Before the Meg, there was a whale. Basilosaurus isis may not have dentition as fearsome as the famed Megalodon, but it was the apex predator of the late Eocene, say paleontologists reporting in PLOS One on the remarkably preserved skeleton of one, found in Egypt. It apparently had telltale skeletons of other animals featuring bite marks – notably on their heads, in the area of what had been its stomach.
An apex (or top) predator is at the top of an ecological pyramid, explains co-author Manja Voss of Berlin’s Natural History Museum. It preys on “lower” animals, which may be other predators, scavengers or plant eaters. They don’t get eaten themselves, either, because they’re the biggest in town and are usually widely distributed, she adds.
Basilosaurus was apparently not only the biggest carnivore in the paleo-heap of its time. The whale bit babies of other whale species in the head, presumably to kill them more efficiently. Before you condemn the extinct marine predators as inhumane or unwhaley, note that the adorable orca – favorite of Sea Worlds everywhere – does exactly the same. Orcas congregate in the calving grounds of sperm whales to eat the kids.
Apropos orcas, Voss points out that apex predators like Basilosaurus usually have specific morphological features like sharp teeth and a long, powerful snout. Orcas are also apex predators, but where they lack sheer bulk and don’t have the biggest teeth in the ocean, they use strategy: They hunt in packs.
The remains of the adult Basilosaurus in question was found in Wadi Al-Hitan, Egypt, of all places. That may surprise contemporaries but not paleontologists, because back in the Eocene – around 56 to 33 million years ago – that area had been a shallow sea. In fact, the name of the site in Cairo, in Arabic, means “Valley of Whales” and is rich in marine fossils.
Voss points out, however, that Basilosaurus got about. B. isis remains have been in North Africa and Jordan; B. cetoides has been found in Atlantic Ocean deposits bordering the Gulf of Mexico to Tethys Sea deposits in western Egypt.
Asked how they identified the Basilosaurus as a whale and not some other marine monster, especially as it had feet, Voss explains that it had distinctive thick, dense tympanic bulla in its ear and whale-type teeth. "Early whales had legs," she shares with Haaretz. "Originally, they were land-dwelling mammals that returned to the sea. The line of basilosaurids, the group that includes Basilosaurus and Dorudon, went extinct, but they are close relatives of modern whales, which no longer have legs."
To be clear, Basilosaurus predated the Megalodon mega-shark of recent cinematic fame. Megalodon swarmed the oceans from the Miocene to Pliocene, about 17 to 2.6 million years before the present, Voss kindly explains.
There were a couple of Basilosaurus species: Basilosaurus isis was about 15 to 18 meters (49 to 59 feet) in length and Basilosaurus cetoides was a bit bigger, about 17 to 20 meters in length – which is roughly the same size as the dread “Meg.” We think.
“These are estimates because this shark is mainly known by teeth, which are the basis for body size calculations,” Voss says. “The teeth of Megalodon are known to reach up to 18 centimeters, those of Basilosaurus were somewhat smaller.”
So the dread Megalodon was not, repeat not, a rival to Basilosaurus – but who was? “There were indeed other predators (but not necessarily top predators) like the smaller Dorudon, crocodiles, sawfish, or 5-meter long sharks like Carcharocles sokolowi from which we found a single tooth,” Voss says. “I would rate only [the extinct shark] Carcharocles sokolowi as a potential top predator according to our present-day knowledge, due to its similarities to the recent great white shark, for example, in size.”
Whale on whale
While excavating this Egyptian Basilosaurus isis specimen, the paleontologists found the remains of sharks, large bony fish and, most numerously, bones from Dorudon atrox, a much punier species of ancient whale.
Most of the fish and the Dorudon whale bones showed signs of breakage and bite marks, were fragmented, and tended to be clustered within the body cavity of the B. isis specimen, the authors wrote.
So, it could be that the Dorudon had scavenged a dead Basilosaurus, and the fish too, the authors write. The thing is that the Dorudon skeletons were from babies that were still dependent on mother’s milk. Also, they had bite marks on their little fossil heads.
Conclusion: Basilosaurus was an apex predator that – whether or not it also scavenged – hunted and ate its prey live. The fish and Dorudon skeletons in the bone cluster were from its meals.
And for dessert, Voss and her colleagues postulate that like the orca today, which often feeds on smaller whales and frequently hunts humpback calves during humpback calving season – so did the Basilosaurus.
Wadi Al-Hitan back then wasn’t a desert site, it was a warm sheltered marine environment, a protected area similar to a gulf or bay, says Voss – and was therefore possibly a calving site for Dorudons. So during the late Eocene, the Basilosauruses would cluster there and bite the baby Dorudons in the head and eat them. As whales do.