It was the "extinction" stamp iirc.
I didn't have an extinction stamp. I had one for the pterasaurs, the iguanodons, (both in the dinosaur room) and the vertebrates (in the first room). For fish I had two in the freshwater room and one in the coral room. My bugs were more spread out, one in the butterfly room, one for "hidden" bugs, and I forget where exactly the third was but it was in the first room.