Evolution of ears and hearing.

[check]

Yes yes, I’m a slacker. I have a short paper (2500 words max) due on Friday for an Earth Sci. class about ‘some aspect of biological evolution’. My chosen topic is the evolution of ears and hearing in animals. I chose it because I’m pretty sure no one else is doing it…and the evolution of eyes and all the other fun stuff was already taken. Anyway, does anyone have and good resources or fun facts about the evolution of ears?

Thanks guy.

 

[iansmith]

http://www.blackwell-synergy.com/servlet/useragent?func=synergy&synergyAction=showTOC&journalCode=joa&volume=199&issue=1-2&year=2001&part=null

Check for
99 Origin of the vertebrate inner ear: evolution and induction of the otic placode
and click on pdf, it should be free.

You can also do a search on talkorigin.org
http://www.talkorigins.org/origins/search.html

I found this piece
http://64.233.161.104/custom?q=cache:Wf1xVrBC5QkJ:www.talkorigins.org/faqs/comdesc/section1.html+ear+evolution&hl=en&ie=UTF-8

 

[check]

Beautiful! Thanks! I found a couple more resources so I'm off to the university to look 'em up.
Thanks again.

 

[check]

Help please!

I've been looking all over...ALL over and I can't seem to find these bits out.

Prior to the development of the tympanic membrane (ear drum) how exactly did amniotes and amphibians hear? Was there just a fluid filled region with tiny hair receptors and no membrane whose purpose was transfer sound from air to fluid? So it was just an inefficent process?

Also, can anyone tell me where I can find, or maybe you could draw me a simple diagram of a PRIMATIVE amphibian ear. Prior to the development of the tympanic ear. Thanks!

 

[gerben]

I think that in the initial stages the animals that started living on land were not very good at hearing air-borne sounds, as they only had sensors that were sensitive to water-borne sound. Because water is more dense than air, hearing in water can work differently. Here is link to a page about hearing in fish:

http://www.dosits.org/animals/produce/2f.htm

Still the sensory organs responsible for hearing water-borne sounds were useful on land as balance sensors. Parts of these balance sensors have specialised into modern ears. I am affraid that not all the intermediate steps are well known nowadays.

I think that a primitive amphibian ear is like a fish's ear.

 

[gerben]

I found this quote:

Evolution II. "When the first amphibia left the Silurian seas two or three hundred million years ago, with their heads resting on the ground, they relied entirely on bone conduction of vibration for hearing. The vibrations in the Earth were transmitted from the bones of their lower jaws to the bone surrounding the inner ear. In order to hear, they probably kept their lower jaws touching the ground" (Nathan 1988:34).
from: http://members.aol.com/doder1/auditor1.htm

 

[gerben]

Ok, and one more:

Some amphibians, such as frogs, have a middle ear that consists of an eardrum and a single bone called the columella. Vibrations of the eardrum are amplified by the columella and transmitted to the inner ear. Frogs also have a eustachian tube connecting the middle ear to the throat. Since amphibians have no outer ear, the eardrum is on the surface of the body. In frogs it can be seen as a circular area on each side of the head.

Other amphibians, such as salamanders, do not have a middle ear or eardrum. These animals hear by picking up vibrations on the ground through the skull or the front legs and shoulder blades. The vibrations are then transferred to the inner ear.

from:http://encarta.msn.com/encyclopedia_761563171_2/Ear.html#p42

 

[check]

Thanks a lot! Just finished the paper now... :)