The evolution of fins to limbs in the land invasion race

Jul 05, 2013
Mudskipper fish and tiger salamanders have similar characteristics to early tetrapod ancestors. Credit: Sandy Kawano

Why did animals with limbs win the race to invade land over those with fins? A new study comparing the forces acting on fins of mudskipper fish and on the forelimbs of tiger salamanders can now be used to analyze early fossils that spanned the water-to-land transition in tetrapod evolution, and further understand their capability to move on land.

Research conducted by Sandy Kawano and Richard Blob at Clemson University compared terrestrial locomotion in tiger and mudskipper fish, which have similar characteristics to early tetrapod ancestors.

The researchers filmed these organisms as they walked over a force platform which measures forces like a bathroom scale but separates them into 3 directions (upward, fore-aft, and side-to-side). They compared the forces experienced by the pectoral fins of the mudskipper fishes to the forelimbs and hind limbs of walking tiger salamanders. The results showed that that mudskippers' pectoral fins experience more medial forces than the limbs of salamanders, and that the could have a played a similar weight-bearing role as the hind limbs.

The evolution of fins to limbs in the land invasion race
Mudskippers' pectoral fins experience more medial forces than the limbs of tiger salamanders. Credit: Sandy Kawano and Richard Blob

Sandy Kawano said: "The transition from fins to limbs marks the most dramatic change in orientation of the locomotor forces from contact with the ground. Using these data we can now evaluate the locomotor capabilities of numerous important fossil taxa that spanned the water-to-land transition in tetrapod evolution. We hypothesise that the medial orientation of the forces on pectoral fins would result in unreasonably high bone stresses in early amphibious fish with fins, which would explain why the evolutionary invasion of land by vertebrates was accomplished instead by tetrapods with limbs with digits."

Salamanders' forelimbs experience more vertical forces than the fins of mudskipper fish. Credit: Sandy Kawano and Richard Blob

Paleontological examinations of the invasion of land by vertebrates suggest that limb-like likely originated in , but direct comparisons of the functional consequences of using early limbs with digits, rather than fins, for terrestrial locomotion had not previously been performed. Salamanders are used to model the general body form of early tetrapods (e.g., Paleozoic amphibians) since their morphology has remained essentially unchanged for at least 150 million years. Mudskippers are similar to early fossil precursors of the : they use "crutching" movements on land similarly to the hypothesised locomotion of Ichthyostega, and their are similar to elpistostegalids, such as Tiktaalik.

Explore further: Deep sea fish eyesight similar to human vision

More information: This work will be presented at 13:30 on Saturday 6th July 2013.

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geokstr
1 / 5 (11) Jul 06, 2013
Duh-uh.

Maybe it's because fins, which evolved for moving in any direction in a liquid where supporting body weight is not an issue, were not as functional on land as limbs, which are much more useful in moving straight ahead and had to be strong enough to overcome gravity, giving a limbed animal more speed and power on land to evade predators or catch prey.

Why didn't they then ask the obvious question - once limbs had been established as superior on land, why didn't land creatures go back to the sea and conquer all the finned ones?

I suppose professors gotta publish.
Neinsense99
3.4 / 5 (10) Jul 06, 2013
Duh-uh.

Maybe it's because fins, which evolved for moving in any direction in a liquid where supporting body weight is not an issue, were not as functional on land as limbs, which are much more useful in moving straight ahead and had to be strong enough to overcome gravity, giving a limbed animal more speed and power on land to evade predators or catch prey.

Why didn't they then ask the obvious question - once limbs had been established as superior on land, why didn't land creatures go back to the sea and conquer all the finned ones?

I suppose professors gotta publish.

They tried. Whales. But limbs optimal for function on land have a higher cost to maintain in the water. Why didn't you ask the question and come to the obvious answer? Would that have cut short your opportunity to pose as smarter than everyone (while appearing obtuse)? Just asking some obvious questions...
geokstr
1 / 5 (3) Jul 07, 2013
They tried. Whales. But limbs optimal for function on land have a higher cost to maintain in the water. Why didn't you ask the question and come to the obvious answer? Would that have cut short your opportunity to pose as smarter than everyone (while appearing obtuse)? Just asking some obvious questions...

Geez, that's what I was implying in my question. Sorry if it was too obtuse for you to grasp that this is just a whole lot of grant money used to produce an article that could probably have been written using common sense.

My whole point was that fins and limbs are dominant in water and on land, respectively, precisely because they were most functional and effective for survival in those environments, for the same reasons that the sight in animals atrophies in caves over generations. Isn't that what evolution is all about?

And the whales and other returnees to the sea? They did actually turn out quite competitive once their limbs had evolved back into flippers, no?
geokstr
1 / 5 (3) Jul 07, 2013
And what's double juicy ironic is for you of all commenters to attack someone for posing "...as smarter than everyone..." The patronization and condescension literally drips from your smarter-than-thou comments, including the ones that aren't personal ad hominem attacks on those who disagree with your self-acclaimed expertise on the subject of, well, everything. You really ought to look in a mirror sometime.

And you, like all your leftist sympathizers on this site, will reflexively rate every comment from a known political opponent as a "1" regardless of the contents of even completely non-political comments, because all leftists hate opposition and want to destroy it. I, on the other hand, even give 5s to you or anyone else if their comments aren't political rantings, aren't abusive, vile, vicious ad hominems, and I agree with the science in them. Unfortunately, that's not most of them, on any even vaguely controversial topic.

Just pointing out some obvious facts...

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