The prehistoric marine reptile that paleontologists once reconstructed with its head on its tail.

Nature · Published 3 October 2026 Swipe more like this →

In short: When Elasmosaurus was first described in 1868, the scientist Edward Drinker Cope famously placed its skull at the end of its tail. This blunder, fueled by a fierce rivalry with Othniel Charles Marsh, became a legendary embarrassment in the history of paleontology, highlighting the challenges of interpreting ancient, incomplete fossil remains.

Elasmosaurus was a massive, long-necked marine reptile that inhabited the Western Interior Seaway of North America during the Late Cretaceous, roughly 80.6 to 77 million years ago. Its discovery in 1867 near Fort Wallace, Kansas, by army surgeon Theophilus Hunt Turner, marked a significant moment in American paleontology. The specimen, cataloged as ANSP 10081, remains the only definitive fossil of the genus. It is a fragmentary skeleton that includes a partial skull, ribs, and an impressive series of 72 cervical vertebrae.

The animal's most striking feature was its extreme neck length, estimated at 7.1 meters. Unlike long-necked sauropod dinosaurs, which achieved length through elongated individual bones, Elasmosaurus relied on a high count of vertebrae. Despite their length, these necks were relatively rigid and could not be arched high above the water. The creature likely used its small, triangular head and sharp, fang-like teeth to snatch fish and marine invertebrates, potentially aided by gastroliths, or stomach stones, to assist in digestion.

The infamous reconstruction error by Cope, who initially mistook the neck for a tail, sparked the Bone Wars—a decades-long, public rivalry between Cope and Marsh. While Cope attempted to destroy the evidence of his mistake by recalling his preprint, the error was widely publicized. Modern analysis suggests that the specimen's unique anatomy and Cope's lack of formal training may have contributed to the confusion. Today, the holotype is stored at the Academy of Natural Sciences of Drexel University, where it continues to provide insights into the evolution of the Elasmosauridae family.

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