The Torvosaurus gurneyi, like T. Rex, was a bipedal carnivore with blade-like teeth more than 4 inches (10 centimeters) in length, they said in a report published in the US journal PLOS ONE.
"This was clearly a fierce predator," Mateus told AFP. "Wherever he arrived, he was the owner and master. No one could rival Torvosaurus during the late Jurassic. This is the equivalent of T. rex but 80 million years before."
The scientists estimate Torvosaurus gurneyi grew up to 33 feet (10 meters) long and weighed some 4 or 5 tons. Its skull measured nearly four-feet (115 centimeters) long, smaller than the T. Rex, but not by a huge margin.
The fossils found in Portugal closely resemble those of a North American dinosaur -- the Torvosaurus tanneri -- and indeed at first the scientists thought the two specimens must be from the same species.
But upon closer analysis of the bones, the researchers determined the species must have evolved separately from the two sides of the proto-Atlantic Ocean over a few million years.
Mateus said it's hard to know how different the two species would have looked when they were living -- there may have been differences in coloring or behavior that would have easily distinguished them.
From the fossil record, the differences are more subtle.
The North American species has 11 or more teeth on its upper jaw, compared to fewer than 11 for the Portuguese dinosaur, the researchers explained. And the mouth bones are shaped and structured differently.
- A 'game-changing' predator -
Discovering such a large predator in this era could really be "a game changer" in terms of how scientists think of the Jurassic food chain, explained University of Kansas paleontologist David Burnham, who was not involved in the research.
"These things were living with giant plant-eating dinosaurs," or sauropods, Burnham explained, herbivores too big for other common Jurassic predators, like the Allosaurus, to attack.
But if the estimates of the new Torvosaurus are right, he said, the carnivore was certainly big and fast enough to catch a small sauropod.
"The blade-like teeth of Torvosaurus are particularly nasty since they would seem to indicate a slash-shred strategy," he added.
The new species is also of interest to paleontologists, because it gives a more detailed picture of the interactions and connections between North America and Europe at the time.
"Finding another (Torvosaurus) species in Portugal is pretty cool, because this is additional evidence that shows a similarity in Jurassic dinosaurs in Europe and in North America," adding to finds of a Stegosaurus and an Allosaurus in both the US West and Portugal, said Ken Carpenter, paleontologist at Utah State University.