Cretaceous Cold Case Solved: Giant Fish Tooth Found Lodged in Ancient Plesiosaur Neck at Chicago Museum

A 1.74-inch Xiphactinus tooth was found embedded in a plesiosaur's neck at the Field Museum, revealing a fatal Cretaceous clash between titans.

By: AXL Media

Published: Apr 28, 2026, 6:23 AM EDT

Source: Information for this report was sourced from the Journal of Vertebrate Paleontology and Earth.com

A Violent Encounter Frozen in the Mooreville Chalk

An unassuming museum drawer at the Field Museum of Natural History has yielded one of the most dramatic pieces of evidence regarding the ferocity of the Western Interior Seaway. Researchers rediscovered a mid-neck vertebra from a subadult Polycotylus latipinnis, a short-necked plesiosaur, which contained a broken tooth driven deep into the bone. Collected in 1949 from the Mooreville Chalk Formation in Alabama, the specimen preserves a literal "smoking gun" of prehistoric combat. The depth of the penetration suggests an attack of immense power, highlighting the vulnerability of marine reptiles that were previously considered the unchallenged masters of their coastal domain.

Advanced Imaging Reveals a High-Speed Underwater Ambush

To identify the attacker without compromising the integrity of the 80 million year old fossil, scientists utilized high-resolution computed tomography (CT) scanning. Lead author Stephanie Drumheller and a team from the University of Tennessee at Knoxville digitally reconstructed the embedded fragment from over 2,000 individual image slices. This process revealed a conical, slightly curved tooth with a large interior pulp cavity, features that excluded sharks and other marine reptiles. The resulting 3D model allowed researchers to confirm that the bite was delivered by Xiphactinus, a predatory bony fish that could reach lengths of up to 20 feet.

The Fatal Price of a Vulnerable Anatomy

The placement of the strike was particularly devastating, located in a mid-neck vertebra where the animal’s trachea, esophagus, and major blood vessels were concentrated. Paleontologists suggest that the force required to wedge a tooth into a cervical vertebra would have likely punctured the airway or triggered catastrophic hemorrhaging. According to co-author Robin O’Keefe, while long necks provided plesiosaurs with a significant predatory reach, they also served as a critical anatomical bottleneck that smaller, faster predators like Xiphactinus could exploit. The lack of healing or infection in the surrounding bone confirms that the injury occurred at or very near the time of the animal's death.