These are reptiles in which the body is more or less completely enclosed by bony plates. This group is first known as fossils from late [Triassic] rocks of Europe, and modern representatives of the group include the turtles and tortoises. Fragmentary remains of turtle shells are among the most common [vertebrate] fossils found in the [Tertiary]. Some of the late Tertiary land tortoises were 3 to 4 feet long. The earliest known turtles in Texas have been found in [Cretaceous] rocks.
Pelycosaurs.—
The pelycosaurs were a group of late [Paleozoic] reptiles some of which were characterized by the presence of a tall fin on their back ([Pl. 40]). The fossils of these unusual creatures are well known from the [Permian] red beds of north-central Texas.
Therapsids.—
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.
Plate 38
Comparison of the dinosaurs. Reproduced with permission of Dr. J. W. Dixon, Jr., and Geology Department, Baylor University, Waco, Texas.
| DINOSAUR STOCKS | SAURISCHIANS | ORNITHISCHIANS | |||||
|---|---|---|---|---|---|---|---|
| DINOSAUR TYPES | THEROPOD | SAUROPOD | ORNITHOPOD | STEGOSAUR | CERATOPSIAN | ANKYLOSAUR | |
| POSTURE | BIPEDAL | QUADRUPEDAL | BIPEDAL AND QUADRUPEDAL | QUADRUPEDAL | QUADRUPEDAL | QUADRUPEDAL | |
| ARMOR | UNARMORED EXCEPT FOR HUGE SHARP TEETH | UNARMORED | UNARMORED (SPEED WAS CHIEF DEFENSE) | BONY PLATES ALONG BACK, SPIKED-TAIL | HORNS, BONY PLATE OVER NECK | KNOBS AND SPIKES OVER [DORSAL] AREA, CLUB-LIKE TAIL | |
| DIET | CARNIVOROUS | HERBIVOROUS | HERBIVOROUS | HERBIVOROUS | HERBIVOROUS | HERBIVOROUS | |
| OTHER DESCRIPTIVE REMARKS | LARGE HEAD WITH POWERFUL JAW, GREATLY REDUCED FORE-LIMBS | HUGE BODY, LONG NECK AND TAIL, SMALL HEAD | SLENDER-BUILD, “DUCK-BILLED” | SHORT NECK, LONG TAIL, SMALL HEAD | SHORT NECK, STOCKY BUILD | “ARMADILLO-LIKE” APPEARANCE | |
| EXAMPLES (AND AGE) J-JURASSIC K-CRETACEOUS | CERATOSAURUS-J ALLOSAURUS-J TYRANNOSAURUS-K | BRACHIOSAURUS-J DIPLODOCUS-J BRONTOSAURUS-J | PARASAUROLOPHUS-K CORYTHOSAURUS-K TRACHODON-K | STEGOSAURUS-J | STYRACOSAURUS-K PROTOCERATOPS-K TRICERATOPS-K | PALEOSCINCUS-K ANKYLOSAURUS-K | |
| SCALE IN FEET | 10 | 10 | 5 | 5 | 5 | 5 | |
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.
