Digitized endocasts and brains: a perspective on measurements and historical analyses of the evolution of 172 fossil and extant amniote specimens

This perspective paper is intended to stimulate future research and discussion of brain evolution in amniotes by sharing 172 digitized endocasts of extinct and extant species spanning 60 million years. Using 3D digital surface scans of physical (<i>e.g.</i>, latex, plaster, resin) endocasts, we measured and compared relative endocranial volumes from dozens of extinct amniote taxa with those (endocasts or brain surface scans) of relevant extant species. Additionally, we offer calculated Encephalization Quotients and neocorticalization from digitized endocasts. Using historical methods of analysis, we find that, on average, neocortocalization of mammals increased over time, which is in agreement with recently published findings. Results also showed that, about 60 million years ago, mammalian neocorticalization averaged about 20%, increasing to a present average of 50%, and reaching a maximum of about 80% in primates within the past 10 million years. These results potentially redefine the allometric boundary between mammals and reptiles and confirm that measurements on a single species can adequately represent the brains of the entire species. We encourage other researchers to use our data, results, and conclusions as a springboard for more updated analyses.