Drimolen cranium DNH 155 documents microevolution in an early hominin species

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, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04-1.95 million years ago, 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 those 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 changes 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. An approximately 2-million-year-old male Paranthropus robustus cranium from Drimolen Main Quarry in South Africa refutes influential ideas of sexual dimorphism in this taxon and instead suggests local microevolution within robust australopiths.

Automated summary

The discovery of a well-preserved adult male cranium, DNH 155, challenges existing hypotheses of sexual dimorphism and clarifies theories regarding hominin phylogeny. This finding represents highly resolved evidence of microevolutionary changes within Paranthropus robustus, indicating local microevolution within robust australopiths.