These may occur on rock walls, but were commonly engraved onto robust bones since at least the beginning of the European Upper Palaeolithic and African Late Stone Age, where it is obvious they served as artificial memory systems (AMS) or external memory systems (EMS) to coin the terms used in Palaeolithic archaeology and cognitive science respectively, exosomatic devices in which number sense is clearly evident (for definitions see d’Errico Reference d'Errico1989; Reference d'Errico1995a,Reference d'Erricob; d'Errico & Cacho Reference d'Errico and Cacho1994; d'Errico et al. Reference d'Errico, Doyon and Colage2017; Hayden Reference Hayden2021).

We also demonstrate that the <Y> sign, one of the most frequently occurring signs in Palaeolithic non-figurative art, has the meaning <To Give Birth>. The position of the <Y> within a sequence of marks denotes month of parturition, an ordinal representation of number in contrast to the cardinal representation used in tallies.