The inner ear of the Paranthropus specimen DNH 22 from Drimolen, South Africa.

Abstract

Morphological variation within the southern African hypodigm of Paranthropus has been the focus of major interest since the earliest discoveries in the "Cradle of Humankind." Given the relevance of the bony labyrinth for investigating fossil primate paleobiodiversity, this article aims to provide additional evidence for assessing the degree of regional variation within Paranthropus through the comparative analysis of the inner ear of DNH 22. As comparative material, 18 southern African hominin specimens from Sterkfontein, Swartkrans, and Makapansgat (plus published data from Kromdraai B), attributed to Australopithecus, early Homo or Paranthropus, as well as 10 extant human and 10 extant common chimpanzee specimens are investigated. A landmark-based geometric morphometric method is applied for quantitatively assessing labyrinthine morphology. Additionally, cochlear parameters and oval window area are measured. In terms of semicircular canal and cochlear shape, DNH 22 most resembles the Paranthropus specimen SKW 18 from Swartkrans. Both specimens differ from the other Paranthropus specimens investigated in this study by an anteroposteriorly large posterior semicircular canal and a cochlea with loose turns in the apical portion. Conversely, the oval window area in DNH 22 closely fits the range observed in Paranthropus from Swartkrans and Kromdraai B. The inner ear of the DNH 22 specimen represents a unique opportunity to provide further insight into the early hominin labyrinthine variation pattern. In particular, the description of DNH 22 raises critical questions on the diversity of the vestibular system and evolutionary pattern of the auditory apparatus in Paranthropus.