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[dinosaur] Crocodilian brain volume + turtle shell evolution (free pdfs)






Ben Creisler
bcreisler@gmail.com

Recent non-dino papers:

Free pdf:


Daniel Jirak & Jiri Janacek (2017)
Volume of the crocodilian brain and endocast during ontogeny.
PLoS ONE 12(6): e0178491
https://doi.org/10.1371/journal.pone.0178491
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0178491


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.


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Free pdf:

Jacqueline E Moustakas-Verho, Judith Cebra-Thomas & Scott F Gilbert (2017)
Patterning of the turtle shell.
Current Opinion in Genetics & Development 45:124-131
doi.org/10.1016/j.gde.2017.03.016
http://www.sciencedirect.com/science/article/pii/S0959437X16302106


Interest in the origin and evolution of the turtle shell has resulted in a most unlikely clade becoming an important research group for investigating morphological diversity in developmental biology. Many turtles generate a two-component shell that nearly surrounds the body in a bony exoskeleton. The ectoderm covering the shell produces epidermal scutes that form a phylogenetically stable pattern. In some lineages, the bones of the shell and their ectodermal covering become reduced or lost, and this is generally associated with different ecological habits. The similarity and diversity of turtles allows research into how changes in development create evolutionary novelty, interacting modules, and adaptive physiology and anatomy.