Deuteronomy 14:7 "These you shall not eat of those that only chew the cud, or of those that only have the cloven hoof"

The Torah gives us two signs to look for in animals (see Positive Mitzvah 149) in order to determine if the animal is kosher.

They must chew their cud and have split hooves. Any animal which does not have both these signs (even if it does have one of them) is not considered to be kosher.