Primordial fish had rudimentary fingers

September 22, 2008

Tetrapods, the first four-legged land animals, are regarded as the first organisms that had fingers and toes. Now researchers at Uppsala University can show that this is wrong. Using medical x-rays, they found rudiments of fingers in the fins in fossil Panderichthys, the “transitional animal,” which indicates that rudimentary fingers developed considerably earlier than was previously thought.

Our fish ancestors evolved into the first four-legged animals, tetrapods, 380 million years ago. They are the forerunners of all birds, mammals, crustaceans, and batrachians. Since limbs and their fingers are so important to evolution, researchers have long wondered whether they appeared for the first time in tetrapods, or whether they had evolved from elements that already existed in their fish ancestors.

When they examined genes that are necessary for the evolution of fins in zebrafish (a ray-finned fish that is a distant relative of coelacanth fishes) and compared them with the gene that regulates the development of limbs in mice, researchers found that zebrafish lacked the genetic mechanisms that are necessary for the development of fingers. It was therefore concluded that fingers appeared for the first time in tetrapods. This reading was supported by the circumstance that the fossil Panderichthys, a “transitional animal” between fish and tetrapod, appeared to lack finger rudiments in their fins.

In the present study, to be published in Nature, medical x-rays (CT scans) were used to reconstruct a three-dimensional image of Panderichthys fins. The results show hitherto undiscovered elements that constitute rudiments of fingers in the fins. Similar rudiments have been demonstrated once in the past, two years ago in Tiktaaliks, which is a more tetrapod-like group. Together with information about fin development in sharks, paddlefish, and Australian lungfish, the scientists can now definitively conclude that fingers were not something new in tetrapods.

“This was the key piece of the puzzle that confirms that rudimentary fingers were already present in ancestors of tetrapods,” says Catherine Boisvert.

Source: Uppsala University

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6 comments

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Modernmystic
5 / 5 (1) Sep 22, 2008
Ok, I'm a soild proponent of evolution, but I'm having a hard time seeing the advantage for fish having fingers. That is unless they were spending some time on land...which I don't think this article is saying.

Perhaps there was no advantage and it was just a "carry over" mutation UNTIL they started invading the land....
photojack
5 / 5 (1) Sep 22, 2008
They could have been a stiffener for fins that were modified as they adapted to locomotion on land. The fact that they have been found much earlier than expected is great and it totally supports Darwinian evolution. Genetics and cladistics will continue to make such links and discoveries as more "transitional animals" are found. SCIENCE PREVAILS!
D666
5 / 5 (2) Sep 22, 2008
Ok, I'm a soild proponent of evolution, but I'm having a hard time seeing the advantage for fish having fingers.


This is a job for..... Exaption! (I'm never sure if I'm spelling that right). Probably the structures were useful for something else, like digging in the muck. Then when the fish started invading the land, they turned out to be useful for that too.
mattytheory
not rated yet Sep 22, 2008
Exaption.. had to look that up; knew the concept, now know the term. Definitely makes sense in this context. Glad I learned something!
ofidiofile
not rated yet Sep 23, 2008
"Our fish ancestors evolved into the first four-legged animals, tetrapods, 380 million years ago. They are the forerunners of all birds, mammals, crustaceans, and batrachians."

okay, this is a silly error... crustaceans are definitely NOT descendants of a fish-like ancestor. they split off from deuterostome coelomates (chordates, hemichordates, echinoderms) along with all other protostome creatures.
D666
5 / 5 (1) Sep 23, 2008

This is a job for..... Exaption! (I'm never sure if I'm spelling that right).


And of course, I didn't. The proper spelling is "Exaptation".

Must. Drink. More. Coffee.

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