The stegosaurs were herbivorous, quadrupedal ornithischians with large projecting plates down the back and heavy spikes on their tails. The Jurassic dinosaur _Stegosaurus_ (Pl. 45) is most typical of the plate-bearing forms. This creature weighed about 10 tons, was some 30 feet long, and stood about 10 feet tall at the hips. _Stegosaurus_ is characterized by a double row of large, heavy, pointed plates which run along the animal’s back. These plates begin at the back of the skull and stop near the end of the tail. The tail was also equipped with four or more long curved spikes which were probably used as a means of defense. The animal had a very small skull which housed a brain that was about the size of a walnut, and it is assumed that these, and all other dinosaurs, were of very limited intelligence. _Stegosaurus_ remains have not been discovered in Texas, but these, like certain other of the extinct vertebrates, are mentioned because of their interesting and unusual form. SUBORDER ANKYLOSAURIA.— The ankylosaurs were four-footed, herbivorous, Cretaceous dinosaurs which had relatively flat bodies. The skull and back of the animal were protected by bony armor, and the club-like tail was armed with spikes. _Paleoscincus_ (Pl. 45), a typical ankylosaur, had large spines projecting from along the sides of the body and tail. The armored spiked back and the heavy club-like tail probably provided _Paleoscincus_ with much-needed protection from the vicious meat-eating dinosaurs of Cretaceous time. [Illustration: Plate 44 SAURISCHIAN DINOSAURS] ALLOSAURUS × ¹/₁₈₀ BRONTOSAURUS × ¹/₂₅₀ [Illustration: Plate 45 ORNITHISCHIAN DINOSAURS] STEGOSAURUS × ¹/₉₀ TRACHODON × ¹/₁₀₀ PALEOSCINCUS × ¹/₂₅ TRICERATOPS × ¹/₁₂₀ SUBORDER CERATOPSIA.— 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. CLASS AVES.— Because of the fragile nature of their bodies, birds are seldom found as fossils. In spite of this, however, some interesting and important fossil bird remains have been discovered. The oldest known bird was found in Upper Jurassic rocks exposed in Germany. This primitive bird, named _Archaeopteryx_, is little more than a reptile with feathers. _Archaeopteryx_ was a pigeon-sized creature which had scales as well as feathers, a lizard-like tail, a toothed beak, and other definitely reptilian characteristics.