The discovery of Sue, the largest and most complete Tyrannosaurus rex fossil ever found (FMNH PR 2081), immediately raised a profound question: what felled this apex predator? This remarkable specimen provides an unparalleled window into the life of a dinosaur that roamed the Earth approximately 67 million years ago. Determining the exact cause of death presents a unique challenge for paleontology. The skeleton itself serves as a detailed medical record, filled with clues that chronicle a difficult life and ultimately suggest a complex demise.
Evidence of a Difficult Life
Sue’s fossilized bones record a lifetime of severe injuries and chronic ailments. Evidence of past trauma is visible in several places, including three broken ribs that healed over time, confirming the dinosaur endured violent encounters. The skeleton also displays clear signs of age-related disease, notably in the tail vertebrae, which show fusion consistent with severe arthritis.
A major long-term health issue was a severe bone infection in the left hind leg. Sue’s left fibula is noticeably swollen to nearly twice the diameter of the right, indicating a painful and debilitating infection. Furthermore, a series of distinct lesions riddle the bones of the lower jaw, which scientists have identified as a sign of an advanced, chronic infection.
This jaw pathology is strongly associated with a protozoan parasite, similar to modern Trichomonas gallinae, which causes trichomonosis in birds. The parasite causes inflammation and tissue damage, eventually eroding the bone and forming the characteristic smooth-edged holes seen on Sue’s mandible. The cumulative effect of such chronic pain and disease would have severely compromised the dinosaur’s overall health and ability to hunt effectively.
Scientific Conclusions on the Cause of Death
The precise moment of Sue’s death remains unknown, as the skeleton lacks clear, catastrophic trauma—such as a crushing fall or a fatal bite wound—that would offer a simple explanation. Instead, the scientific consensus points toward complications arising from the animal’s advanced age and the debilitating illnesses recorded on the bones. Sue was one of the most geriatric T. rex specimens discovered, estimated to be around 28 years old at the time of death.
The parasitic jaw infection is often cited as the most likely immediate factor contributing to death. In its advanced stages, the infection would have caused significant swelling in the throat and mouth, making it excruciatingly painful, or even impossible, for the massive predator to swallow. An inability to eat or drink would have quickly led to starvation or dehydration for an animal that required a tremendous caloric intake.
The combination of the painful arthritis, the chronic bone infection in the leg, and the terminal jaw disease suggests a slow decline rather than a sudden event. These systemic health issues would have drastically reduced Sue’s mobility and hunting prowess. Death was likely caused by organ failure, starvation, or suffocation resulting from the parasitic infection. The body simply succumbed to the accumulated toll of a long and challenging life.
The Taphonomy of Sue: What the Fossil Record Reveals
Taphonomy is the study of how an organism decays and becomes fossilized. The skeleton was found nearly 90 percent complete by bulk, an exceptional degree of preservation for a large dinosaur. This completeness suggests the body was not exposed to scavengers for long before being covered.
Evidence indicates Sue died in or near a seasonal stream bed and was rapidly buried by mud and sediment shortly thereafter. This quick entombment protected the remains from being scattered and damaged by other animals or environmental weathering. Although the body was quickly covered, the bones were slightly jumbled or disarticulated by the rushing water.
The rapid burial is the reason scientists were able to recover so much of the skeleton and retain the delicate evidence of the dinosaur’s diseases and injuries. The excellent preservation of the bones has allowed for detailed pathological study, transforming Sue from a mere fossil into a singular biological case study of a Tyrannosaurus rex.