I read another of those silly questions asking, essentially, how could Noah fit 5.6 million known species onto his ark. I hope to get past the silliness and land on some actual history.
The Torah just has two lines on the subject, Genesis 7:2-3.
Of all the clean animals you shall take for yourself seven pairs, a male and its mate, and of the animals that are not clean, two, a male and its mate.
Also, of the fowl of the heavens, seven pairs, male and female, to keep seed alive on the face of the earth.
Leviticus 11 lays out the specifications for clear and unclean animals. Those include mammals, birds, reptiles, amphibians, fish, and even snails and insects. Far more unclean animals are listed than clean animals, since those had consequences. Clearly the writers made an effort to include as many varieties as they thought people of their time and place might come in contact with.
So how many might that be? Not 5.6 million. But surely more than 100. 500? 1000? 5000?
Forget about how they would fit on the ark or get along or anything else ark-related. Assume that fish could fend for themselves and that snails and insects. Let’s just include mammals, birds, reptiles, and amphibians and stop at the genus level so we don’t have to worry about species of cattle. How many different types of animals would people of that time and place know and have to make decisions about?