(Portland, OR) -- A 400-million-year-old species has returned to the Oregon Zoo. 25 Pacific lamprey moved in this week. The ancient fish predate dinosaurs and even trees. Guests can see the lamprey in the Cascade stream and pond section of the Great Northwest area. They're often suctioned onto the glass showing their sucker-like mouths and rings of sharp yellow teeth. The lamprey stay at the zoo through the winter, and are transported to tributaries of the upper Columbia and Snake rivers once they're ready to spawn.