Defender of the Future is an entirely new game universe with virtually no ties to the original Mega Drive/Genesis titles; the team working on Defender of the Future was not the same team that worked on the original games. It was released in 2000 for the Dreamcast, developed by Appaloosa Interactive (the company formerly known as Novotrade International), and its soundtrack is composed by Tim Follin. It was later published on PlayStation 2 by Acclaim Entertainment.
Defender of the Future bore a different storyline from that of the Mega Drive/Genesis games; it is generally regarded as an alternate universe. The story was written by science fiction author David Brin, who had already written a few stories about intelligent dolphins in his Uplift universe.
Source: Wikipedia, Ecco the Dolphin: Defender of the Future , available under the CC-BY-SA License.