Data from: Flightless birds are not neuroanatomical analogs of non-avian dinosaurs

Background: In comparative neurobiology, major transitions in behavior are
thought to be associated with proportional size changes in brain regions.
Bird-line theropod dinosaurs underwent a drastic locomotory shift from
terrestrial to volant forms, accompanied by a suite of well-documented
postcranial adaptations. To elucidate the potential impact of this
locomotor shift on neuroanatomy, we first tested for a correlation between
loss of flight in extant birds and whether the brain morphology of these
birds resembles that of their flightless, non-avian dinosaurian ancestors.
We constructed virtual endocasts of the braincase for 80 individuals of
non-avian and avian theropods, including 25 flying and 19 flightless
species of crown group birds. The endocasts were analyzed using a
three-dimensional (3-D) geometric morphometric approach to assess changes
in brain shape along the dinosaur-bird transition and secondary losses of
flight in crown-group birds (Aves). Results: While non-avian dinosaurs and
crown-group birds are clearly distinct in endocranial shape, volant and
flightless birds overlap considerably in brain morphology.
Phylogenetically informed analyses show that locomotory mode does not
significantly account for neuroanatomical variation in crown-group birds.
Linear discriminant analysis (LDA) also indicates poor predictive power of
neuroanatomical shape for inferring locomotory mode. Given current
sampling, Archaeopteryx, the oldest known bird, is inferred to be
terrestrial based on its endocranial morphology. Conclusion: The results
demonstrate that loss of flight does not correlate with appreciable amount
of neuroanatomical changes across Aves, but rather is partially
constrained due to phylogenetic inertia, evident from sister taxa having
similarly shaped endocasts. Although the present study does not explicitly
test whether endocranial changes along the dinosaur-bird transition are
due to acquisition of powered flight, the prominent relative expansion of
the cerebrum, in areas associated with flight-related cognitive capacity,
suggests that the acquisition of flight may have been an important initial
driver of brain shape evolution in theropods.