A remarkable find in paleontology has come from Torres del Paine National Park in Chile. About a year ago, scientists discovered the fossilized remains of a pregnant ichthyosaur, nicknamed Fiona. Recently in 2009, scientist Judith Pardo-Pérez discovered something extraordinary. This unprecedented find unlocks tremendous clues into the reproductive behavior of these long lost marine reptiles that once ruled the Earth, some 131 million years ago during the Cretaceous period.
Fiona, an ichthyosaur of the species Myobradypterygius hauthali, is about 11.5 feet (3.5 meters) long. Her vertebrae are peculiar as they are disproportionately large compared to what is normal for her body size. Each vertebra is about 0.6 inches (1.5 cm) tall. This incredible anatomical feature has captured paleontologists’ imaginations and can help us understand what these evolutionary adaptations allowed these ancient monsters to do.
From the fossilized plants and animals found at the site, researchers figured out that Fiona’s final meal was made up of smaller fishes. The coolest part of this discovery is the most surprising—scientists found a nearly full-term fetus curled up between Fiona’s ribs. This microscopic fetus is roughly the size of a 15-centimeter (6-inch) preterm infant. This little detail makes Fiona one of just three known pregnant ichthyosaurs from the Cretaceous! That makes this fossil all the more rare and important.
Fiona’s head on orientation means she had her baby tail first. This birthing adaptation, known as alloparental care, is found in today’s dolphins and whales. This surprising finding enriches our picture of reproductive strategies among marine reptiles. This suggests, once again, the striking parallel development of ancient ichthyosaurs to their modern marine mammal cousins.
After first removing the surrounding matrix, in 2022 researchers finished carving and chiseling away all of Fiona’s fossil, which had been preserved in exquisite detail. Advances in technology have allowed scientists to analyze the fossil using CT scans, revealing a comprehensive view of her entire skeleton and providing deeper insights into her anatomy and life history.
The finding of Fiona greatly increases the scientific community’s appreciation ichthyosaur biology. It raises new questions about their ecology and evolutionary history during the Cretaceous period. It gives us a truly unique window into how these ancient animals lived. They showed a rich suite of complex reproductive behavior similar to that of modern marine sonar-active animals.
