Systematics and taxonomyThe related Podocnemididae is either treated as a distinct family or as a subfamily (Podocnemidinae) in the Pelomedusidae. The African side-necked turtles are then also demoted to subfamily rank, as the Pelomedusinae. As taxonomic rank is only meaningful as part of a sequence (a biological "family" has no fixed meaning on its own), both treatments are technically correct. Ultimately, the issue hinges upon the Austro-American side neck turtles (Chelidae). These Pleurodira are less closely related to the Podocnemididae and Pelomedusidae than these are to each other. If all three are ranked as full families, the Chelidae is treated as a basal (evolution), basal lineage, while the other two are united in the Taxonomic rank, superfamily Pelomedusoidea. This treatment is preferred here, because it allows more convenient placement of prehistoric pleurodires (e.g. the Bothremydidae).
Further reading*Edward Drinker Cope. 1868. An Examination of the REPTILIA and BATRACHIA obtained by the Orton Expedition to Equador [sic] and the Upper Amazon, with notes on other species. ''Proc. Acad. Nat. Sci. Philadelphia'' 20: 96-140. (Pelomedusidæ, new family, p. 119). *Goin CJ, Goin OB, Zug GR. 1978. ''Introduction to Herpetology: Third Edition.'' San Francisco: W.H. Freeman and Company. xi + 378 pp. . (Family Pelomedusidae, pp. 271–272).