A museum in Buenos Aires has revealed the replica of a 65 million-year-old skeleton of a marine dinosaur known as a plesiosaur.

The exhibition inauguration of the skeleton replica of a giant plesiosaurus can be seen at the Natural Science Museum in Buenos Aires on December 19, 2018.
The exhibition inauguration of the skeleton replica of a giant plesiosaurus can be seen at the Natural Science Museum in Buenos Aires on December 19, 2018. (AFP)

Argentine paleontologists unveiled on Wednesday the replica of a 65-million-year-old skeleton of a plesiosaur marine reptile found in a Patagonian lake in 2009.

"We've been working since 2009 until now to liberate the fossil from the rock surrounding it, making a reproduction and hanging it here in the museum hall," paleontologist Fernando Novas of the Bernardino Rivadavia Natural Science Museum in Buenos Aires told AFP.

The skeleton of a giant plesiosaurus, an extinct marine reptile, seen during its exhibition inauguration at the Natural Science Museum in Buenos Aires, on December 19, 2018.
The skeleton of a giant plesiosaurus, an extinct marine reptile, seen during its exhibition inauguration at the Natural Science Museum in Buenos Aires, on December 19, 2018. (AFP)

The fossil is of a marine reptile found in Cretaceous period rocks close to the southern town of El Calafate, 2,800 kilometers from Buenos Aires.

The remains of this plesiosaur are the most complete found in Argentina and were discovered in rocks submerged in Lake Argentino at the foot of the Andes mountains.

"It was around 50 centimetres under the water and part of the lake had to be drained to take out the rocks," said scientist Marcelo Isasi.

Four tons of rocks had to be removed to unearth the fossil remains, found just 500 metres from an international airport.

A visitor is pictured next to the skeleton replica of a giant plesiosaurus reptile at the Natural Science Museum in Buenos Aires, on December 19, 2018.
A visitor is pictured next to the skeleton replica of a giant plesiosaurus reptile at the Natural Science Museum in Buenos Aires, on December 19, 2018. (AFP)

Plesiosaurs were huge marine reptiles that lived in seas throughout the entire planet inhabited the entire planet, with long necks, tiny heads and sharp teeth.

It was an era before the Andes existed and when Argentine Patagonia lay underwater.

The fossil is nine meters long with each fin measuring 1.3 metres.

Source: AFP