Montana Earth Science Picture of the Week

"The best-preserved dinosaur remains in the world belong to ‘Leonardo’, a 77 million year old Brachylophosaurus. Around 90% of the body is covered with fossilized soft tissue."

Guinness World Records L.T.D.

A "treasure" is discovered . . .
Leonardo was discovered near Malta, Montana on July 27, 2000 when Dan Stephenson of Minot, North Dakota noticed the exposed mid-section of Leonardo’s tail and part of its pelvis in a large channel sandstone deposit within the Judith River Formation. This particular formation is made up of sediments (mud, sand) that were deposited during the late Cretaceous Period when the environment in eastern Montana was similar to that found today in the Mississippi Delta region.

More than just bones . . .
This photo, taken in Malta, Montana, shows Leonardo along with paleontologist Nate Murphy, head of the Judith River Dinosaur Institute. What’s sets Leonardo apart from other dinosaur fossils is that 90 % of his skeleton is covered with (fossilized) tissue, including skin, scales, muscle, foot pads . . . Even his last meals, which included ferns, conifers, and magnolias, were fossilized in his stomach. Minerals have replaced the soft tissue and stomach contents just as they do when wood becomes “petrified”. In addition to being a 77 million year-old “mummy” that will keep scientists busy for years, Leonardo is one of only four brachylophosaurus* specimens uncovered to date, and he is the first fully articulated sub-adult ever found. Leonardo is believed to have been 3 or 4 years old when he died.

Nature’s takes it course . . .
When an animal dies, decay bacteria move in to begin consuming the soft tissue. Scavengers show up to nibble on the flesh and flies stop by to lays eggs in the carcass. As maggots hatch from these eggs they help consume the rotting flesh. Usually within a matter of weeks or months most of the soft stuff has decomposed. The bones, which may take years to be weathered away, often become scattered by wind, water, or scavengers.

Rare circumstances . . .
If a dinosaur died in just the right place, possibly along a river or on a delta, it might have become buried by sediment. If this happened soon after the animal died its body would have been somewhat protected from the elements, and it might have become fossilized. However, it is even more unusual to find a dinosaur fossil that includes anything but bones, indicating that burial rarely happened before the soft tissue rotted away. In fact, Leonardo is one of only four dinosaur fossils ever found to be classified as a "mummy" because of the amount of soft tissue that was preserved. Unfortunately, the other three were uncovered in the early 1900s, when excavation and preservation techniques were not as advanced as they are today.

Good news! . . .
On April 16, 2005 the Montana Legislature passed a bill that will provide $500,000 “seed money” to build a Great Plains Dinosaur Park in Malta, Montana. Without the funds, it is possible that Leonardo would have been moved to another state where scientists could study him. The Judith River Dinosaur Institute hopes to raise another $1.5 million to build the center. Currently Leonardo, and several other important dinosaur discoveries, are being stored at the institute’s “field station” (a converted tire garage in Malta).

*Brachylophosaurus: a species of duck-billed dinosaur

Terms: petrify, delta (of a river)