Name Meaning:  Tyrant Lizard King

Geologic Era:  Late Cretaceous

Location Discovered:  Colorado

Estimated Range:  Canada to New Mexico/Texas

Size:  12.3 meters long (based on Sue; fragmentary remains found elsewhere suggest larger possible size)

Extinction Date:  65 million years ago (K-T extinction)

Easily one of the most recognized dinosaur names, Tyrannosaurus is also one of the best studied dinosaurs of North America.  Our specimens are both casts, but give an idea as to the impressive stature of this animal.  Both specimens are casts from Sue, the Tyrannosaurus on display in the Field Museum in Chicago, Illinois.  The tooth includes the root portion, and only the top third would have been exposed above the jawline.  The claw is a cast of a pedal ungual, or foot claw.  

Tyrannosaurus rex’s skeleton shows some strong adaptations for hunting, such as powerful leg muscles and very good binocular vision.  This would have given Tyrannosaurus the ability not only to detect prey, but to chase it down as well.  Tyrannosaurus’s olfactory bulb in the brain is very well developed as well, giving it a keen sense of smell.  This also points to Tyrannosaurus possibly being a scavenger as opposed to active hunter.  

However, one does not necessarily exclude the other.  Most predators will gladly scavenge a carcass, as it means less expended energy on their part.  Tyrannosaurus could have easily caught its own food, but would not have passed up a free meal.  Its large size also meant that it could bully other predators away from their kills, such as Nanotyrannus or Acheroraptor.  When confronted with an belligerent Tyrannosaurus, most smaller predators would take the wiser route and retreat.  Confrontation may have happened between Tyrannosaurus and others of its species, however.

If the Sue specimen is any indication, Tyrannosaurus rex lived a rough lifestyle.  A list of Sue’s (healed) injuries include:

-damaged shoulder blade

-torn tendon in right arm

-3 broken ribs

-left fibula twice the size of right (evidence of bone infection)

-evidence of arthritis in tail

-parasitic infection holes in jaw


Sue’s age at time of death appears to be 28 years old, making her the oldest known Tyrannosaurus rex.  The holes in the jaw, originally thought to be healed bite marks, are now thought to be a protozoan infection similar to Trichomonas gallinae, a parasite that infects modern birds.  This parasite leaves lesions similar to what is found on Sue’s jaw.  Whether or not this infection ultimately killed her is unknown, but the list of injuries she survived is impressive.  

One unique feature of Tyrannosaurus rex is its growth rate.  As seen in the graph below, Tyrannosaurus grew relatively steadily until it was about 10 years old, then underwent the growth spurt to end all growth spurts.  Unlike the related species pictured with it, Tyrannosaurus roughly tripled its body mass in around 5 years (years 14-18).  This would have put phenomenal stress on the body of Tyrannosaurus rex.  

Add this to the stresses of reproduction, particularly on females, and this would explain why about half of the known T-Rex specimens appear to have died within a few years of reaching sexual maturity.  This live dangerously and die young scenario may seem counter-intuitive, but it does appear to have served the species well, as it had one of the larger ranges of tyrannosaurids.

There used to be a case for sexual dimorphism with Tyrannosaurus, but that does not appear to be the case.  What used to be used to set skeletons apart was body morphology, specifically gracile (slender) and robust (heavier looking).  It is now that that these are more age related differences than anything else, with the gracile specimens representing younger animals and the robust ones older animals.  

There is only one Tyrannosaurus rex specimen conclusively shown to be female.  She is called B-rex, and she has medullary tissue evident in her bones.  This tissue is also present in female birds who are ovulating.  What this means is the B-rex was a female of reproductive age, and she had died while she was ovulating.  Medullary tissue is used as a calcium source for eggshells, and males would have no need for this tissue.  Medullary tissue also strengthens the link between theropod dinosaurs and birds.

Image Credits:

Full Skeleton:  “Sues skeleton” by Connie Ma from Chicago, United States of America – Sue, the world’s largest and most complete dinosaur skeleton.Uploaded by FunkMonk. Licensed under CC BY-SA 2.0 via Commons – https://commons.wikimedia.org/wiki/File:Sues_skeleton.jpg#/media/File:Sues_skeleton.jp


Growth Curve:”Tyrantgraph”. Licensed under Public Domain via Commons – https://commons.wikimedia.org/wiki/File:Tyrantgraph.png#/media/File:Tyrantgraph.png


Life Restoration:  http://spinops.blogspot.com/2014/06/tyrannosaurus-rex.html