Classify these animals by either a mammal or reptile; 
Lizard, Alligator, Elephant, Crocodile, Lion, Dolphin, Snake, Platypus, Chimpanzee
Turtle
Yes, I grouped these animals as mammals and reptiles. Here is the categories;
Mammals: Lion, Elephant, Dolphin, Platypus, Chimpanzee
Reptiles: Turtle, Crocodile, Snake, Lizard, Alligator