Redescription of the geikiid <i>Pelanomodon</i> (Therapsida, Dicynodontia), with a reconsideration of ‘<i>Propelanomodon</i>’

<p>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 <i>Pelanomodon</i>, <i>Propelanomodon</i>, and <i>Geikia</i>. Here, all known specimens of tuskless geikiid dicynodonts from the upper Permian Karoo Basin of South Africa are reevaluated. The genus <i>Pelanomodon</i> 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 (<i>Pelanomodon moschops</i>) that exhibited cranial dimorphism as adults. The nominal species <i>Pe</i>. <i>moschops</i> and <i>Pe</i>. <i>rubidgei</i> differ only in degree of facial boss development and are most parsimoniously interpreted as sexual dimorphs. <i>Propelanomodon</i> is considered to represent the juvenile morphotype of <i>Pelanomodon moschops</i>, as indicated by the geographic and stratigraphic overlap of the two taxa, the lack of any small skulls of the <i>Pelanomodon</i> morphotype in well-sampled localities, and the presence of specimens of intermediate size and morphology. ‘<i>Propelanomodon</i>’ 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 <i>Pelanomodon</i> and the abundant cryptodont taxa <i>Aulacephalodon</i>, <i>Oudenodon</i>, and <i>Tropidostoma</i> suggests that <i>Pelanomodon</i> had a unique growth trajectory. Based on available stratigraphic data, <i>Pelanomodon</i> was restricted to the uppermost Permian <i>Daptocephalus</i> Assemblage Zone of the South African Beaufort Group and was a victim of the end-Permian mass extinction.</p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">www.tandfonline.com/UJVP</a></p> <p>Citation for this article: Kammerer, C. F., K. D. Angielczyk, and Jörg Fröbisch. 2015. Redescription of the geikiid <i>Pelanomodon</i> (Therapsida, Dicynodontia), with a reconsideration of ‘<i>Propelanomodon</i>’. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1030408.