The Dinosaurs of Wyoming - Wyoming State Geological Survey ...

CHAPTER VIII
The Different Kinds of Dinosaurs
Scientists are not agreed as to whether the reptiles commonly
called Dinosaurs do in reality constitute a definite.
natural group. The animals are so diverse in size, ranging
from a height of a few inches to a length of many feet (about
80 feet for the longest). They have specialized, during their
nine millions of years, into amphibious, plant-eating animals;
huge carniyorous types; armored reptiles; beaked, planteating,
aquatic and dry-land types, in such an amazing array
that even paleontologists become dizzy trying to figure it all
out.
All of these creatures. however, have characters in common,
and we are not yet ready to give up Sir Richard Owen's
group name-Dinosauria. 'These common characters are
most readily seen in the arrangement of the three hip bones.
or pelvis. These three bones are called ischium, ilium and
pubis; all three of 'which take part in the formation of the hip
socket-acetabulum-for articulation with the leg bonefemur.
Matthe,Y (1915, p. 27) o'ins the following conyenient
groupings as a basis for further discussion:
"Group I: Theropoda-the Carnivorous Dinosaurs. Provided
with sharp pointed teeth, sharp claws, bipedal (walking
on two legs-see Frontispiece), with bird-like hind feet, generally
three-toed; the fore limbs adapted for grasping or tearing,
but not for support of the body. The head is large, neck of
moderate length, body unarmored.
"Dinosaurs of this group in America occur in the upper
Jurassic Period-Ornitholestes; and Upper Cretaceous-Tyrannosaurus
and others.
"Group II: Sauropoc1a-·the amphibious Dinosaurs. Provided
"'ith blunt-pointed teeth and blunt claws, quadrupedal.
with elephant-like limbs and feet, long neck and small head.
Unarmored American representatives are: Brontosaurus, Diplodocus,
Camarasaurus, and Brachiosaurus, from Colorado and
Wyoming. Upper Jurassic and Comanchean.
. "Group III: Predentata-the beaked Dinosaurs. Provided
with a horny beak on the front of the j'aw, cutting or grinding
teeth behind it. All plant-eaters, with hoofs instead 'of claws,
and many of them heavily armored. Mostly three short toes
on the hind foot. four or five on the fore foot.
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