In early 2023, a research team unearthed fossils in the Dominican Republic that reshaped understanding of prehistoric predators in the Caribbean, Reuters reported. The discovery included a tooth and two vertebrae dating back to around six million years ago.
The fossils were found by chance when a work crew was preparing a new roadbed, leading paleontologists to a find, according to Discover Magazine. The tooth closely resembled those of South American sebecids, and the partial remains suggest an animal up to about 7 feet (2 meters) long.
"That emotion of finding the fossil and realizing what it is—that's indescribable," said Lazaro Viñola Lopez, a graduate student in paleontology at the University of Florida and lead author of the research, according to Reuters.
Until now, the most recent fossils of sebecids were found in Colombia and dated to about 10.5 to 12.5 million years ago. The Dominican Republic fossils date to about 5 to 7 million years ago, indicating that sebecids existed five million years longer than previously thought.
After the demise of the dinosaurs following an asteroid strike 66 million years ago, mammals became Earth's dominant land animals, while sebecids—land-living crocodiles that are cousins of today's crocodiles and alligators—became apex predators in South America, Reuters reported. Sebecids were at the top of the food chain during the age of mammals, alongside terror birds and saber-toothed marsupials. Terror birds were giant flightless birds up to about 10 feet (3 meters) tall with hooked beaks.
Sebecids were tall, crocodile-like species that replaced dinosaurs as apex predators, with the largest reaching roughly 20 feet (6 meters) long. They differed from contemporary crocodiles in that they lived primarily on land. They used their long limbs to sprint after prey and had longer legs and a more upright stance, capable of running to chase down prey.
Sebecids had a narrow and deep skull, superficially resembling that of a meat-eating dinosaur. Their teeth were similar to those of carnivorous dinosaurs, and like many other crocodiles, sebecids had protective armor made of bony plates called scutes embedded in their skin.
About 30 years ago, researchers discovered two serrated teeth in Cuba dating back about 18 million years, building on a series of fossil discoveries across the islands, Newsweek reported. A similar 29-million-year-old tooth was found in Puerto Rico, compounding the enigma of the Caribbean's predatory history. However, neither the Cuban nor the Puerto Rican fossil could definitively show what particular predator reigned atop the Caribbean food chain. Put together, the fossils were suggestive but far from enough to identify the particular animal from which they had come, Newsweek reported.
The discovery may support the hypothesis that a pathway of temporary land bridges or a chain of islands once connected the mainland to the Caribbean islands, which sebecids may have crossed. "The distance between the islands and northern South America was significantly shorter than what it is today. This likely facilitated the dispersal of sebecids from South America," Viñola said. The researchers stated that sebecids would have had difficulty swimming across from South America to what is today the Dominican Republic, suggesting land routes were essential for their migration.
"It is amazing to think that these fast-moving, dinosaur-like terrestrial crocs with serrated teeth specialized for cutting meat survived in the Caribbean hunting sloths, rodents, and whatever else was around up until just a few million years ago," said Jonathan Bloch, curator of vertebrate paleontology at the Florida Museum of Natural History at the University of Florida and study co-author.
"This shows how important islands can be as a biodiversity museum, preserving the last members of some groups that have gone extinct everywhere," Viñola said. The theory that islands often provide a haven for species that go extinct elsewhere fits with the observations regarding sebecids, Discover Magazine reported. The lack of easy access for competition allowed sebecids to remain top predators in the Caribbean.
The sebecid find in the Dominican Republic may serve as a catalyst for paleontologists to dig deeper in the Caribbean, Discover Magazine reported. Paleontologists working in the region have primarily focused on caves, but as construction activities increase, other mysteries may emerge or be resolved. "The sebecid is only the tip of the iceberg," Viñola said, according to Discover Magazine.
"The presence of a large predator is really different than what we imagined before—and it's exciting to think about what might be discovered next in the Caribbean fossil record as we explore back further in time," Bloch concluded.
The research paper is titled "A South American sebecid from the Miocene of Hispaniola documents the presence of apex predators in early West Indies ecosystems" and was published in the Proceedings of the Royal Society B: Biological Sciences.
The article was written with the assistance of a news analysis system.