Researchers from the State Natural History Museum in Braunschweig said the rare fossil ichthyosaur find from northern Germany is 130 million years old, dating from the Lower Cretaceous era. Most ichthyosaur fossils previously found date from the Jurassic era, millions of years earlier.
The newly discovered ichthyosaur species, unearthed during road work in 2005, has been called Acamptonectes densus, "Stiff Swimmer."
The neck vertebrae were so tightly arranged the species "couldn't move its neck, so it must have shot through the water like a dart," museum paleontologist Ulrich Joger told the BBC.
"It's a spectacular find," he said. "It raises new questions about the [Jurassic] extinction theory."
The marine predator fed on fish and would have looked something like a dolphin, experts said, though the species are not related.