Dr. Hess as an interesting couple of paragraphs on what way constitute clean/unclean animals:
Genesis 1 suggests that the Israelite worldview understands three parts to the world: the sky, the sea, and the earth. The locomotion of animals appropriate to each sphere helps to determine whether they are clean. In general, a species whose locomotion is appropriate to that part of the world is clean. Thus birds that fly with wings, fish that swim with scales, and animals that walk with legs and hooves are clean. However, animals that do not have such characteristics of locomotion— and especially those that move back and forth between the spheres of sky, water, and land— are understood as unclean. Thus lizards that move between the water and the land and ostriches who don’t fly are unclean. However, this does not explain all the clean/ unclean distinctions. Another distinction considers carnivores that are unclean because they eat blood and therefore violate a universal prohibition. There may also be a sense of wholeness and balance in animals, just as in the priesthood (Lev. 21: 18– 24) and in matters of social justice and dealings with one’s neighbors (Lev. 24: 19– 20). So also sacrificial animals that have any abnormalities are considered unworthy (Lev. 22: 20, 22– 25). The result of the exclusion of large groups of animals as unclean places large numbers of species off limits to Israel and thereby protects these animals.
In ancient Israelite law the “clean” land animals, the ones that were permitted for eating and sacrifice, included the ox, the sheep, and the goat. These animals had the longest history of domestic association with the early Israelites, going back to their earliest known period, which they remembered as a time where their ancestors were pastoral nomads (Deut. 26: 5). The pig, an animal normally kept by settled (nonnomadic) peoples, appeared relatively late in Israelite domestic experience and was therefore never included among the “clean” animals. The horse and the camel also were relatively late entrants in the Israelite domesticated animal scene. We may apply somewhat the same logic to the Hittite animal world. Animals such as the ox, the sheep, and the pig were kept by the Hittites and their ancestors long before the horse and mule were introduced. Corresponding categories of sacrifice and clean versus unclean animals applied there as in Israel. At eighteenth-century BC Mari there is also evidence of the distinction between clean and unclean animals. In Mari treaties, puppies, goats, and young bulls or calves were unacceptable for sacrifices in confirming the treaties. Only the foal of a she-ass could be used. Thus the animals sacrificed were those closest to Israel, most like them, and most valued by them. This may imply a substitutionary role for these sacrifices, in some sense taking the place of the Israelite themselves.Hess, Richard S.. Israelite Religions: An Archaeological and Biblical Survey (Grand Rapids: Baker Publishing Group.) pp. 187-189.
The quote is from Hess’s book on Israelite Religion is an interesting discussion to have because, as Dr. Hess explains it, most discussions about Israel’s religion are from the prescriptive texts found in Scripture. But that does very little to explain how Israel actually worshiped in real life. That sort of perspective can be useful when trying to understand everything following Deuteronomy.
It’s worth checking out (for those who enjoy a thick, academic slog). The 50+ page references list in the back is probably worth the price of the book.