Tempo and Pattern of Avian Brain Size Evolution.

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Anatomy

Background:

• Avian relative brain sizes rival primates, yet evolutionary patterns are unclear.
• Understanding brain-body scaling is key to avian brain evolution.
• Theropod dinosaurs and early birds' brain evolution requires further investigation.

Purpose of the Study:

• To investigate the brain-body scaling relationship across avian evolution.
• To identify drivers of brain size evolution in birds and their ancestors.
• To reconstruct deep-time patterns of brain-body co-variation.

Main Methods:

• Utilized a dataset of over 2,000 modern birds, fossil birds, and theropod dinosaurs.
• Inferred brain-body co-variation patterns across geological time.
• Analyzed brain-body size integration and evolutionary rates.

Main Results:

• No significant relative brain size increase occurred during the theropod-bird transition or flight evolution.
• Theropods and basal birds exhibited weaker brain-body size integration, enabling rapid changes.
• Major brain size shifts in Neoaves post-extinction were linked to body size reduction.
• Parrots and corvids achieved large brains through distinct pathways: parrots via body size reduction, corvids via simultaneous body and brain size increase.

Conclusions:

• Early adaptive radiation in brain size provided a foundation for later selection and stabilization in birds.
• Brain-body size integration dynamics played a crucial role in avian brain evolution.
• Distinct evolutionary strategies contributed to the high relative brain sizes observed in modern bird clades.