These land bridges surfaced when sea levels dipped allowing the famous plated dinosaur -- and other dinosaur species -- to cross.

    "Both coasts were very close and the basins between them could emerge occasionally," said study leader Fernando Escaso of the University of Autonoma in Madrid, Spain.

    All of the world's continents were clumped together into one giant landmass called Pangaea when dinosaurs first roamed the planet. At the end of the Jurassic Period, about 150 million years ago, the supercontinent began slowly separating and North America, Europe and Africa began to drift apart giving birth to the Atlantic Ocean.

    There were times during this million-years long transformation when sea levels rose and fell. Sometimes, land bridges emerged between the newly sundered landmasses. It was then dinosaurs like Stegosaurus would have been able to cross.

    Easily recognized by any dinosaur enthusiast, Stegosaurus was a bizarre looking herbivorous creature that had a back adorned by a double row of vertical plates and a tail studded with spikes. It was once thought these strange accessories were for protection or used to radiate heat from the dinosaur's body.

    But now most scientists think the body armor was probably just an extreme example of the elaborate and colorful displays animals use to recognize each other as the same species.

    The scientists unearthed the new Stegosaurus fossils -- which included a tooth and parts of the animal's spinal column and leg bones -- near the city of Batalha, in central Portugal. Preliminary analyses show the fossils to be indistinguishable from a species previously found only in North America, called Stegosaurus ungulatus.

    While the similarity bolsters the land-bridge case, it provides no information on when the land bridges emerged.

    "At present, it isn't possible to know the structure, frequency and duration of these land bridges," Escaso told LiveScience.

    Peter Makovicky, a paleontologist at the Field Museum in Chicago who was not involved in the study, said the new Stegosaurus discovery supports something largely suspected in the past and helps flesh out some of the geological history of the region.

    "It documents the second genus of dinosaurs that's well-known from the Jurassic of North America to be present in Europe, and thereby gives evidence that there was a fairly strong connection between these areas during that time,"¡± Makovicky said in a telephone interview.

    The only other dinosaur for which bones have been found in both North America and Europe is a species of Allosaurus, a large meat-eating dinosaur similar to Tyrannosaurus rex, but without the latter's stubby arms.

    The new finding will be detailed in an upcoming issue of the German science journal Naturwissenchaften.

    (Agencies)