Ichthyosaurs were giant marine reptiles. Fossils indicate that they possessed dorsal fins and tails, as do fish, even though their closest relatives were terrestrial reptiles that had neither dorsal fins nor aquatic tails. The dorsal fins and tails of ichthyosaurs and fish are examples of:

Adaptations to a common environment and examples of convergent evolution.

Explanation:

Ichthyosaurs were the giant marine reptiles but it possess tails and dorsal fins though this is not a common character of reptiles. But the presence tails and dorsal fins states that it was an adaptation which was required at that time.

This giant reptile was an mixture of modern fish and dophins. It also had dorsal fin for swimming in water and has vertical tail which was used for the propulsive stroke. They were air breathing but had some part of their life in water as well like other reptiles.

Convergent evolution can be defined as the evolution of similar features in the species found at different period.

Some of the fishes like dolphins and other fishes shows convergent evolution to ichthyosaurs.

exists as it is today

casts off matter as planetary nebula.

begins nuclear fusion at its core

enters red giant phase

becomes a white dwarf

becomes a black dwarf

Tiles

Explanation:

The solar system is formed over 4 billion years ago. It is formed from big cloud and gases called nebular.

The nebular collapsed and be one denser. The core of nebular becomes hot and undergo nuclear fusion reaction. nuclear reactions tends to expand it outwards. The gravitational collapse is balanced by the expansion due to fusion energy.

It will then expand and cool to become red giant. It will then shrink and heat up again to become white dwarf. These will slowly cool down for years.