What a Croc!

About once every other month, I have a nightmare about being stalked by a giant crocodylian. I blame Alligator. The 1980 horror movie – which is surprisingly good for a Jaws-wannabe – was a near-constant presence on television when I was a kid. The gory spectacle immediately became one of my favorite creature features, and my dreams have been haunted by enormous, snap-jawed alligators ever since.

My love of prehistory only fueled the nightmares. Books and museum displays taught me that oversized alligators were not just Hollywood inventions. During the Late Cretaceous, over 73 million years ago, the roughly 40-foot alligatoroid Deinosuchus crushed unwary dinosaurs in its jaws. These monsters were real. A full-sized reconstruction of the amphibious predator is on display at the Natural History Museum of Utah, and the skeleton looks every bit as nightmarish as the monsters that lurk in the back of my sleeping mind.

But enormous crocodylians were not just a thing of the distant past. Species larger than any modern croc lived relatively close to us in time, and even overlapped with our close ancestors and cousins. Paleontologists Christopher Brochu and Glenn Storrs have just named one such creature that hid in the rivers and lakes of prehistoric Kenya between 2 and 4 million years ago.

Brochu and Storrs named the predator Crocodylus thorbjarnarsoni. The animal was an older cousin of Africa’s modern Nile crocodile (Crocodylus niloticus). But the fossil crocodile was larger. While the biggest Nile crocodile ever recorded was a little short of 21 feet, Crocodylus thorbjarnarsoni may have been over 27 feet long. If the estimates of Brochu and Storrs are correct, the newly-named fossil form was the largest species of Crocodylus ever.

Granted, that’s not as gargantuan as Deinosuchus, but a 27-foot crocodile would have surely been scary enough for the prehistoric humans of the Turkana Basin. As Brochu and Storrs lay out in the abstract of the paper describing the crocodile, “[Crocodylus thorbjarnarsoni] would have been the largest predator in its environment, and the early humans found in the same deposits were presumably part of its prey base.”

At least some prehistoric crocodiles snagged humans from time to time. Two years ago, Brochu and a different set of collaborators described a roughly 1.8 million year old “horned” crocodile they named Crocodylus anthropophagus. This croc – which reached lengths of 25 feet or more – was found in the same deposits as Homo habilis and Paranthropus boisei, and was probably the carnivore responsible for distinctive toothmarks on the bones of prehistoric humans found at Olduvai Gorge. We’re lucky to have those frightening traces.

When feeding, crocodylians violently disarticulate carcasses of large prey so that they can horf down chunks of flesh and bone. More than that, the digestive acids of crocodylians are quite strong and can break down bone. There would be little left of any human consumed by the prehistoric archosaurs. If Crocodylus thorbjarnarsoni really did catch or scavenge humans, as it probably did, we’re not likely to find much evidence of those meals.

But there’s more to the new paper than the destructive powers of the huge fossil crocodile. Brochu and Storrs also investigated the record of the genus Crocodylus in Africa. For years, crews searching for early humans considered the crocodile fossils they found to be Nile crocodiles or direct predecessors of the modern species. This isn’t the case. While the big picture of crocodile relationships is in flux, it seems that Crocodylus anthropophagus and Crocodylus thorbjarnarsoni were close relatives, but neither was a direct ancestor of the modern Nile crocodile. Given what we know now, Brochu and Storrs note, the genus Crocodylus first appeared in Africa about 7 million years ago, followed by an unfolding of different forms that is still being untangled. The Nile crocodiles that wait in ambush today are a fragment left over from a radiation of equally frightening prehistoric species.

References:

Brochu, C., & Storrs, G. (2012). A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of Crocodylus in Africa. Journal of Vertebrate Paleontology, 32 (3), 587-602 DOI: 10.1080/02724634.2012.652324