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, 12 (6), e0178491
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Volume of the Crocodilian Brain and Endocast During Ontogeny

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Volume of the Crocodilian Brain and Endocast During Ontogeny

Daniel Jirak et al. PLoS One.

Abstract

Understanding complex situations and planning difficult actions require a brain of appropriate size. Animal encephalisation provides an indirect information about these abilities. The brain is entirely composed of soft tissue and, as such, rarely fossilises. As a consequence, the brain proportions and morphology of some extinct vertebrates are usually only inferred from their neurocranial endocasts. However, because the morphological configuration of the brain is not fully reflected in the endocast, knowledge of the brain/endocast relationship is essential (especially the ratio of brain volume to endocast volume or the equivalent proportion of interstitial tissue) for studying the endocasts of extinct animals. Here we assess the encephalic volume and structure of modern crocodilians. The results we obtained using ex vivo magnetic resonance imaging reveal how the endoneurocranial cavity and brain compartments of crocodilians change configuration during ontogeny. We conclude that the endocasts of adult crocodilians are elongated and expanded while their brains are more linearly organised. The highest proportion of brain tissue to endocast volume is in the prosencephalon at over 50% in all but the largest animals, whereas the proportion in other brain segments is under 50% in all but the smallest animals and embryos. Our results may enrich the field of palaeontological study by offering more precise phylogenetic interpretations of the neuroanatomic characteristics of extinct vertebrates at various ontogenetic stages.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. MR images of crocodilian brains.
T2w coronal image of an embryo—scan time 3 h 21m (A), T1w coronal image of an early juvenile—scan time 9 h 6 m (B), T1w sagittal image of a late juvenile—scan time 2 h 36 m (C), T2w sagittal image of an adult—scan time 7 m (D), T1w sagittal image of an adult—scan time 40 m (E). Scale bar– 5 mm (A, B, C) and 10 mm (D, E). Double-headed arrows in (E) show the typical area of the interstitium.
Fig 2
Fig 2. 3D reconstructions of the brains and endocasts of crocodilians at various ontogenetic stages divided into four major brain sectors.
3D reconstructions of an embryo (A), early juvenile (B), late juvenile (C), adult (D) and larger adult (E) from ventral (bottom left), lateral (upper left), dorsal (upper right) and lateral (bottom right—major brain sectors coloured) perspectives for each specimen. Brain—dark blue; endocast—light blue. Major brain sectors: olfactory (Olf)—violet, prosencephalic (Pros)—green, mesencephalic (Mes)—yellow and rhombencephalic (Rhomb)—red. Scale bar— 10 mm.

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References

    1. Healy SD, Rowe C. A critique of comparative studies of brain size. Proc R Soc Lond B Biol Sci. 2007; 274: 453–464. - PMC - PubMed
    1. Brasier MD, Norman DB, Liu AG, Cotton LJ, Hiscocks JEH, Garwood RJ, et al. Remarkable preservation of brain tissues in an early Cretaceous iguanodontian dinosaur. Geological Society, Special Publications. 2016; doi: 10.1144/SP448.3 - DOI
    1. Hopson JA. Paleoneurology In: Biology of the Reptilia, New York: Academic Press, 1979.
    1. Rogers SW. Allosaurus, crocodiles, and birds: evolutionary clues from spiral computed tomography of an endocast. Anat Rec. 1999; 257: 162–173. - PubMed
    1. Mace GM, Harvey PH, Clutton-Brock TH. Brain size and ecology in small mammals. J Zool. 1981; 193: 333–354.

Grant support

D.J. and J.J. were funded by the Czech Science Foundation (P302/12/1207). J.J. was also funded by the Czech Science Foundation (13-12412S). We thank Martin Kundrát for providing crocodilian sample collection.
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