Over the last 20 years, it has been shown that birds and mammals are startlingly similar in their cognitive repertoire. Even the most intelligent taxa from each group – great apes and large corvids and parrots – match each other in most domains of cognition. This functional similarity is remarkable considering that birds and mammals shared a last common ancestor about 325 million years ago. Moreover, avian brains are small and lack a cerebral cortex arranged in layers. My talk will focus on recent discoveries showing that birds and mammals independently evolved brains with dramatically increased neuron numbers in the telencephalon and cerebellum, brain parts associated with higher cognition. This brain information processing capacity surge in birds and mammals is associated with the elaboration of at least partly non-homologous neural circuitry. Moreover, similar functions are processed in different, non-homological forebrain regions. Extreme neuron packing densities in birds partly explain why they have similar cognitive levels as mammals, but volumetrically much smaller brains. Astoundingly, phylogenetic analysis suggests that as few as four major changes in neuron-brain scaling in over 300 million years of evolution pave the way to intelligence in endothermic land vertebrates.