Final answer:
Evidence of decompression sickness in whale fossils suggests that they were deep-diving mammals like modern whales, refuting the notion that they were land-dwelling. The presence of specific ankle bones in Rodhocetus also supports their aquatic adaptation from terrestrial ancestors.
Step-by-step explanation:
The discovery of small gashes in whale fossils suggesting signs of decompression sickness or 'the bends' can allow scientists to draw several conclusions. Firstly, these signs imply that the whales experienced decompression sickness, which occurs when an animal surfaces too quickly after being at a depth where the pressure causes gases to dissolve in their bloodstream. Whales, being deep-diving mammals, would only experience this in a marine environment. This could therefore refute the option that the fossils are from a land-dwelling animal.
In addition to this, fossils indicating the bends support the theory that these ancient whales behaved similarly to modern whales, which dive deeply and surface quickly. This behavior is not associated with volcanic activity nor does it have any relevance to the age of the fossils; hence, both options B and C seem less likely based on the evidence of the gashes alone. Also, Rodhocetus, an aquatic mammal related to whales, had an ankle bone otherwise unique to land animals. This further suggests that ancient whales, like Rodhocetus, had terrestrial ancestors but had since evolved to a fully aquatic lifestyle.