Eternauta patagonica was an ichthyosaur which lived around Argentina during the late Jurassic Period 152-145 million years ago.
Fossils of this Jurassic marine reptile, consisting of a well-preserved skull measuring nearly four feet long, a flipper, and fragments of ribs, were found in the Vaca Muerta (“Dead Cow”) Formation of west-central Patagonia, Argentina, whose rock layers date to the end of the Jurassic and beginning of the Cretaceous Periods. The particular stratum in which these ichthyosaur fossils were found in dates to the Tithonian Stage of the Jurassic Period, approximately 152-145 million years ago, but a more specific date couldn’t be determined. These fossils were originally described in 1990 as a specimen of Platypterygius. Then in 1997, it was re-described as a species of Caypullisaurus. Finally in 2025, it was described once again as its own separate genus, named Eternauta, “the eternal sailor”.
Eternauta was identified as a member of the ichthyosaur family Ophthalmosauridae, and more specifically the sub-family Platypterygiinae. It was closely related to Athabascasaurus and Brachypterygius.
Based upon the size of Eternauta’s skull, and comparing it with the size of the skulls of Grendelius mordax, Nannopterygius saveljeviensis, and Platypterygius americanus and these animals’ overall length, Eternauta likely had a total length of 14-15 feet (4.25-4.5 meters).
Eternauta lived alongside other marine reptiles including the ichthyosaurs Arthropterygius, Catutosaurus, and Caypullisaurus, the marine crocodylomorphs Cricosaurus and Dakosaurus, the sea turtles Neusticemys and Notoemys, and the giant pliosaur Pliosaurus.
Below is a hypothetical reconstruction of Eternauta. The head is based upon the well-preserved skull from the holotype specimen, while the remainder of the body is based upon Brachypterygius, which it was believed to be closely related to.
Eternauta patagonica. © Jason R. Abdale (March 18, 2026).
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