Complex sentence: The extinction of megalodon correlates with the decline of many small mysticete lineages; it is possible that it was quite dependent on them as a food source, and that megalodon may have been too large to sustain itself on the declining tropical food supply.
Split into simpler sentences: The extinction of megalodon correlates with the decline of many small mysticete lineages; it is possible that it was quite dependent on them as a food source. Megalodon may have been too large to sustain itself on the declining tropical food supply.