No modern bird has teeth;
though the fact that in some modern species we find the teeth
appearing in a rudimentary form is another illustration of the
law that animals tend to reproduce ancestral features in their
development. A more reptilian character in the Ichthyornis group
is the fact that, unlike any modern bird, but like their reptile
ancestors, they had biconcave vertebrae. The brain was relatively
poor. We are still dealing with a type intermediate in some
respects between the reptile and the modern bird. The gannets,
cormorants, and pelicans are believed to descend from some branch
of this group.
The other group of Cretaceous birds, of the Hesperornis type,
show an actual degeneration of the power of flight through
adaptation to an environment in which it was not needed, as
happened, later, in the kiwi of New Zealand, and is happening in
the case of the barn-yard fowl. These birds had become divers.
Their wings had shrunk into an abortive bone, while their
powerful legs had been peculiarly fitted for diving. They stood
out at right angles to the body, and seem to have developed
paddles. The whole frame suggests that the bird could neither
walk nor fly, but was an excellent diver and swimmer.
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