Zeuglodon, more commonly known as Basilosaurus, is technically a water mammal. However, when it was originally investigated, it was believed that it was presumably a maritime reptile, and as a result, it was given the Latin name Basilosaurus, which means “King lizard” in English. Because this was an official designation, it couldn’t be changed into a correct version rendering the name permanently fixed.

The family, Basilosauridae of extinct primitive whales, includes the genus Basilosaurus, which roamed the world’s oceans during the Eocene era that lasted between 55.8 million to 33.9 million years ago.


While the genus Basilosaurus lacked digits, they were related to terrestrial animals, which is the reason they are listed in that order, even though they were not whales. They ranged in length from 40-70 ft. Basilosaurus species were narrower than most current whales and resembled colossal eels in appearance for reference. They had tiny arms on the rear of the bodies, which were probably used for courtship. 

The skull of a Basilosaurus noted for its jaws
The skull of a Basilosaurus noted for its jaws

Basilosaurus did not have a baleen like many contemporary whales of its size; instead, they utilized their teeth to consume food. The decreased limbs would likely have been ineffective for movement; thus, the animal may have moved in an oscillating manner to push itself through the water. This motion up and down may have also allowed it to lunge after prey in short bursts.


Basilosaurus had teeth that would grind down anything that they bit. The huge jaws of Basilosaurus would have been employed to ambush prey that was not particularly small, such as small whales or large fish that, while lesser than Basilosaurus, were nevertheless too big for almost all other carnivores to handle.

Depending on the particular species of Basilosaurus, their diet will differ. Fish and sharks have been found inside the remains of Basilosaurus Cetoides. The same tendency was displayed by Basilosaurus Isis. However, it is likely that it preferred Dorudon, an extinct dolphin-like sea animal.


Around 40 million years ago, during the Eocene era, Basilosaurus flourished. These aquatic creatures most likely inhabited the ancient Tethys Ocean. This region evolved into the current Indian Ocean and the Atlantic Ocean when continental plates drifted and altered. 

Basilosaurus skeleton exhibiting the species size
Basilosaurus skeleton exhibiting the species size

Basilosaurus fossils have been found in Egypt, Northern Africa, Jordan, and Pakistan, indicating that they were widespread in this region while it was submerged. They developed into marine mammals akin to contemporary whales. In actuality, the first known species of prehistoric whale was the Basilosaurus. However, Basilosaurus is not the ancestor of contemporary whales.


The mammals of the Basilosaurus genus were more streamlined than that of most current whales and resembled colossal eel-like creatures in appearance. They have tiny limbs on the rear of the bodies, which were presumably used for mating. 

There isn’t really enough information to study or even speculate on how Basilosaurus reproduced. As of right now, it is impossible to identify the sexual dimorphism of Basilosaurus based on the fossil evidence that is currently present. 


In the ocean, Basilosaurus was an apex predator. They possessed enormous size, were carnivorous, and could devour anything with their fangs. Injury and illness may well have detrimental consequences on Basilosaurus, just like they would on any creature. 

Basilosaurus at the DC Natural History museum
Basilosaurus at the DC Natural History Museum

Basilosaurus that were young or old were more susceptible to any effect. The population of Basilosaurus might have deteriorated from shifts in their availability of food. These species may have competed for food, making it difficult for the weaker members to survive.

The earliest Basilosaurus fossils date to about 34 million years ago. The Basilosaurus, like many other species that went extinct at that time, was probably influenced by a major catastrophe that signaled the end of the Eocene era. Based on the presence of collision zones, it might have been a meteor, or a slow cooling that affected all species’ food supply, eventually causing the demise of Basilosaurus.

Facts about the Basilosaurus

  1. Basilosaurus was, on average, 70 ft long.
  2. Basilosaurus would weigh, on average, 10 tons.
  3. The correct scientific name for Basilosaurus is Zeuglodon.
  4. Basilosaurus was marine mammals and not marine reptiles.
  5. Basilosaurus had a small brain-to-body ratio.


Was Basilosaurus the first whale?

They are sea creatures that resemble current whales in their evolution. In actuality, the first known species of primordial whale was the basilosaurus. However, Basilosaurus is not the ancestor of contemporary whales. This entire genus vanished approximately 34 million years ago.

What were Basilosaurus bones used for?

Although Basilosaurus wasn’t given its scientific name until the early 18th century, its bones were known for a long time and had been utilized by people in the Southern United States as support posts or andirons for fires. Of course, no one at the time realized that these preserved items were truly the remains of a long-gone primordial whale.

Was Basilosaurus a dinosaur?

Although they are also extinct creatures, basilosaurus doesn’t belong to dinosaurs. Scientists categorize Basilosaurus as a mammalian rather than a dinosaur or reptilian because of its dental tissues. Since its initial discovery by scientists, it has undergone numerous classifications. In fact, when given the name Basilosaurus, people initially thought it was a lizard.

Were Basilosaurus great swimmers?

Examination of the Basilosaurus bones has shown that its range of motion was relatively constrained. Muscle connections along the backbone suggest that Basilosaurus had fairly weak musculature and was unable to swim or dive for a lengthy period of time, at least not faster than it might have pursued prey. Its fluid-filled vertebrae rendered them unsuited for diving to extreme depths.

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