by doing
this.
"What we've
discovered is that some early tetrapods definitely did not have the
ability to walk on land. We at this stage are not actually sure which
animals - or group of animals - were the first to do this."
Co-author Prof Jenny
Clack from the University of Cambridge added: "Our
reconstruction demonstrates that the old idea, often seen in popular
books and museum displays, of Ichthyostega looking and
walking like a large salamander, with four sturdy legs, is
incorrect."
Fundamental question
Commenting on the
study, Dr Susannah Maidment of London's Natural History Museum, said
understanding where we came from, or where all the things that live
on the land came from, is one of the most fundamental questions.
"What this study
suggests is that this animal, which has been traditionally thought of
as the first four legged animal to walk on land wasn't walking on
land at all.
"It sends us
almost back to the drawing board...I guess it even sends you back to
the field to look for more fossils."
The research, reported
in a paper in Nature, was funded by the Natural Environment
Research Council.
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