n.

The Dinosaurs originated, so far as we can judge, as lizard-like
reptiles with comparatively long limbs, long tails, five toes on each
foot, tipped with sharp claws, and with a complete series of sharp
pointed teeth. It would seem probable that these ancestors were more
or less bipedal, and adapted to live on dry land. They were probably
much like the modern lizards in size, appearance and habitat:[2]

From this ancestral type the Dinosaurs evolved into a great variety of
different kinds, many of them of gigantic size, some herbivorous, some
carnivorous; some bipedal, others quadrupedal; many of them protected
by various kinds of bony armor-plates, or provided with horns or
spines; some with sharp claws, others with blunted claws or hoofs.

[Illustration: Fig. 6.--Outline Restorations of Dinosaurs. Scale
about nineteen feet to the inch.]

These various kinds of Dinosaurs are customarily grouped as follows:

I. _Carnivorous Dinosaurs_ or _Theropoda_. With sharp pointed teeth,
sharp claws; bipedal, with bird-like hind feet, generally
three-toed;[3] 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. The principal Dinosaurs of this group in America are

_Allosaurus_, _Ornitholestes_--Upper Jurassic period.

_Tyrannosaurus, Deinodon, Albertosaurus, Ornithomimus_--Upper Cretacic
period.

[Illustration: Fig. 7.--Skulls of Dinosaurs, illustrating the
principal types--_Anchisaurus_ after Marsh, the others from
American Museum specimens.]

II. _Amphibious Dinosaurs_ or _Sauropoda_. With blunt-pointed teeth
and blunt claws, quadrupedal, with elephant-like limbs and feet, long
neck and small head. Unarmored. Principal dinosaurs of this group in
America are _Brontosaurus_, _Diplodocus_, _Camarasaurus_
(_Morosaurus_) and _Brachiosaurus_, all of the Upper Jurassic and
Comanchic periods.

III. _Beaked Dinosaurs_ or _Predentates_. With a horny beak on the
front of the jaw, cutting or grinding teeth behind it. All
herbivorous, with pelvis of peculiar type, with hoofs instead of
claws, and many genera heavily armored. Mostly three short toes on the
hind foot, four or five on the fore foot. This group comprises animals
of very different proportions as follows:

1. _Iguanodonts._ Bipedal, unarmored, with a single row of serrated
cutting teeth, three-toed hind feet. Upper Jurassic, Comanchic and
Cretacic. _Camptosaurus_ is th