Birds are extraordinarily intelligent and they can rival mammals in terms of relative brain size and behavioural complexity. The clade originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. Recent studies have shown that corvids and some parrots are capable of cognitive achievement comparable to those of great apes. They manufacture and use tools, solve puzzles, and plan for future needs. Futhermore, they share with humans and a few other animal groups a rare capacity for vocal learning.
Over the last decades, several discovered fossils of theropods and early birds have enriched our knowledge of the evolution of the avian skull. Now, the discovery of an exceptionally well preserved braincase from an Upper Cretaceous (~80 Ma) enantiornithine bonebed in southeastern Brazil shed light on the early evolution of the avian braincase, brain and inner ear.
Enantiornithes are the most diverse group of Mesozoic birds. The clade shows a mosaic of characters, reflecting their intermediate phylogenetic position between the basal-pygostylians and modern bird, and their remains, ranging from the size of hummingbirds to turkeys, have been collected on every continent except Antarctica. MPM-334-1 (Museu de Paleontologia de Marília, São Paulo State) is a diminutive basicranium of a skeletally mature enantiornithine bird. The endocast comprises impressions from the external surfaces of most of the medulla, parts of the cerebellum, and the ventral portion of the optic tectum.
MPM-334-1 displays a mosaic combination of plesiomorphic dinosaurian traits and a set of endocranial transformations: a flexed brain that are remarkably similar to those of extant birds, a ventralized foramen magnum and ‘crown-like’ endosseous labyrinth. The new study lead by Luis Chiappe, suggest a more complex scenario for the evolution of the avian skull and central nervous system than had previously been understood, with key features of the modern avian endocranium evolving much earlier than what was formerly thought.
Chiappe LM, Navalón G,Martinelli AG, Nava W, Field DJ. 2022 Fossil basicranium clarifies the origin of theavian central nervous system and inner ear. Proc. R. Soc. B289: 20221398. https://doi.org/10.1098/rspb.2022.1398
Chiappe, L. M., Ji, S. & Ji, Q. Juvenile birds from the Early Cretaceous of China: implications for enantiornithine ontogeny. Am. Mus. Novit. 3594, 1–46 (2007).