A Rare, Pregnant Ichthyosaur Fossil Discovered in Chile Is Revealing More Secrets About the Early Cretaceous World

The fossil helps scientists better understand not just the animal, but our planet’s geology

Sara Hashemi

– Daily Correspondent

July 8, 2025 3:51 p.m.

Some 131 million years ago, a pregnant ichthyosaur roamed the waters of what is now the Torres del Paine National Park in Chile. After a dramatic event, like an underwater landslide, covered her in sediment, her body remained hidden until 16 years ago, when scientists stumbled upon the nearly pristine fossil of the animal—a dolphin-like marine predator—and unearthed it for further research.

Since then, studies of the creature have offered scientists a series of surprises that shed light on the biology of the prehistoric species and the Early Cretaceous world that supported it.

Glaciers in Chile’s Patagonia region have been melting in recent years, exposing fossils underneath. Judith Pardo-Pérez, a paleontologist at the University of Magallanes in Chile, discovered the ichthyosaur in 2009. When she returned to the site the following year, Pardo-Pérez spotted bones that indicated the presence of a six-inch-long fetus.

Two years ago, the 11-foot-long fossil was airlifted into the sky in five pieces and flown to the Natural History Museum Río Seco in Punta Arenas, Chile. An analysis of the ichthyosaur, identified as Myobradypterygius hauthali, was published in the Journal of Vertebrate Paleontology in February.

But that wasn’t all the rare fossil had in store: After the paper’s publication, scientists conducted a CT scan that uncovered a previously overlooked detail: The mother ichthyosaur was carrying not one, but two fetuses, as Live Science’s Soumya Sagar reported in April. A future paper will describe that finding.

The researchers named the fossil Fiona after the ogre in Shrek, because its bones briefly turned green from a reaction to the glue used to protect them, reports Kenneth Chang at the New York Times. “Extremely green, like fluorescent green,” adds Pardo-Pérez to the publication. “After that, we washed it with liquids, and then she came back to the normal color.”

Fiona promises to teach scientists a lot about the biology and evolution of ichthyosaurs. For one, while some earlier ichthyosaurs gave birth to their newborns head first, the positioning of the first fetus described in the paper suggests it would have come out the birth canal tail first, like modern dolphins and whales, per Live Science.

The researchers also found small fish vertebrae in Fiona’s ribcage, which they believe constitute her last meal. They identified signs of a healed injury in her fin and fused bones that might have been caused by an infection.

The rocks around the fossil also tell a story. At the time of Fiona’s death, during the Early Cretaceous, the Earth was undergoing rapid geological changes. Matt Malkowski, a sedimentary geologist at the University of Texas at Austin and a study co-author, suggests continental breakup may have been the reason behind Fiona’s demise, he says in a statement. As South America broke off from the supercontinent of Gondwanaland, volcanoes and earthquakes shook the Earth, causing landslides.

It was likely one of these underwater landslides that got Fiona caught in a flow of sediment. The ichthyosaur’s snout was burrowed in about four inches of sand when she hit the seafloor, and her body was rapidly buried. “Probably these landslides might have trapped the ichthyosaurs and threw them to the bottom of the canyon and covered them with sediment,” Pardo-Pérez tells the New York Times.

There are 87 other ichthyosaurs in the glacial field where Fiona was found, and the researchers are working to understand the reasons behind their deaths, too. It doesn’t seem like they all died at the same time—and preliminary data suggest multiple landslides could be to blame.

“We’re conducting an array of geochemical analyses to understand as much as we can about the environment of this ocean basin at the time,” Malkowski says in the statement. “We’re working on teasing out whether or not this is a single event or multiple events and what the triggers were.”

The scientists also found several neonates and newborns in the area, Pardo-Pérez tells Flora Lichtman of Science Friday, which suggests that the site served as a nursery for the prehistoric animals. She hopes to find more pregnant ichthyosaurs in future expeditions, as that would help support the nursery hypothesis.