title: Endoskeletal structure inCheirolepis(Osteichthyes, Actinopterygii), An early ray-finned fish.
abstract: As the sister lineage of all other actinopterygians, the Middle to Late Devonian (Eifelian-Frasnian)Cheirolepisoccupies a pivotal position in vertebrate phylogeny. Although the dermal skeleton of this taxon has been exhaustively described, very little of its endoskeleton is known, leaving questions of neurocranial and fin evolution in early ray-finned fishes unresolved. The model for early actinopterygian anatomy has instead been based largely on the Late Devonian (Frasnian)Mimipiscis, preserved in stunning detail from the Gogo Formation of Australia. Here, we present re-examinations of existing museum specimens through the use of high-resolution laboratory- and synchrotron-based computed tomography scanning, revealing new details of the neuro-cranium, hyomandibula and pectoral fin endoskeleton for the EifelianCheirolepis trailli. These new data highlight traits considered uncharacteristic of early actinopterygians, including an uninvested dorsal aorta and imperforate propterygium, and corroborate the early divergence ofCheirolepiswithin actinopterygian phylogeny. These traits represent conspicuous differences between the endoskeletal structure ofCheirolepisandMimipiscis. Additionally, we describe new aspects of the parasphenoid, vomer and scales, most notably that the scales display peg-and-socket articulation and a distinct neck. Collectively, these new data help clarify primitive conditions within ray-finned fishes, which in turn have important implications for understanding features likely present in the last common ancestor of living osteichthyans.
authors.affiliation: Department of Earth Sciences University of Oxford South Parks Road Oxford OX1 3AN UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Giles
authors.affiliation: Department of Organismal Biology and Anatomy University of Chicago 1027 E. 57th Street Chicago IL 60637 USA; Committee on Evolutionary Biology University of Chicago 1025 E. 57th Street Chicago IL 60637 USA.
authors.forename: Michael I
authors.initials: MI
authors.lastname: Coates
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences The University of Manchester Manchester M13 9PL UK; The Manchester X-Ray Imaging Facility School of Materials The University of Manchester Manchester M13 9PL UK.
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Garwood
authors.affiliation: Department of Life Sciences Imperial College London Silwood Park Campus Buckhurst Road Ascot SL5 7PY UK.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brazeau
authors.affiliation: The Joint Engineering and Environmental Processing Beamline Diamond Light Source The Harwell Science and Innovation Campus Didcot OX11 0DE UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Atwood
authors.affiliation: Department of Earth Sciences Natural History Museum Cromwell Road London SW7 5BD UK.
authors.forename: Zerina
authors.initials: Z
authors.lastname: Johanson
authors.affiliation: Department of Earth Sciences University of Oxford South Parks Road Oxford OX1 3AN UK.
authors.forename: Matt
authors.initials: M
authors.lastname: Friedman
keywords: Devonian; computed tomography; neurocranium; palaeontology