Not
infrequently as large as an ostrich (five to six feet high), with
teeth set in grooves in its jaws, and the jaws themselves joined
as in the snake, with a great capacity of bolting its prey, the
Hesperornis would become an important element in the life of the
fishes. The wing-fingers have gone, and the tail is much
shortened, but the grooved teeth and loosely jointed jaws still
point back to a reptilian ancestry.
These are the only remains of bird-life that we find in the
Mesozoic rocks. Admirably as they illustrate the evolution of the
bird from the reptile, they seem to represent a relatively poor
development and spread of one of the most advanced organisms of
the time. It must be understood that, as we shall see, the latter
part of the Chalk period does not belong to the depression, the
age of genial climate, which I call the Middle Ages of the earth,
but to the revolutionary period which closes it. We may say that
the bird, for all its advances in organisation, remains obscure
and unprosperous as long as the Age of Reptiles lasts. It awaits
the next massive uplift of the land and lowering of temperature.
In an earlier chapter I hinted that the bird and the mammal may
have been the supreme outcomes of the series of disturbances
which closed the Primary Epoch and devastated its primitive
population.
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