Re: Paleobiological implications of dinosaurian hyoids

["Steve Brusatte" <dinoland@lycos.com>]

On Wed, 16 Jan 2002 08:53:40  
 Thomas R. Holtz, Jr. wrote:
>> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
>> Steve Brusatte
>>
>> I have come to the opinion that dinosaurian hyoids are most
>> certainly understudied (although, as Wanger said, they may be
>> more common than the literature makes it seem).
>
>Actually, it is even broader than you suggest.  VERTEBRATE hyoids are
>understudied, not merely those on that particularly lovely branch of Amniota
>we call Dinosauria.

Yep, even mammal hyoids (despite the mammal bias that you mention) seem to be 
understudied.  

>> However, when
>> present these bones can give insights into the vocalization
>> abilities of dinosaurs, along with information on the dinosaurian
>> tongue (which can further be used to possibly deduce feeding
>> habits, muscle mass, etc.).  Not to pry, but is anyone currently
>> doing any work on dinosaurian hyoids?  If not, and even if so, I
>> would be most interested to possibly begin looking closer at them
>> next year when I finally have access to a college library.
>
>There is some excedingly excellent work being done on one aspect of modern
>animal hyoids: Elizabeth Brainerd's studies of amniote breathing.  Here's
>the abstract from SVP 2001:
>http://www.bio.umass.edu/biology/brainerd/svp/abstract.html

Thanks for the link.  That's interesting research...  Ceratobranchials are 
known from _Acanthostega_.  These bones are deeply groved, and may, according 
to Coates and Clack, have supported branchial arteries that aided in breathing. 
 Actually, these ceratobranchials represent some of the strongest evidence that 
_Acanthostega_ was aquatic (along with the weak limbs, deep tail, etc.).  

Brainerd discusses, in the abstract, buccal oscillation behavior in extant 
amphibians.  I wonder how this behavior evolved...perhaps it was a 
heat-shedding adaptation that evolved once tetrapods (or stegocephalians, 
depending on which phylogeny you use) became terrestrial, and hence divorced 
themselves from a fully aquatic existence.  I don't know the exact physics 
(somebody help out here, please), but it may have been that it is easier to 
dump heat in water, meaning that once tetrapods "left" water they may have 
needed a new apparatus to dump heat.  Or, perhaps the buccal oscillation 
behavior may have evolved as an olfactory tool, which would have also been 
needed once tetrapods "conquered" land.

>In brief, a summary:
>Everything you know about breathing is wrong.  (Okay, a little overboard
>there, but bear with me).  Mammalian breathing is damned peculiar compared
>to the system used by other groups of vertebrates.  For example, we need to
>use our lungs and diaphragm to sniff and to pant; this is not true for
>reptiles.

>The work on living taxa alone is complex, but has broad implications for the
>evolution and diversity of olfaction, heat regulation, and above all
>respiration.  Thus, it is somewhat of a mammalian bias (understandable,
>since that system is the best studied) to assume that hyoid adaptations =
>tongue adapations.

Certainly.  The shift of ceratobranchials as gill supports to 
olfactory/regulatory/respiratory/chewing structures is certainly worth a major 
study of its own.  

>Cool stuff.  The next time I was at the zoo after SVP 2001 I watched their
>alligator, and it indeed did a bit of buccal oscillation in between
>breathing.

What an interesting topic.  Hopefully Brainerd will publish a detailed study 
soon...or, has she already?

Steve

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