In an earlier post, I discussed why a unicorn appeared on the mappemonde created by Pierre Desceliers. Since then, I reexamined a digital copy of the map and found another representation of unicorns that Desceliers placed in Africa.
The choice of depicting a pair of unicorns probably originated from a description of the rhinoceros. Medieval authors looked at ancient Greek, Roman, and Persian descriptions of rhinos and deer and conflated them with the European notion of the unicorn. So when the accounts of one-horned beasts in Subsaharan Africa arrived in mainland Europe, Pierre Desceliers most likely equated it with the unicorn.
First, the entire mappemonde:
Close up of Africa and the unicorn:
The unicorns right side up: