Tangentially, there is recent discussion of the idea that the neocortex is homologous to structures that do exist in the avian forebrain, eg that mammalian neocortex vs avian forebrain is almost the same processing units, wired with almost the same way connectivity, but just with a slightly different spatial organization:

http://www.sciencedirect.com/science/article/pii/S0960982212... Harvey J. Karten. Neocortical Evolution: Neuronal Circuits Arise Independently of Lamination.

Some evidence is that some genes which correlate with cortical layers in mammals show up in these other places in avians.