Browsing by Author "Bazzana, KD"

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    Endocasts of the basal sauropsid Captorhinus reveal unexpected neurological diversity in early reptiles
    (Wiley, 2022-10-14) Bazzana, KD; Evans, DC; Bevitt, JJ; Reisz, RR
    Captorhinids are a group of Paleozoic amniotes that represents one of the earliest‐diverging clades of eureptiles. Although captorhinids are one of the best‐known and most well‐studied clades of early amniotes, their palaeoneuroanatomy has gone largely unexamined. We utilized neutron computed tomography to study the virtual cranial and otic endocasts of two captorhinid specimens. The neurosensory anatomy of captorhinids shows a mixture of traits considered plesiomorphic for sauropsids (no expansions of the cerebrum or olfactory bulbs, low degree of encephalization, low ossification of the otic capsule) and those considered more derived, including moderate cephalic and pontine flexures and a dorsoventrally tall bony labyrinth. The inner ear clearly preserves the elliptical, sub‐orthogonal canals and the short, rounded vestibule, along with an unusually enlarged lateral canal and a unique curvature of the posterior canal. The reconstructed neurosensory anatomy indicates that captorhinids were sensitive to slightly higher frequencies than many of their contemporaries, likely reflecting differences in body size across taxa, while the morphology of the maxillary canal suggests a simple, tubular condition as the plesiomorphic state for Sauropsida and contributes to the ongoing discussions regarding the phylogenetic placement of varanopids. This study represents the first detailed tomographic study of the brain and inner ear of any basal eureptile. The new data described here reveal that the neuroanatomy of early sauropsids is far more complex and diverse than previously anticipated, and provide impetus for further exploration of the palaeoneuroanatomy of early amniotes. © 2024 American Association for Anatomy.
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    Neurosensory anatomy of Varanopidae and its implications for early synapsid evolution
    (Wiley, 2021-11-14) Bazzana, KD; Evans, DC; Bevitt, JJ; Reisz, RR
    Varanopids are a group of Palaeozoic terrestrial amniotes which represent one of the earliest‐diverging groups of synapsids, but their palaeoneurology has gone largely unstudied and recent analyses have challenged their traditional placement within synapsids. We utilized computed tomography (CT) to study the virtual cranial and otic endocasts of six varanopids, including representative taxa of both mycterosaurines and varanodontines. Our results show that the varanopid brain is largely plesiomorphic, being tubular in shape and showing no expansion of the cerebrum or olfactory bulbs, but is distinct in showing highly expanded floccular fossae. The housing of the varanopid bony labyrinth is also distinct, in that the labyrinth is bounded almost entirely by the supraoccipital‐opisthotic complex, with the prootic only bordering the ventral portion of the vestibule. The bony labyrinth is surprisingly well‐ossified, clearly preserving the elliptical, sub‐orthogonal canals, prominent ampullae, and the short, undifferentiated vestibule; this high degree of ossification is similar to that seen in therapsid synapsids and supports the traditional placement of varanopids within Synapsida. The enlarged anterior canal, together with the elliptical, orthogonal canals and enlarged floccular fossa, lend support for the fast head movements indicated by the inferred predatory feeding mode of varanopids. Reconstructed neurosensory anatomy indicates that varanopids may have a much lower‐frequency hearing range compared to more derived synapsids, suggesting that, despite gaining some active predatory features, varanopids retain plesiomorphic hearing capabilities. As a whole, our data reveal that the neuroanatomy of pelycosaur‐grade synapsids is far more complex than previously anticipated. © 1999-2024 John Wiley & Sons, Inc or related companies.