Dinosaur 'mummies' reveal a surprise hoofed feet

Two fossilised "mummies" unearthed by scientists in the badlands of Wyoming of the duckbilled dinosaur Edmontosaurus reveal the external anatomy in exquisite detail, including the surprising presence of hooves on the feet – a first for any dinosaur.

The two Edmontosaurus individuals, dating to the very end of the dinosaur age 66 million years ago, were a young adult roughly 40 feet long and a two-year-old juvenile about half that length. The contours of the external fleshy surface of the two dinosaurs were preserved over the skeleton by a thin clay layer about one-hundredth of an inch thick that formed after they died.

Because the shape of an animal's soft tissue is rarely preserved in fossils, it usually is difficult to reconstruct the appearance of dinosaurs and other extinct creatures. But these two had extensive continuous areas of preserved external skin surface, providing the most complete, fleshed-out view of a large dinosaur to date.

"We're seeing the full profile of the dinosaur for the first time," said University of Chicago palaeontologist Paul Sereno, who led the study published in the journal Science. "We're confident what it looked like."

The dinosaurs are not mummies in the same sense as bodies elaborately preserved in ancient Egypt for the afterlife. But similar fossils were found more than a century ago in the same locale – though not excavated as painstakingly as these – that were dubbed mummies, and the term stuck.

These Edmontosaurus individuals lived during the Cretaceous Period shortly before an asteroid collision abruptly ended the age of dinosaurs. Edmontosaurus, which munched plants with its broad and flat snout that vaguely resembled a duckbill, roamed western North America alongside apex predator Tyrannosaurus, horned dinosaur Triceratops and armoured dinosaur Ankylosaurus.

"It is by far and away the most common dinosaur" in its ecosystem, Sereno said of Edmontosaurus. "It was giant herds. It's the cow of its day." Its length - reaching about 42 feet – rivalled that of Tyrannosaurus. Other fossils with teeth marks show it was a favourite meal for T.rex.