Are endocasts good proxies for brain size and shape in archosaurs throughout ontogeny?

Akinobu Watanabe, Paul M. Gignac, Amy M. Balanoff, Todd L. Green, Nathan J. Kley, Mark A. Norell

Research output: Contribution to journalArticle

Abstract

Cranial endocasts, or the internal molds of the braincase, are a crucial correlate for investigating the neuroanatomy of extinct vertebrates and tracking brain evolution through deep time. Nevertheless, the validity of such studies pivots on the reliability of endocasts as a proxy for brain morphology. Here, we employ micro-computed tomography imaging, including diffusible iodine-based contrast-enhanced CT, and a three-dimensional geometric morphometric framework to examine both size and shape differences between brains and endocasts of two exemplar archosaur taxa – the American alligator (Alligator mississippiensis) and the domestic chicken (Gallus gallus). With ontogenetic sampling, we quantitatively evaluate how endocasts differ from brains and whether this deviation changes during development. We find strong size and shape correlations between brains and endocasts, divergent ontogenetic trends in the brain-to-endocast correspondence between alligators and chickens, and a comparable magnitude between brain–endocast shape differences and intraspecific neuroanatomical variation. The results have important implications for paleoneurological studies in archosaurs. Notably, we demonstrate that the pattern of endocranial shape variation closely reflects brain shape variation. Therefore, analyses of endocranial morphology are unlikely to generate spurious conclusions about large-scale trends in brain size and shape. To mitigate any artifacts, however, paleoneurological studies should consider the lower brain–endocast correspondence in the hindbrain relative to the forebrain; higher size and shape correspondences in chickens than alligators throughout postnatal ontogeny; artificially ‘pedomorphic’ shape of endocasts relative to their corresponding brains; and potential biases in both size and shape data due to the lack of control for ontogenetic stages in endocranial sampling.

Original languageEnglish
Pages (from-to)291-305
Number of pages15
JournalJournal of Anatomy
Volume234
Issue number3
DOIs
StatePublished - Mar 2019

Fingerprint

Proxy
ontogeny
brain
Alligators and Crocodiles
Brain
Chickens
alligators
chickens
Neuroanatomy
Rhombencephalon
Alligator mississippiensis
intraspecific variation
sampling
micro-computed tomography
iodine
Prosencephalon
Gallus gallus
Iodine
Artifacts
tomography

Keywords

  • Alligator
  • Gallus
  • diffusible iodine-based contrast-enhanced computed tomography
  • geometric morphometrics
  • micro-computed tomography
  • neuroanatomy

Cite this

Watanabe, Akinobu ; Gignac, Paul M. ; Balanoff, Amy M. ; Green, Todd L. ; Kley, Nathan J. ; Norell, Mark A. / Are endocasts good proxies for brain size and shape in archosaurs throughout ontogeny?. In: Journal of Anatomy. 2019 ; Vol. 234, No. 3. pp. 291-305.
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Are endocasts good proxies for brain size and shape in archosaurs throughout ontogeny? / Watanabe, Akinobu; Gignac, Paul M.; Balanoff, Amy M.; Green, Todd L.; Kley, Nathan J.; Norell, Mark A.

In: Journal of Anatomy, Vol. 234, No. 3, 03.2019, p. 291-305.

Research output: Contribution to journalArticle

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AU - Gignac, Paul M.

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