Final answer:
The presence of Cynognathus fossils in both South America and South Africa is most likely due to the movement of tectonic plates, which over time caused the continents of Pangaea to split and drift apart, rather than factors like migration or selective fossilization conditions.
Step-by-step explanation:
Fossils of the mammal-like reptile Cynognathus, are found only in South America and South Africa, which suggests a significant explanation related to historical geology rather than the organism's behavior or ecological factors. The statement that most likely explains the occurrence of Cynognathus fossils in these two regions is B) The movement of tectonic plates has caused the surface of Earth to change.
During the Mesozoic Era, the continents were not arranged as they are today. This was a time when all the continents were joined together in a supercontinent called Pangaea. As the tectonic plates on which the continents lie moved over time, Pangaea began to split, and the continents gradually drifted to their present-day positions. This means that the regions now known as South America and South Africa were once part of the same landmass, allowing species like Cynognathus to reside in both without having to cross oceans.
Other options are less plausible; for instance, Cynognathus was not a strong swimmer, making it unlikely to migrate across wide oceans in search of food (A). It is also highly unlikely that the conditions for fossilization only existed in South America and South Africa (C), and there is no evidence to suggest that Cynognathus existed as two distinct populations on different continents but lived nowhere else (D).