Paleontologist: Plesiosauromorphs were gigantic, long-necked marine reptiles that ruled the oceans during the age of the dinosaurs. Most experts believe that plesiosauromorphs lurked and quickly ambushed their prey. However, plesiosauromorphs probably hunted by chasing their prey over long distances. Plesiosauromorph fins were quite long and thin, like the wings of birds specialized for long-distance flight. Which one of the following is an assumption on which the paleontologist's argument depends? ['Birds and reptiles share many physical features because they descend from common evolutionary ancestors.', 'During the age of dinosaurs, plesiosauromorphs were the only marine reptiles that had long, thin fins.', "The shape of a marine animal's fin affects the way the animal swims in the same way as the shape of a bird's wing affects the way the bird flies.", 'A gigantic marine animal would not be able to find enough food to meet the caloric requirements dictated by its body size if it did not hunt by chasing prey over long distances.']