Still catching up with posts I need to write given that the past two weeks were just major paper after major paper. Given that the last two I did were on the recently named sebecoid Tewkensuchus (more here) and on the unrecognized diversity that slumbers among modern American crocodiles (see here), it sure would be convenient if there was one that sorta ties into both of those....
Oh yeah, what convenient timing for "A South American sebecid from the Miocene of Hispaniola documents the presence of apex predators in early West Indies ecosystems", written by Lázaro W. Viñola López and colleagues and published literally just last night as of the time I'm writing this.
What's this paper about? Simple, the description of sebecid fossil remains from the island of Hispaniola. Sebecids of course being terrestrial crocodile relatives that lived throughout much of the early Cenozoic in South America. The remains admittedly aren't anything to write home about, consisting of two vertebrae and a tooth with the group's iconic blade-like serrated morphology (aka ziphodonty), but the implications are nonetheless quite interesting. Not only is it the best evidence we have for insular sebecids and would have been the islands apex predator, but it also extends the survival of Sebecidae by perhaps up to 5 million years. This means the group might have survived until the Early Pliocene.
The Hispaniola sebecid, tentatively assigned to Sebecus sp., as illustrated by Machuky Paleoart
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
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Duerosuchus is a rather small crocodilian from the Eocene of Spain. When initially described it was placed closely to the clade Brevirostres (Gators and Crocs), but a later phylogenetic analysis found out that it was actually a member of the Planocraniidae.
Planocraniidae is a family of terrestrial crocodilians (or more basal Eusuchians) that lived in Eurasia and America during the Paleocene and Eocene. The family also includes the much larger Boverisuchus magniforns from Germany and Boverisuchus vorax from America, as well as Planocrania from China. Effectively speaking, Boverisuchus is the animal previously known as Pristichampsus, because Pristichampsus was based on fragmentary material that wasn't diagnostic enough. So out with the old, in with the new.
Planocraniids were one of multiple groups of crocodiles inhabiting the Eocene rainforests, adapted to a more running lifestyle with toes tipped by hooves and later ziphodont (compressed and serrated) teeth. At least in Boverisuchus. The teeth of Duerosuchus and Planocrania were already flattened, but not serrated. The other three prominent croc groups in the Eocene jungles of the northern hemisphere were crocodiles, represented by "Asiatosuchus" in Spain, alligatoroids, present with Diplocynodon, and Sebecids, a group thats much more ancient and not part of the crown group of crocodiles. Sebecids are present with Iberosuchus, another terrestrial hunter, but one that was much larger than Duerosuchus. (bottom image by Ortega et al.)
