What are the biological fundaments of cognition? Until recently we assumed that the cerebral cortex is a conditio sine qua non for all higher cognitive operations. Only mammals like humans have a cortex. But now we learn that some birds are able to produce cognitive processes that are on par with apes. The problem is that birds have very small brains without a cortex. How is that possible? I will argue that a) birds do not have a cortex but a palliumthat is partly homologous to that of the cortex (implication #1: cortical lamination is not a requirement for complex cognition); b) similar neural circuits can be found in the forebrains of birds and mammals (implication #2: some cognitive function require certain circuits. These then evolve convergently in practically the same way in the different branches of evolution); c) brain size does not correlate when comparing birds and mammals (implication #3: brain size or neuron numbers are useless proxies for cognitive complexity when comparing brains that have different anatomical designs).