🦴 Evidence of a terrible battle between Cretaceous giants

About 100 million years ago, the oceans of the Cretaceous period could be the stage of fierce battles between giant predators. A recent discovery in Alabama provides proof: a fossil still bears the mark of a violent confrontation between two sea monsters.

It was while studying a specimen of a marine reptile, named Polycotylus and housed at the Chicago Field Museum, that researchers made a surprising find. On a cervical vertebra, they discovered a large tooth deeply embedded in the bone. This mark indicates the animal likely suffered a fatal attack.


To identify the biter, the team used a medical imaging technique: computed tomography. This process allowed for the 3D reconstruction of the embedded tooth without damaging the fossil. Led by two students, this work determined that the attacker was a Xiphactinus, a large carnivorous fish.

According to the analysis, this bite likely did not correspond to a predation attempt. Indeed, Xiphactinus was known to swallow its prey whole, as evidenced by other fossils. This would therefore have been a confrontation, potentially linked to the defense of territory or a resource. Located at the neck level, the injury would have quickly caused death.

The rocks of the Mooreville Chalk geological formation in Alabama are rich in comparable fossils. Traces of bites from sharks, fish, and other marine reptiles are frequently observed there. These elements paint a picture of an ecosystem where aggressive interactions occurred regularly, even among large predators.

The giant predators of the Cretaceous seas

The oceans that covered part of North America about 100 million years ago were home to impressive fauna. Among them, Xiphactinus, a fish that could reach 20 feet (six meters) in length, fed mainly on smaller prey that it swallowed whole. Its powerful jaw and sharp teeth made it a formidable hunter.

Polycotylus, on the other hand, was a marine reptile belonging to the plesiosaur group. Recognizable by its long neck and four flippers, it moved with agility to capture fish and cephalopods. These animals occupied different ecological niches, but their territories could overlap.

Interactions between these large predators were probably rare, as each generally avoided unnecessary risks. However, conflicts could arise during the defense of space or a food source.