It was the spread of the flowering plants that provided the springboard for primate evolution. By 65 million years ago, toward the end of the Cretaceous period, the Angiosperms (flowering plants) had already become well established, and broad-leafed, fruit-bearing trees began to dominate the vast forests that eventually covered much of the Earth.
Fossil fruits and seeds indicate that the inland forests seem to have been dominated by species related to today's sweet-sop, Annona squamosa, and sour-sop, Annona muricata, with mangrove and swamp palms in coastal regions. Early forms of pistachio, walnuts, and mango appear to have been present. Trees such as bay, cinnamon, magnolias, and black gum trees grew alongside palms, Sequoia conifers and climbing plants such as vines and lianas.
The birds had already adapted to this change by feeding on fruit and nectar from the flowering plants. The new plants meant that a wider range of food became available, and in greater abundance. It was a mutually beneficial relationship, in which the birds ate the fruit and thereby helped to distribute seeds on their bills and feet and by defecation. Insects already played an active part in this relationship by transmitting pollen from plant to plant in their search for nectar.
The primates were able to exploit this ecology to great advantage. Their immediate ancestors were in all probability insectivores and it may well have been the presence of insects that initially led them to adapt to a life in the trees. Birds' eggs too could have provided an additional
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