Simplify the following text for a Grade 11 native English-speaking person.
Original: Cetology ( from Greek , kÄ `` tos , `` whale '' ; and , - logia ) is the branch of marine mammal science that studies the approximately eighty species of whales , dolphins , and porpoise in the scientific order Cetacea .
Simplified: Cetology is the branch of marine mammal science that studies the approximately eighty species of whales , dolphins , and porpoise in the scientific order Cetacea .