The therapsids were a mammal-like group of reptiles which were well developed for a terrestrial existence. Although the remains of these primitive reptiles are not particularly important fossils, study of the therapsids has provided much valuable information about the origin of the mammals. Members of this group appeared first in the middle Permian and persisted until the middle Jurassic, but therapsid remains have not been reported from Texas. [Illustration: Plate 38 Comparison of the dinosaurs. Reproduced with permission of Dr. J. W. Dixon, Jr., and Geology Department, Baylor University, Waco, Texas.] DINOSAUR SAURISCHIANS ORNITHISCHIANS STOCKS DINOSAUR THEROPOD SAUROPOD ORNITHOPOD STEGOSAUR CERATOPSIAN ANKYLOSAUR TYPES POSTURE BIPEDAL QUADRUPEDAL BIPEDAL AND QUADRUPEDAL QUADRUPEDAL QUADRUPEDAL QUADRUPEDAL ARMOR UNARMORED EXCEPT UNARMORED UNARMORED (SPEED BONY PLATES HORNS, BONY KNOBS AND SPIKES FOR HUGE SHARP WAS CHIEF ALONG BACK, PLATE OVER NECK OVER DORSAL AREA, TEETH DEFENSE) SPIKED-TAIL CLUB-LIKE TAIL DIET CARNIVOROUS HERBIVOROUS HERBIVOROUS HERBIVOROUS HERBIVOROUS HERBIVOROUS OTHER LARGE HEAD WITH HUGE BODY, LONG SLENDER-BUILD, SHORT NECK, SHORT NECK, “ARMADILLO-LIKE” DESCRIPTIVE POWERFUL JAW, NECK AND TAIL, “DUCK-BILLED” LONG TAIL, STOCKY BUILD APPEARANCE REMARKS GREATLY REDUCED SMALL HEAD SMALL HEAD FORE-LIMBS EXAMPLES CERATOSAURUS-J BRACHIOSAURUS-J PARASAUROLOPHUS-K _STEGOSAURUS-J_ STYRACOSAURUS-K PALEOSCINCUS-K (AND AGE) ALLOSAURUS-J DIPLODOCUS-J CORYTHOSAURUS-K PROTOCERATOPS-K _ANKYLOSAURUS-K_ J-JURASSIC _TYRANNOSAURUS-K_ _BRONTOSAURUS-J_ _TRACHODON-K_ _TRICERATOPS-K_ K-CRETACEOUS [Illustration] [Illustration] [Illustration] [Illustration] [Illustration] [Illustration] SCALE IN FEET 10 10 5 5 5 5 [Illustration: Plate 39 Comparison of Mesozoic flying and swimming reptiles. Reproduced with permission of Dr. J. W. Dixon, Jr., and Geology Department, Baylor University, Waco, Texas.] [Illustration: FLYING REPTILES—PTEROSAURS] GROUP AGE TEETH TAIL HEAD SIZE EXAMPLE