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Re: Slitted bird irises?

There is a paper on skimmer irises (Zusi, R and D Bridge 1981. On the slit 
pupil of the Black Skimmer Rhynchops niger). J Field Ornithology 52: 338-340). 
It is freely available at:


The view of the authors (and Dick Zusi knew his skimmers) is that the slit 
pupil was an adaptation to a larger pupil size (as skimmers are partly 
nocturnal) in that the slit allowed less light in during the day when 
thoroughly contracted. Obviously this feature is an evolutionary novelty in 

Ronald Orenstein 
1825 Shady Creek Court
Mississauga, ON
Canada L5L 3W2

> On May 6, 2015, at 7:05 PM, Dann Pigdon <dannj@alphalink.com.au> wrote:
>> 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
> _____________________________________________________________