Technically, I suppose, no dinosaur mummies have been found, if you consider that a mummy consists of preserved skin and tissue. However, fossilized dinosaur skin and tissue has been found in recent years. Using a broader definition of mummy, I believe that these discoveries qualify as mummies.
Dakota the Hadrosaur
Asmall part of a duck-billed hadrosaur (including a section of the tailbone and some vertebrae) was originally found in 1999 by a 16-year-old named Tyler Lyson on his family's land in dinosaur-rich Marmath, North Dakota. Thinking that he hadn't found much, he ignored the find for a time.
In 2004, he returned to the site and uncovered some of the dinosaur's fossilized skin. At that point he called in outside help. Lyson told reporters later, "I didn't have very high hopes for the animal. I figured the excavation would take two to three weeks, I'd have a hadrosaur tail, it would make a nice museum piece, but scientifically it would not be that impressive."
One of Dr. Philip Manning's students saw the 65 million-year-old fossil and reported the find to his professor. Manning helped Lyson raise over a million dollars to excavate the entire dinosaur; then he and other scientists from the University of Manchester in the UK worked with Tyler and other volunteers in the excavation which was completed in 2006.
From sciencedaily.com: Dakota "was the first-ever find of a dinosaur where the skin 'envelope' had not collapsed onto the skeleton. This has allowed scientists to calculate muscle volume and mass for the first time. The fact that the skin is mostly intact allows for the exciting possibility that some of its original chemistry is still present.... Among the exciting discoveries are a fleshy pad on Dakota's palm, hooves on its feet made of keratin, and well-preserved skin scales that vary in size and shape across the body, tail, arms and legs of the dinosaur."
From world-science.net: "Dakota may alter our understanding of how dinosaurs looked and moved.... Its backside...seems to be 25 percent larger than previously thought, suggesting it could have run 45 kilometers (28 miles) an hour—50 percent faster than T. rex. The skin also shows evidence of a possibly striped camouflage pattern in some areas, researchers said. A pattern of banding was found in the larger and smaller scales, something that in modern reptiles is often associated with color patterns...."
Leonardo the Brachylophosaurus
Here are the facts about the dinosaur and its death and "mummification." Leonardo was a young Brachylophosaurus (a two-legged, plant-eating duck-billed dinosaur). Approximately 3 or 4 years old when it died, this Brachylophosaurus is the first youngster of this species to have been discovered. It is also the best preserved fossilized dinosaur found in the last 70 years (according to a report in USA Today). The dinosaur would have been 20 feet long at the time of its death and weighed about 2,000 pounds.
Scientists aren't sure but they suspect that Leonardo became trapped on a sandbar and dried out before it was covered in sand. Over the centuries and millennia, he became fossilized and turned into a 6-and-one-half ton piece of sandstone. Most amazingly, 80 percent of its skin and muscles are intact. Scientists can even see the remains of its last meal (a half-digested wad of 40 types of ferns and evergreen wood
The discovery has helped paleontologists rewrite their knowledge of the Brachylophosaurus.Instead of a long neck (that is usually pictured), they see now that the Brachylophosaurus had a thick neck with bulging shoulder muscles. They also see the finely scaled skin, a comb which ran along its back, and the cartilage of its beak and claws.
You can read more about the discovery of Leonardo (and many others) here.
Books about Dinosaurs
Dinosaur Books for Children