Three-dimensional X-ray-computed tomography of 3300- to 6000-year-old Citrullus seeds from Libya and Egypt compared to extant seeds throws doubts on species assignments

Societal Impact Statement The watermelon (Citrullus lanatus subsp. vulgaris) is among the world's most important fruit crops. We here use C-14 dating and morphometric analysis to test whether ancient seeds can be identified to species level, which would help document food expansion, innovation, and diversity in Northeastern Africa. We dated a Libyan seed to 6182?6001 calibrated years BP, making it the oldest Citrullus seed known. Morphometric analysis could not reliably assign ancient seeds to particular species, but several seeds showed breakage patterns characteristic of modern watermelon seeds cracked by human teeth. Our study contributes to the understanding of the early history of watermelon use by humans, who may have mostly snacked on the seeds, and cautions against the use of morphology alone to identify Citrullus archaeological samples.