Most people, when conjuring an image of crocodiles, alligators, or gharials, picture hulking, scaly reptiles lurking in muddy waters—menacing relics from a prehistoric past. To the casual observer, crocodilians appear to be “living fossils,” creatures that have slithered through time largely unchanged since the Mesozoic Era. But that image, long entrenched in popular imagination and even among some biologists, is being shattered by a sweeping new study led by researchers from the University of Central Oklahoma and the University of Utah. The truth, as it turns out, is far more fascinating: crocodilians are not stagnant survivors—they are shape-shifting marvels of evolutionary resilience.
This research peels back the curtain on over 230 million years of history, revealing that today’s crocodilians are merely the surviving tip of an evolutionary iceberg—a remnant of a once-dizzyingly diverse lineage known as crocodylomorphs. These ancient relatives weren’t just swamp-dwellers waiting for prey. They were fast-moving land predators, herbivores, ambush hunters, even generalists with flexible diets and lifestyles that may have been the key to their astonishing survival across two of Earth’s most dramatic mass extinction events.
Crocodylomorphs: The Ancestors That Endured Chaos
Crocodylomorphs emerged in the Late Triassic, around 230 million years ago, as a sub-group within Pseudosuchia, a broad clade that includes both the ancestors of modern crocodilians and a wide range of extinct relatives. The earliest crocodylomorphs bore little resemblance to today’s crocodiles. Many were terrestrial, with long legs and upright gaits more akin to dogs than lizards. They occupied ecological roles that ranged from predator to plant-eater to opportunistic scavenger.
What separates crocodylomorphs from the many other pseudosuchians of their time is not just their evolutionary lineage, but their astounding flexibility—especially when it came to diet. That flexibility may have made all the difference when the end-Triassic mass extinction wiped out up to 75% of species, including all other non-crocodylomorph pseudosuchians. The generalist crocodylomorphs, capable of surviving on a wide range of food and adapting to multiple habitats, emerged from the carnage and began a long journey of ecological innovation.
After the Fire: The Explosion of Crocodilian Ecologies
Following the end-Triassic extinction, crocodylomorphs diversified with a vengeance. They radiated across land and water, assuming roles we rarely associate with crocodilians today. There were land-based hypercarnivores with slicing teeth. There were herbivores with crushing molars, and even burrowers that adapted to digging. Some were sleek runners, while others were stocky ambush predators. Their forms mirrored a zoological kaleidoscope: some resembled wolves, others were more pig-like, some even mimicked the functions of birds or small dinosaurs.
By the Jurassic and Cretaceous periods, crocodylomorphs were thriving in ecosystems worldwide. They lived in rivers and oceans, on plains and in forests, adapting to whatever the environment demanded. Their diversity rivaled that of early mammals and surpassed it in some ecosystems.
This “bananas” burst of forms and lifestyles, as lead researcher Keegan Melstrom colorfully described, persisted for millions of years—until a long, slow decline began to set in during the Late Cretaceous. For reasons not entirely understood, even the adaptable terrestrial generalists began to vanish. Only two major ecological forms weathered the second great planetary extinction: the semiaquatic generalists and a few aquatic carnivores. When the asteroid impact at the end of the Cretaceous drove non-avian dinosaurs to extinction, these few crocodylomorph survivors were among the few large reptiles to live on.
Unlocking the Secrets of Ancient Diets
Understanding why some crocodylomorphs lived while others vanished required an enormous investigative effort. The research team embarked on a global fossil expedition—both physically and intellectually. Over seven countries and four continents, they examined fossil skulls and jaws, scrutinizing the telltale clues etched in bone.
Teeth are remarkably honest historians. The sharp, blade-like dentition of a predator tells of flesh-tearing meals, while flat, grinding surfaces suggest a life of chewing tough plants. Skull shape determines bite force and range of motion. Together, these clues allow paleontologists to reverse-engineer the diets and ecological roles of long-extinct animals. The researchers analyzed 99 extinct crocodylomorph species and 20 living crocodilian species, comparing them with over 130 species of mammals and lizards to construct a detailed database of dietary ecology.
What emerged was a tapestry of dietary possibilities far richer than anyone had expected. Early crocodylomorphs filled ecological roles that today are occupied by very different animal groups. One might be a plant-munching herbivore akin to a beaver. Another, a fast terrestrial predator echoing the habits of a cheetah. The adaptability in feeding styles—and, by extension, in ecological niches—was stunning.
Why Generalists Survive While Specialists Perish
The study reinforces a growing recognition in paleobiology: generalists, animals that can live in many environments and eat a wide variety of foods, are more likely to survive planetary-scale catastrophes than specialists. This concept has been largely shaped by research into mammalian survival, but this is the first time it has been rigorously applied to the crocodylomorph lineage.
Whereas many mammal groups earned their reputation for resilience by thriving in a variety of habitats and consuming diverse diets, crocodylomorphs had been underestimated. “There’s been a bias in extinction studies toward mammals,” said co-author Randy Irmis, paleontologist at the Natural History Museum of Utah. “But crocodilians are just as informative, and perhaps more ancient in their evolutionary lessons.”
During both the end-Triassic and end-Cretaceous events, the pattern repeated: those crocodylomorphs that could switch diets and shift habitats survived. Hyper-specialists—creatures fine-tuned to narrow conditions—went extinct.
It’s a valuable lesson for today’s biodiversity crisis. As Earth’s climate warms, as ecosystems fragment under human influence, and as extinction rates soar, the traits that once protected crocodylomorphs might offer clues to which species will make it through the current upheaval.
Echoes in Today’s Crocodilians
All living crocodilians—whether the American alligator of the Everglades, the Nile crocodile of Africa, or the critically endangered gharial of India—belong to a narrow lineage of semiaquatic generalists. These animals, while appearing conservative in behavior and form, carry the evolutionary DNA of a once fantastically adaptable family.
They still display a surprising amount of dietary flexibility. Juveniles will eat whatever fits in their mouths: insects, snails, small fish. Adults, too, are opportunists—taking everything from fish and amphibians to mammals and, occasionally, carrion. This behavioral elasticity may be a living echo of the adaptability that once allowed their ancestors to survive global catastrophes.
Yet today’s crocodilians face new threats—ones they can’t simply evolve their way out of. Habitat destruction, pollution, poaching, and climate change are eroding the environments where they have thrived for millions of years. Species like the Cuban crocodile and the gharial, already critically endangered, are now fighting a battle that might not be winnable without human intervention.
What Evolution Teaches Conservation
It’s tempting to romanticize the survival of crocodilians as destiny, as though sheer toughness allowed them to bulldoze through extinction events. But the fossil record reveals a more nuanced story. Crocodylomorphs weren’t immune to change—they were attuned to it. They adapted. They shifted gears. They evolved over and over again.
Their survival was not guaranteed. It was earned—through ecological flexibility, evolutionary experimentation, and, at times, sheer luck.
This history provides both a warning and a guide. “If species today show generalist tendencies,” said Irmis, “they might be more resilient. But it’s no guarantee. We need to preserve their habitats if we want to give them that chance.”
It’s a caution wrapped in awe. For hundreds of millions of years, the crocodilian lineage has weathered the worst the planet could throw at it. Its record of survival is not a badge of invincibility, but a lesson in the value of adaptability—one that modern humans, stewards of Earth’s sixth mass extinction, would do well to heed.
A Legacy Carved in Bone and Water
To understand crocodilians is to understand a story longer and more complex than humanity’s own. It’s a saga of survival, innovation, and change. While we often think of them as relics, frozen in time, they are in fact dynamic survivors of a deep and branching evolutionary history.
Next time you see one gliding silently through murky water or basking on a riverbank, remember: this creature’s ancestors outlived monsters, meteorites, and millennia. They adapted, reinvented themselves, and held on while entire worlds crumbled.
What survives today may seem uniform, but beneath that leathery skin lies the legacy of an empire that once ruled in many forms. And if we play our cards right, it’s a legacy that might continue into a future where adaptability once again defines survival.
Reference: For a while, crocodile: crocodylomorph resilience to mass extinctions., Palaeontology (2025). DOI: 10.1111/pala.70005