Rise of European Carnivores Driven by Climate Change, Not Competition, Study Finds

Cats, dogs, and bears rule the predator world today, but for tens of millions of years, their ancestors were minor players. A new study tracking the body sizes of ancient meat-eating mammals across Europe suggests that the story of how these animals eventually rose to dominance is far more complicated than scientists once believed, and that a long-popular explanation may simply be wrong.

For decades, the leading theory held that the group of mammals that gave rise to modern carnivores, including cats, dogs, bears, and seals, outcompeted a rival group of now-extinct predators called hyaenodonts during the Eocene epoch, roughly 56 to 34 million years ago. Under this framework, carnivorans were simply better built for the job, and the contest ended with one group winning and the other losing. But that picture was drawn almost entirely from fossils found in North America. When researchers turned to the European fossil record, they found a very different story.

A team of paleontologists examined 155 species of ancient predatory mammals from Europe, tracking how their body sizes changed from about 57 million years ago to about 23 million years ago. Rather than a clean case of competitive replacement, they found that climate shifts appear to be associated with which animals got bigger and diversified, a result that questions the idea that competition alone explains the outcome. The study was published in the journal Biology Letters.

How Climate Change Reshuffled Ancient Carnivores in Europe

Around 40 million years ago, Earth went through a brief but intense warming period. In Europe, this warming reshaped habitats, pushing them toward drier, more open landscapes. New large predators arrived from Asia and Africa, mixing with species already living across the region.

What the researchers found was telling: right around this warming event, the range of body sizes among carnivore ancestors in Europe expanded markedly. Before this period, most of these animals were small, generally under 2 kilograms. Afterward, their sizes ranged from roughly 300 grams all the way up to 28 kilograms. The rival hyaenodonts, meanwhile, showed no equivalent expansion in their size range, and no collapse either. That pattern is not what a competitive squeeze-out would produce.

“The observed BM patterns therefore do not follow the expected double-wedge pattern of competitive replacement,” the authors wrote, referring to a classic model in which one group’s rise mirrors another group’s decline.

Europe and North America Tell Opposite Stories

One reason this study stands out is the direct comparison it draws between Europe and North America. In North American fossils, carnivore ancestors rose to ecological dominance considerably earlier, by roughly 16 million years, even though both groups entered the fossil record on both continents at about the same time. Some previous research found North American patterns more consistent with competitive pressure on hyaenodonts. In Europe, the story played out very differently.

Body size patterns on the two continents also diverged. In North America, the widest variety of predator body sizes appeared early, during the first half of the Eocene, and then leveled off. In Europe, that expansion came later, tied to the warming event around 40 million years ago. Crucially, that steadiness among European hyaenodonts, contrary to the North American pattern, hints that the two groups may have divided the landscape by size and diet rather than directly displacing each other, though body-mass data alone cannot confirm the interpretation.

The Real Driver Behind the Rise of Modern Carnivores

So when did hyaenodonts actually disappear from Europe? Not when carnivore ancestors expanded their size range, but roughly 7 million years later, during a dramatic global cooling event around 34 to 33.5 million years ago. That event brought large-scale glaciation, plummeting temperatures, shifts in ocean currents, and changes in land connections between Europe and Asia that fundamentally restructured ecosystems. Native European hyaenodonts went extinct progressively through this upheaval, and carnivore groups from Asia and Africa moved in to fill the void.

Nothing in the body-mass record supports a simple picture in which hyaenodonts were pushed out by their competitors. Their decline and disappearance instead coincided with major environmental upheaval, extinctions, and migrations that reshaped Europe’s predator communities. By the middle of the Rupelian age, roughly the early Oligocene, the largest carnivore ancestors in Europe were outweighing the largest remaining hyaenodonts, reaching body masses close to 100 kilograms.

Even the statistical models the team used, which tested several scenarios of how body size changes over time, failed to detect a sustained directional push in either group consistent with one driving out the other. Body size ranges fluctuated while average sizes stayed relatively stable, a pattern that fits poorly with classic competition models.

Rather than a battle with a winner and a loser, the authors suggest that carnivore ancestors and hyaenodonts may have simply coexisted for millions of years, each responding to their environments independently, until climate change tipped the scales for good. To describe this, they borrow a phrase from a famous 1980 study comparing the ancient fates of clams and brachiopods, two groups of shelled marine animals: the two groups of predators were, in essence, “ships that pass in the night.”

That framing carries real weight. In Europe, carnivoran mammals eventually came out on top, but according to this research, their dominance there had less to do with being better competitors and more to do with being in the right place when the climate shifted. Their ecological rise in Europe may be less a trophy of evolutionary combat than the outcome of ecological upheavals that unfolded alongside major shifts in ancient climate.

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