Wallabies don't see like quokkas

Wiebke Ebeling from Curtin University and Jan Hemmi from The University of Western Australia have discovered that the color vision of wallabies is more similar to that of dogs than of quokkas. If you’re like me, the first thing you thought upon reading that sentence was, ‘what the hell is a quokka?’

Here it is:

Quokka, photographed by Loetifuss, 9/23/2005

I know, I know. So cute!

The important point is that like wallabies, quokkas are marsupials. This means that wallabies are much more closely related to quokkas than they are to placental mammals, like dogs. However most placental mammals (except for some primates) have only two types of cones and thus have limited color vision (they're dichromates). In contrast, many marsupials, including quokkas, are trichromatic, having three types of cones. Yet, the closely related wallaby is a dichromate.

How do we know? Well, by training the critters to indicate whether two light panels appeared to be the same color.

Light stimuli were projected onto diffuser flaps that also served as the trigger when the animal pushed to indicate a stimulus choice. If correct, a food reward was delivered into a feeder bowl under the stimuli.
Photo copyright: W. Ebeling.
doi:10.1371/journal.pone.0086531.g001

It’s pretty clear that the wallabies are dichromatic. What’s not clear is why they differ in this fundamental way from other, closely related marsupials. 

Wiebke Ebeling, & Jan M. Hemmi (2014). Dichromatic Colour Vision in Wallabies as Characterised by Three Behavioural Paradigms PLOS ONE DOI: 10.1371/journal.pone.0086531.