teeth are part of a shark & fossils of shark teeth are discovered on the side of a cliff ->  fossils of sharks are discovered on the side of a cliff  a fish is a kind of aquatic animal & a shark is a kind of fish ->  sharks are a kind of aquatic animal  fossils of sharks are discovered on the side of a cliff & sharks are a kind of aquatic animal & if fossils of a aquatic animal or plant are found in a place then that place used to be covered by water in the past ->  if fossils of sharks are found on the side of a cliff, then the side of the cliff used to be covered by water in the past  if fossils of sharks are found on the side of a cliff, then the side of the cliff used to be covered by water in the past & sharks live in shallow seas -> the side of the cliff used to be a shallow sea