Illustrations of this are to be seen everywhere. Among mammalia we have
the carnivora, which from Eocene times have been becoming more and more
specialised, till they have culminated in the cat and dog tribes, which
have reached a degree of perfection both in structure and intelligence
fully equal to that of any other animals. In another line of
development, the herbivora have been specialised for living solely on
vegetable food till they have culminated in the sheep, the cattle, the
deer, and the antelopes. The horse tribe, commencing with an early
four-toed ancestor in the Eocene age, has increased in size and in
perfect adaptation of feet and teeth to a life on open plains, and has
reached its highest perfection in the horse, the ass, and the zebra. In
birds, also, we see an advance from the imperfect tooth-billed and
reptile-tailed birds of the secondary epoch, to the wonderfully
developed falcons, crows, and swallows of our time. So, the ferns,
lycopods, conifers, and monocotyledons of the palaeozoic and mesozoic
rocks, have developed into the marvellous wealth of forms of the higher
dicotyledons that now adorn the earth.
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