Dorudon, an ancient whale

We like to focus on a fossil whale every October since we are close to Halloween. This month we look back at the cetacean evolutionary tree and talk about the Dorudon (Dorudon atrox). This primitive cetacean swam the ancient Eocene oceans of what is now Egypt and the United States, along with the Basilosaurus. Just for reference, the Eocene corresponds to about 40 to 34 million years ago! So let’s find out more about Dorudon together!

Dorudon, the “spear-toothed” whale

Dorudon’s name translates to “spear-toothed.” In fact, having spear-shaped teeth is one of Dorudon’s defining features. Unlike modern whales with mostly similar-shaped teeth inside their mouths, Dorudon had “heterodont” teeth. It means Dorudon’s teeth had different shapes and still consisted of incisors, canines, premolars, and molars. With such impressive teeth, it is easy to imagine Dorudon being a formidable predator. Quite amazingly, scientists were able to find fossilized Dorudon stomach contents. They included fish bones, convincing researchers that it fed on fish. However, given the side of its mouth and teeth, we now believe Dorudon could also prey on other small marine mammals.

Slide your finger left and right to see the difference between heterodont and homodont teeth. Left is Dorudon (credit: Erika Anderson) and right is a killer whale skull (credit: Millard H. Sharp)

A type of Basilosaurid ancient whale

Dorudon was once mistaken for its much larger cousin, Basilosaurus. Paleo-scientists actually mistook this species for a juvenile Basilosaurus. In fact, they are quite similar, belong to the same family, and are thought to be the first fully aquatic cetaceans. However, under closer examination, scientists found that Dordudon calves had Basilosaurous teeth markings, showing that though Dorudon was a big predator, it still was on the menu for larger predators. You can read more about Basilosaurus in last year’s October “Whale of the Month” post here.

Hunting without echolocation

Although experts are almost certain Dorudon could hear very well underwater, it could not echolocate like modern toothed whales. Imagine how hard hunting must have been for these predators! Their head was long, with a very narrow snout. From what scientists could gather, they lacked a bulbous melon, which is necessary to echolocate. For ancient whales to be able to echolocate, they had to wait another 15-20 million years or so. Indeed, scientists hypothesized that the Cotylocara macei in the Oligocene could potentially echolocate. The early Oligocene is also thought to be the period where odontocetes (toothed whales) and mysticetes (baleen whales) diverged.

Dorudon could hear really well, but could not echolocate like modern whales – Credit: David Arruda

Valley of the Whales

Dorudon was first discovered and classified in the 19th century at Wadi Al-Hitan, known as “Whale Valley.” Located in the Western Desert of Egypt, Whale Valley is a gold mine of Archaeoceti fossils and a fantastic opportunity to study how whales have evolved. Wadi Al-Hitan is a highly protected zone protected under Egyptian law forbidding any action that may destroy the natural environment.

Thanks for Reading! For more information check out our sources:

  • Uhen, M.D., 1996. Dorudon atrox (Mammalia, Cetacea): form, function, and phylogenetic relationships of an archaeocete from the late middle Eocene of Egypt (Doctoral dissertation, University of Michigan).
  • Wadi Al-Hitan (Whale Valley)
  • Geisler, J.H., Colbert, M.W. and Carew, J.L., 2014. A new fossil species supports an early origin for toothed whale echolocation. Nature508(7496), pp.383-386.

Now that you know everything about our fossil friend, find out about its cousin, Basilosaurus:

Basilosaurus, the “King of Lizards” – October 2020

Naomi Mathew is a PhD student at University of Louisiana at Lafayette. She works on bioacoustics in marine mammals from the Gulf of Mexico. She is the co-founder of Whale Scientists. You can read more about her here

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