Ysterfontein 1, South Africa

Ysterfontein 1 is a collapsed coastal rock shelter that hosts a Middle Stone Age (MSA) shell midden deposit presenting evidence of coastal adaptation in the MSA defined as systematic, recurrent use of coastal resources and subsistence-dependent on the sea. Modern human behavioral innovations from the MSA include the earliest indicators of full coastal adaptation evidenced by shell middens, yet many MSA middens remain poorly dated.²³⁰Th/U burial dating of ostrich eggshells (OES) from Ysterfontein 1 are consistent with other age constraints and preserve stratigraphic principles; age-depth modeling of²³⁰Th/U burial ages indicate it was deposited between 119.9 to 113.1 kya. Stable carbon, nitrogen, and oxygen isotopes of OES indicate that during occupation the local environment was dominated by C₃ vegetation and was initially significantly wetter than at present but became drier and cooler with time. Integrating archaeological evidence with OES,²³⁰Th/U ages and stable isotopes shows the following: (1) Ysterfontein 1 is the oldest shell midden known, providing minimum constraints on full coastal adaptation by ~120 thousand years; (2) despite rapid sea-level drop and other climatic changes during occupation, relative shellfish proportions and sizes remain similar, suggesting adaptive foraging along a changing coastline; (3) the lithic techno-complex is similar to other west coast assemblages but distinct from potentially synchronous industries along the southern African coast, suggesting human populations were fragmented between seasonal rainfall zones; and (4) accumulation rates (up to 1.8 m per thousand years) are much higher than previously observed for dated, stratified MSA middens, implying more intense site occupation akin to Later Stone Age middens.