TORREJON DE VELASCO, Spain -- Skulls of saber-toothed tigers, beasts with 25 cm (10 inch) teeth which stalked subtropical jungle millions of years ago, have been found on the outskirts of Madrid.

Spanish paleontologist Jorge Morales discovered the fossilized remains of some 45 saber-toothed tigers, with an unusually large number of skulls completely intact, on a barren hill 30 km (19 miles) south of the Spanish capital.

"We'll be here for years, there are things here that you just don't find elsewhere," Morales said. "We are finding complete skeletons, normally there are lots of broken bones, fragments," This is the third summer Morales and his 25-strong international team have spent at the site in their painstaking search for fossils.

"We have found the remains of 30 complete craniums of the medium sized saber-tooth, and 15 of the big saber-tooth," Morales told Reuters on Thursday.

"Of the medium-sized one, no other complete example is known of. We've got 30!" he said.

The tigers were larger than a lion and had claws that could measure 10 centimeters.

The remains are thought to be nine to 10 million years old.

The oldest known fossils thought to be from a member of the human family were found in Chad last month and are thought to be six to seven million years old.

*** Quicksand Trap?***** Morales, who has also worked in Namibia and Kenya, said there was an unusual concentration of carnivorous animals on the hill compared with other sites.

"We think there was some kind of trap here...like quick sand. The herbivores could have been trapped by the quick sand and that attracted the carnivores...to try to eat them," he said.

Other theories are that there was a cave or hole that animals became trapped in.

Excavations began after miners of mineral Sepiolite found fossils, and informed the Madrid Science Museum.

Apart from saber-toothed tigers, the paleontologists have come across fossils of a zebra, a giraffe with a larger head and shorter legs than its descendants, the elephant-like mastodon, birds of prey, bears, tortoises, antelope and a rhinoceros.

Although there are still years of work to be done, this summer's digging season ends on August 14.

Morales and his team will fill the holes they have dug with sand bags and cover them with earth to preserve the site until their return next year.