Abstract

Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry (DMQ), which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new ~2.04-1.95 Ma fossil specimen from DMQ that challenges this view. DNH 155 is a well-preserved, adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike that seen in adult P. robustus specimens from other, chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny, and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological change in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.