The ancient marine creature Basilosaurus remains one of the most compelling figures in paleontological history. Its name, which translates to “King Lizard,” is misleading; the initial discoverer mistook the massive, serpentine fossils for those of a giant reptile, a misunderstanding corrected when scientists later identified it as an archaic whale. Reaching up to 66 feet in length, the sheer size of Basilosaurus naturally raises the question of how such a colossal predator sustained itself. Examination of its anatomy and fossil record reveals an apex predator that dominated the oceans of its time.
Defining Basilosaurus
Basilosaurus was an early, fully aquatic member of the whale lineage, living approximately 41 to 34 million years ago during the late Eocene epoch. Unlike modern whales, which have streamlined bodies and specialized skulls, Basilosaurus possessed an extremely elongated, slender, and eel-like body structure. This unusual shape, with its long tail and vertebrae, contributed to the early misidentification as a marine reptile.
The typical length of the two confirmed species, B. cetoides and B. isis, ranged from about 49 to 66 feet, making it one of the largest animals of the Paleogene period. Despite its great length, its vertebrae were hollow and fluid-filled, suggesting its movement was restricted, likely limiting it to swimming near the ocean surface. Basilosaurus was part of the Basilosauridae family, representing a transitional form committed entirely to a life in the water.
The Primary Diet of Basilosaurus
Direct fossil evidence confirms that Basilosaurus was a top-tier marine predator, consuming a diet that included both large fish and smaller marine mammals. The most specific and compelling evidence comes from a fossil discovery in the Wadi Al Hitan, or “Valley of Whales,” in Egypt. This site yielded an adult B. isis skeleton with preserved gut contents located within its body cavity.
These contents consisted of fragmented remains of large bony fish, as well as the bones of juvenile Dorudon atrox, a smaller, dolphin-like relative of Basilosaurus. The Dorudon specimens were juveniles, confirmed because they were still nursing on mother’s milk. This specialized feeding on young whales suggests that Basilosaurus actively hunted in the Dorudon calving grounds.
The diet was not solely focused on whale calves, as Basilosaurus also consumed large fish, including sharks up to about 20 inches in length. The variety of prey items, ranging from large fish to sizable marine mammals, positions Basilosaurus as an opportunistic and powerful hunter. This pattern of preying on other cetaceans and a diverse range of large vertebrates is comparable to the feeding strategies seen in the modern killer whale, Orcinus orca.
Fossil Evidence Supporting Apex Predation
The physical characteristics and fossilized interactions of Basilosaurus provide clear proof of its predatory status. Unlike filter-feeding whales, Basilosaurus possessed heterodont dentition, meaning it had different types of teeth in its mouth. The front of the jaw featured pointed, canine-shaped incisors and sharp teeth designed for grasping and puncturing prey.
Further back in the jaw, the cheek teeth were distinctly flattened, serrated, and triangular. These teeth featured shearing facets, indicating that the upper and lower teeth actively sliced across each other to cut and chew food, a stark contrast to modern toothed whales that swallow prey whole. This robust dental morphology, marked by signs of destructive wear, points to the forceful crushing of large, hard objects, such as the bones of other mammals.
Digital and three-dimensional analysis of fossilized juvenile Dorudon skulls further solidifies the predator-prey relationship. These skulls display specific puncture marks and bone modifications that precisely match the size, spacing, and morphology of an adult Basilosaurus’s dentition. Researchers determined that the bites were often delivered from a lateral position across the head, suggesting an active hunting technique rather than simple scavenging. This direct evidence confirms that Basilosaurus was an active, meat-eating hunter that occupied the highest level of the marine food chain in the late Eocene oceans.