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

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.