200 Years. 200 Stories. Story 61: “Marine Reptile or Ancient Whale? ”

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illustration of Basilosaurus fossil
Detail of Plate XXII from Richard Harlan's 1835 article on Basilosaurus in the Transactions of the Geological Society of Pennsylvania. The large figure at the top is a fragment of the upper jaw. Several damaged but still intact teeth are shown along the bottom left edge of the upper jaw.

Marine Reptile or Ancient Whale?

Academy naturalist Richard Harlan published several reports in the 1830s on the incomplete fossil remains of a massive creature. Harlan believed the animal’s huge vertebrae (backbones) resembled those belonging to extinct marine reptiles that resided in Europe. The fragment of its upper jaw was hollow, which confirmed Harlan’s suspicion that the creature was a reptile. On the other hand, the few teeth on that jaw differed from one another, which suggested the creature was a mammal. Harlan was still convinced the animal was a marine reptile. He named it Basilosaurus, which means ruling lizard.

Some of Harlan’s American colleagues disagreed, including fellow Academy member Samuel George Morton who thought Basilosaurus was an ancient whale. On the other side of the Atlantic, there was a similar debate about the animal’s identity. Harlan went to England to present his case to the Geological Society of London. Prior to the meeting, he met with Richard Owen, one of the leading scientists of the day. They examined the fossils using the latest techniques, and Owen convinced Harlan that the form and microscopic anatomy of the teeth proved Basilosaurus was a whale. Owen renamed it Zeuglodon (yoked tooth), yet the animal is still known as Basilosaurus because Harlan’s name came first. Later discoveries of more complete fossils confirmed that the animal was a primitive whale that may have measured 70 feet in length.

There’s a lot going on in our Vertebrate Paleontology Department! We have Harlan’s Basilosaurus specimens in our behind-the-scenes collection. To see our scientists at work, you can visit our Fossil Prep Lab on weekdays. Don’t forget to bring your questions about fossil identification!