Critical Reasoning (CR) | Re: Paleontologist: Plesiosauromorphs were gigantic, long-necked marine

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