UV Vision in Dinosaurs

[Balaur]

This has been bugging me for a while. Most birds can see in the ultraviolet spectrum. My question is, is it possible in dinosaurs, and can we know that from fossils?

[Newt]

Can we know it from fossils?  No.  The pigments responsible for vision in various wavelengths do not fossilize.  However, that doesn't mean it is impossible to know; we can use phylogenetic bracketing to deduce the condition in dinosaurs.  So, if both a descendant group (Aves) and a sister group (Crocodylia) of the dinosaurs have the same UV-sensitive pigments, then most likely that same pigment was ancestral for dinosaurs (though certain groups may have lost it).

A class of UV-sensitive pigments called SWS1 is ancestral to vertebrates, but in some groups SWS1 pigments have mutated to become most sensitive to violet light.  This apparently happened early in bird evolution, and all modern birds that have UV vision have secondarily evolved UV-sensitive pigments from violet-sensitive ones. (By the way, most birds cannot see in UV, only certain lineages). A quick search has not netted any info on crocodilian UV sensitivity, so no help there.  I'll keep looking.

So, UV vision in dinosaurs is certainly possible, but present evidence known to me does not show that it was definitely present.  It is also possible, even likely, that UV sensitivity in dinosaurs varied greatly among groups, as it does in extant birds and mammals.

http://mbe.oxfordjournals.org/content/24/8/1843.full.pdf