Bluuughhhhhhh. I forgot the clocks were going to move forward last weekend, and my schedule is completely off-kilter. But after slamming most of a big cup of coffee, I'm here to talk about a really cool whale. The Eocene was a great time to be a mammal. After taking their first shaky steps into the limelight during the Paleocene, mammals took over the world in the Eocene. Whales were among the most immediately successful groups, and Basilosaurus was one of the earliest whales fully adapted for marine life. It had a fusiform body and a powerful fluked tail, with its forelimbs adapted into flippers. They ranged in size from 15-20 meters, making them not only one of the earliest large whales, but possibly the largest animal in the Paleogene period.
It's no secret that I love taxonomy, so let's talk about it!
There are two species of Basilosaurus: The type species, B. cetoides and the slightly smaller B. isis. ‘Basilosaurus’ means ‘King Lizard,’ which is weird because, you know, it’s a whale. It’s called that because its discoverers thought it was some kind of sea serpent thanks to its weird body proportions. After the realization it was a whale, the name Zeuglodon was suggested as a replacement. However, since Basilosaurus was the first name given, it had priority, and Zeuglodon became a junior synonym. It gets wackier. Another junior synonym is Alabamornis. This means 'bird from Alabama,' and was given to what was thought to be a big bird's shoulder bone in 1906, but was actually a pelvis of Basilosaurus. And on the less scientific side of things, in 1845, Dr. Albert Koch unveiled the skeleton of a giant sea serpent he called “Hydrarchos,” which would have been really cool if it wasn't really fake. It was probably two Basilosaurus skeletons stuck together, but we don't know for certain because it was destroyed in 1871 by the great Chicago fire.
Despite looking like a modern whale in many respects, Basilosaurus was still weird. Compared to modern predatory whales, it has a proportionally longer body and neck. Its head was smaller, with no room for a melon (the adorable name for the hearing organ toothed whales have in their foreheads). It had a smaller brain too, and probably wasn’t as social or intelligent as say, an orca. Its flippers also had a functioning elbow joint, like sea lions. It was probably best at swimming in two dimensions near the water’s surface, rather than diving.
Perhaps the strangest thing, though, is its pair of tiny hind limbs and pelvis disconnected from the vertebral column. Some whales today have tiny, vestigial hind limbs, but they're reduced to a few useless bones hidden beneath the skin. Basilosaurus' back legs were recognizable as such, and were used for... something. Maybe holding onto each other while mating, almost certainly not for biking.
This animal was widespread throughout the Tethys sea, the ancient waterway between Gondwana and Laurasia in the Mesozoic. As Africa and Eurasia moved toward each other, it was beginning to split in the Eocene, but it still covered swaths of land in shallow, warm sea. The two species of Basilosaurus have different teeth, and probably fed on different prey. B. cetoides typically ate large fish and sharks. B. isis, though, is known to eat Dorudon, a smaller basilosaurid whale. Specimens of Dorudon have been found with bite marks in the skull, attributed to Basilosaurus, and the damage done to the skeletons around it suggest B. isis hunted by delivering a fatal wound to the head before tearing the body apart with its jaws, which sounds metal as hell.
Basilosaurus has always been a favorite mammal of mine. It has a certain elegance and beauty I've always admired, the first of the cetacean giants. Although I'm not a particularly religious or spiritual person, there's something magical about seeing such a huge animal swimming in open waters. I hope I captured some that mystified feeling with this drawing. I first saw Basilosaurus in the second episode of Walking with Beasts, wherein a pregnant B. isis has to find food at the beginning of a climate crisis. WWB constitutes a good 70% of my Cenozoic knowledge. It probably won't be long before I've drawn every mammal featured in it, and I swear I'm not doing that on purpose. Mammals aren't really my strong suit, especially not whales, but I had a lot of fun drawing this. And part of the point of this blog is to teach myself about groups I otherwise don't really study, so I guess you could say I did a good job of that.
Riley Black, 2009 – The Rise and Fall of Alabamornis
Gingerich, 1998 – Paleobiological Perspectives on Mesonychia, Archaeoceti, and the Origin of Whales
Voss, et al. 2019 – Stomach contents of the archaeocete Basilosaurus isis
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