We saw, however, that this
northern region was singularly warm until long after the spread
of the mammals. Other experts, impressed by the parallel
development of the mammals and the flowering plants, look to the
elevated parts of eastern North America.
Such evidence as there is seems rather to suggest that South
Africa was the cradle of the placental mammals. We shall find
that many of our mammals originated in Africa; there, too, is
found to-day the most primitive representative of the Tertiary
mammals, the hyrax; and there we find in especial abundance the
remains of the mammal-like reptiles (Theromorphs) which are
regarded as their progenitors. Further search in the unexplored
geological treasures and dense forests of Africa is needed. We
may provisionally conceive the placental mammals as a group of
the South African early mammals which developed a fortunate
variation in womb-structure during the severe conditions of the
early Mesozoic. In this new structure they would have no
preponderant advantage as long as the genial Jurassic age
favoured the great reptiles, and they may have remained as small
and insignificant as the Marsupials.
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