Climate chaos caused a mass extinction of top marine predators

Earth’s ancient oceans once held marine predators that could rival the fiercest movie monsters. In the Late Jurassic and Early Cretaceous, the seas were ruled by titanic predators. With jaws measuring up to two meters and teeth sharp enough to shred bone, pliosaurids were apex hunters.

Ichthyosaurs, with their streamlined bodies, resembled swordfish but grew far larger and swam faster. Crocodile-like thalattosuchians dominated the coasts and deeper waters alike.

For millions of years, these animals sat atop marine food webs. Their dominance seemed unshakable. Then, something changed. The fossil record tells a story of sudden disappearance.

One by one, these giants vanished. In their place, a new lineup of marine predators took over – mosasaurs with eel-like tails, long-necked plesiosaurs, and rapidly diversifying sharks. What triggered this massive reshuffling of ocean life?

Mass extinction of marine predators

Scientists believe the answer lies in a dramatic period during the middle Cretaceous, around 94 million years ago, when top marine predators were lost in a mass extinction event.

According to a new study led by Valentin Fischer of the Université de Liège in Belgium, this shift was driven by severe environmental changes. The findings highlight a time of both ecological collapse and evolutionary opportunity.

At the heart of the change is a period known as the Cenomanian/Turonian transition. It marked the peak of a greenhouse world, the hottest interval in the last 541 million years.

Atmospheric carbon dioxide soared and ocean circulation faltered. Vast parts of the ocean floor became anoxic (deprived of oxygen) making life impossible for many marine species.

Nutrients like sulphur and iron were thrown out of balance. These shifts cascaded throughout the food web. As Fischer’s team suggests, this extreme climate moment destabilized the entire marine ecosystem, especially at the top where large predators thrived.

Top predators faced a deadly filter

Valentin Fischer and his colleagues aimed to understand how this transition shaped marine reptile evolution. To do so, they built a comprehensive dataset.

The researchers studied the evolutionary relationships of hundreds of marine reptile species, mapping which groups went extinct and when. Then, they compiled the largest collection to date of two-dimensional and three-dimensional anatomical data on marine reptiles.

The team combined data on the phylogenetic relationships of hundreds of marine reptile lineages to analyze how extinctions were distributed in the tree of life.

Then, they used the largest sample of 2D and 3D data on marine reptiles ever assembled to analyze the effect of these extinctions on the predatory capabilities of Cretaceous marine reptiles.

“Our analyses showed that the Cenomanian-Turonian transition is associated with elevated rates of extinction and that these extinctions disproportionally targeted some groups of large and fast predators, in a stepwise manner,” said Fischer.

New marine predators hunted differently 

What does it mean for a predator to disappear from an ecosystem? Not just an empty niche, but a major change in how animals hunt, compete, and survive.

Fischer’s study found that predator skulls from before and after the transition had markedly different shapes. This affected feeding behavior in a fundamental way.

For example, skull shapes of predators were significantly different after the transition, notably resulting in distinct bite force, said Fischer.

This means that while new predators took over, they hunted differently. Some may have focused on smaller prey, while others developed crushing bites for armored victims. The loss of long-distance fast swimmers, like ichthyosaurs, opened the door for other body plans and strategies.

The end of one era sparked another

The extinction of familiar marine predators didn’t signal the end of danger in the seas. It marked a rebirth. Mosasaurs surged in diversity and size, eventually becoming the new apex predators.

Sharks too adapted, evolving faster and with more varied diets. The marine ecosystems of the Late Cretaceous looked different not just in species but in structure and dynamics.

This was not merely evolution marching on. It was evolution restructured by crisis. An environmental shock turned the oceans into both a graveyard and a cradle. Out of loss came transformation. Understanding these moments helps us grasp how life on Earth responds to extreme climate events.

The research was presented at the European Geosciences Union General Assembly (EGU 2025).

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