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
RHAMPHORHYNCHOIDS JURASSIC WELL LONG TAIL WITHOUT SMALL [Illustration]
DEVELOPED WITH CREST MAXIMUM _RHAMPHORHYNCHUS_
FLATTENED WINGSPAN
RUDDER AT OF 2 FEET
END
PTERODACTYLOIDS JURASSIC JAW PARTLY SHORT OR WITH SMALL FROM SIZE [Illustration]
AND OR NO TAIL OR LARGE OF _PTERANODON-K_
CRETACEOUS COMPLETELY CREST SPARROW
TOOTHLESS, TO GIANTS
HORNEY BEAK WITH SPAN
OF 25′
[Illustration: MESOZOIC SWIMMING REPTILES]