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Re: Slitted bird irises?

On Wed, May 6th, 2015 at 5:37 PM, "Haaramo, Mikko K" 
<mikko.haaramo@helsinki.fi> wrote:

> All,
> Which modern bird have a slitted iris?
> I  googled it and only one I could find were skimmers (_Rynchops_).
> Question rises why dinosaurs are reconstructed with ones, even if nocturnal 
> birds don't have
> them?

Most (if not all) crocodilians have slitted irises, whereas most birds don't.  
If you use birds and 
crocs as phylogenetic brackets for inferring dinosaurian physiology, then the 
likelihood of at least 
some nocturnal dinosaurs having slit pupils would seem to be about 50:50.

Both groups of extant archosaur would seem to represent radiations from a 
highly specialised 
ancestor, so chances are that neither is a very good analogue for the average 
dinosaur (if the 
notion of an 'average' dinosaur is of any use at all, given their wide 
diversity of forms). The best 
we can say is that nocturnal archosaurs have the genetic potential to evolve 
slit pupils, based on 
their presence in crocodilians, but that there is no firm requirement to do so, 
based on the lack of 
split pupils in nocturnal birds.


Dann Pigdon
Spatial Data Analyst               Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj