Meeting Abstract
32.4 Sunday, Jan. 5 08:45 Getting inside the head of ancient ray-finned fishes GILES, S*; FRIEDMAN, M; University of Oxford, UK; University of Oxford, UK sam.giles@earth.ox.ac.uk
The endocranial cavity is found inside the skull of vertebrates, and represents the space in which the brain and associated nervous tissues sit. During fossilisation, these soft tissues rot away, leaving a void. This may become filled with sediment, producing an endocranial cast, or endocast. If preserved, this infilling can be used to study the endocranial anatomy of the animal to which it belonged. Preservation of these infillings, however, is understandably rare. Moreover, traditional investigative techniques are time consuming and often destructive in their nature, particularly the use of Sollas’ grinding technique. The advent of computed tomography (CT) has provided a non-invasive way of studying the internal cavities of extinct and extant species alike. We applied lab-based CT to the crania of two fossil ray-finned fishes: Mimipiscis, from the Late Devonian (~385-380Ma) of Western Australia; and Kentuckia, from the early Carboniferous (~360-350Ma) of Kentucky. These taxa represent two early members of the clade that today comprises nearly half of all living vertebrates. Both of these taxa are key in analyses of early ray fin relationships, with Mimipiscis resolved as the more stemward of the two. Our models reveal somewhat unexpected features of the endocranial cavity of Mimipiscis, in particular poorly developed optic lobes and anterolaterally directed olfactory tracts. Comparison with other taxa shows that these characters are found elsewhere in outgroups to the ray fin clade, such as the lobe-finned fishes. In contrast, large optic lobes and anteriorly directed olfactory tracts are found in Kentuckia, uniting this taxon with other ray-finned fishes, to the exclusion of Mimipiscis. These new morphological data confirm current hypotheses on early ray fin interrelationships while providing insights on when key innovations arose in the brains of these fishes.
