Triceratops (TRI-serr-oh-tops) Plant eater, 30 feet long, Late Jurassic Period. 145 million years ago located in western North America, Montana. Triceratops is named for its three long horns. Though the horns look scary, they were thin and not a good defense against T. rex. So, what did Triceratops use their horns for? Maybe they just scraped them against the horns of other Triceratops in contests for mates.