The ancient lineage that survived the end-Triassic extinction

Nature · Published 19 October 2026 Swipe more like this →

In short: Modern crocodiles are just the surviving remnants of a much more diverse group. Once home to massive predators and upright-walking ancestors, the Crocodylomorpha have navigated radical evolutionary shifts, from terrestrial hunters to marine specialists, over hundreds of millions of years.

The Crocodylomorpha lineage represents a remarkable evolutionary success story. While modern crocodilians are primarily known as aquatic ambush predators, their ancestors were far more ecologically varied. The earliest members, known as 'sphenosuchians,' were slender, small-bodied animals with elongated limbs capable of walking upright. These primitive forms persisted until the end of the Jurassic period. The oldest known member of this group, Trialestes, lived in Argentina approximately 231 to 225 million years ago.

During the Jurassic, the group underwent significant morphological diversification. Some lineages, such as the Thalattosuchia, adapted to marine environments, while others occupied terrestrial niches as herbivores or omnivores. Even into the Miocene, terrestrial groups continued to coexist with their aquatic relatives. The group's diversity was eventually curtailed by the end-Cretaceous extinction event. The Notosuchia were a particularly diverse group inhabiting the Southern Hemisphere during the Cretaceous period. The Sebecidae, which were large predatory members of this group, survived in South America until about 12 million years ago.

Today, the lineage is represented by living species like the Orinoco crocodile (Crocodylus intermedius), a massive predator in the Orinoco River basin. Unlike their extinct relatives, which could reach sizes more than three times that of modern forms, the Orinpect Orinoco crocodile reaches up to 6.7 meters in length. While some extinct members, such as Deinosuchus riograndensis, were giants, the modern survivors face different pressures, including critical endangerment due to habitat loss and historical hunting. An adult Orinoco crocodile can weigh over 400 kg and possesses 68 teeth. While these predators are capable of attacking humans, such rare incidents are infrequent.

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