A study published in the journal Science describes two well-preserved Edmontosaurus annectens skeletons recovered from the Lance Formation in Wyoming. The fossils, a late juvenile labeled Ed Jr. and an early adult called Ed Sr., retained an almost life-sized three-dimensional imprint of skin, muscles, and feet through a process the authors termed clay templating.
The research team led by paleontologist Paul Sereno explained that as each carcass decayed, a microscopic biofilm on the skin attracted fine clay particles that formed a shell one-hundredth of an inch thick. The organic tissue later vanished, leaving a fragile cast that preparators exposed grain by grain and recorded with high-resolution scans.
Ed Sr. measured about twelve metres long; Ed Jr. was roughly half that size and around two years old. Both bodies carried a midline feature that began as a fleshy neck crest, became a single row of spikes over the hips, and extended down the tail, where Ed Sr. ended in three horn-like spikes. Wrinkles across the ribcage suggested thin skin, while most of the surface displayed pebble-like scales one to four millimetres wide.
The hind feet displayed three wedge-shaped hooves with flat undersides that worked with a fleshy heel pad, and smaller hooves appeared on the forelimbs. “These duck-billed dinosaur mummies contain many premieres: the earliest documented hooves of a land vertebrate and the first confirmed reptile with hooves,” said Sereno, according to the German broadcaster n-tv.
The team concluded that the animals usually moved on all fours while feeding but could shift to a bipedal run when speed was needed. “It’s the first known trace of animals with hooves capable of bipedal locomotion,” said Stephanie Baumgart of the University of Florida in an interview with Reuters.
Edmontosaurus lived about 66 million years ago, just before an asteroid ended the Cretaceous era. “It’s by far the most common dinosaur of its ecosystem,” said Sereno, according to Reuters, noting that its herds shared the landscape with Triceratops, Ankylosaurus, and Tyrannosaurus rex. The Badlands region’s so-called Mummy Zone likely still holds many more specimens, he added.
The preparation of this article relied on a news-analysis system.