Basilosaurus was a large, ancient predatory whale that lived during the late Eocene epoch, approximately 41.3 to 33.9 million years ago. Despite its name, which translates to “king lizard,” this formidable creature was a marine mammal, not a reptile. It possessed a remarkably long, slender, and serpentine body, reaching lengths of about 17 to 20 meters (56 to 66 feet). As a top predator in its ancient aquatic environment, Basilosaurus played a significant role in the marine ecosystems of its time.
Origins of Discovery
The discovery of Basilosaurus fossils occurred in the southeastern United States. In the 1830s, bones were found in Alabama and Louisiana. American naturalist Richard Harlan received a vertebra from Judge Henry Bry of Ouachita Parish, Louisiana, and additional fragments from Judge John Creagh of Clarke County, Alabama. Harlan misidentified these remains as belonging to a giant reptile, and named the creature Basilosaurus in 1834.
Harlan presented his findings, including jaw and teeth fragments, to anatomist Richard Owen in England in 1839. Owen, recognizing the mammalian characteristics, particularly the double-rooted teeth, correctly identified the animal as an early whale. He proposed renaming it Zeuglodon, meaning “yoked tooth,” to reflect its true nature. However, the original name Basilosaurus was retained despite its misleading name.
Unraveling Whale Evolution
The discovery of Basilosaurus proved significant for understanding whale evolution. Its unique anatomy provided evidence for the transition of whales from terrestrial ancestors to fully aquatic life. A key feature was its small, vestigial hind limbs, likely non-functional for land movement. Though not used for walking, these limbs had functional joints and may have played a role in mating.
Unlike modern whales that swallow prey whole, Basilosaurus possessed various types of teeth, indicating it could chew its food. The structure of its vertebral column, while elongated, suggested a tail fluke and an undulating, eel-like swimming style. These features solidified Basilosaurus’s position as an early, fully aquatic cetacean, unable to support itself on land, and a clear link in whale evolution.
Global Footprint of Basilosaurus
While the initial discoveries of Basilosaurus cetoides were concentrated in the United States, particularly in Alabama, Louisiana, and Mississippi, the creature’s geographic range was much broader. A second species, Basilosaurus isis, was later identified from fossil finds in Egypt. This species is well-represented in Wadi El Hitan, known as the “Valley of the Whales.”
Beyond these primary locations, Basilosaurus fossils have been unearthed in other regions globally. Discoveries include specimens from Pakistan, Jordan, Tunisia, Morocco, Peru, and England. This widespread distribution indicates Basilosaurus inhabited a vast ancient marine realm, including the Tethys Sea (a precursor to the modern Mediterranean) and parts of the Northern Atlantic Ocean.