The fossil remains of Mesosaurus were important to Alfred Wegener because they suggest that the two continents where they were found (specifically South America and Africa) could have been joined in the past. Mesosaurus was a freshwater reptile, and its fossils were found in both continents, which provided evidence for Wegener's theory of continental drift. This indicated that these continents were once connected, since it would be unlikely for Mesosaurus to have migrated across the vast oceans that separate them today. Therefore, the correct choice is:
They suggest the two continents where they were found could have been joined.