Going for a stroll Carnivorous crocodile-like monsters used to terrorize the Caribbean While low sea levels helped sebecids spread, rising waters left them isolated. Elizabeth Rayne – May 16, 2025 1:10 pm | 21 Credit: By Ghedoghedo, CC BY-SA 3.0 Credit: By Ghedoghedo, CC BY-SA 3.0 Story text Size Small Standard Large Width * Standard Wide Links Standard Orange * Subscribers only   Learn more How did reptilian things that looked something like crocodiles get to the Caribbean islands from South America millions of years ago? They probably walked. The existence of any prehistoric apex predators in the islands of the Caribbean used to be doubted. While their absence would have probably made it even more of a paradise for prey animals, fossils unearthed in Cuba, Puerto Rico, and the Dominican Republic have revealed that these islands were crawling with monster crocodyliform species called sebecids, ancient relatives of crocodiles. While sebecids first emerged during the Cretaceous, this is the first evidence of them lurking outside South America during the Cenozoic epoch, which began 66 million years ago. An international team of researchers has found that these creatures would stalk and hunt in the Caribbean islands millions of years after similar predators went extinct on the South American mainland. Lower sea levels back then could have exposed enough land to walk across. “Adaptations to a terrestrial lifestyle documented for sebecids and the chronology of West Indian fossils strongly suggest that they reached the islands in the Eocene-Oligocene through transient land connections with South America or island hopping,” researchers said in a study recently published in Proceedings of the Royal Society B. Origin story During the late Eocene to early Oligocene periods of the mid-Cenozoic, about 34 million years ago, many terrestrial carnivores already roamed South America. Along with crocodyliform sebecids, these included enormous snakes, terror birds, and metatherians, which were monster marsupials. At this time, the sea levels were low, and the islands of the Eastern Caribbean are thought to have been connected to South America via a land bridge called GAARlandia (Greater Antilles and Aves Ridge). This is not the first land bridge to potentially provide a migration opportunity. Fragments of a single tooth unearthed in Seven Rivers, Jamaica, in 1999 are the oldest fossil evidence of a ziphodont crocodyliform (a group that includes sebecids) in the Caribbean. It was dated to about 47 million years ago, when Jamaica was connected to an extension of the North American continent known as the Nicaragua Rise. While the tooth from Seven Rivers is thought to have belonged to a ziphodont other than a sebacid, that and other vertebrate fossils found in Jamaica suggest parallels with ecosystems excavated from sites in the American South. The fossils found in areas like the US South that the ocean would otherwise separate suggest more than just related life forms. It's possible that the Nicaragua Rise provided a pathway for migration similar to the one sebecids probably used when they arrived in the Caribbean islands. Walking the walk So how did sebecids get from one land mass to the other on foot? They were made for it. Sebecids evolutionarily diverged from crocodiles during the Jurassic period. They had skulls similar to those of theropod dinosaurs, with a high rostrum (which holds the teeth along with the palate and nasal cavity) that was long and narrow. Their mouths were full of ziphodont teeth, which are compressed along the sides and have a serrated edge made for tearing flesh. Most important among the adaptations that made sebecids terrestrial animals were legs longer than their crocodilian brethren—legs made for walking on land. “Considering their terrestrial adaptations, their dispersal may have been either facilitated by some ephemeral terrestrial connection or string of large and closely spaced islands or occurred on a natural raft,” the research team said in the same study. Though they have been found across South America, earlier specimens of sebecids are best documented in the south of the continent, while later specimens surfaced in the north and tropical zones. Both the ziphodont teeth and concave vertebrae are found among the fossils found in the Dominican Republic, Cuba, and Puerto Rico, giving them away as sebecids. The locations of the fossils are consistent with the types of environments these carnivores were thought to inhabit as the Eocene gave way to the Oligocene. After they ended up in the Caribbean, the original population of sebecids eventually became isolated as sea levels rose, leaving the sub-populations on islands surrounded by water. The sebecids were apex predators in South America and are thought to have stayed at the top of the food chain in their new hunting grounds. Some sebecid remains have been found with fossils of terrestrial and semiaquatic vertebrates, such as sloths and turtles, that supposedly were their prey. Not only did sebecids get around, but they also lasted 5 million years longer in the Caribbean than they did in South America. This might have been because certain plant and animal species that died out on the mainland continued to survive on the islands. Crocodiles and predatory birds took over as apex predators after the sebecids died out. Even with a mouth full of knives, you can’t be at the top forever. Proceedings of the Royal Society B, 2025.  DOI: 10.1098/rspb.2024.2891 Elizabeth Rayne Elizabeth Rayne is a creature who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. She lurks right outside New York City with her parrot, Lestat. When not writing, she is either shapeshifting, drawing, or cosplaying as a character nobody has ever heard of. Follow her on Threads and Instagram @quothravenrayne. 21 Comments