What could explain the presence of their fossils in such diverse parts of the world?

The fossils are in several areas because the animals were very widely distributed and this is how the evolution of the different species is shown in different parts of the world.

Fossils are skeletal remains of animals impregnated in stone, if these are not found, their chemical composition becomes petroleum and that is how the formation of oil arises.

Explanation:

Another reason was that many animals lived together on two continents, these two continents suffered many ruptures due to the appearance of volcanoes and movements of the tectonic plates and that is how the lands separated and new seas appeared, and the species dispersed throughout the world evolving each one differently according to the environment where it was stimulated.