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Pelanomodon (Therapsida, Dicynodontia) redescribed

Ben Creisler

A new paper:

Christian F. Kammerer, Kenneth D. Angielczyk & Jörg Fröbisch (2015)
Redescription of the geikiid Pelanomodon (Therapsida, Dicynodontia),
with a reconsideration of ‘Propelanomodon.’
Journal of Vertebrate Paleontology (advance online publication)

Cryptodont dicynodonts are some of the most abundant therapsid taxa in
the upper Permian fossil record. Despite extensive taxonomic study of
these families, the species diversity of geikiid cryptodonts remains
problematic, particularly for the set of edentulous taxa in the genera
Pelanomodon, Propelanomodon, and Geikia. Here, all known specimens of
tuskless geikiid dicynodonts from the upper Permian Karoo Basin of
South Africa are reevaluated. The genus Pelanomodon is redescribed
based on a series of skulls representing a range of sizes. All
tuskless geikiids from the Karoo Basin are considered to represent a
single species (Pelanomodon moschops) that exhibited cranial
dimorphism as adults. The nominal species Pe. moschops and Pe.
rubidgei differ only in degree of facial boss development and are most
parsimoniously interpreted as sexual dimorphs. Propelanomodon is
considered to represent the juvenile morphotype of Pelanomodon
moschops, as indicated by the geographic and stratigraphic overlap of
the two taxa, the lack of any small skulls of the Pelanomodon
morphotype in well-sampled localities, and the presence of specimens
of intermediate size and morphology. ‘Propelanomodon’ specimens are
distinctive among juvenile dicynodonts in having a significantly
narrower intertemporal region than adults. Analysis of intertemporal
width relative to total skull size in Pelanomodon and the abundant
cryptodont taxa Aulacephalodon, Oudenodon, and Tropidostoma suggests
that Pelanomodon had a unique growth trajectory. Based on available
stratigraphic data, Pelanomodon was restricted to the uppermost
Permian Daptocephalus Assemblage Zone of the South African Beaufort
Group and was a victim of the end-Permian mass extinction.