Re: Ears

["Matthew Bonnan" <mbonnan@hotmail.com>]

Tom Hopp wrote:

"And, before we dismiss the notion of external ears in dinosaurs completely,
consider the "eared" owls."

The notion of external ear structures in dinosaurs was not dimissed by me, 
I'm just saying it's doubtful.  Because dinosaurs and other sauropsids have 
a very similar otic region, this would suggest a similar type of external 
ear.  Yes, some owls are "eared," but these "ears" are display feathers that 
have nothing to do with hearing -- see Proctor and Lynch (1993) Manual of 
Ornithology for some discussion on hearing in birds and "eared" owls.  
Perhaps some dinosaurs had feather or scale structures that looked like ears 
(who knows?), but a fleshy, cartilaginously supported external pinna?  I 
don't know: the extant relatives of dinosaurs do not support such an 
interpretation -- if such an external pinna existed in dinosaurs, what 
tissues do you think it would have developed from?  What muscles would 
control it, if at all?  If feathers instead of a fleshy pinna played a role 
in hearing, do we know of any examples of external ear-like structures in 
birds that support this?  I'm not sure, but I don't believe so -- I would 
gladly like to be shown the error of my ways, however.  For instance, take 
the fact that owls have changed their facial structure partly to act as a 
"dish" off of which sounds can bounce towards their ears.  Because they are 
presumably constrained by their sauropsid ancestry, they evolved a flatter 
face instead of external ear structures.

Anyways, it's always been an interesting topic to me.

Matthew F. Bonnan, Ph.D.
Department of Biological Sciences
Western Illinois University
Macomb, IL 61455
(309) 298-2155
mbonnan@hotmail.com
MF-Bonnan@wiu.edu

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