An unusual prehistoric fish with fins near its butt has helped to solve
the mystery over why most animals, including humans, have paired limbs.
The fish, Euphanerops, is possibly the first creature on the planet to
have evolved paired appendages, which in this case were fins. The
370-million-year-old species is described in the latest issue of Biology
Letters.
"Fins are the world's first limb-like appendages," lead author
Robert Sansom told Discovery News. "Paired limbs would subsequently
develop from paired fins in the transition from sea to land, but the first
evolution of paired appendages was a big, important step in the evolution and
development of vertebrates," which are animals with a backbone or spinal
column.
PHOTOS: Faces of Our Ancestors
Sansom, a researcher at both the University of Leicester and the
University of Manchester, and colleagues Sarah Gabbott and M.A. Purnell
analyzed 36 Euphanerops specimens unearthed in Quebec, Canada. This was a
jawless fish that lived long before dinosaurs first emerged.
Many living fish have a single anal fin, located at the center back of
the fish’s underside near its rear end. The fin is thought to help maintain
control of body position.
Euphanerops, however, evolved two such fins. Some subsequent fish did
not evolve the paired appendages, so fish with all sorts of fin combinations
existed for a while.
"What this research leads us to believe is that, at this early
stage (in evolutionary history), vertebrates were trying out lots of different
body plans, some familiar, some less familiar, and only some that
survived," Sansom explained.
The change happened at a radical point in fish history when some of them
were starting to evolve jaws and teeth. (There is currently a big chicken and
egg-type debate among fish experts as to which evolved first: teeth or jaws.)
These attributes likely emerged for reasons similar to fish gaining fins --
improved hunting and escape skills.
As Sansom shared, "The evolution of paired appendages and more
sophisticated fins will probably be for improved locomotion, potentially
related to an arms race between tracking down prey and avoiding
predators."
He continued, "Paired fins allow for more sophisticated control of
movement."
This movement, which at first just happened underwater, later helped
some species make the transition from water to land.
Heather King of the University of Chicago and colleagues studied living
lungfish to see how that transition might have happened.
"Lungfish are very closely related to the animals that were able to
evolve and come out of the water and onto land, but that was so long ago that
almost everything except the lungfish has gone extinct," she explained.
King and her team found that lungfish could, as their name suggests,
blow up with air like a balloon, giving their body buoyancy. Their scrawny back
paired appendages can then either sort of hop or actually walk by alternating
the movement of these limbs.
Co-author Neil Shubin said, "This shows us -- pardon the pun -- the
steps that are involved in the origin of walking."
Since those first steps from water to land were taken, some animals
evolved four limbs for walking. Even for these animals, like dogs and cats, the
limbs come in pairs. For that innovation, we can probably thank the unusual,
long-extinct jaw-less fish Euphanerops.
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