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Sue: The largest and most complete T.rex fossil ever discovered

Sue: The largest and most complete T.rex fossil ever discovered

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During a fossil-hunting expedition in 1990, marine archaeologist and paleontologist Susan Hendrickson discovered a few large vertebrae jutting out of an eroded cliff near Faith, S.D. They turned out to be part of the largest Tyrannosaurus rex skeleton ever discovered.

Hendrickson found the bones while searching a ranch on the Cheyenne River Indian Reservation. Hendrickson worked for the Black Hills Institute of Geological Research when she made the discovery. It took six people 17 days to extract the dinosaur’s bones from the ground.

The fossil is known as Specimen FMNH PR 2081, but was dubbed Sue in honor of Hendrickson.

Custody battle

Shortly after the discovery was made, a dispute arose over who owned the land and who had the rights to the skeleton.

The Black Hills Institute had paid Maurice Williams, the landowner, $5,000 for the right to excavate the skeleton. Williams later contended the fee was for the right to search the property for fossils, but not the right to excavate and claim them. Since Williams was a member of the Sioux tribe, the group also became involved.

The case was further complicated because Williams’ land was being held in trust by the U.S. government for tax-relief purposes. This means the sale would’ve required the consent of the government.

In 1992, the FBI seized Sue, and a custody battle began in federal court. The court ruled that the fossil was to remain property of the trust. The U.S. Supreme Court validated the ruling in 1994. Sue was awarded to Williams and the Bureau of Indian Affairs.

The bureau gave Williams permission to sell Sue and suggested that the fossil be auctioned. In October 1997, the Field Museum in Chicago purchased Sue at the public auction for $8,362,500. This was the most money ever paid for a fossil at auction.

Sue the dinosaur


Sue’s skeleton went on display at the Field Museum in Chicago in May 2000. It was displayed in the museum’s main Stanley Field Hall before being moved to a new “private suite” in 2018. It is now part of the “Evolving Planet” exhibit.


Originally, scientists weren’t sure how to attach Sue’s gastralia, so they were left off the skeleton. Gastralia are rib-like bones that stretch across the belly. Though they are commonly called belly ribs, they aren’t actual ribs. Gastralia are developed in the skin itself.

Gastralia are rare but aren’t exclusive to the T. rex. They’re also found in other dinosaurs, crocodiles and the tuatara, a small reptile native to New Zealand. It’s also thought that the underside of turtle shells developed from expanded gastralia.

Research from the past two decades has uncovered what the gastralia are for and where they should go. Scientists believe they helped the T. rex breathe. They were added to Sue’s skeleton in 2018 before the new suite opened.

Other changes included lowering the arms, installing the wishbone and shifting the posture.


Scientists have determined that Sue lived to the upper end of the life expectancy of a T. rex, which was about 28 years. Like trees, dinosaur bones have growth rings. After examining the rings, scientists determined Sue had an adolescent growth spurt — gaining as much as 4.5 pounds per day — and reached full size at age 19.

Tyrannosaurus rex species

The T. rex was one of the largest land predators ever. The name Tyrannosaurus rex means “king of the tyrant lizards.”

The T. rex is in a family of large predatory dinosaurs with small arms and two-fingered hands. T. rex fossils have been found in western North America from Alberta, Canada, to Texas.

A 2012 study determined that the T. rex had the strongest bite of any land animal that ever lived. The dinosaur’s bite could exert up to 12,814 pounds of force, which is roughly equivalent to the force of a medium-size elephant sitting down.

The T. rex had a 5-foot-long skull and a mouth full of serrated teeth. The largest tooth of any carnivorous dinosaur ever found was 12 inches long. The T. rex’s teeth were wide and somewhat dull.

These large carnivores primarily ate herbivorous dinosaurs. They scavenged and hunted and ate hundreds of pounds at a time.

Fossils vs. casts

Sue is the most complete T. rex fossil ever found, with 250 bones out of the approximately 380 bones in a T. rex. By bone volume, the skeleton is 90% complete.

For a fossil to form, sediment has to first cover an animal’s body. The soft tissues rot away and leave behind the hard tissue — teeth and bones. Over time, the sediment hardens into rock encasing the bones. Minerals from the surrounding groundwater and sediment gradually replace some of the bones’ original minerals. A fossil can also be a preserved imprint, like a footprint or a leaf.

Casts are sometimes displayed instead of real fossil skeletons. They are made from molds of fossil bones. If there is a missing bone in a skeleton, that shape can be carved like a sculpture. This is based on existing bones or on references of bones from similar individuals.

Sue’s mounted skeleton at the Field Museum is made up of fossilized bones, except for the skull, which is a cast. Sue’s real skull is displayed in a freestanding case for easy access to scientists. The skull alone weighs 600 pounds.

The museum also stores an unassembled cast of Sue’s skeleton for further study. Other copies of the dinosaur’s skeleton were assembled and sent to museums and science centers around the world.


Sue is one of the most famous fossils in the world. About 50 T. rex skeletons have been unearthed since the species was identified in 1905, but only a quarter of them are considered nearly complete, meaning more than half the dinosaur’s bones were retrieved. Sue’s skeleton is rare and valuable to science because it is the largest and most complete.

Because Sue’s bones were so well-preserved, they have taught scientists many things about the life of a T. rex, including growth, age, intellect, diet, diseases, injuries and how they moved.

Because the species had olfactory bulbs bigger than the cerebrum (the thinking part of the brain), scientists determined that the T. rex had an incredible sense of smell.

Sue was also the first T. rex skeleton to be discovered with a wishbone, which provided support for scientists’ theory that birds are a type of living dinosaur.

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