Rabbi Shmuel Waldman writes in Beyond a Reasonable Doubt (2004 Edition) on page 100:

When the Torah classifies certain animals which are permissible to eat, it mentions that they must have two signs: they must chew their cud and they must have true cloven hooves (Leviticus 11:1-8; Deuteronomy 14:4-8). Of those animals which are not kosher, the Torah mentions that only four have one of the two signs (while all other non-kosher animals are missing both signs). The camel, rabbit (arneves), and hare (shafan) chew their cud but don’t have split hooves, while the pig has split hooves but does not chew its cud. And the Talmud (Tractate Chullin 59-60) … states, based on a Scriptural citation, that these are the only four species which have only one of the two characteristics of the kosher animal.

And that’s the way it is, even today – these are still the only species in the world which either only chew their cud but do not have split hooves, or only have split hooves but do not chew the cud (but not both). That assertion may not strike you as particularly outstanding until you think about it a little. Was Moses a zoologist? Did he travel the entire globe and examine every species on earth? Was he in Africa, Asia, America, Australia, or anywhere else studying the animal kingdom? Yet, no other animals in the entire world other than the four mentioned in the Torah have only one of the two signs which make an animal kosher.

Rashi and Tosafos who lived in France in the 11th and 12th centuries, before major parts of the world were known to France, interpreted Tractate Chullin at 59a, to mean that the Torah was saying that the four animals enumerated were the only ones exhibiting the features the Torah mentions. And, of course, Tractate Chullin, was committed to writing centuries before Rashi and Tosafos lived.