'Fiona' the ichthyosaur was preserved for millions of years after a landslide

An ichthyosaur called “Fiona” has recently stirred curiosity from far beyond scientific circles. She measured about 11 feet (3.4 meters) during life, and met a swift end when her long snout planted itself several inches into the sand, setting the stage for an unusual preservation.

Fiona was carefully excavated in five segments from a glacial field in Patagonia in 2023.

Lead author Judith Pardo-Pérez from the University of Magallanes and the Cape Horn International Center in Chile worked with a large team to transfer the fossil to the Natural History Museum Río Seco for a closer look at her condition.

Nearly complete ichthyosaur skeleton

The Hauterivian stage was a slice of the Early Cretaceous period, and Fiona’s bones add crucial information about marine reptile life from that time.

Her almost complete skeleton is especially significant, since findings in that part of the Southern Hemisphere are quite limited.

Scientists believe she was an apex predator when she roamed ancient waters. The wide distribution of these creatures in various latitudes suggests they adapted to a range of environmental conditions.

Fiona is the only fully preserved and excavated pregnant ichthyosaur known from Chile. A fetus still inside her body highlights how these reptiles gave birth to live young, a trait associated with advanced marine reptiles.

Fossil and burial mystery

Inside her body were fossilized fish vertebrae, which indicate that her last meal had not yet been digested. The fetus was also mostly intact and appeared ready for birth, with its tail oriented toward what would have been the exit path from the mother.

The fossil reveals a story of sudden burial. Scientists suspect an underwater landslide pushed down a heavy flow of sand that covered Fiona almost instantly, and led to excellent conditions for the preservation of both mother and unborn baby.

“We were conducting our research with different objectives, they are very synergistic,” remarked co-author Matt Malkowski, an assistant professor at The University of Texas at Austin’s Jackson School of Geosciences.

Malkowski uses methods in stratigraphy to understand landscape shifts and was drawn into the Fiona project when he met Pardo-Pérez in Torres del Paine National Park.

Certain geological signatures suggest multiple landslides hit that region over an extended period. More than 80 other ichthyosaurs rest in the same glacial field, hinting at repeated catastrophic flows that buried these animals in a similar manner.

The breakup of continents

At the time of Fiona’s burial, South America was in the process of separating from what is now Africa.

Malkowski said the opening up of a narrow oceanic passageway between the continents may have affected global climate, currents and habitats for marine life.

“If you are the apex predator in the ocean at the time, these are all things you care about,” he said. “You care about migration pathways. You care about places that you can hunt and fish and do your thing. You care about places where you can reproduce.”

Fossil reveals injury and anatomy

A set of fused fin bones suggests Fiona recovered from an earlier injury or infection. The skeletal details of both mother and fetus reveal aspects of paleopathology seldom seen in marine reptiles from this period.

“The discovery of the Fiona ichthyosaur provides valuable information regarding the species, its paleobiology, and paleoecology,” said Pardo-Pérez.

She explained that new imaging methods could uncover unique structural characteristics that enhance the understanding of these creatures’ anatomy.

Fiona’s remarkable condition highlights how precise timing in burial can preserve entire skeletons. She shows evidence of normal feeding habits, advanced pregnancy, and well-developed bones typical of a robust adult.

Shifting landscapes and marine life

Shifting landscapes might have affected marine life across what is now South America. The possibility of a narrow oceanic passage once connecting the continent to modern-day Africa could have shaped currents and sea temperatures.

Malkowski’s sedimentary techniques might reveal whether repeated events scattered fossils through various layers or whether a single, larger catastrophe occurred. That knowledge helps paint a broader picture of how ocean basins evolved in the distant past.

Researchers continue to analyze trace minerals from the rock surrounding Fiona and the other ichthyosaurs.

Fluctuations in these minerals may show how ancient seas adapted to tectonic transformations, and influenced predators that roamed the waters.

Fossil reshapes views on ichthyosaurs

Fiona marks a turning point in how scientists view ichthyosaur populations in southern latitudes.

Each piece of data gleaned from her skeleton contributes to a fuller understanding of the biology, reproduction, and survival of these reptiles under shifting conditions.

Experts remain excited about what this discovery implies for future excavations in Patagonia. Rapid glacial melting reveals previously unreachable regions that may hide additional creatures from the Early Cretaceous.

Malkowski’s involvement is a reminder that paleontology and sedimentology share common goals. He is not a traditional fossil hunter, yet his methods complement the anatomy-based approach led by Pardo-Pérez.

The story is still unfolding

Researchers emphasize that Fiona’s story is still unfolding. Some suspect each additional ichthyosaur in the area may introduce additional information about variations in diet, growth patterns, or injury history.

“Moreover, its skeleton will allow us to delve deeper into aspects of its anatomy through new studies and the use of medical technology,” said Pardo-Pérez.

New scanning technology will bring sharper insight into the mother’s physiology and her pup’s final stage of development. 

The collection of samples around her remains is planned in order to understand local climate conditions at the time. This may shed light on the triggers behind multiple burial episodes, shaping an ongoing narrative in southern Chile’s fossil record.

Fiona testifies to how ancient catastrophes can preserve a life story for millions of years. Her unusual circumstances give paleontologists a vital look into an extinct species that is still full of surprises.

The study is published in the Journal of Vertebrate Paleontology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–