Final answer:
Angiosperms dominate most terrestrial ecosystems due to their evolutionary innovations, such as flowers and fruits, which aid in pollination and seed dispersal. They became dominant during the Mesozoic era and today make up approximately 90 percent of all plant species.
Step-by-step explanation:
Angiosperms, also known as flowering plants, began to dominate terrestrial landscapes in the Mesozoic era, particularly during the Cretaceous period. From their origins in the Jurassic period, around 160 to 125 million years ago, these plants have undergone extensive diversification. With over 300,000 species, angiosperms comprise about 90 percent of all plant species, making them the most widespread and diverse group of plants on Earth. Their dominance is attributed to evolutionary innovations such as flowers and fruits. Flowers facilitate diverse and effective pollination strategies, often in coevolution with insects, while fruits provide protection for the developing seeds and aid in their dispersal.
The two structures that enable angiosperms to thrive in most terrestrial ecosystems are the flower, which evolved from modified leaves and is responsible for reproduction, and the fruit, which emerges from the fertilized ovary and helps in distributing seeds. This evolutionary success has made angiosperms integral to ecosystems and human agriculture, as most crop and ornamental plants belong to this group.