Episode 492: Basilosaurids

Further reading:

Giant early whale Basilosaurus hunted the calves of other whales

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Let’s look at some extinct whale ancestors this month, basilosaurids.

We talked about the ancestors of whales in episode 72, about weird whales. After mosasaurs went extinct at the same time as the non-avian dinosaurs, 66 million years ago, basilosaurids evolved to fill the ecological niche they left. Mosasaurs were big marine reptiles while basilosaurids were big marine mammals, but in many ways basilosaurids looked more like mosasaurs than they did modern whales.

Basilosaurids differed from their ancestors in that they were fully aquatic. They didn’t come out of the water at all and probably couldn’t. They did still have hind legs, but they were tiny and scientists think the animal probably only used the legs to help stay in place while mating. The hind legs were really small in comparison to the body, only 14 inches long, or 35 cm, in a 52-foot specimen, or 16 meters. Tyrannosaurus rex would look at that and say, “you’ve got really small legs, bruh.” Its front legs were larger and more flipper-like, although it still had an elbow joint that modern whales have lost, although modern seals still have an elbow joint.

The reason Basilosaurids have a name that sounds an awful lot like a dinosaur name is because the person who described the first one scientifically thought it was a reptile. That was a man named Richard Harlan, an early paleontologist, who thought the fossils he was sent belonged to a marine reptile, possibly a mosasaur relation. In 1839 he named it Basilosaurus, which means “king lizard.” Then he took the fossils to another Richard, Richard Owen, who gave them a second look. Owen pointed out that the teeth didn’t look anything like reptile teeth and that the animal was probably some kind of whale. He and Harlan decided to rename the animal Zeuglodon, but it was too late! The first name was published, and Basilosaurus stayed king lizard despite not being a reptile. That didn’t stop many paleontologists from using Zeuglodon instead for quite a while, which has caused all kinds of confusion.

Fossils of that particular species are especially common in the southern United States, so common in some places that the fossilized vertebrae were sometimes used as house supports. We talked about Basilosaurus in the paleontological frauds episode, because bones from six different basilosaurs formed the fake sea serpent skeleton exhibited around the United States and Europe in 1845.

Basilosaurus did look a little bit like a sea serpent in that it was very long and relatively slender, and its body wasn’t rigid like a modern whale’s. It grew up to 66 feet long, or 20 meters, and probably longer, and is sometimes described as eel-like. It probably had small flukes at the end of the tail, but it didn’t swim like a modern whale. Its vertebrae were large, hollow, and filled with fluid. This made Basilosaurus buoyant but probably also meant it had trouble diving very deeply.

There are only two species in the genus Basilosaurus, although there are lots of other Basilosaurids in other genera. The other Basilosaurus was slightly smaller and is most well known from an incredible bone bed in Egypt called Wadi al Hitan.

Around 35 million years ago, Wadi al Hitan was a shallow coastal area full of life. It wouldn’t have looked all that weird to us at first glance, because a lot of the animals and plants that lived there were early relations of the ones that are still around today. These included sea cows that ate marine plants, various crocodilians, sea turtles, sea snakes, lots of birds, includi