A manga by the great Ken Ishikawa and his friend Go Nagai (creator of the also famous Mazinger Z), adapted into a television series that was more light-hearted than the more horrific and psychotic manga, the closest animated show to the original is the New Getter Robo OVA which combines elements of the original manga with the sequel manga, Shin Getter Robo.
Plot
Dinosaurs have come back.
External Links
Official
Other Sources
Other Wikis
http://gonagai.wikia.com/wiki/Go_Nagai_wiki
References