Plesiosaurs and erupting volcano, artwork. The volcanic eruption (background) will lay down a thick layer of ash that will kill the plesiosaurs (foreground). The ash will also preserve them as fossils. The era is some 70 million years ago in what will one day become Antarctica. The well-preserved fossil skeleton of a juvenile plesiosaur was recovered in Antarctica in 2005, and unveiled in 2006. It is one of the most complete plesiosaur fossil skeletons ever found. Plesiosaurs were marine reptiles that inhabited the seas throughout the Jurassic and Cretaceous periods from around 200 to 65 million years ago. Here, they are shown as viviparous (giving birth to live young rather than laying eggs), but this is not yet certain.