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Redescription of the cranial skeleton of the Early Devonian (Emsian) sarcopterygian Durialepis edentatus Otto, 2007 (Dipnomorpha; Porolepiformes)

Citation

Giles, Sam; Mondéjar-Fernández, Jorge; Friedman, Matt (2020), Redescription of the cranial skeleton of the Early Devonian (Emsian) sarcopterygian Durialepis edentatus Otto, 2007 (Dipnomorpha; Porolepiformes), Dryad, Dataset, https://doi.org/10.5061/dryad.rfj6q576v

Abstract

Porolepiforms represent a clade of Devonian stem lungfishes, divided into the cosmine-bearing and likely paraphyletic ‘Porolepidae’ (e.g., Porolepis, Heimenia) and the cosmine-free and stratigraphically younger Holoptychiidae (e.g., Holoptychius, Glyptolepis, Laccognathus). Data on the dermoskeleton are available for both groups, but are more limited for ‘porolepids’. Here we present new information on the ‘porolepid’ Durialepis edentatus from the Emsian (Early Devonian) of Germany based on micro-CT scanning. The material comprises an articulated skull of a single three-dimensionally preserved individual. The arrangement of the cheekbones of Durialepis edentatus recalls that of Porolepis brevis, with the occurrence of two subsidiary squamosals. However, the parieto-ethmoidal and postparietal shields are roughly equal in size, a condition similar to that of Glyptolepis groenlandica and intermediate between Porolepis brevis and holoptychiids. A large parasymphysial tooth plate displays five tooth rows with three large tusks in the median row, another intermediate arrangement between the primitive condition of Porolepis sp. (eight rows) and holoptychiids (five or fewer rows). Remarkably among porolepiforms, this dental plate is perfectly symmetrical. Despite the occurrence of cosmine and rhombic scales, the combination of traits displayed in Durialepis deviates from Porolepis in several ways, reflecting features shared with holoptychiids to the exclusion of other ‘porolepids’.  Durialepis edentatus is thus a key addition to our knowledge of ‘porolepid’ anatomy. Because Durialepis edentatus preserves much of the cranial and postcranial skeleton in a single individual, it represents a suitable early dipnomorph representative for inclusion in phylogenetic analyses on sarcopterygians and early osteichthyans.

Methods

The specimen was scanned using a Nikon Metrology HMX ST 225 CT scanner at the Natural History Museum, London, with the following settings: 205 kV; 160 µa; 6284 projections; 0.5 mm copper filter; with a resulting voxel size of 85.7 µm. Data were segmented manually in Mimics Innovation Suite V.18.0 (http://biomedical.materialise.com/mimics; Materialise, Leuven, Belgium) and resultant PLY files exported into and rendered in Blender V.2.77a (http://www.blender.org; Blender Institute, Amsterdam, Netherlands).

The following data are made available: raw TIFF stack (converted in ImageJ from .vol file) and associated metadata file; Mimics file containing loaded dataset and segmentation; 3D PLY files exported from Mimics.

Funding

Natural Environment Research Council, Award: NE/J500045/1

Royal Society