Paleontologists working in Chile have recently unearthed a vast graveyard of prehistoric Ichthyosaurs, an ancient order of large marine reptiles that lived from 250 million to 66 million years ago.

Some 46 Early Cretaceous “fish lizard” fossils were preserved in sediment in Torres del Paine National Park, near the Tyndall Glacier in southern Chile.

The nearly complete skeletons included both embryotic and adult Ichthyosaurs. The largest specimen measured more than 5 meters, or 16 feet, in length. Some even contained soft tissues, Live Science notes.

 “This concentration is unique for Chile and South America, making the fossil site significant internationally,” Wolfgang Stinnesbeck, a researcher from Heidelberg University's Institute of Earth Sciences in Germany and leader of a study published May 22 in the journal Geological Society of America Bulletin, said in a statement.

The discovery of the Ichthyosaur graveyard in Chile has been described as the greatest find of Ichthyosaurs ever and establishes the park as the primary site for Early Cretaceous marine reptiles worldwide.

“It's the most recent great find in their history,” Christian Salazar, a paleontologist and natural history museum curator in Germany, told The Independent. “That's going to answer a lot of questions about how they became extinct, where they migrated to and how they lived.”

Scientists actually uncovered the fossil graveyard in 2004 after it was exposed by a receding Patagonian glacier. Paleontologists have spent the last few years studying the remote site, which can only be reached by hiking 14 hours through rugged terrain.  

Researchers say Chile’s Ichthyosaurs, which resembled modern-day dolphins with their torpedo-shaped bodies, long snouts and flippers, were probably killed during a series of catastrophic mudslides around 150 million years ago. The air-breathing reptiles became “entombed” in a muddy grave at the bottom of an ancient underwater canyon.

“The [Ichthyosaurs] became disoriented in the turbidity currents,” Stinnesbeck said. “They were sucked down hundreds of meters into the deep ocean.”

Ichthyosaurs were around at the same time as dinosaurs and pterosaurs, but may have gone extinct before their terrestrial and avian cousins. Scientists theorize that a global depletion of oxygen in the oceans, brought on by volcanism, may have led to the mass die-off of Ichthyosaurs, Discovery notes.

The first complete Ichthyosaur skeletons were discovered in England in the early 19th century. 

Last year, paleontologists uncovered a new species of Ichthyosaur in Iraq. The discovery suggested that the Cretaceous marine reptiles were the last survivors of a group on the decline and changed scientists’ understanding of the evolution and extinction of the ancient fish lizard.