Cochlear shape distinguishes southern African early hominin taxa with unique auditory ecologies

Abstract

Insights into potential differences among the bony labyrinths of Plio-Pleistocene hominins may inform their evolutionary histories and sensory ecologies. We use four recently-discovered bony labyrinths from the site of Kromdraai to significantly expand the sample for Paranthropus robustus. Diffeomorphometry, which provides detailed information about cochlear shape, reveals size-independent differences in cochlear shape between P. robustus and Australopithecus africanus that exceed those among modern humans and the African apes. The cochlea of P. robustus is distinctive and relatively invariant, whereas cochlear shape in A. africanus is more variable, resembles that of early Homo, and shows a degree of morphological polymorphism comparable to that evinced by modern species. The curvature of the P. robustus cochlea is uniquely derived and is consistent with enhanced sensitivity to low-frequency sounds. Combined with evidence for selection, our findings suggest that sound perception shaped distinct ecological adaptations among southern African early hominins.

A new early hominin calcaneus from Kromdraai (South Africa)

“…Fossils from the Kromdraai site have been primarily attributed to P. robustus (Braga et al, 2013, 2021; Braga & Thackeray, 2016; Broom, 1938a, 1938b, 1943; Grine, 1982); however, some specimens have been suggested to belong to early Homo (potentially H. habilis ) (e.g., Braga & Thackeray, 2003). Unfortunately, there are no published calcanei that are definitively attributed to either species, making it difficult to provide the KW 6302 calcaneus with a taxonomic affiliation.…”

“…Fossils from the Kromdraai site have been primarily attributed to P. robustus (Braga et al, 2013(Braga et al, , 2021Broom, 1938aBroom, , 1938bBroom, , 1943Grine, 1982); however, some specimens have been suggested to belong to early Homo (potentially H. habilis) (e.g., Braga & Thackeray, 2003). Unfortunately, there are no published calcanei that are definitively attributed to either species, TA B L E 6 Mahalanobis distance p-values for significant differences between the KW 6302 calcaneus and other fossils calculated based on covariance matrices of different genera/(sub)species (Deloison, 1986;Feibel et al, 1989;Braga & Thackeray, 2003;Deloison, 2004;Gebo & Schwartz, 2006).…”

“…The Kromdraai fossiliferous site (26°00′41”S, 27°44′60″E) is one of the palaeokarsts truncated by surficial erosion, situated along the southern flank of the Blaauwbank River (Gauteng Province, South Africa). The Plio‐Pleistocene site has borne many early hominin fossils and is listed among the UNESCO World Heritage Sites often referred to as the “Cradle of Humankind” (e.g., Braga et al, 2013, 2017, 2021; Braga & Thackeray, 2003; Broom, 1938a; Broom, 1938b; Thackeray et al, 2001; Vrba, 1981). Some fossiliferous deposits in the Kromdraai area were discovered in 1895 by David Draper, who collected fossiliferous breccias and sent them to the British Museum of Natural History (de Graaff, 1961; Malan, 1959).…”

“…The renewed excavations at Kromdraai since 2014 resulted in the in situ recovery of faunal (Fourvel et al, 2016, 2018; Pavia, 2020) and fossil hominin assemblages (Braga et al, 2017, 2021) from Unit P. The fossil remains from Unit P are fragmented but with a very good degree of preservation. Although cranial and postcranial fossil hominin specimens have been recovered, there is no definitive association between them.…”

“…The renewed excavations at Kromdraai since 2014 resulted in the in situ recovery of faunal (Fourvel et al, 2016(Fourvel et al, , 2018Pavia, 2020) and fossil hominin assemblages (Braga et al, 2017(Braga et al, , 2021 from Unit P.…”