When GURPS 4e first came out, it came out with just a few animals and monsters in the back of the Basic Set.
But as Clay Dowling points out, there has been a steadily supply of monsters available for GURPS.
If you don't believe either of us, check this out:
List of Published GURPS Creatures
When GURPS Dungeon Fantasy came out, it also had just a relatively small handful of monsters in the second book, although successive books all included at least a couple of monsters - and Dungeon Fantasy Monsters 1 includes 30 more (well, more than that if you count every sub-type as a new monster, ala D&D monster books).
Between all the DF books, Banestorm, Fantasy, and a few others, there are plenty of monsters to use in a GURPS DF game. I know, because I'm doing just that.