Evidence that the south american and african continents were once joined includes evidence from their coastlines such as

- Matching fossil distributions.

Explanation:

As per the question, there are historical evidences like 'matching fossil distributions' that substantiates the claim of South American and African continents being joined at a time and also that they were separated quite later than that as the fossil distributions are the remains left behind by the people who inhabited the place at that time. Thus, the discovery of identical fossil distributions from the coastlines of the two continents evidentially proves their merged or joined existence at a time in the history. Thus, 'matching fossil distributions' is the answer.