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Brain modularity across the theropod–bird transition

Ben Creisler

A new paper:

Amy M. Balanoff, Jeroen B. Smaers and Alan H. Turner (2015)
Brain modularity across the theropod–bird transition: testing the
influence of flight on neuroanatomical variation.
JOURNAL OF ANATOMY (advance online publication)
DOI: 10.1111/joa.12403

Living birds constitute the only vertebrate group whose brain volume
relative to body size approaches the uniquely expanded values
expressed by mammals. The broad suite of complex behaviors exhibited
by crown-group birds, including sociality, vocal learning, parental
care, and flying, suggests the origins of their encephalization was
likely driven by a mosaic of selective pressures. If true, the
historical pattern of brain expansion may be more complex than either
a gradual expansion, as proposed by early studies of the avian brain,
or a sudden expansion correlating with the appearance of flight. The
origins of modern avian neuroanatomy are obscured by the more than 100
million years of evolution along their phylogenetic stem (from the
origin of the modern radiation in the Middle Jurassic to the split
from crocodile-line archosaurs). Here we use phylogenetic comparative
approaches to explore which evolutionary scenarios best explain
variation in measured volumes of digitally partitioned endocasts of
modern birds and their non-avian ancestors. Our analyses suggest that
variation in the relative volumes of the endocranium and cerebrum
explain most of the structural variation in this lineage. Generalized
multi-regime Ornstein-Uhlenbeck (OU) models suggest that powered
flight does not appear to be a driver of observed variation,
reinforcing the hypothesis that the deep history of the avian brain is
complex, with nuances still to be discovered.