The correct answer is option 'C': Gymnosperms are dominant plants and first birds appear.

The Jurassic period is a division of the Mesozoic era, which lasted from approximately 201 to 145 million years ago. It is known for several significant developments in the natural world, including the dominance of gymnosperms as plants and the appearance of the first birds.

1. Dominance of Gymnosperms:
During the Jurassic period, gymnosperms became the dominant group of plants. Gymnosperms are seed-bearing plants that do not produce flowers or fruits. They include conifers, cycads, and ginkgoes. Gymnosperms were well-adapted to the terrestrial environment and played a crucial role in shaping the landscape during this time.

2. Diversification of Reptiles:
The Jurassic period witnessed the radiation and diversification of reptiles. Many different types of reptiles evolved and thrived during this time. Some of the notable reptiles include marine reptiles like ichthyosaurs and plesiosaurs, as well as terrestrial reptiles like sauropods (long-necked herbivorous dinosaurs) and theropods (carnivorous dinosaurs).

3. Origin of Birds:
One of the most significant developments during the Jurassic period was the appearance of the first birds. Birds evolved from a group of small, feathered theropod dinosaurs. Archaeopteryx, a famous fossil from the late Jurassic, is considered one of the earliest known birds. Birds played an essential role in the ecosystem as they adapted to various habitats and ecological niches.

4. Extinction of Dinosaurs and Rise of Angiosperms:
The extinction of dinosaurs, including many other organisms, occurred at the end of the Cretaceous period, which followed the Jurassic period. Therefore, dinosaurs did not become extinct during the Jurassic period. The rise of angiosperms (flowering plants) also took place after the Jurassic period, during the Cretaceous period.

In conclusion, the Jurassic period of the Mesozoic era was characterized by the dominance of gymnosperms as plants and the appearance of the first birds. It was a time of diversification and radiation for reptiles, including dinosaurs. The extinction of dinosaurs and the rise of angiosperms occurred in the subsequent Cretaceous period.