Data from: New information on Brindabellaspis stensioi Young, 1980, highlights morphological disparity in Early Devonian placoderms

Acid prepared specimens of the placoderm Brindabellaspis stensioi (Early
Devonian of New South Wales, Australia) revealed placoderm endocranial
anatomy in unprecedented detail. Brindabellaspis has become a key taxon in
discussions of early gnathostome phylogeny, and the question of placoderm
monophyly versus paraphyly. The anterior orientation of the facial nerve
and related hyoid arch structures in this taxon resemble fossil
osteostracans (jawless vertebrates) rather than other early gnathostomes.
New specimens of Brindabellaspis now reveal the previously unknown
anterior region of the skull, including an exceptionally elongate
premedian bone forming a long rostrum, supported by a thin extension of
the postethmo-occipital unit of the braincase. Lateral bone overlap
surfaces indicate an unusual anterior position for the jaws. Digital
rendering of a synchrotron radiation scan reveals a uniquely specialised
ethmoid commissure sensory canal, doubled back and fused into a midline
canal. The visceral surface of the premedian bone has a plexus of
perichondral bone canals. An updated skull roof reconstruction of
Brindabellaspis adds to the highly variable dermal skull patterns of the
probably non-monophyletic ‘acanthothoracids’. The unusual morphology
revealed by the new specimens suggests that the earliest known reef fish
fauna contained a diverse range of fishes with specialised ecological
roles.