Researchers from the University of Chicago have documented a remarkably well-preserved hadrosaur dinosaur exhibiting hooves. Science correspondent Nikolay Grinko has the details.
It’s challenging for us today to grasp the sheer diversity of dinosaurs, a group that vanished from the Earth in what, geologically speaking, was an instant. This event occurred 66 million years ago when a 10-kilometer asteroid struck our planet, creating the immense Chicxulub crater. Prior to that, for a full 150 million years, dinosaurs dominated the globe, constituting the overwhelming majority of terrestrial vertebrates. It’s no wonder paleontologists are still uncovering around 50 new species of these creatures annually—a new find happens roughly once a week. Furthermore, these aren’t just variations of known reptiles, but entirely new, previously unknown species!
Given such morphological variety, the “terrible lizards” seem to have devised every conceivable feature: crests, spikes, horns, scales, feathers, a size spectrum ranging from tiny to colossal, adaptations for walking, tree-climbing, flight, and swimming, and much, much more… Perhaps one of the few traits considered entirely uncharacteristic of dinosaurs for a long time was the presence of hooves; the initial hoofed mammals, known as Condylarthra, appeared around the Paleogene epoch, precisely after the dinosaurs went extinct.
However, in a recent publication, scientists from the University of Chicago describe fossils of the hadrosaur Edmontosaurus annectens that transformed into astonishingly detailed “mummies,” preserving minute elements of skin, scales, and even hooves. These duck-billed Edmontosaurus were discovered in central Wyoming. In addition to their flattened jaws, they possessed a fleshy neck crest and body ornamentation, large spurs on their hips and tail, and evidence suggests they led a semi-aquatic lifestyle, wading in shallows and foraging from the bottom of water bodies.
Edmontosaurus are quite familiar to scientists, but the fossils discussed in the paper were “conserved” in a rather unusual manner. Before the process of fossilization (replacement of dead tissue with minerals) began in their bodies, they were encased in a thin layer of clay. The resulting clay shell that has survived to our time became so delicate it could practically be blown away, yet it perfectly preserved precise imprints of the dinosaur’s external tissues. More often, archaeologists deal only with fossilized bones, having to infer what muscles and internal organs may have looked like, and rarely getting any insight into the skin. These Wyoming Edmontosaurus, though partially preserved, were enclosed in a thin clay carapace that captured the finest ridges and indentations of their outer coverings.
For the first time, researchers gained a complete, detailed understanding of a large dinosaur with scientific certainty. For instance, details about the scaling were documented. The largest, multi-sided scales were positioned along the lower body and tail, while the majority of the animal’s surface was covered in very fine scales, only 1–4 millimeters in diameter—surprisingly small for a dinosaur that could reach over 12 meters in length. Thin folds preserved on the rib cage suggest that this Edmontosaurus‘s skin was relatively thin.
But the most surprising discovery came from studying the hind limbs: this dinosaur possessed hooves. The tips of each of its three rear toes were encased in a wedge-shaped hoof structure resembling that of a horse. This suggests that Edmontosaurus stakes a claim as the earliest known vertebrates on Earth to possess hooves. It seems unlikely they will be displaced from this pedestal anytime soon.
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