Thalassocnus was a species of marine sloths that lived in what is now known as Chile and Peru during the Late Miocene, 7 million years ago to the Late Pliocene, 3 million years ago. Thalassocnus was similar in shape to the other giant sloths of the time, but unlike them Thalassocnus was semi-aquatic, the reason for this change in life style is still unknown, but it may have to do with the other ground sloths being more successful than it, therefore it took to the sea so it didn't have to compete with the others sloths. Thalassocnus had longer arms than other sloths, this adaptation was probably used to help it dig and grab its food in its underwater environment. It was also armed with 5 large claws that were probably used for defense against the many predators that it had to live with such as the Zygophyseter, Acrophyseter and Megalodon.

Diet: Marine plants.

Casualties: one Hadrokirus.

Cause of death: killed by Hadrokirus during a fight between the two.

Hadrokirus was a species of seal that lived on the Pacific coast of South America 6 million years ago during the Late Miocene. Despite its size Hadrokirus preferred to feed on crustaceans and small vertebrates even though it would have been capable of killing larger animals.

Diet: Crustaceans, small vertebrates and carcasses.

Casualties: one Thalassocnus, five crabs and it also mawled a man.

Cause of death: killed by a Thalassocnus during their fight.

Anomaly incident: An anomaly opened on the tiny island of Nauru near Anibare Beach and a pair of Thalassocnuses came through it.

Meanwhile the ARC sent out a team to the anomaly's location.

But back on the island a Hadrokirus came out of the anomaly and proceeded to enter the ocean and feed on 5 crabs.

When the ARC team arrived on Nauru they headed towards the anomaly's coordinates.

On their way to the anomaly they passed Buada Lagoon and found one of the Thalassocnuses in the water. Quickly they tranquilized it and brought it to the anomaly where they were able to send it back to its time period.

Meanwhile somewhere else on the island a group of teenagers were hanging out at the old phosphate cantilevers when they encountered the other Thalassocnus that was currently relaxing on the beach.

The teens quickly ran off to alert the authorities and tell them what they had seen.

While all of that was going on, in a different part of the island a man was walking down the beach, but unbeknownst to him the Hadrokirus was sleeping nearby.

Unfortunately when the man turned the corner he stepped on the Hadrokirus's tail flippers causing the animal to wake up and savagely mawl the man's left leg before dragging itself back into the water.

As the day continued on the island, the ARC team got reports of another Thalassocnus and a man who had been attacked by very large seal.

Realizing what the situation had become the ARC team split up into two teams so they could deal with both creatures at the same time.

The first team used a boat to find the Hadrokirus that was heading toward the old phosphate cantilevers.

The second team arrived at the old phosphate cantilevers and soon found the Thalassocnus still just relaxing in the sand.

However the Thalassocnus's peaceful day was interrupted when the Hadrokirus came rushing out of the water.

This surprised the Thalassocnus and out of instinct it slashed the Hadrokirus's face and the two began to fight.

The Hadrokirus knocked the Thalassocnus on to its back and bit down on the sloth's right arm. The Thalassocnus retaliated by sinking its claws into the seal's neck.

The two brawlers were tearing each other apart until the Hadrokirus bit down hard on the Thalassocnus's throat and crushed its windpipe killing it.

But before the Thalassocnus died it jabbed its claws one last time into the Hadrokirus's neck and severed a main artery causing the seal to bleed to death.

The two animals were brought back to the ARC and are currently in cold storage.