The Sea Beasts From One Billion B.C.
While out on patrol, Aquaman and Aqualad spot a ship being attacked by a giant sea monster, and with the help of their undersea friends manage to save the ship from being sunk. Without the ship to trash, the sea monster makes a getaway, and before the two heroes can go after it, they're signaled to board a ship. There Aquaman is asked to see Professor Richards, a famous zoologist. Agreeing, Aquaman goes to the scientist, leaving Aqualad to continue their patrol.
Arriving at Dr. Richard's lab, the doctor explains to Aquaman that he had finally perfected an evolution ray that could evolve or devolve any living thing, however upon showing it to his assistant, John Cook, he was soon held at gun point as his assistant stole the device. Aquaman realizes that the evolution device was what created the sea monster he saw earlier, the doctor shows Aquaman how to set the gun to reverse the damage it does and Aquaman sets off to find Cook.Returning home sharing his findings with Aqualad, the two set out to look for Cook who is hiding out in the ocean. Upon finding him, Cook uses the device to devolve some sea creatures and sets them to attack Aquaman and Aqualad. The two summon an army of sea creatures to help them fight off the prehistoric monsters, however Cook then uses his weapons to change that army into prehistoric creatures as well.
With Aquaman and Aqualad preoccupied with battling prehistoric sea creatures, Cook sends a number of the monsters to attack a nearby ship, prompting Aquaman and Aqualad to save the passengers, and Cook steals the cargo on board. Aquaman tracks down Cook's secret underwater cave and knocks him out. Switching the evolution ray to evolve the sea creatures, Aquaman begins changing his undersea friends back to normal, however the device is jammed and the sea creatures are evolved into their future evolutions before Aquaman can shut the device off. Before he can fix the error he made, he and Aqualad are attacked by a giant future-evolved blow-fish.