The ceratopsians, or horned dinosaurs, are another group of dinosaurs
that are known only from rocks of Cretaceous age. These plant-eating
dinosaurs possessed beak-like jaws, a bony neck frill which extended
back from the skull, and one or more horns. _Triceratops_ (Pl. 45) is
the largest of the horned dinosaurs (some forms were as much as 30 feet
long), and the skull measured 8 feet from the tip of the parrot-like
beak to the back of the neck shield.