Today, we know that the Basilosaurus is the first ancient whale humanity has ever found. But back when it was first described, the animal's huge proportions earned it the name of 'king lizard'. And although technically incorrect, the name isn't undeserved; during its day, the Basilosaurus ruled the waters of Tethys with an iron flipper and a really impressive set of teeth.
This creature lived 40 to 35 million years ago, during a part of geologic time known as the late Eocene. The dinosaurs were quite well gone by this time, and mammals were well on the way to dominating the planet. The Basilosaurus was also a mammal -- a whale, no less -- and could grow up to 60 feet (a bit over 18m) in length. Needless to say, you can't skip meals and grow so large. But this species likely had no issues getting full, as the Basilosaurus was, by all indications, a formidable apex predator.
It was first described in 1834 from fragments of a skeleton found in the US. Due to the sheer scale of the fossils, their striking similarity in shape and function to marine predatory dinosaurs, poor availability, and the limits of paleontological understanding of the day, the species was initially assumed to have been a dinosaur -- and christened the 'king of the lizards', Basilosaurus.
The academic story of this genus starts with B. cetoides, the first ancient whale species ever discovered, which was unearthed in Louisiana around 1830 by Richard Harlan and still serves as the type species of Basilosaurus.
Details from the dig and the wider goings-on around the fossils aren't very good from the time, but we do know that bones from this dig were sent to the American Philosophical Society by Judge Henry Bry of Ouachita County, Louisiana and Judge John Creagh of Clarke County, Alabama, according to the Encyclopedia of Alabama. Here, they were examined by Richard Harlan, one of the US's earliest paleontologists and naturalists, who would end up christening the new species.
Upon first examination, Harlan was very excited. Comparing the bones he received to those of Plesiosaurus and Mosasaurus, two species of marine dinosaurs that were already described at the time, he concluded that the new species grew no less than 80–100 ft (24–30 m) long. Still, there were enough structural similarities between its vertebrae and those of Plesiosaurus, as well as between its skull and that of Mosasaurus, for Harlan to assume that the species were related. At the very least, he assumed, they lived around the same time.
The first signs that this name wasn't really spot-on came when Harlan took his specimens to the UK for consultation with his peers there. Richard Owen, a controversial figure but a superb paleontologist, observed that the animal's molars were two-rooted. No known fish or reptile at the time showed the same structure, and Owen suggested the animal might have been a whale instead. The two even agreed to rename it Zeuglodon cetoides ("whale-like yoke teeth").
A few years later the other known species, B. isis, would be described based on fragments of bone recovered from Egypt. Although the first full skeleton of B. isis wouldn't be unearthed until 2016, the discovery of this species and its fossil association with species that were known to have been whales at the time further suggested that all Basilodons were, in fact, mammals. This was helped by the fact that Basilosaurus fossils actually became quite common over time, so much so that in the 19th century they were even used as andirons, furniture, or decoration.
Over the years, paleontologists have wisened up to the fact and tried to change the genus' name. However, zoological naming conventions meant that the original name stuck. Today, the Basilosaurus is the state fossil for Alabama and Mississippi.
How did it used to live?
One thing that Harlan got right about the Basilosaurus was that it was large. This whale was bigger even than some predatory dinosaurs that came before it, and it undoubtedly threw its weight around the ancient, lost sea of Tethys.
Another thing it definitely threw around were bites. Unlike most whales today, Basilosaurus didn't filter feed, it hunted. Its jaws were lined with several types of teeth, including molars and canines, which are specialized for chewing and ripping, respectively. Such teeth are characteristic of meat-eating species.
Two other important characteristics of the species are a skull asymmetry and a relatively low intracranial volume. The first is a trait it shares with modern toothed whales such as orcas. Today, this asymmetry is associated with whales' ability to produce high-frequency sounds for echolocation; Basilosaurus likely didn't have this ability, however, and its skull was asymmetrical in order to house a fatty sensory organ meant to help it hear underwater. The lack of room for a big brain inside its skull likely means that Basilosaurus was not a social species, like whales are today, and that it also wasn't as capable from a cognitive standpoint.
Such traits can be indicative of an evolutionary 'work-in-progress'. The Basilosaurus seems to have been the first whale species to live entirely underwater, marking the point where the lineage of walking whales finally took the plunge.
It most likely spent its day as a solitary hunter, or at most, one that lived in small groups. Social interactions are extremely demanding, from a cognitive point of view, and Basilosaurus' brain just seems to have been too small to adequately navigate living in a group.
Still, who needs big brains when you have big brawns? Analysis of fossilized, scarred Dorudon skull bones -- this is another genus of prehistoric whale that was the preferred prey of Basilosaurus -- suggests that the king of lizards could bite down with 3,600 pounds per square inch (PSI).
To put things into perspective, that's 233 times more pressure than a fully-loaded M1A2 main battle tank exerts on the ground under its tracks. Most industrial hydraulic presses in use today exert between 1,000 to 3,000 PSI, which is still under the estimated high ofr Basilosaurus. You do not want to get bitten by one of these.
With big bites, however, also comes good manners. Wear patterns on Basilosaurus teeth suggest that the animal bit and then chewed its food, unlike most predators today, whose teeth are specialized in ripping chunks of meat off the bone, that are then gulped up whole. In regards to what they ate, stomach contents seem to indicate that B. cetoides hunted fish and large sharks exclusively, while we know from Dorudon skulls that B. isis would also hunt these. Dorudon was a larger animal, related to today's dolphins, and B. isis likely focused on delivering a killing blow to its head before tearing it apart while feeding (many Dorudon skeletons, especially those showing signs of predation from Basilosaurus, are found disarticulated).
King no more
The Basilosaur genus went extinct, with our last fossil evidence of them hailing from around 40 million years ago. They didn't leave behind any direct descendants which, judging from their teeth, isn't the worst thing to have ever happened.
We're not entirely sure why they disappeared. Sometime around 40 million years ago, something happened to bring these toothy kings low. However, the fact that other toothed and baleen whales are around today suggests these smaller relatives of the Basilosaurus out-competed them in the end. It might have been their big brains, it might have been their social nature, it could even have been their more modest appetites; for now, it remains a mystery.