| Previous episode|
To Hell... and Back?
| Following episode|
Water Dwellers is the 1st episode of Walking with Monsters.
The first episode begins with an illustration of the giant impact hypothesis: approximately 4.4 billion years ago when the Earth was formed, it is conjectured that a planet-like object referred to as Theia collided into the early Earth, dynamically reshaping the Earth and forming the moon.
Early Cambrian (530 MYA)
The episode then jumps ahead to the Cambrian Explosion, showing the first diversification of life in the sea. Strange predators called Anomalocaris feed on Trilobites, then fight with each other, whereupon the wounded loser is attacked and nibbled on by a school of Haikouichthys.
Early Silurian (418 MYA)
The Haikouichthys are shown to evolve into Cephalaspis, an armored jawless fish which is said to have the first good sense of touch. One Cephalaspis is chased by a Brontoscorpio — a giant scorpion — but due to her electric touch sensing ability, she dodges the attack and the Brontoscorpio gets eaten by a Pterygotus, a 3 m long eurypterid hiding in the sea floor. Cameroceras also live in these waters. The film also shows a school of Cephalaspis swimming from the ocean to rivers where they spawn. A group of Brontoscorpio crawl on land and also arrive at theCephalaspis's spawning pool. The Brontoscorpio feast, but there's too many Cephalaspis for them to eat at once. One Brontoscorpio moults and misses the feast.
Late Devonian (360 MYA)
We move forward in time to the Devonian, when Cephalaspis has evolved into Hynerpeton (though it must first pass through the lobe-finned fish stage), amphibian-like tetrapods. Though they can go on land, Hynerpeton have to keep wet, and must return to the water, where sharks like Stethacanthus and a two ton killer fish, Hyneria, can hunt them down. Later a Stethacanthus is eaten by a Hyneria. One male Hynerpeton finds a mate, but just after spawning, he and his mate are ambushed by a Hyneria. They escape to land, but the narrator explains Hyneria has strong fins that can propel herself out of the water. The episode ends with the male Hynerpeton gets eaten by the Hyneria, which has crawled onto land. And right at the end the narrator says that amphibians leave the waters and their eggs change. They have a hard shell which protects the young inside. The First Reptiles Evolved. The spider is about to attack them.