Leviticus 11 is the most obvious one:
11 The Lord spoke again to Moses and to Aaron, saying to them, 2 “Speak to the sons of Israel, saying, ‘These are the creatures which you may eat from all the animals that are on the earth. 3 Whatever divides a hoof, thus making split hoofs, and chews the cud, among the animals, that you may eat. 4 Nevertheless, you are not to eat of these, among those which chew the cud, or among those which divide the hoof: the camel, for though it chews cud, it does not divide the hoof, it is unclean to you. 5 Likewise, the [a]shaphan, for though it chews cud, it does not divide the hoof, it is unclean to you; 6 the [b]rabbit also, for though it chews cud, it does not divide the hoof, it is unclean to you; 7 and the pig, for though it divides the hoof, thus making a split hoof, it does not chew cud, it is unclean to you. 8 You shall not eat of their flesh nor touch their carcasses; they are unclean to you.
basically if it doesn't a: chew cud(like a cow) and b) have a split hoof it's unclean and thus not ok