Sensational discovery: First hoofed dinosaur found
Today, it is widely accepted that many dinosaurs had feathers. But the idea of prehistoric reptiles with hooves is far less familiar, largely because no such fossils had ever been found. That changed with a recent study published in Science. Researchers have now discovered two exceptionally well-preserved fossils of the duck-billed dinosaur Edmontosaurus annectens, which appear to show clear evidence of hoof-like structures. The fossils were unearthed in the so-called “Mummy Zone” of the Lance Formation in Wyoming – a roughly six-mile-wide area renowned for its exceptionally preserved dinosaur remains.
The study explains that toes II to IV on the hind feet of E. annectens were covered by keratinized hoof sheaths with flat undersides that enclosed spade-shaped bones. Similar structures were also present on the forefeet, though positioned somewhat differently. Such hooves have never been documented in any other terrestrial vertebrate. Remarkably, the hoof sheaths on the middle toes measured about 15 centimeters – roughly twice the length of the bones within.
Beyond this remarkable anatomical discovery, the fossils also revealed additional soft-tissue features: a fleshy crest along the back that would have reached about 28 centimeters (roughly 11 inches) in height in a fully grown animal, a row of spines running down the tail and polygonal scales ranging from one to nine millimeters in size. These details were visible only thanks to the exceptional state of preservation, made possible by the unique conditions at the discovery site.
Preserved in clay
The carcass first dried out during a drought, then was rapidly buried by river sediment during a flood and filled with sand. A thin clay layer – less than a millimeter thick – settled on the skin’s surface, preserving its outer shape as a kind of “clay template.” This type of fossilization had previously been observed only in low-oxygen marine environments, making this the first documented case in a terrestrial river system.
Significance for paleontology
The discovery holds major significance for paleontology: Edmontosaurus annectens is now recognized as the oldest known land vertebrate with true hooves, making it the earliest known example of hoofed locomotion in evolutionary history. The findings suggest that hooves began to develop in early hadrosaur species as far back as the Early Cretaceous – long before they evolved in mammals.
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