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Owl ears, troodontid ears



Jaime Headden and I have discussed the possibility of convergences between
troodontid and owl auditory anatomy on this list in the past.

Specifically, I read the 2006 SVP abstract by Castanhinha and Mateus and
prepared reconstructions of troodontids with facial disks on my website:

http://web.me.com/jasonbrougham/Site/Illustrations/Pages/species_reconstructions.html#6

Jaime is wholly correct that owls have a large, laterally expanded,
squamoso-occipital wing, which is the ossified cartilago metotica. It
allows the auditory canal to open anterolaterally. In owls it is also
expanded by pre- and post-  auricular folds of soft tissue. Mr. Headden
believes that owl - style pinpoint hearing depends on this geometry.

The external auditory regions of all published troodontid fossils are
absent or fragmentary. The region may be complete in Mei long, but it was
not prepared out of the matrix, and it is overlain in part by the left
proximal ulna.

I have two questions for experts on the list.

One, is there any chance that troodontids could have had a cartilago
metotica or an analog? On the face of it, it seems entirely possible that
there could have been a homologous cartilage extending laterally from the
paroccipital process of the occipital, and/or the squamosal. The ONLY
evidence I could find for any cartilaginous structure in the ear of a
deinonychosaur was in Currie (Dromaeosaurus, 1995, page 584), where he
mentioned that the proximalmost and distalmost portions of the stapes were
probably cartilaginous.

Two, how do echolocating birds like Steatornis achieve their acoustic
navigation with posterolateral facing meatuses? For references on this ear
geometry I suggest looking at the ventral views of the skulls given here:

http://www.skullsite.com/images/dbimages/large/steatorniscaripensis_b.jpg

You can see that the quadrate lies more lateral than the external acoustic
meatus. (Although this specimen of Steatornis is missing the right
quadrate)

Finally, I also realized that feathery facial disks used in hearing have
arisen multiple times in birds. I found them in Steatornis, owlet
nightjars, and Strigops habroptilus. Owlet nightjars do have wide
squamoso-occipital wings, but less so the other two.

The bird with the most obvious convergence with owls, and the one named
for it, is Strigops habroptilus. There is a great image of a skull in
ventral view here:

http://www.skullsite.com/completelist/speciesinfo.cfm?spec=1297
http://www.skullsite.com/images/dbimages/large/strigopshabroptila_b.jpg

It again seems to have a posterolateral facing auditory canal.

Any thoughts?

-Jason