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Publication - Dr Joseph Keating

    The dermal skeleton of the jawless vertebrate Tremataspis mammilata (Osteostraci, stem-Gnathostomata)

    Citation

    [deceased], JO, Keating, J & Donoghue, P, 2019, ‘The dermal skeleton of the jawless vertebrate Tremataspis mammilata (Osteostraci, stem-Gnathostomata)’. Journal of Morphology, vol 280., pp. 999-1025

    Abstract

    Osteostracans are the closest jawless relatives of jawed vertebrates,
    informing the gradual assembly of the vertebrate mineralised skeleton.
    Conflicting interpretations of their dermal skeletal histology arise
    from failure to account for topological variation, obscuring their
    significance in elucidating vertebrate skeletal evolution. To resolve
    this, we characterize the cranial and trunk dermal skeleton of a single
    individual of Tremataspis mammillata (Osteostraci, Thyestiida) at
    submicron resolution using synchrotron‐ and computed‐ tomography. Our
    results show that the architecture of the Tremataspis dermal
    skeleton is, for the most part, conserved over the skeleton and is
    broadly consistent with previous histological hypotheses based on 2D
    thin section study. We resolve debate over the homology of the basal
    layer, identifying it as osteogenic acellular isopedin rather than
    odontogenic elasmodine or metaplastic ossification of the stratum
    compactum of the dermis. We find topological variation between all
    dermal skeletal elements studied, and particularly between the cranial
    and postcranial dermal skeleton. This variation can be largely explained
    by reduction in differentiation due to geometric constraints imposed
    within smaller skeletal elements, such as scales. Our description of the
    dermal skeleton of Tremataspis mammillata provides a foundation
    for interpreting data from cursory topological samples of dermal
    skeletal diversity obtained in other osteostracans. This reveals general
    aspects of histological structure that must be ancestral for
    osteostracans and, likely, ancestral jawed vertebrates. Finally, we draw
    the distinction between hypotheses and descriptions in palaeohistology.

    Full details in the University publications repository