How Ancient Crocodile-Like Predators Ruled the Islands of the Caribbean
NHM's scientist discovers that sebicids, ancient land-dwelling crocodile-like beasts, reigned over the West Indies as apex predators after vanishing from South America
Published April 29, 2025
Dinosaurs (at least the ones that weren’t birds) were gone by the start of the Age of Mammals, but fierce predators stalked ancient South America. Diverse carnivores like huge snakes and terror birds, along with enormous caimans, and land-dwelling relatives to crocodiles—the sebicids—hunted across the continent. While South America had more than its share of nightmare-fueling beasts, whether or not an apex predator hunted on the islands of the Caribbean was unknown—until now.
Filling an apex predator-sized hole in the islands’ prehistory, an international team of researchers (including NHM’s Dr. Jorge Velez-Juarbe) published a new study in the journal Proceedings of the Royal Society B detailing the first definitive proof that sebicids reined in the islands of Cuba, Dominican Republic, and Puerto Rico, during the Age of Mammals millions of years after the terrestrial crocodile-like predators went extinct on the mainland. What’s more, the discovery makes clear how these ancient hunters reached the islands in the first place: they probably walked.
“We were thrilled when we found the teeth in the field in Puerto Rico and the Dominican Republic,” says co-author Dr. Jorge Velez-Juarbe of the Natural History Museum of Los Angeles County. “But it was the moment we identified the vertebrae that confirmed our discovery beyond doubt—we had found Caribbean sebecids!”
Sebecids split from crocodiles during the Jurassic and survived the mass extinction that claimed the dinosaurs. Their skulls were more like meat-eating theropod dinosaurs than their modern crocodilian relatives, they had a gait more like a mammal, and longer legs along with other adaptations for hunting on land. Analysis of their teeth from South America shows that sebecids sat at the top of the food web, dining on an array of terrestrial mammals.
Their discovery on the islands upends more than a century of debate about how vertebrates made their way to the West Indies, suggesting that these ancient land-dwelling creatures walked from the continent along with the diverse menagerie of life in the ancient West Indies.
The international research team made the definitive identification through fossilized vertebrae and multiple teeth from Cuba, Dominican Republic, and Puerto Rico. The specialized saw-like teeth—serrated for rending flesh—clearly identified the specimen as a crocodile relative, but three different groups had independently evolved these specialized teeth, so identifying the ancient croc was difficult at first. The team compared CT scans of the specimens with fossil records from the West Indies, North and South America, and taking into account the geographical and geologic timelines it was highly suggestive they were looking at sebecids. While the teeth shared many characteristics, it was the vertebrae that confirmed their identity as belonging to sebecids.
The study marks the first record of a sebecid outside of South America in the Cenozoic—the Age of Mammals that began roughly 66 million years ago. While sebecids date back to the Cretaceous and survived the asteroid and subsequent mass extinction of the dinosaurs, they finally died off in South America around 11 million years ago due to changing climate and vanishing habitats. Surprisingly, the study finds they survived considerably longer in the ancient Caribbean.
“Much like their counterparts on land, apex predators on islands are crucial for preserving ecological balance among native and endemic species,” says Dr. Velez-Juarbe “Throughout Earth’s history, crocodiles and their extinct relatives have filled this role time and again across both continents and islands. Discovering that sebecids once reigned as apex predators in the Caribbean was an exciting surprise!”
Walking to Island Refuges
The lack of an apex predator in the West Indies had fueled the argument against a land connection between ancient South America and the West Indies, but the discovery supports a journey overland for the islands’ vertebrates. Just as rising sea levels reshape our modern coasts, the ancient Caribbean was subject to changes in global sea level which, combined with the rising of regional landmasses, resulted in a path for South American vertebrates to cross into the West Indies resulting in the diverse life found on the islands. Researchers argue that local tectonic events combined with lower sea levels cleared the path around 33 million years ago, whether that connection was through a continuous landspan or a closely spaced group of islands is still up for debate, but the presence of an apex predator adapted to life on land makes the former argument more likely.
Sebecids would have shaped life in the West Indies both in their presence and absence. Islands have a long and well-known track record as safe harbors for species that die off on the mainland, acting like natural biodiversity museums. While climate change and habitat loss claimed their continental relatives, sebecids on the West Indies hung on for at least five million more years. As the last of the sebecids vanished from the West Indies, their last stop before exiting the planet, other predators arrived to fill the void over the intervening millions of years, reshaping the food web into the one we know today.
“We’ve long suspected that crocodyliforms played a far more significant role in shaping the ecology of ancient West Indian faunas throughout the Cenozoic, but much of their story remains untold,” says Dr. Velez-Juarbe. “Fieldwork in the tropics can be demanding but highly rewarding, so we are fully committed to continuing our explorations across the Greater Antilles. Who knows what other surprises await us, helping to unravel the complex origins of the Greater Antillean terrestrial fauna?”
