The Trachodon mummy is a very well preserved fossil of Edmontosaurus annectens, a duckbilled dinosaur. It was found by Charles Hazelius Sternberg and his three sons near Lusk, Wyoming, USA in 1908. Although Sternberg was working under contract to the British Museum of Natural History, Henry Fairfield Osborn of the American Museum of Natural History managed to secure the mummy for $2,000.
The mummy was found lying on its back with its head pulled under its body, while its right arm stuck out into the air. The skin of the chest and abdominal region was pulled into the body cavity, and the tail, hind feet, and hind portion of the pelvis had eroded away. The hands of the Edmontosaurus and other species unearthed later suggested the presence of webbed feet, but was later found to be inconsistent with footprint evidence. It has since then been proposed that hadrosaur forefeet have a hard, horseshoe-shaped pad. The webbed skin was later found to be from the postmortem displacement of loose skin of the hand.
In 1912, Osborn came up with a description of the fossil and a theory to its mummification:
"After a natural death (in other words, not death by predators) the body lay exposed to the sun for a long time, perhaps on a sand bar or in a stream. The muscles and soft internal tissues became completely dried and shrunken while the skin, hardened and leathery, shrank around the limbs and was drawn down along the bones. In the stomach and abdominal areas the skin was drawn within the body cavity, while along the sides of the body and on the arms, it was formed into creases and folds. At some later date, the "mummy" may have been caught in a sudden flood and carried downstream and rapidly buried in fine sand and clay. A cast, or impression, of the skin formed in the sand before the skin and other soft parts decayed. There is no remnant of the actual skin preserved only its imprint."