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The Sauropods
To complete the picture of the Sauropods, we must add that the
whole class is characterised by the extraordinary smallness of
the brain. The twenty-ton Brontosaur had a brain no larger than
that of a new-born human infant. Quite commonly the brain of one
of these enormous animals is no larger than a man's fist. It is
true that, as far as the muscular and sexual labour was
concerned, the brain was supplemented by a great enlargement of
the spinal cord in the sacral region (at the top of the thighs).
This inferior "brain" was from ten to twenty times as large as
the brain in the skull. It would, however, be fully occupied with
the movement of the monstrous limbs and tail, and the sex-life,
and does not add in the least to the "mental" power of the
Sauropods. They were stupid, sluggish, unwieldy creatures,
swollen parasites upon a luxuriant vegetation, and we shall
easily understand their disappearance at the end of the Mesozoic
Era, when the age of brawn will yield to an age of brain.
The next order of the Deinosaurs is that of the biped
vegetarians, the Ornithopods, which gradually became heavily
armoured and quadrupedal. The familiar Iguanodon is the chief
representative of this order in Europe. Walking on its three-toed
hind limbs, its head would be fourteen or fifteen feet from the
ground. The front part of its jaws was toothless and covered with
horn. It had, in fact, a kind of beak, and it also approached the
primitive bird in the structure of its pelvis and in having five
toes on its small front limbs. Some of the Ornithopods, such as
the Laosaur, were small (three or four feet in height) and
active, but many of the American specimens attained a great size.
The Camptosaur, which was closely related to the Iguanodon in
structure, was thirty feet from the snout to the end of the tail,
and the head probably stood eighteen feet from the ground. One of
the last great representatives of the group in America, the
Trachodon, about thirty feet in length, had a most extraordinary
head. It was about three and a half feet in length, and had no
less than 2000 teeth lining the mouth cavity. It is conjectured
that it fed on vegetation containing a large proportion of
silica.
In the course of the Jurassic, as we saw, a branch of these
biped, bird-footed vegetarians developed heavy armour, and
returned to the quadrupedal habit. We find them both in Europe
and America, and must suppose that the highway across the North
Atlantic still existed.
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