The Atlanteans are believed to be the only humans in the Ecco universe that are known to have existed. They lived in a civilization they constructed named Atlantis, which they constructed with their highly advanced technology. Their technological capabilities were so great they invented the Glyphs and teleport rings and even discovered and experimented with time travel.
The Atlanteans were forced into a war with the Vortex race when the Vortex sought to harvest the creatures of earth for food. It is not known what kind of weapons the Atlanteans used because none are ever found in the ruins of the city. The population had to flee during the war as the city was laid to ruin and sunk beneath the waves. However, before its destruction, the survivors escaped into an unknown era in the past using the Time Machine. Before their escape, they left behind a history of the war, recorded in Glyphs, in the Atlantean Library. This suggests that they had some knowledge of cetacean behaviour and singing. It is not known how they discovered time travel, what they used it for (other than the escape) or how they interacted with the local wildlife.
Are the Atlanteans human?
It is assumed that they are humans for several few reasons. As the words used in the game universe are almost exclusively Singer terminology, it is highly unlikely that they would use the word "human" to describe themselves. Furthermore the cultural sculptures in Atlantis depict humans and resemble those found in our own world. Although none are found in Atlantis itself, there are ruined buildings on islands all over the ocean and sunken ships below the surface.