Echoes from the past: New insights into the early hominin cochlea from a phylo-morphometric approach

We investigate cochlear variation, an indirect evidence of auditory capacities among earlyhominins and extant catarrhine species, in order to assess (i) the phylogenetic signal ofrelative external cochlear length (RECL) and oval window area (OWA), (ii) the evolution-ary model with the highest probability of explaining our observed data, (iii) some homininancestral nodes for RECL and OWA. RECL has a high phylogenetic signal under a Brown-ian motion model, and is closely correlated with body mass. Our model-based methodhas the advantage over parsimony-based methods of incorporating branch lengths in aphylo-morphospace, and this shows RECL shifted towards significantly higher values atthe Homo erectus-Homo sapiens node. We also observe that the StW 53 and KB 6067 fossilspecimens from Sterkfontein and Kromdraai likely represent one or two distinct, smaller-bodied and less derived hominin form(s) compared to Paranthropus specimens representedat Swartkrans.