“Sue,” the famous Tyrannosaurus rex skeleton, is a monumental paleontological discovery. Discovered in 1990 by Sue Hendrickson in South Dakota, this fossil is among the largest and most well-preserved T. rex specimens ever found, over 90 percent complete. Now a centerpiece at the Field Museum of Natural History in Chicago, Sue’s presence often prompts a common question: was Sue male or female? Determining the sex of a fossilized dinosaur is a complex challenge.
The Challenges of Sexing Dinosaurs
Determining the sex of extinct animals presents significant difficulties. A primary challenge is the lack of soft tissue preservation, as reproductive organs rarely fossilize. This necessitates relying on skeletal features, where scientists look for consistent differences in bone structure, a phenomenon known as sexual dimorphism. However, such skeletal differences can be subtle, unreliable, or even indistinguishable in many dinosaur species.
Skeletal features often considered include variations in pelvic shape, the robusticity of limb bones, or characteristics of the skull. These traits, while sometimes indicative of sex in modern animals, are frequently ambiguous in the fossil record, complicated by individual variation, age, or post-mortem changes to the bones.
A more reliable indicator for female dinosaurs is the presence of medullary bone. This specialized, calcium-rich bone tissue forms inside the long bones of female birds during their egg-laying period, providing the calcium needed for eggshell production. Its discovery in certain dinosaur fossils, including a different T. rex specimen, strongly suggests the individual was a reproductively active female. Yet, medullary bone is rarely preserved, and its absence does not rule out an individual being female, only that it was not laying eggs at the time of death.
Examining Sue’s Specific Anatomy
Scientists have meticulously examined Sue’s anatomy, but its sex remains elusive. Sue is notably large, measuring approximately 12.3 to 12.4 meters (40.4 to 40.7 feet) long and standing 3.66 to 3.96 meters (12 to 13 feet) tall at the hips. While its size and robust build are impressive, these characteristics alone are not reliable indicators of sex in T. rex, as individual variation or age could account for such traits. There is no clear consensus among paleontologists on whether male or female T. rex individuals were consistently larger or more robust.
Similarly, Sue’s pelvic structure has been scrutinized, but it does not offer a clear male or female signature. Although pelvic differences can sometimes indicate sex in modern animals, Sue’s pelvic bones do not provide such conclusive evidence. The absence of medullary bone in Sue’s remains is a significant factor. This means scientists cannot definitively classify Sue as female based on this highly reliable indicator. While growth lines found in Sue’s bones indicate it was around 28 to 33 years old at the time of its death, this information helps determine its age but provides no clues about its sex.
The Enduring Mystery of Sue’s Sex
Sue’s sex remains unknown and cannot be definitively determined. The challenges inherent in sexing fossilized dinosaurs, coupled with the lack of clear sexual dimorphism in Tyrannosaurus rex and the absence of medullary bone in Sue’s skeleton, contribute to this mystery. No anatomical feature in Sue provides a conclusive male or female signature, despite study.
Even without a definitive sex assignment, Sue remains an important specimen for understanding Tyrannosaurus rex biology. Its exceptional completeness and preservation have allowed scientists to conduct detailed studies on the species’ movement, growth, and pathologies. Paleontological research is an ongoing process, and while Sue’s sex is a mystery, future discoveries or advanced analytical techniques might one day shed more light on this question.