Extended Data Fig. 4: Comparative fourth premolar morphology and dimensions.

a, Comparison of the Ledi-Geraru LD 750-115670 P₄ to other pre-2.0 Ma hominin specimens. All A.L. specimens attributed to A. afarensis. OMO 75-14 and LD 350-1 are attributed to Homo^1,2, StW 404 and OMO L51-79 are attributed to Paranthropus¹. LD 750-115670 measures 11.4 mm MD x 12.4 mm BL. Mesial is oriented up and lingual is oriented to the right. Scale bar in centimetres; images are to scale. b, Bivariate plot of P₄ crown dimensions. The LD 750-115670 premolar (magenta star) falls at the upper range of A. afarensis P₄ areas and just outside the range of eastern African early Homo. Authors’ data supplemented by references in Extended Data Table 1. c, Premolar cusp apices are marked in yellow with the outline of anterior fovea to aid identification of trait. d, Protoconid-metaconid cusp apex distance relative to overall BL breadth in unworn Hadar A. afarensis P₄ specimens (n = 8 including A.L. 966-1, in D) and LD 750-115670. This specimen falls outside the known range of variation for unworn P₄s from Hadar (unpublished data from W.H.K.). e, Ratio of Bouri (A. garhi) P⁴ area to LD 750 P₄ area compared to bootstrapped ratios of upper to lower P4 areas from Pan troglodytes (n = 98P₄s/95P⁴s) and Gorilla gorilla (n = 119P₄s/120P⁴s). The ratio of the Bouri upper premolar to the lower LD 750 specimen could be resampled within the 95% confidence intervals of the randomly selected gorilla (two-way p-value = 0.486) and chimpanzee (two-way p-value = 0.402) samples; although there are no lower A. garhi premolars, the size of LD 750 does not preclude it from being within the appropriate size range for A. garhi based on gorilla and chimp models of upper premolar areas compared to lower premolar areas. The 95% confidence intervals were calculated from the bootstrapped distributions using the percentile method; no adjustments were made for multiple comparisons. Authors’ data supplemented by references in Extended Data Table 1.