Avian cerebellar floccular fossa size is not a proxy for flying ability in birds
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Date
2013
Authors
Walsh, Stig A.
Iwaniuk, Andrew N.
Knoll, Monja A.
Bourdon, Estelle
Barrett, Paul M.
Milner, Angela C.
Nudds, Robert L.
Abel, Richard L.
Sterpaio, Patricia Dello
Journal Title
Journal ISSN
Volume Title
Publisher
Public Library of Science
Abstract
Extinct animal behavior has often been inferred from qualitative assessments of relative brain region size in fossil
endocranial casts. For instance, flight capability in pterosaurs and early birds has been inferred from the relative size of the
cerebellar flocculus, which in life protrudes from the lateral surface of the cerebellum. A primary role of the flocculus is to
integrate sensory information about head rotation and translation to stabilize visual gaze via the vestibulo-occular reflex
(VOR). Because gaze stabilization is a critical aspect of flight, some authors have suggested that the flocculus is enlarged in
flying species. Whether this can be further extended to a floccular expansion in highly maneuverable flying species or
floccular reduction in flightless species is unknown. Here, we used micro computed-tomography to reconstruct ‘‘virtual’’
endocranial casts of 60 extant bird species, to extract the same level of anatomical information offered by fossils. Volumes of
the floccular fossa and entire brain cavity were measured and these values correlated with four indices of flying behavior.
Although a weak positive relationship was found between floccular fossa size and brachial index, no significant relationship
was found between floccular fossa size and any other flight mode classification. These findings could be the result of the
bony endocranium inaccurately reflecting the size of the neural flocculus, but might also reflect the importance of the
flocculus for all modes of locomotion in birds. We therefore conclude that the relative size of the flocculus of endocranial
casts is an unreliable predictor of locomotor behavior in extinct birds, and probably also pterosaurs and non-avian dinosaurs.
Description
Sherpa Romeo green journal: open access
Keywords
Cerebellar flocculus , Floccular fossa , Brain cavity , Flying ability , Extinct birds , Pterosauars , Birds--Flight
Citation
Walsh, S. A., Iwaniuk, A. N., Knoll, M. A., Bourdon, E., Barrett, P. M., Milner, A. C., ... & Dello Sterpaio, P. (2013). Avian cerebellar floccular fossa size is not a proxy for flying ability in birds. PLoS ONE, 8(6), e67176. doi:10.1371/journal.pone.0067176