Sue the T. rex: Discovery of the Most Complete Tyrannosaurus

Sue is one of the largest and most complete skeletons of Tyrannosaurus rex ever found. It was discovered on 12 August 1990 by Sue Hendrickson near Faith, South Dakota, and became the subject of a federal seizure, years of litigation and, in 1997, the most expensive fossil sale up to that time. Since 2000 Sue has been displayed at the Field Museum of Natural History in Chicago, where it has transformed scientific understanding of how Tyrannosaurus lived, grew and suffered injury.

Background: Tyrannosaurus before Sue

Tyrannosaurus rex was named in 1905 by Henry Fairfield Osborn, based on fossils found by Barnum Brown of the American Museum of Natural History, including the 1902 skeleton from Hell Creek, Montana. Through most of the twentieth century, however, the dinosaur was known from only a handful of partial skeletons.

The late Cretaceous rocks of the northern Great Plains, especially the Hell Creek Formation of Montana and the Dakotas, are the main source of Tyrannosaurus fossils. By the 1980s commercial fossil companies as well as museums were prospecting there. One of the best known was the Black Hills Institute of Geological Research, a private company in Hill City, South Dakota, run by Peter Larson and his brother Neal.

The discovery in 1990

In the summer of 1990 a Black Hills Institute team was working in the Hell Creek Formation on the Cheyenne River Indian Reservation in western South Dakota. On the morning of 12 August the team’s truck had a flat tyre, and most of the group drove to the town of Faith to have it repaired.

Sue Hendrickson, an experienced fossil and amber collector, stayed behind and walked along a sandstone cliff she had wanted to examine. At its base she noticed weathered fragments of bone, and looking up she saw large vertebrae protruding from the cliff face. When the team returned, Peter Larson identified the bones as those of a Tyrannosaurus.

Over about 17 days the team removed tonnes of overlying rock and excavated the skeleton, which lay in a jumbled but remarkably complete state. The specimen was named “Sue” in honour of its discoverer. The land belonged to Maurice Williams, a rancher and member of the Cheyenne River Sioux Tribe, and the Black Hills Institute paid him 5,000 dollars for the fossil.

The seizure and legal battle

The institute took the bones to Hill City and began preparing them, with plans for a museum built around the skeleton. Ownership, however, soon came into question. Williams’s land was held in trust by the United States government, an arrangement under which the land could not be sold or transferred without the approval of the Department of the Interior. The Cheyenne River Sioux Tribe also claimed the fossil.

In May 1992 agents of the FBI, supported by members of the National Guard, seized the skeleton from the Black Hills Institute and moved it to storage at the South Dakota School of Mines and Technology in Rapid City. The seizure caused uproar among fossil collectors and local residents.

In 1993 the federal district court ruled that the fossil was part of the land, which meant it had belonged to Williams and that the 5,000-dollar sale was invalid without government approval. The ruling was upheld on appeal. The court decided that Williams owned the fossil, with the United States holding it in trust for him.

Peter Larson and the Black Hills Institute also faced a long federal investigation into their fossil collecting. In a trial in 1995 Larson was convicted on charges relating mainly to customs violations in unrelated matters; he was sentenced to two years in prison and served about 18 months. Many palaeontologists considered the prosecution excessive, while others welcomed stricter control of fossils taken from public and tribal lands.

The 1997 auction

With the courts’ approval, Williams consigned the skeleton to Sotheby’s for auction. Many palaeontologists feared that Sue would disappear into a private collection, beyond the reach of researchers.

The sale took place in New York on 4 October 1997. The Field Museum of Natural History in Chicago, backed by McDonald’s, Walt Disney World Resort and private donors, won the auction with a bid that, with the auction house’s premium, totalled 8.36 million dollars. At the time this was by far the highest price ever paid for a fossil.

In return for their support, McDonald’s funded a public fossil preparation laboratory at the Field Museum, and Disney received casts of the skeleton for display. Part of the preparation work was carried out in view of visitors, both in Chicago and at Disney’s Animal Kingdom in Florida.

Preparation and display

Preparing the bones took tens of thousands of hours. Technicians removed rock, repaired fractures and made casts of every bone. The real skull, about 1.5 metres long and weighing several hundred kilograms, was too heavy to mount on the skeleton, so it was displayed separately in a case and replaced on the mount by a cast.

Sue was unveiled in the Field Museum’s main hall, Stanley Field Hall, on 17 May 2000. In 2018 the skeleton was dismantled and moved to a new dedicated gallery in the museum’s Evolving Planet exhibition. The remounted Sue, revealed in December 2018, includes the gastralia, or belly ribs, and corrections to its posture based on research since 2000.

What Sue reveals

Sue has become one of the most thoroughly studied dinosaurs in the world. In 2003 Christopher Brochu published a detailed monograph describing every bone, which became a standard reference for Tyrannosaurus anatomy.

Size and age. Sue is about 12.3 metres long and stands about 4 metres high at the hips. Estimates of its living weight vary between studies, mostly falling between about 8 and 9.5 tonnes. In 2004 Gregory Erickson and colleagues counted growth rings in Sue’s bones and estimated that it died at about 28 years old, older than any other Tyrannosaurus then studied. The same research suggested that Tyrannosaurus grew extremely fast during its teenage years.

Injuries and disease. Sue’s skeleton records a hard life. It shows healed broken ribs, damage to a shoulder bone and an infected, healed lower leg bone. Several fused tail vertebrae may reflect injury or disease. Smooth-edged holes in the lower jaw were once interpreted as bite wounds from another tyrannosaur; in 2009 Ewan Wolff and colleagues proposed instead that they were caused by an infection similar to trichomonosis, a parasitic disease of modern birds of prey.

Bird-like features. Sue preserves a furcula, or wishbone, one of the first identified in Tyrannosaurus. Together with air spaces in its bones, it underlines the close relationship between tyrannosaurs and birds. Studies of the skull’s braincase indicated a well-developed sense of smell.

Sex unknown. The skeleton is often called “she”, but its sex cannot be determined from the bones. The Field Museum refers to the specimen simply as SUE.

By the numbers

Timeline

• 1990, 12 August: Sue Hendrickson finds the skeleton near Faith, South Dakota.
• 1990, August: The Black Hills Institute excavates the skeleton and pays Maurice Williams 5,000 dollars.
• 1992, May: FBI agents seize the skeleton and move it to Rapid City.
• 1993: A federal court rules that the fossil belongs to Williams, held in trust by the United States.
• 1995: Peter Larson is convicted on largely unrelated customs charges.
• 1997, 4 October: Sotheby’s sells Sue to the Field Museum for 8.36 million dollars.
• 2000, 17 May: Sue is unveiled at the Field Museum in Chicago.
• 2018, December: The remounted skeleton opens in its own gallery in the Evolving Planet exhibition.

Consequences and legacy

The Sue case changed the world of fossil collecting in the United States. It highlighted the legal complexity of fossils found on private, tribal and federal land, and fuelled long debates between museums, academic palaeontologists, commercial collectors and landowners. It also showed that a single fossil could command a price comparable to a major work of art.

Later sales have gone far beyond Sue’s price. In 2020 another Tyrannosaurus excavated by the Black Hills Institute, known as Stan, sold at auction in New York for 31.8 million dollars. Many scientists worry that such prices make important specimens harder for public museums to acquire.

For the public, Sue became a celebrity. Casts toured widely in travelling exhibitions, and the Field Museum’s playful social media presence for SUE made the dinosaur one of the best-known fossils in the world. Its bones remain available to researchers, helping to answer questions about how the last great predators lived before the Chicxulub impact ended the age of dinosaurs.

Why it matters

Sue gave scientists an almost complete view of the most famous dinosaur, revealing how it grew, how long it lived and what injuries and illnesses it survived. The fight over its ownership reshaped the legal and ethical debate over fossil collecting, and its purchase by a public museum ensured that it remained available for study and for millions of visitors.