Need a hint?
All these words have to do with a group of vertebrates in the Animal Kingdom. So if you were thinking bacteria, plants, or invertebrates -- don't!
So what are vertebrates?
"Vertebrates" are any animals with backbones. These would include fish, birds, reptiles, and mammals. The backbone doesn't have to be made out of hard material. Sharks, a type of fish with cartilaginous skeletons, are still considered vertebrates!
Okay, I'm ready to look at the list again.
I give up! What's the answer?