Birds and mammals show remarkable convergence in their neurocognition and thermal physiology despite being phylogenetically separated for 325 million years of evolution. This elaboration in neurocognition is hypothesised to be directed at increasing the caloric intake through efficient foraging to power tachymetabolic endothermy. To gain a better understanding of how and why cognitive abilities evolved in today’s endothermic birds and mammals, knowledge from several fields is required to provide unique perspectives in the construction of a more complete view of cognitive evolution in deep time. This thesis first introduces the emerging field of Palaeocognition, and how it may be studied, in a largely theoretical paper. Then, we compare species at important phylogenetic positions within Mammalia (Synapsida) and Archosauria (Sauropsida) with focus on core cognitive functions. Three empirical papers are dedicated to study the evolution and ontogeny of inhibitory control and visual working memory, which are thought to increase foraging success the better they are developed. We found that motor control was poor in American alligators compared to mammals and birds and especially common ravens. Furthermore, we found that visual working memory was more complex and developed in American alligators and birds compared to non-primate mammals, and we suggest that visual acuity may be a prerequisite for more complex visual working memory to evolve. We also found that within archosaurs, American alligators had less robust visual working memory representations than birds, which may be due to ectotherms’ lower potential to dedicate expensive neurons to such functions. Lastly, we find that both mammals and birds can protect their visual working memory from distractions, but that interfering distractions of value to the subject distract more than non-valuable ones. Lastly, this thesis also dedicated two empirical papers to the study of social cognition, specifically the acoustic basis for individual recognition in American alligators and social cognition associated with allopreening in palaeognath birds. We find that alligators have bellows that are individually distinct, which can provide a basis for the evolution of individual recognition. In palaeognaths, we find no evidence of allopreening. We then discuss this absence in relation to the similarities in neurocognition and reproductive systems with non-avian paravian dinosaurs and make inferences on the grooming behaviours of these extinct animals.