By Will Dunham
WASHINGTON (Reuters) -Two fossilized “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 (12.2 meters) 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 (0.025 cm) 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 paleontologist 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.
“They do not resemble human mummies of Egyptian style. And at least for our mummies, there’s no DNA, there’s no tissue structure, there’s nothing. It’s a clay mask,” Sereno said.
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 armored 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 (12.8 meters) – rivaled that of Tyrannosaurus. Other fossils with teeth marks show it was a favorite meal for T. rex.
“There’s no question that it’s on the menu,” Sereno said.
“It’s not an animal that would be easy to take down. That’s why you needed something the size of Tyrannosaurus.”
CONVERGENT EVOLUTION
Mammals such as horses, cows, goats and sheep evolved hooves, structures that protect the toes, support an animal’s weight, offer traction and absorb shock from the impact of walking and running. But Edmontosaurus did so millions of years earlier. It is the first dinosaur, the first reptile and the first land vertebrate known to have evolved hooves.
“It’s for hard land, efficiently walking – maybe even running – over the surface,” Sereno said.
Its hooves are an example of a phenomenon called convergent evolution in which disparate organisms independently evolve similar features – like the wings of birds, bats and the extinct flying reptiles called pterosaurs – while adapting to similar environments or ecological niches.
Edmontosaurus appears to have walked on all fours when moving slowly and on two legs when running, Sereno said.
“The only animal we can even point at as a parallel or an analog is a kangaroo,” Sereno said.
As a result, the hooves of its forelimbs differed from those of its hindlimbs.
The fossils showed Edmontosaurus boasted a continuous midline feature on its body, with a fleshy crest along the neck and trunk that changes over the hips into a single row of spikes running down the tail. Its skin was covered in tiny, pebble-like scales, most no bigger than those of an average lizard.
It appears the two Edmontosaurus individuals died, perhaps in a drought, and their desiccated carcasses were later covered in a flash flood that left them coated in a film of clay, called clay templating.
Using historical photos and field investigation, the researchers rediscovered where in east-central Wyoming some dinosaur mummies were excavated in the early 20th century. During field work in this “mummy zone,” Sereno said, they also found fossils of Tyrannosaurus and Triceratops, to be detailed in separate studies. Sereno said the Tyrannosaurus fossil suggested it may have been feathered.
“The T. rex doesn’t even have scales,” Sereno said.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
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