weighed only
twenty-one pounds, or half the weight of a whale vertebra of the same
bulk. The skeleton of a whale seventy-four feet in length has recently
been found by Mr. F.A. Lucas of the Brooklyn Museum to weigh seventeen
thousand nine hundred and twenty pounds. The skeleton of a dinosaur of
the same length may be roughly estimated as not exceeding ten thousand
pounds.

_Proofs of Rapid Movements on Land._ Lightness of skeleton is a
walking or running or flying adaptation, and not at all a swimming
one; a swimming animal needs gravity in its skeleton, because
sufficient buoyancy in the water is always afforded by the lungs and
soft tissues of the body. The extraordinary lightness of these
dinosaur vertebrae may therefore be put forward as proof of supreme
fitness for the propulsion of an enormous frame during occasional
incursions upon land[22]. There are additional facts which point to
land progression, such as the point in the tail where the flexible
structure suddenly becomes rigid, as shown in the diagram of vertebrae
below; the component joints are so solid and flattened on the lower
surface that they seem to demonstrate fitness to support partly the
body in a tripodal position like that of a kangaroo. I have therefore
hazarded the view that even some of these enormous dinosaurs were
capable of raising themselves on their hind limbs, lightly resting on
the middle portion of the tail. In such a position the animal would
have been capable not only of browsing among the higher branches of
trees, but of defending itself against the carnivorous dinosaurs by
using its relatively short but heavy front limbs to ward off attacks.

There are also indications of aquatic habits in some of the giant
dinosaurs which render it probable that a considerable part of their
life was led in the water. One of these indications is the backward
position of the nostrils. Many, but not all, water-living mammals and
reptiles have the nostrils on top of the head, in order to breathe
more readily when the head is partly immersed. Another fact of note,
although perhaps less conclusive, is the fitness of the tail for use
while moving about in the water, if not in rapid swimming.

The great tail, measuring from twenty-eight to thirty feet, was one of
the most remarkable structures in these animals, and undoubtedly
served a great variety of purposes, propelling while in the water,
balancing and supporting and defending while on land. In _Dip