b. They suggested that the two continents where they were found could have been joined.
Explanation:
Mesosaurus fossils were found in the East of South America and South Africa. The mesosaurus was a marine reptile, but it was not capable of swimming long distances. If the two continents were located where it is now, then it would have been improbable that they would find fossils in both areas. In addition, the likelihood that the mesosaurus evolved and came about at the same time in separate areas, is even less.
Thus, this suggested that these two continents may have been joined in the past.
