Future Turtle is an alternate timeline counterpart of Turtle who survived in both Future Trunks' and Cell's timelines, as seen in the TV special Dragon Ball Z: The History of Trunks and Dragon Ball Super.
The History of Trunks
His life was the same as his main timeline counterpart up until the time when the Androids came. During the time Future Trunks was fighting the androids, he was hiding and living in a submarine near Kame House with Future Master Roshi, Future Oolong and Future Puar.
"Future" Trunks Saga
Main article: "Future" Trunks Saga In the anime, when Fused Zamasu used his Absolute Lightning in his battle against Goku and Vegeta, the impact is felt across the Warth. A hurricane is caused and Future Turtle is seen holding onto the roof of Kame House.
Whenever Future Trunks is fighting fused Zamasu after Vegito defused back into Goku and Vegeta, all living beings on the Earth give their energy to Trunks. Turtle is seen glowing as he gives his energy to Trunks. He was later killed along with the remaining humans of the future timeline when Infinite Zamasu used Chou Makouhou Barrage to attack Earth.
Second Future Timeline
While Future Turtle died during Fusion Zamasu's final attack to wipe everyone out, he still exists in the second future timeline created by Whis' alterations.