Crocodile-Like Creatures Survived in the Caribbean, Outlasting Their Mainland Relatives

A recent discovery of fossils in the Dominican Republic has shed light on the extinction timeline of sebecids, a crocodile-like group of reptiles. These findings indicate that these resilient predators survived as recently as 4.5 million years ago, significantly later than previously believed.

Published in the journal Proceedings B of the Royal Society on April 30, this research alters the understanding of ancient Caribbean ecosystems. The Age of Reptiles ended approximately 66 million years ago with the mass extinction that wiped out non-avian dinosaurs, ushering in an era dominated by mammals. In South America, however, sebecids continued to thrive long after the dinosaurs’ demise, becoming top predators well into the Cenozoic Era.

Characterized by their long limbs and blade-like teeth, sebecids differed from modern alligators and crocodiles, suggesting they hunted on land much like theropod dinosaurs. These formidable reptiles, however, went extinct in South America around 10 million years ago.

According to Christopher Brochu, a vertebrate paleontologist at the University of Iowa who did not participate in this research, the idea of witnessing these creatures in their natural habitat is fascinating. The discovery of sebecid fossils post-Cretaceous primarily in South America and parts of Europe had been documented, but intriguing serrated teeth were also found across the Caribbean, leading to some uncertainty about their origin.

During a field study in the Dominican Republic led by vertebrate paleontologist Lazaro Viñola López, the team uncovered vertebrae and serrated teeth that strongly suggested the presence of sebecids. Notably, the anatomy of their vertebrae, flattened in sebecids compared to other crocodilian relatives, confirmed their identification.

Remarkably, the recently found tooth measures about 12 millimeters in length and is believed to belong to a late surviving sebecid species. This finding marks the first evidence of sebecids in the Caribbean, with the possibility that other teeth discovered on nearby islands belong to the same group. These teeth date back as far as 29 million years, during which other reptiles with similar adaptations had already vanished from adjacent continents.

The vertebrae and tooth from the Dominican Republic are significantly younger, between 4 and 7 million years old, indicating that sebecids persisted in the Caribbean long after their South American relatives had disappeared. They serve as the last known representatives of the notosuchians, a broader group of reptiles originating in the Jurassic Period.

Jonathan Bloch, a vertebrate paleontologist involved in the research, expressed astonishment over the implications. As the fossil record on Caribbean islands stretches back to the Age of Dinosaurs, these findings challenge existing paradigms regarding the historical presence of land predators in the region.

The sebecids may have made their way to the Caribbean via ancient land bridges or through vegetation rafts. The islands once hosted diverse fauna, including gharials, large rodents, sloths, and even monkeys, now absent from the region.

This discovery has broader implications for understanding the evolutionary trajectory of Caribbean species. Researchers had previously assumed that the absence of land predators allowed various now-extinct birds to evolve towards ground-dwelling and even flightless forms. Evidence of sebecids, potentially reaching lengths of two meters or more, complicates this narrative, particularly given the much larger species like Barinasuchus, which could reach ten meters and weigh nearly two tons.

Pedro Godoy, a vertebrate paleontologist at the University of São Paulo, remarked that the findings highlight the significant role that these reptiles played in past ecosystems until their eventual extinction, countering assumptions that link them strictly to prehistoric eras prior to the Cretaceous mass extinction.