#sebecus

Now full disclosure, these remains are NOT the first evidence of what could be sebecids from the Caribbean. Previous discoveries include teeth from the early Miocene of Cuba as well as the early Oligocene of Puerto Rico. However, what makes the Hispaniola remains so much more important is surprisingly the presence of vertebrae. Hear me out. Sure, the teeth are iconic and easily identifyable, however, ziphodont teeth are not unique to sebecids and have also evolved independently in more "modern" crocodiles such as planocraniids and mekosuchines. Sure, mekosuchines were definitely not hanging out on Hispaniola and planocraniids are accepted to have died out during the Eocene, but nonetheless this means that ziphodont teeth could also belong to another type of croc. HOWEVER, the vertebrae from Hispaniola are described as amphicoelous, while animals closer to todays crocs would have procoelous  vertebrae. Ergo, ziphodont teeth + amphicoelous vertebrae = sebecid, making these remains the first unambiguous evidence for Caribbean sebecids.

A simplified phylogeny showing the repeated evolution of ziphodont teeth in crocodyliforms while also highlighting the diferences in notosuchian and eusuchian vertebrae.

Case and point for why thats important? Well while the remains from Cuba and Puerto Rico are most likely also sebecids based on their age and geography, there are even older fossil remains of a ziphodont croc from the Middle Eocene of Jamaica. While sebecids were already around back then, so were the planocraniids, hooved crocodile-relatives found across North America and Eurasia. And since Eocene Jamaica has faunal similarities with North America, this particular ziphodont is more likely to be a planocraniid than a sebecid.

While the Cuban and Puerto Rican teeth are likely those of sebecids, the Eocene Jaimacan ziphodont croc could have easily been a planocraniid similar to the widespread genus Boverisuchus, illustrated here by Corbin Rainbolt.

Those that read my post on Tewkensuchus might remember my barely coherent ramblings about how confusing and poorly understood the paleogeography of sebecids is. Well for what its worth, if we ignore all the chaos caused by Europe's part in the equation, the South American history is relatively straight forward. The Paleogene record spans both remains found in the far South as well as Eocene records further north at lower latitudes. It's not entirely clear how sebecids got to the islands, but it is speculated that they could have rafted or even traveled across temporary land bridges that formed at times of lower sea levels. Whatever the case, by the early Oligocene sebecids seem to have made it to Puerto Rico and would have likely been isolated from the mainland and from other island populations when various marine passages opened, splitting the island chains. This may have been a blessing in disguise, as by the Miocene sebecids were restricted to tropical environments at low and mid latitudes and further habitat collapse, tied in part to the disappearance of the Pebas Mega Wetlands, eventually lead to their extinction on the mainland by the early Late Miocene.

But if the fossils from Hispaniola are anything to go by, then they clung onto life for another 5 million years in the Caribbean, retaining their spot as the islands apex predators until possibly as late as the Early Pliocene. Alas, they couldn't evoid extinction forever and unless we find even younger remains the Hispaniola sebecid represents the last hold out of the once diverse group Notosuchia.

Predator guilds and their distribution in South America throughout the Paleogene (a), Neogene (b) and late Quaternary (c).

But in a way, they didn't go without leaving their mark on the island. After sebecids went extinct, there seems to have been a push by native birds towards more terrestrial life, with some species losing the ability to fly alltogether. Some birds of prey seem to have taken up the mantle of terrestrial predator, leading to owls like Ornimegalonyx on Cuba and even the only distantly related Cuban crocodile threw its hat into the ring when it came for the spot of apex predator.

Top: A cuban crocodile hunting a small species of ground sloth, illustrated by Manusuchus Bottom: A general overview of the fauna found on Cuba during the Pleistocene, including flightless birds, cuban crocodiles and terrestrial owls, illustrated by Joschua Knüppe