The best indication that dreaming serves a necessary biological function is provided by the fact

most organisms, especially mammals experience what is known as REM rebound.

Explanation:

An increasing frequency of rapid eye movement [ REM sleep] that occurs after period of sleep deprivation is regarded as REM rebound.

The REM sleep is described to be important for normal brain development especially in the infants, because ,it stimulates part or region of the brain used in learning. This is why, infants are believed to spend more time in REM sleep than the adults.

Note that, REM means Rapid Eye Movement.

the answer is d. chordata