Using 3D scanning technology, a team from the Austria National History Museum unearthed the fossil of the creature, called Dissimilites intermedius, a layer at a time, and then created a video of how the creature lived and moved.
The ammonite was discovered in sediment which formed at the bottom of the ocean during the Cretaceous period some 128 million years ago, but now lies at the top of the Dolomite mountains in the Alps.
The scientists said that the computer tomography had allowed them to see far more than they would ever have been able to with the naked eye, with the creature was exposed a layer at a time.
The team, led by Alexander Lukeneder, also discovered the body was covered with spines each between three and 4mm long.
"The fossil is of a previously unknown creature which is a type of Ammonite," the Daily Mail quoted a museum spokesman as saying.
"Computer tomography and a complicated 3D reconstruction programme were used to help reconstruct not only the appearance of the fossil, but also to work out how it moved by the position of the impressions left by its limbs."
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The spokesman added that the prehistoric Tethys Ocean, which existed between the continents of Gondwana and Laurasiam, had left behind millions of years-worth of sediment at the bottom of the sea.Gondwana would break up to form much of the Southern Hemisphere, and Laurasia would form much of the Northern Hemisphere.
As the centuries passed and the Alps folded out of the sea, some of the former sea bottom sediment ended up on the peaks of the Dolomites.
And it was here in the Puez-Geisler-Natural Park, at a height of around 2600m, that a section of the former seabed was discovered -- with the thickest density of fossils from pre-history yet discovered.
Lukeneder and his team have been working on the 150metre section for three years, and discovered the fossil of the ammonite last year.
Details of the finding are published in the journal Acta Palaeontologica Polonica.