During an excavation, amidst the Patagonian winds and hard rock, a fossil began to turn green. It was an unexpected reaction: the adhesive applied to protect the bones, fragile after millions of years beneath the ice, had interacted with plant matter trapped in the rock’s cracks. This greenish hue earned the fossil the nickname Fiona, like the ogre from Shrek.
But Fionais much more than a ogre-themed name. It is the first complete ichthyosaur ever excavated in Chile and, even more remarkably, the only known pregnant female from the Hauterivian — a stage of the Early Cretaceous dating back 131 million years. Her skeleton, discovered at the edge of the Tyndall Glacier in Torres del Paine National Park — an area increasingly exposed by glacial retreat — belongs to the species Myobradypterygius hauthali, originally described in Argentina from fragmentary remains.
The discovery, led by Judith Pardo-Pérez, a researcher at the University of Magallanes and the Cabo de Hornos International Center (CHIC), and published in the Journal of Vertebrate Paleontology, offers an unprecedented glimpse into ancient marine life — from how these majestic reptiles reproduced to how they adapted to oceans vastly different from those of today.
An Ichthyosaur Maternity Ward in Patagonia
(Image Courtesy of Irene Viscor)
So far, 88 ichthyosaurs have been found on the Tyndall Glacier. Most of them are adults and newborns. Two key facts stand out: food was abundant, and no other predators were competing with them.
Fiona, who measures nearly 13 feet long, is still encased in five blocks of rock. Despite the challenge, she was transported to a local clinic, where CT scans allowed researchers to study her skull and body. Her species was identified thanks to one of her fins.
“There’s no other like it in the world,” says Pardo-Pérez.
The limbs were remarkably elongated, suggesting this animal was built for long-distance swimming.
Inside her, there were more surprises. One of them was her stomach contents, which revealed what may have been her last meal: tiny fish vertebrae. But the most striking find was a fetus, about 20 inches long, already in a position to be born.
“We believe these animals came to Magallanes — the southern tip of Chilean Patagonia — from time to time to give birth, because it was a safe refuge,” Pardo-Pérez says. “We don’t know how long they stayed, but we do know that mortality was high during the first few days of life.”
One of the big unanswered questions is where they went next, as there are no records of Myobradypterygius hauthali, apart from a piece of fin found in Argentina. The most abundant remains come from southern Germany, but those date back to the Jurassic period, meaning they’re older.
Palaeontologist Erin Maxwell suggests, “In many modern ecosystems, species migrate to higher latitudes during the summer to take advantage of seasonally abundant resources and then move to lower latitudes in winter to avoid harsh conditions,” she explains. “We believe Mesozoic marine reptiles may have followed similar seasonal patterns.”
Read More: Species of Ichthyosaur Is Largest Known Marine Reptile at 80 Feet Long
Sea Dragon Graveyard
The environment where Fiona was discovered — dubbed the “sea dragon graveyard” — also has much to reveal.
According to geologist Matthew Malkowski of the University of Texas at Austin, the Hauterivian age is particularly intriguing because it coincided with major planetary changes: the breakup of continents, intense volcanic episodes, and phenomena known as “oceanic anoxic events,” during which vast areas of the ocean were depleted of dissolved oxygen for hundreds of thousands of years.
One such poorly understood event, the Pharaonic Anoxic Event, occurred around 131 million years ago, near the end of the Hauterivian, and still raises questions about its true impact on marine life.
“We don’t have a firm grasp of how significant these events were for marine vertebrates, and geological records like that of the Tyndall Glacier allow us to explore the relationship between life, the environment, and Earth’s past conditions,” Malkowski notes.
Evolution of Ichthyosaurs
Reconstruction of Fiona. (Image Courtesy of Mauricio Álvarez)
Don’t be misled by their body shape. “Ichthyosaurs are not related to dolphins,” clarifies Pardo-Pérez.
Although their hydrodynamic silhouettes may look nearly identical, the former were marine reptiles, while the latter are mammals. This resemblance results from a phenomenon known as convergent evolution: when species from different lineages develop similar anatomical features to adapt to the same environment.
Ichthyosaurs evolved from terrestrial reptiles that, in response to ecological and climatic changes, began spending more time in the water until they fully adapted to a marine lifestyle.
However, they retained traces of their land-dwelling ancestry, such as a pair of hind flippers — absent in dolphins — passed down from their walking forebears. They lived and thrived in prehistoric oceans for about 180 million years, giving them ample time to refine a highly specialized body: their forelimbs and hindlimbs transformed into flippers; they developed a crescent-shaped tail for propulsion, a dorsal fin for stability, and a streamlined body to reduce drag in the water.
Remarkably, like whales and dolphins, “ichthyosaurs had a thick layer of blubber as insulation to maintain a higher body temperature than the surrounding seawater and gave birth to live young, which meant they didn’t need to leave the water to reproduce,” explains Maxwell.
Whales and dolphins also descend from land-dwelling ancestors, but their transition happened over a comparatively short evolutionary timespan, especially when measured against the long reign of the ichthyosaurs.
“Their evolution hasn’t had as much time as that of ichthyosaurs,” notes Pardo-Pérez. “And yet, they look so similar. That’s the wonderful thing about evolution.”
Read More: Did a Swimming Reptile Predate the Dinosaurs?
Fossils on the Verge of Disappearance
One of the key factors behind the remarkable preservation of the fossils found in the Tyndall Glacier is the way they were buried. According to Malkowski, Fiona and her contemporaries were either trapped or swiftly covered by underwater landslides and turbidity currents — geological processes that led to their sudden entombment.
But the good fortune that protected them for millions of years may now be running out. As the glacier retreats, exposing fossils that were once unreachable, those same remains are now vulnerable to wind, rain, and freeze-thaw cycles, which crack the surrounding rock. As vegetation takes hold, roots accelerate erosion and eventually conceal the fossils once again.
“While climate change has allowed these fossils to be studied, continued warming will also eventually lead to their loss,” Maxwell warns. In Fiona’s story, scientists find not only a record of ancient life, but also a warning etched in stone and bone: what time reveals, climate can reclaim.
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María de los Ángeles Orfila is a science journalist based in Montevideo, Uruguay, focusing on long-form storytelling. Her work has appeared in Discover Magazine, Science, National Geographic, among other outlets, and in leading Uruguayan publications such as El País and El Observador. She was a fellow in the 2023 Sharon Dunwoody Mentoring Program by The Open Notebook and often explores the intersections of science, culture, and Latin American identity.
