Dinosaurs under the big sky



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Discovery Opportunity: How did the T-rex change as it grew to adult-size?

The Museum of the Rockies has 13 partial skeletons of T-rex and 4 of these specimens have good skulls: Custer T-rex, Wankel T-rex, Montana’s T-rex and Catherine/B-rex. Compare the T-rex skulls in the growth series. The skull of the T-rex changed shape as it grew up. Juveniles had larger eyes and more teeth than adults. Juveniles had 26 upper teeth and 34 lower teeth. Adults had 24 to 26 upper teeth and only 24 lower teeth. T-rex is one of the only dinosaur species to have lost tooth sockets as they grew older. In other words, the number of teeth in a T-rex’s mouth got smaller as the T-rex got older. This has to do with diet. Juveniles had small, sharp, blade-shaped teeth to cut flesh, whereas adults had large, blunt, rounded teeth for crushing bone. Jack Horner hypothesizes that this loss of tooth sockets has to do with T-rex adults being bone-crushing scavengers.




SCIENTIFIC RESEARCH ON T-REX FOSSILS
As visitors circle the base of Montana’s T.rex, panels highlight information about T-rex discovered through scientific research. The panels cite the specific published scientific paper used as the source of information.


Panel: DID T-REX GET SICK?

Holes in the jaws of T-rex are the result of a type of disease called Trichomonas, known to affect the jaws of modern birds. MOR 008, the Custer T.rex, may have died from this disease. The panel images show location of holes in MOR 008 (Custer T.rex) and MOR 1125 (B-rex).



Panel: BIENNIAL TOOTH REPLACEMENT

Dinosaurs were continuously replacing their teeth. T.rex teeth lasted only two years before being lost and replaced with a new tooth. We humans replace all of our teeth only once during our lifetime.


Panel Images:

- Section through T.rex jaw showing tooth replacement (old tooth and new tooth).

- Von Ebner lines in the dentine of a Tyrannosaurus rex tooth. Von Ebner lines record daily

increments of growth as the tooth formed.



Panel: HOW LONG DID TYRANNOSAURUS LIVE?

We determine the age of dinosaurs and other vertebrate animals by counting their growth lines (similar to counting tree rings). T.rex was sexually mature at about 12 years and reached full growth at about 20 years. The oldest T.rex known is only about 25 years of age. T.rex grew fast and died young!


Panel Image: Graph showing the percentage of growth achieved at different ages for five MOR T-rex specimens.

Panel: HOW RARE WAS T-REX?

Large top predators are extremely rare in their ecosystems. Tyrannosaurus was large, but not uncommon, and therefore was not likely a top predator. Its abundance suggests it was likely an opportunistic feeder, eating dead, sick and weak prey similar to hyenas. The hyena population is twice the combined population of lions, leopards and cheetahs.


Panel Images:

- Hyena, lion, leopard, cheetah

- Pie chart showing distribution percentages of different dinosaur species in the Hell

Creek Formation: Triceratops (40%); Tyrannosaurus (24%); Edmontosaurus (20%);



Thescelosaurus (8%); Ornithomimus (5%); Pachycephalosaurus (1%); Ankylosaurus (1%).

Panel: WHICH DINOSAURS DID T.REX EAT?

Based on fossil evidence such as bite marks and contents of coprolites (fossilized dung), Tyrannosaurus ate other Tyrannosaurus, Anzu, Pachycephalosaurus, Thescelosaurus, Ankylosaurus, Edmontosaurus, Ornithomimus, Dromaeosaurus, Triceratops, and Leptoceratops. A series of panels provide examples of dinosaur species eaten by T-rex. Two nearby display cases contain fossil evidence of T-rex eating Triceratops and Edmontosaurus.



Panel: T-REX ATE TRICERATOPS

Panel images show T-rex bite marks on upper and lower surfaces of a Triceratops pelvis.


Display Case: TRICERATOPS PELVIS BITTEN BY A T-REX

Studies of the puncture marks (red arrows) in this pelvic bone by former graduate

student Greg Erickson determined that T-rex had bitten the bone with a bite force of

2,900 pounds, a force proportionately similar to the bite of a hyena. Note: The absence

of any healing around the holes indicates that the Triceratops was dead before the

punctures were made. There is no evidence to indicate that the T-rex killed the



Triceratops – only that the T-rex ate the Triceratops. The bite marks on both the upper and

undersides of the pelvis indicate that the body of the Triceratops had been completely torn

apart, as the pelvic bone is normally deeply embedded in muscle.

Panels: T-REX ATE DUCK-BILLS, PACHYCEPHALOSAURS, AND OTHER T-REX

Panel images show T-rex bite marks on a duck-bill ulna (forearm) and toe bone. Another panel shows fossil evidence from Tyrannosaurid coprolite (fossilized dung) from Canada and preserved muscle tissue found in coprolite. Other images show T-rex bite marks on T-rex fossils.



Display Case: T-REX ATE EDMONTOSAURUS

T-rex ate Edmontosaurus! In the display case, the red arrow points to the broken end of

a Tyrannosaurus tooth embedded in the ridge of the nose of the Edmontosaurus skull.

Examination of the bone around the tooth reveals that the Edmontosaurus was dead when

the T-rex broke its tooth. The Edmontosaurus probably protected itself from predators by

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