DOI: 10.5061/dryad.612jm64b4
title: The three-dimensionally articulated oral apparatus of a Devonian heterostracan sheds light on feeding in Palaeozoic jawless fishes

description: Attempts to explain the origin and diversification of vertebrates have
 commonly invoked the evolution of feeding ecology, contrasting
 the passive suspension feeding of invertebrate chordates and
 larval lampreys with active predation in living jawed vertebrates. Of the
 extinct jawless vertebrates that phylogenetically intercalate
 these living groups, the feeding apparatus is well-preserved only
 in the early diverging stem-gnathostome heterostracans. However
 its anatomy remains poorly understood. Here we use X-ray
 microtomography to characterise the feeding apparatus of the
 pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855).
 The apparatus is composed of thirteen plates
 arranged approximately bilaterally, most of which articulate from
 the postoral plate. Our reconstruction shows that the oral plates
 were capable of rotating around the transverse axis, but likely
 with limited movement. It also suggests the nasohypophyseal
 organs opened internally, into the pharynx. The functional
 morphology of the apparatus in Rhinopteraspis precludes
 all proposed interpretations of feeding except for
 suspension/deposit feeding and we interpret the apparatus as
 having served primarily to moderate the oral gape. This is consistent
 with evidence that at least some early jawless gnathostomes were
 suspension feeders and runs contrary to macroecological scenarios
 that envisage early vertebrate evolution as characterised by a
 directional trend towards increasingly active food acquisition.
description: <em>Rhinopteraspis dunensis </em>NHMUK PV P 73217 was
 scanned using a Nikon Metrology XTH 225ST X-ray tomography instrument
 based in Bristol Palaeobiology, University of Bristol. Two scans were
 undertaken, each composed of two stacked scans. The first scan included
 the whole headshield at a voltage of 223 kV and a current of 193 μA, with
 3141 projections, and with a 1 mm Sn filter, obtaining a dataset with
 63.41 μm voxel resolution. The second scan targeted the oral region
 specifically, including the posterior third of the rostrum, the orbital,
 oral, and pineal parts of the headshield, and the anterior quarter of the
 dorsal and ventral discs, at a voltage of 180 kV and a current of 178 μA,
 with 3141 projections of 8 frames and 708 ms each, and with a 0.5 mm Cu
 filter, achieving a voxel resolution of 22.91 μm.The resulting tomographic
 datasets were segmented in Mimics v.25 (materialise) to create 3D
 models. 
description: # The three-dimensionally articulated oral apparatus of a Devonian
 heterostracan sheds light on feeding in Palaeozoic jawless fishes
 This dataset contains
 supplementary data associated with Dearden *et al.* 2024 *Proceedings of
 the Royal Society B: Biological Sciences*. This data takes the form of two
 sets of 3D surface models derived from CT scans of the Palaeozoic jawless
 fish *Rhinopteraspis dunensis* NHMUK PV P 73217. ## Description of the
 data and file structure The data is provided in two zipped folders, each
 of which corresponds to one scan set. The details of these scans are
 provided in the related Open Access paper. The first folder
 "Rhinopteraspis_High_Resolution" comprises the 3D models derived
 from a higher resolution CT scan of the oral region of NHMUK PV P 73217.
 The second folder "Rhinopteraspis_Low_Resolution" comprises
 additional 3D models derived from CT scans of the entire specimen of NHMUK
 PV P 73217 including all plates not fully captured in the above scan. All
 files are provided in the .ply format. This format of surface file is
 readily openable in freeware like Meshlab and Blender. ## Sharing/Access
 information This data is described in : * Dearden *et al.* 2024 The
 three-dimensionally articulated oral apparatus of a Devonian heterostracan
 sheds light on feeding in Palaeozoic jawless fishes. *Proceedings of the
 Royal Society B: Biological Sciences*