Researchers from the University of Southampton in Britain and the University of Liege in Belgium have named the fossil -- found in Iraq in the 1950s but now the subject of new studies -- Malawania anachronus, which means "out of time swimmer."
Despite coming from the Cretaceous period -- from 145 million to 66 million years ago -- Malawania represents the last-known member of a kind of ichthyosaur long believed to have gone extinct during the Early Jurassic, more than 60 million years earlier.
Hundreds of Ichthyosaur fossils from the time of the dinosaurs have been discovered.
"They ranged in size from less than one to over 20 meters [3 feet to 60 feet] in length. All gave birth to live young at sea, and some were fast-swimming, deep-diving animals with enormous eyeballs and a so-called warm-blooded physiology," lead study author Valentin Fischer of the University of Liege said.
Malawania anachronus appears characterized by an evolutionary stasis, the researchers said; they seem not to have changed much between the Early Jurassic and the Cretaceous, a very rare feat in the evolution of marine reptiles.
"Malawania's discovery is similar to that of the coelacanth in the 1930s: It represents an animal that seems 'out of time' for its age," Fischer said. "This 'living fossil' of its time demonstrates the existence of a lineage that we had never even imagined."