Mauritania dwarfs South America: about 1,038,352 km² km² against 17,840,000 km² km². At true size Mauritania is about 17.2× larger — the whole of South America fits into Mauritania roughly 17 times.
The old Mercator map treated both about equally (1.1× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Mauritania fits 17× into South America.