Surfing The Wierd

Saturday, July 26, 2008

Evolution of Mammalarian Ears

http://www.livescience.com/ani Human Ears Evolved from Ancient Fish Gills

By Bjorn Carey, LiveScience Staff Writer

posted: 19 January 2006 12:21 am ET

Your ability to hear relies on a structure that got its start as a gill opening in fish, a new study reveals.

Humans and other land animals have special bones in their ears that are crucial to hearing. Ancient fish used similar structures to breathe underwater.

Scientists had thought the evolutionary change occurred after animals had established themselves on land, but a new look at an old fossil suggests ear development was set into motion before any creatures crawled out of the water.

The transition

Researchers examined the ear bones of a close cousin of the first land animals, a 370-million-year-old fossil fish called Panderichthys. They compared these structures to those of another lobe-finned fish and to an early land animal and determined that Panderichthys displays a transitional form.

In the other fish, Eusthenopteron, a small bone called the hyomandibula developed a kink and obstructed the gill opening, called a spiracle.

However, in early land animals such as the tetrapod Acanthostega, this bone has receded, creating a larger cavity in what is now part of the middle ear in humans and other animals.

Missing link

The new examination of the Panderichthys fossil provides scientists with a critical "missing link" between fish gill openings and ears.

"In Panderichthys, it is much more like in tetrapods where there is no longer such a 'kink' and the spiracle has widened and opened up," study co-author Martin Brazeau of Uppsala University in Sweden told LiveScience. "[The hyomandibula] is quite a bit shorter, but still fairly rod-like like in Eusthenopteron. It's like a combination of fish and tetrapods."

However, it's unclear if early tetrapods used these structures to hear. Panderichthys most likely used their spiracles for ventilation of either water or air. Early tetrapods probably passed air through the opening. Scientists would need preserved soft tissue to say for sure.

"That's the question that we're starting to investigate, whether early tetrapods used it for some ventilation function as well," Brazeau said. Whether it was for the exhalation of water or air, it's not really clear. We can infer that it's quite expanded and improved from fish."

This research is detailed in the Jan. 19 issue of the journal Nature.

Invention Allows Humans to Breathe Like Fish

By Bill Christensen

posted: 06 June 2005 09:07 am ET

Alan Izhar-Bodner, an Israeli inventor, has developed a way for divers to breathe underwater without cumbersome oxygen tanks. His apparatus makes use of the air that is dissolved in water, just like fish do.

(From Breathe like a fish!)

The system uses the "Henry Law" which states that the amount of gas that can be dissolved in a liquid is proportional to the pressure on the liquid. Raise the pressure - more gas can be dissolved in the liquid. Decrease the pressure - gas dissolved in the liquid releases the gas. This is exactly what happens when you open a can of soda; carbon dioxide gas is dissolved in the liquid and is under pressure in the can. Open the can, releasing the pressure, and the gas fizzes out.

Bodner's system apparently uses a centrifuge to lower pressure in part of a small amount of seawater taken into the system; dissolved gas is extracted. The patent abstract reads:

A self-contained open-circuit breathing apparatus for use within a body of water naturally containing dissolved air. The apparatus is adapted to provide breathable air. The apparatus comprises an inlet means for extracting a quantity of water from the body of water. It further comprises a separator for separating the dissolved air from the quantity of water, thereby obtaining the breathable air. The apparatus further comprises a first outlet means for expelling the separated water back into the body of water, and a second outlet means for removing the breathable air and supplying it for breathing. The air is supplied so as to enable it to be expelled back into the body of water after it has been breathed.

Human beings have been thinking about how to breathe underwater since they started swimming. This long-held desire plays an important part in one of the first great science fiction novels, Jules Verne's 20,000 Leagues Under the Sea.

It consists of a reservoir of thick iron plates, in which I store the air under a pressure of fifty atmospheres. This reservoir is fixed on the back by means of braces, like a soldier's knapsack. (Read more about Jules Verne's diving apparatus)

(Check out this Functional Captain Nemo Diving Suit)

More recently, I distinctly remember an episode of the sixties sf series Voyage to the Bottom of the Sea in which a scientist decides that the best way to breathe underwater is to give himself gills. Alas, once equipped with gills, and fully acclimated to life in the sea, Dr. Jenkins and his associate lie in wait outside the submarine Seaview, converting every diver who emerges from the ship into mermen.

(From The Amphibians - aired Mar-08-1965)

And, of course, everyone remembers the scene in which intrepid Jedi Obi-Wan Kenobi and Qui-Gon Jin don pencil-sized breathing masks to explore the swamp lakes of Naboo in The Phantom Menace. This trick is used again in the most recent Star Wars movie.

(Hmm, perhaps those small cylinders are centrifuges...)

Read more at Like a Fish: Revolutionary Underwater Breathing System, or take a look at more inventions from 20,000 Leagues Under the Sea and the Functional Captain Nemo Diving Suit. Also, an excellent recent novel, Starfish by Peter Watts, refers to a "recycler" that can be implanted directly in the diver. Thanks to alert reader Adi for pointing this story out.

(This Science Fiction in the News story used with permission from Technovelgy.com - where science meets fiction.)

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