Spanish scientists have unearthed what could be Europe's largest dinosaur boneyard, finding the remains of 65-foot plant-eaters never before discovered on the continent.
The paleontologists believe they have found eight different species amid the 8,000 fossils discovered so far.
The range of species they are finding at the 80-million-year-old site and their state of conservation is virtually unparalleled in Europe and challenges long-held beliefs about the way in which dinosaurs became extinct.
• Click here to visit FOXNews.com's Evolution & Paleontology Center.
"This is completely beyond what we expected to find," Francisco Ortega, co-director of the excavation, told The Times. "This represents a huge leap in our understanding of the Upper Cretaceous [period]."
Dozens of experts are working around the clock to excavate the site. It was discovered in June during construction work for a new high-speed rail link between Madrid and Valencia.
Paleontologists, who kept the discovery under wraps, have until the end of November to remove the skeletons of several hundred dinosaurs before the diggers move back in.
Researchers have not finished excavating the entire area of Lo Hueco, near the city of Cuenca, in western Spain. But they say they have retrieved most of the fossils from the path of the railway.
The find is from a period paleontologists have little information on in Europe. Most of the sites dating from that period have been found in the Americas.
Scientists had long believed that the diversity of dinosaurs declined sharply as they approached the end of their time on earth. Paleontologists working in Lo Hueco, though, have been amazed to find a wide variety of dinosaurs from the period.
"Everything indicates that the dinosaurs were enjoying great evolutionary vigor when they suddenly disappeared," said José Luis Sanz, the co-director of the dig.
Ortega said the find should help shed light on the extinction of the dinosaurs in Europe and whether they also died out as a result of the huge meteorite that struck modern-day Mexico.
The different species found include three, perhaps four, different types of Titanosaurus -- huge, long-necked creatures that munched on plants and walked on four thick legs.
More than 100 individual Titanosaurus have been found at the site, some of them with thick armor-plating on their backs, a feature not previously seen in Europe.
Many dinosaur skeletons that are nearly intact have also been unearthed.
"We have found very complete individuals [dinosaurs] and skull fragments" from Titanosaurus, said Ortega.
Other dinosaurs found are believed to include Struthiosaurus, a small, armored, quadrupedal plant-eating dinosaur.
Until now, only incomplete fossils had been found in Austria and Romania.
Researchers also believe they have found two or three types of Dromaeosaurus -- small, fast-moving predators with sharp teeth and deadly, sickle-like claws. They have also found a Rhabdodon, a small, two-legged plant-eater with a long tail, short neck and a bulky body.
Researchers also say there is a wealth of other plant and animal species at the site that could provide a treasure trove of information about one of Europe's least-understood periods. They must still sift through 20 tons of sediment and say they can expect to find dozens of other smaller species.
"This is the equivalent of 80 to 100 times the size of a normal excavation in terms of time and money," Ortega said.