Sue has helped us make important discoveries about T.rex
Sue is the first T. rex ever found with a tiny ear bone called a stapes. The more than six-inch-long, pencil-thin ear bone transmits sound vibrations from the eardrum to the inner ear. This delicate ear bone is almost never preserved in dinosaur fossils and promises to give scientists a better understanding of the evolution of ear bones and hearing in dinosaurs and birds. The shape, size and orientation of the external ear hole also may be a feature unique to the tyrannosaurid family, including T. rex.
Sue’s skeleton includes the first furcula, or wishbone, ever found in a T. rex. Present in bird skeletons, the wishbone provides evidence for interpreting the relationship of advanced theropods (a group of two-legged, meat-eating dinosaurs) to birds, the descendants of dinosaurs. The furcula will also help scientists investigate the function of wishbones in dinosaurs.
Birdlike Leg Muscles
Soft tissues are almost never preserved in dinosaurs, but Sue’s beautifully preserved bones reveal detailed evidence of the attachments and orientations of the dinosaur’s limb muscles. This has allowed scientists to reconstruct the most accurate picture ever, from hip to foot, of the birdlike hind limb muscles in Tyrannosaurus.
A mass of gnarled, bony overgrowths fusing two of Sue’s vertebrae together also preserves a remarkable anatomical feature rarely seen in fossil dinosaurs: detailed, natural mold impressions of tail muscles.
A Fast-Walking Dinosaur
Based on an analysis of Sue’s well-preserved foot bones, Field Museum research associate Matt Carrano, an expert on dinosaur posture and locomotion, concluded that Sue’s top speed was probably a fast walk of about 15 miles per hour, about the maximum speed of an elephant. While this may seem slow for a T. rex, Carrano has pointed out that most of Sue’s dinosaur contemporaries would not have been nearly as swift.
The Neck Bone’s Connected to the Skull Bone
Sue’s skeleton contains a pair of tiny bones that lie between the first neck vertebra and the back of the skull. Called proatlas bones, these are rarely seen in dinosaur fossils and are the first ever found in a T. rex. Birds do not have proatlas bones. Their presence in both an advanced theropods such as T. rex and in the ancient theropod Herrerasaurus may help scientists tease apart anatomical transformations and evolutionary relationships in the transition from advanced theropods to birds.
3-D Picture of the Skull
The Field Museum’s research on Sue marked the first time that a high-resolution, industrial x-ray scanner was used to create a detailed, 3-D image of the inside of a T. rex skull. (One famous early study involved cutting a T. rex skull in half, altering the fossil forever.) These CT images, interpreted by Field Museum paleontologist Chris Brochu and published in the Journal of Vertebrate Paleontology, showed very large olfactory bulbs—indicating that Sue had a keen sense of smell. Also discovered in the skull was a new air sinus never seen before in a T. rex. Detailed analyses of the nerve passages in Sue’s braincase revealed new evidence from T. rex that birds are flying theropod (two-legged, meat-eating) dinosaurs.
A Sensitive Snout
An extensive series of holes in the upper jawbone of Sue’s skull appear to be aligned in a pattern. This observation, new to T. rex, suggests that the dinosaur’s snout was highly sensitive to touch.
New Clues to Evolutionary Relationships of Dinosaurs and Birds
Unusually well-preserved fossils like Sue are invaluable for resolving debates about evolution. Field Museum researchers studying the 90-percent complete T. rex skeleton and skull have discovered important new evidence supporting the theory that birds are descended from theropod dinosaurs. Findings include the wishbone, the birdlike limb muscles, birdlike air sacs (pneumatization) throughout the skeleton and skull, and several features in Sue’s braincase—revealed for the first time through high-resolution X-ray (CT) images of the skull.
In a recent study featured on the cover of the journal Nature, scientists determined that T. rex reached its massive adult size due to an extraordinary growth spurt that stretched from about 14 to 18 years of age. Scientists studied the bones of Sue and other T. rex specimens to find that, during the peak in its growth spurt, T. rex gained 2.1 kilograms per day, developing into a more than 5,000 kilogram giant, one of the largest terrestrial carnivorous animals ever. T. rex grew faster but had a shorter lifespan than an African elephant, the only living land animal of a comparable size.
In the same study, scientists discovered that Sue was 28 years old at the time of death. By counting lines in tyrannosaurid bones that correspond to annual growth cycles, researchers found that T. rex could live for about 30 years, one-third of which would have been spent at adult size. Judging by evidence of disease, arthritis, and broken bones, scientists believe that Sue was a “train wreck” at death and probably died of natural causes.
Tough Life of a Tyrannosaur
Sue’s bones display several abnormalities, from a deformed right arm to jaws riddled with holes. Initially, scientists assumed that these oddities were battle wounds from clashes with other dinosaurs. Now scientists believe most of Sue’s bone abnormalities are just healed-over evidence of injuries, infections, and diseases—the normal wear-and-tear of life in the Cretaceous.
Male or Female?
Before Sue was found, body size and anatomical differences were used to speculate whether a T. rex was male or female. One important clue was believed to be the location of a v-shaped tail bone called a chevron. It had been suggested that Sue was a female, based on the assumption that the first chevron was positioned far from the pelvis in female crocodiles. But after piecing together the skeleton, scientists discovered that Sue’s first chevron was actually closer to the pelvis, more like that of males in some living reptiles. After surveying living reptiles and other theropod dinosaur specimens, Field Museum scientists concluded that the position of the chevron varies too widely to make it a good indicator of gender, even in modern reptiles. The bottom line: we may never know if Sue was male or female.
Was T. rex Warm-Blooded?
More and more evidence points to the fact that some dinosaurs were fast-moving, and perhaps warm-blooded animals. Living warm-blooded birds and mammals (like humans) have a series of bones in their nasal passages, called turbinates, that help to warm and humidify air before it enters their lungs. The x-ray scans of Sue’s skull allowed Field Museum scientists to look for this warm-blooded feature for the first time in T. rex. While thin bony structures were found in Sue’s nose, it was concluded that they were not turbinates. This does not necessarily prove that T. rex was not warm-blooded; it may mean that turbinates evolved later on in the theropod-bird lineage, and that these dinosaurs had some other mechanism for warming the air they breathed.