Carthage College Archives - The Big Dinosaur Podcast

Episode 200 is all about Tyrannosaurus rex, the king of the dinosaurs.

We also interview Thomas Carr, Associate Professor of Biology at Carthage College, Director of the Carthage Institute of Paleontology, and Senior Scientific Adviser to the Dinosaur Discovery Museum. He can be found on Twitter @TyrannosaurCarr, on Facebook, on his blog Tyrannosauroidea Central, and on Google Scholar.

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In this episode, we discuss:

News:

A new alvarezsaurid, Qiupanykus zhangi, was found with an oviraptorosaur egg that it may have been eating source

A new 23ft sauropodomorph, Yizhousaurus sunae, was found in southern China source
A lesson plan for teaching paleontology to children from Julián Nájera is published in both English source
- and Spanish source

Andrew Farke’s 2013 article on the ethics of digitizing fossils source
Fossils that were recently returned to China are now on display in Zhengzhou, in Henan Province source
Two elephants at the Perth Zoo in Australia went on a tour to meet and greet the animatronic dinosaurs source

The dinosaur of the day: Tyrannosaurus

One of the last non-avian dinosaurs before they went extinct
Named in 1905 by Henry Fairfield Osborn

Name means “tyrant lizard king”
Named for its large size and for presumably being the apex predator of its time
Bipedal carnivore

Had a giant skull
Had a long, heavy tail
Had short forelimbs with two clawed digits, though they were still powerful

One of the largest known carnivorous theropods
May have grown up to 40 ft (12.3 m) long, up to 12 ft (3.66 m) tall at the hips, and weighed up to 8.4 to 14 metric tons (9.3 to 15.4 short tons)
May have grown larger, but need more fossils

Probably an apex predator, probably ate hadrosaurs, ceratopsians, ankylosaurs, and possibly sauropods
Jack Horner used to say it was a scavenger, but it was mostly to start people critical thinking
However, most predators scavenge when the opportunity arises, so T. rex probably did too

Lived in the Cretaceous in what is now western North America (on Laramidia)
T. rex fossils have been found in different ecosystems (inland, coastal, subtropical, semi-arid plains)
Had a wider range than other tyrannosauroids

More than 50 T. rex specimens have been identified, some nearly complete
Tyrannosaurus is the type genus of Tyrannosauroida (superfamily), Tyrannosauridae (family), and Tyrannosaurinae (subfamily)
Arthur Lakes first found T. rex teeth in 1874 in Golden, Colorado

John Bell Hatcher found bones in eastern Wyoming in the early 1890s (thought to be Ornithomimus grandis at first, but now considered to be T. rex)
Edward Drinker Cope found vertebrae fragments in South Dakota in 1892, and originally classified them as Manospondylus gigas (ceratopsid) but now considered to be T. rex
Manospondylus gigas means “giant porous vertebra” and refers to the openings in the bone for blood vessels

Osborn recognized the similarities between T. rex and Manospondylus in 1917. However, Manospondylus was too fragmentary, so he did not synonymize them
Black Hills Institute found the type locality of Manosponylus in June 2000 and found more tyrannosaur bones. They were considered to be from the same individual, and the same as those of a T. rex
An ICZN ruling in 2000 said that a name that’s been considered valid for 50 years can’t be replaced by a name considered invalid during that time (plus some other stipulations, all of which apply here), so T. rex name stays

Barnum Brown found the first partial T. rex skeleton in Wyoming in 1900. Osborn originally named it Dynamosaurus imperiosus in a paper in 1905
In 1902, Brown found another partial T. rex skeleton in Montana (Hell Creek Formation). Osborn described this skeleton as the holotype of T. rex in the same 1905 paper where he described Dynamosaurus
In 1906, Osborn said the two specimens were synonyms, and said T. rex was the valid name

The Dynamosaurus bones are in the collections of the Natural History Museum in London
Other synonyms include Dinotyrannus megagracilis and ?Stygivenator molnari
Only holotypes of Dinotyrannus and Stygivenator have been found, and they are now considered to be juvenile T. rex

Dinotyrannus megagracilis was originally named Albertosaurus megagracilis (found in the same formation as T. rex)
Also Aublysodon lancensis, which is now considered to be either a juvenile T. rex or Nanotyrannus
Debates on the validity of Nanotyrannus lancensis (some think that skull is a juvenile T. rex)

Differences include Nanotyrannus having more teeth. Some scientists think the two should be separate until more studies are done
Thomas Carr (in our interview) mentioned that the description of Nanotyrannus (damage to the skull, described juvenile features or features of T. rex)
Some controversy over whether Tarbosaurus bataar from Mongolia is a second species of Tyrannosaurus or its own genus

In 1955 Evgeny Maleev named Tyrannosaurus bataar from Mongolia. This was renamed Tarbosaurus bataar by 1965, and many think they are sister taxon (Tarbosaurus had a narrower skull, and a different kind of bite). Although, studies in 2014 and 2016 found they are closely related, and in 2016 Steve Brusatte, Thomas Carr, and others found Tyrannosaurus may have been from Asia and possibly descended from Tarbosaurus. Also, T. rex may have driven tyrannosaurids native to North America to extinction via competition. (However, 2006 study found large tyrannosaurs may have been in North America as early as 75 million years ago, though it’s not clear if that was T. rex, a new species of T. rex, or a new tyrannosaur genus)
On August 12, 1990 Sue Hendrickson found the most complete and largest T. rex skeleton in the Hell Creek Formation in South Dakota found so far (about 85% complete)
The T. rex was nicknamed Sue, and there was a legal battle over who owned it (covered in the documentary Dinosaur 13). In 1997 it was settled in favor of the original land owner, Maurice Williams, and then the Field Museum of Natural History bought the skeleton at auction for $7.6 million (the most expensive dinosaur so far). Between 1998 and 1999 the Field Museum spent 25,000 hours preparing the bones. Sue went on display May 17, 2000

Sue is one of the most famous T. rex
Sue the T. rex has a Twitter account and over 42,000 followers
A study of Sue found she was full grown at age 19 and died at age 28, possibly from a bite to the back of the head (not confirmed, later studies did not find bite marks). She had damage to the back of her skull, possibly was trampled after her death. Possible that Sue died of starvation after getting a parasitic infection from eating contaminated meat. She may have gotten an inflammation in her throat, and been unable to swallow food (based on her having smooth-edged holes in her skulls similar to modern day birds that have had the same parasite)

Another famous T. rex is Stan, nicknamed in honor of Stan Sacrison. Stan was found in 1987 in the Hell Creek Formation in South Dakota, though wasn’t collected until 1992 (originally thought to be a Triceratops skeleton)
Stan is 63% complete and on display at the Black Hills Institute of Geological Research in Hill City, South Dakota (many casts in museums all over the world are of Stan)
Stan had many pathologies: broken and healed ribs, broken and healed neck, and a hole in the back of his head, about the size of a T. rex tooth

Jack Horner found five T. rex skeletons in Montana in 2000
In 2001, a crew from the Burpee Museum of Natural History found a 50% complete juvenile T. rex in Hell Creek in Montana, nicknamed Jane. Jane was thought to be the first known skeleton of Nanotyrannus, but now thought to be a juvenile T. rex (she’s on display at the Burpee Museum)
Because a wide range of T. rex specimens have been found, scientists have estimated its lifespan and how fast it grew

The smallest known T. rex is the “Jordan theropod”, estimated to weigh 66 lb (30 kg), and died at age 2, and the largest is Sue (estimated to weigh 12,460 lb or 5,650 kg and died at age 28)
Juvenile T. rex tend to be under 4,000 lb (1,800 kg) until they are around 14, and then they grow quickly, gaining an average of 1,300 lb (600 kg) each year for four years, and then growth slows
Another study found the growth rate to be faster, at 4,000 lb (1,800 kg), which is very different, though the authors said it had a smaller gap between its actual growth rate and the one expected of it based on its size

The slow down of its growth rate may indicate maturity. B-rex, a 16 to 20-year old T. rex found in Montana, was found to have medullary tissue in its femur. (Medullary tissue is only found in female birds during ovulation, so B-rex was able to reproduce)
More than half of the known T. rex specimens died within 6 years of reaching maturity, as seen in other tyrannosaurs, and some modern large birds and mammals
Not many juvenile T. rex fossils have been found, possibly due to low mortality rates (they grew up, so were not fossilized as juveniles), or because not enough fossils found, or because fossils collected tend to be larger

Thomas Holtz Jr. suggested in 2013 that dinosaurs “lived fast and died young” (reproduced quickly unlike mammals that take longer to reproduce)
Gregory Paul also said that T. rex reproduced quickly and died young, possibly because they lived dangerous lives
Scientists analyzed the variation in body types of T. rex and found two types, the “robust” type and the “gracile” type. The robust type has been attributed to females (had a wider pelvis, maybe to pass eggs through, and a smaller chevron on the first tail verebra, also possibly to help eggs pass through). However, a 2005 study cast doubts on sexual dimorphism. Also, Sue had a full-sized chevron on the first tail vertebra, so that doesn’t help differentiate.

Instead of sexual dimorphism, the differences in body types could be because of geography or age (older animals are “robust”)
Only B-rex is likely female (only female birds have medullary tissues naturally, however studies have found crocodiles do not have medullary tissue)
T. rex had a large head, and could bite in the backs and necks of dinosaurs that were prey

Montana State University has the largest T. rex skull found so far (59 in or 150 cm long, compared to Sue’s 55.4 in or 141 cm long skull), that was found in the 1960s and recently reconstructed (press release came out in 2006)
Skull had large fenestrae (openings) to reduce weight
Had a narrow snout but the skull was wide in the back, helped with having good binocular vision

Had good binocular vision (eye sockets faced mainly forwards)
Kent Stevens found that T. rex had great vision. Study found that T. rex had a binocular range of 55 degrees, better than a hawk, and T. rex would have been able to see objects as far as 3.7 mi (6 km) away
Lawrence Witmer and Ryan Ridgely found that T. rex had heightened sensory abilities (rapid eye and head movements, ability to sense low frequency sounds, and a good sense of smell)

If T. rex hunted its prey would include Triceratops, Ankylosaurus, and hadrosaurs that may have had complex social behaviors, so precision was important to get in and out
T. rex had large olfactory bulbs and nerves, so may have been able to smell carcasses from far away (comparable to modern vultures)
Could hear low frequency sounds

Had a relatively large brain for adult non-avian dinosaurs
In 2012, Karl Bates and Peter Falkingham said that T. rex had the most powerful bite of any land animal. They found an adult could have between 7,800 and 12,800 lb of force in its back teeth (some scientists have estimated higher)
Greg Erikson and Paul Gignac said in 2017 T. rex could have bite forces of 1,900 to 7.700 lb, and could crush bones

Stephan Lautenschlager and others found that T. rex could open its jaw around 80 degrees, and could have a wide range of jaw angles for biting
Tip of the upper jaw was U-shaped, which meant it could rip out more tissue and bone in one bite, though that was stressful on its front teeth
Had heterodont teeth (different shapes)

Jaws had up to 60 teeth
Teeth have been described as “like lethal bananas”
Largest tooth found so far was 12 in (30.5 cm) long, including the root when it was alive

T. rex had heterodont teeth with different functions, according to a 2012 study. The front teeth were for gripping and pulling, the side teeth were for tearing flesh, and the back teeth diced up pieces of meat. T. rex teeth were wide and a bit dull, so it could withstand force by struggling prey
T. rex may have had a septic bite. William Abler hypothesized that teeth serrations may have had pieces of meat with bacteria in them, which would make T. rex bites deadly, like Komodo dragons were thought to have. Jack Horner said T. rex serrations were more cube-like than round in shape, like a Komodo dragon’s teeth. However, all salivia could contain deadly bacteria, so may not have been a method for killing prey
T. rex had an S-shaped curved neck, that was short and muscular

In 2007, Eric Snively and Anthony Russell found that T. rex neck muscles were so strong T. rex would have been able to throw a piece of meat that weighed 110 pounds 15 feet into the air and catch it again
According to Michael Habib, T. rex had thick neck muscles to hold its skull and give it a more powerful bite force (neck muscles compete for space in the shoulder with arm muscles, and the neck is bigger than the arms). According to Habib, long arms are more easily broken and take more energy and can get disease, so short arms may have been more beneficial
A 2016 study suggested that large theropods like Tyrannosaurus had lips that covered their teeth, based on the fact that they had enamel, and enamel needs to stay hydrated

Thomas Carr and others found in 2017 that tyrannosaurs had large, flat scales on their snouts, with small keratinized patches. They suggested that tyrannosaurs had sensory neurons under the scales on their faces and may have used them to identify objects, measure the temperatures of nests, and pick up eggs and hatchlings (headlines were about mating)
Compared to the rest of its body, T. rex arms are relatively small, at about 3.3 ft (1 m) long. They have large areas for muscle attachment, so were probably very strong
Osbon said in 1906 that the forelimbs may have been used to grasp a mate while mating. Others have suggested T. rex used its arms to help it get up after falling.

Arms may have been used to hold down prey while tearing it to pieces with its jaws
Forelimb bones had thick cortical bone, which may mean it could withstand heavy loads. An adult T. rex biceps brachii muscle could life 439 lb (199 kg), and it had other muscles to make it even more powerful
Arms had a limited range of motion. Shoulder joints could only move 40 degrees and elbow joints could only move 45 degrees

All these factors may mean T. rex used its arms to hold struggling prey
One scientists, Steven Stanley, said T. rex may have used its arms for slashing prey, especially juvenile T. rex (arms grew slower in proportion to their bodies)
Earlier tyrannosaurs like Eotyrannus had proportionately longer arms than T. rex, and as tyrannosaurs got bigger over time, their arms got shorter. Some scientists therefore think this group would have eventually lost its arms, if it kept evolving. But will never know for sure

When T. rex was first found, they had only found the humerus part of the forelimb. So, Osborn mounted his T. rex in 1915 to have three fingers, like Allosaurus. Lawrence Lambe had described the two fingers of Gorgosaurus, a close relative, in 1914, but this was not confirmed for T. rex until 1989 when the Wankel rex was found with complete forelimbs (Sue also has complete forelimbs)
T. rex had many hollow bones, to help reduce weight
Had a long tail that helped balance head and body

Tail sometimes had over 40 vertebrae
Juvenile T. rex may have had feathers but adult T. rex probably had no feathers. Skin impressions found show it had a pebble-like structure
Others say: No direct evidence that T. rex had feathers, but it’s likely to have had feathers on at least parts of the body (related species had feathers)

Example: Dilong had feathers (scientists think feathers may have been related to body size, where juveniles were feathered then shed them and only had scales when they got bigger because they no longer needed the insulation, though some large tyrannosaroids had feathers covering most of the bodies, so not sure this hypothesis is true)
Another example is Yutyrannus, which was 30 ft (9 m) long and weighed up to 3,100 lb (1,400 kg), and had feathers on various parts of its body, which may mean its whole body was covered in feathers
Skin impressions of a T. rex specimen found in Montana in 2002 (nicknamed “Wyrex”) showed small patches of scales

Possible that feathers in tyrannosauroids varied based on body size, climate, or other factors
In March 2005, Mary Higby Schweitzer and others said they had found soft tissue from the marrow cavity of a T. rex leg bone, found in the Hell Creek Formation. It had blood vessel tissue and microstructures resembling blood cells, that somewhat resembled ostrich blood cells and vessels. Not clear if something strange happened to preserve these, or if the material is original. Though if it is original, it would help scientists figure out some of the DNA content of dinosaurs. It’s possible no one had found this before because they did not think it was possible, and so were not looking. Since then these tissue-like structures have been found in two more tyrannosaurs and a hadrosaur
In 2007, Asara and others found that seven traces of collagen proteins found in T. rex bone most closely matched those in chickens. Finding proteins in fossils so old changed scientists’ views of fossils. Before, it was thought fossilization replaced all living tissue with minerals

More studies in 2008 showed the close connection between T. rex and modern birds
In 2008, Thomas Kaye and others questioned the soft tissue in T. rex, saying that it was actually slimy biofilm made by bacteria. They found that what had been thought to be remnants of blood cells were actually framboids (had iron presence), which were microscopice mineral spheres with iron. The researchers had found similar spheres in other fossils from different periods, including ammonite. In the ammonite the spheres were found in a place where the iron could not have been related to the presence of blood
Schweitzer criticized the study, sayind there is no reported evidence that biofilms can produce branching, hollow tubes, like the ones she found in her study

In 2011, San Antonio, Schweitzer, and others published details on the parts of the collagen that had been recovered, which was the inner parts of the collegen coil, as expected from a long period of proten degradation
For a long time it was thought T. rex and other dinosaurs were ectothermic (cold-blooded)
In the 1960s, Bob Bakker and John Ostrom challenged this idea in the Dinosaur Renaissance

T. rex was thought to be endothermic (warm-blooded) and active
Growth rates indicate it had a high metabolism
Reese Barrick and William Showers looked at the oxygen isotope ratios in a T. rex torso vertebrae and tibia (this ratio is sometimes used to determin the temperature of the bone when it was deposited). They found very little difference in temperature (only 4 to 5 degrees C or 7 to 9 degrees F), which they said indicated that T. rex had a constant internal body temperature, known as homethermy, and had a metabolism in between ectothermic reptiles and endotermic mammals.

Some scientists said that the ratio of osygen isotopes in fossils from today do not necessarily represent the same ratio in the past, and may have changed during fossilization.
In later papers, Barrick and Showers said they found similar results in Giganotosaurus
Even if T. rex had evidence of homeothermy, does not mean it was endothermic

T. rex may have been a warm-blooded metabolism through gigantothermy, where its surface area was small compared to its volume and mass, which meant less area for heat to escape the body, which raised its base temperature
Several footprints have been found that may have been from a T. rex: one track found in 1983 in New Mexico that was 33 in (83 cm) long and 28 in (71 cm) wide, one track found in 2007 in Montana that was 28 in (72 m) long (not clear if it was T. rex), and one track found in 2016 in Wyoming that are thought to be either from a juvenil T. rex or a Nanotyrannus
Lots of different estimates for max speed, mostly 25 mph (40 kph), some as low as 11-25 mph (18-40 kph) and some as high as 45 mph (72 kph); based on tracks found but not many have been found of large theropods running

Another study in 2017 found T. rex could reach a max speed of 17 mph (27 kph)
Most recent research on T. rex locomotion suggests T. rex reached max speeds of 25 mph (40 kph), and that faster speeds were not possible because they required very big leg muscles. However, it’s unknown how large T. rex leg muscles were
In 2007, a study with computer models estimated running speeds of up to 18 mph (29 kph)

Even a max speed of 11 mph (18 kph) is faster than a lot of prey, like some hadrosaurs and ceratopsians
Lots of debates over whether T. rex could run or not
Possible that T. rex did not run

T. rex may have been slow to turn (may have taken 1 to 2 seconds to turn 45 degrees), based on its center of mass being far from its center of rotation
In 1993 Jack Horner and Don Lessem said that T. rex was slow and probably could not run, because the ratio of its femur and tibia was larger than 1, like in many other large theropods and in modern elephants
In 1998 Christiansen said the T. rex leg bones were not much stronger than elephants, and suggested a max speed of 25 mph (40 kph), but that this was based on many dubious assumptions

In 1995 Farlow and others said that T. rex, weighing between 5.4 and 7.3 metric tons (6 to 8 short tons), would have been seriously or fatally hurt if it fell while moving quickly, and its small arms could not help on impact. However, giraffes can run up to 31 mph (50 kph), though they can break a leg or fatally hurt). Could be that T. rex ran when necessary
In 2017, William Sellers and others found via a computer model that T. rex could not run because of high skeletal loads. They estimated T. rex to weigh 7 tons and the model showed that moving more than 11 mph (18 kph) would have shattered the T. rex leg bones
In 2011 Heinrich Mallison proposed that T. rex and other dinosaurs could have moved quickly by power walking (found a few similarities in dinosaurs and race-walkers, with less muscle mass in the ankles and more muscle mass in the hindquarters). However, John Hutchinson cautioned that scientists must first look into dinosaurs muscles to see how frequently they contracted

However, T. rex had hollow bones and other features to be lightweight, and other animals such as ostriches have long, flexible legs and can run fast but take slow strides as well
T. rex also had larger leg muscles than any current living animal
Gregory S. Paul said that T. rex had a large ilium bone to help support large muscles for running, and other features, and that one formula to calculate speed was not that reliable, because it was too sensitive to bone length, making long bones artificially weak. He also said the risk of being hurt while fighting may have been worth the risk for T. rex falling while running

In 2010 Scott Persons suggested that T. rex may have had strong caudofemoralis (tail) muscles to help with its speed (had certain muscle arrangements with some similarities to modern reptiles)
The caudofemoralis may have helped with running, agility, and balance
Additionally, T. rex tail muscle mass may have been underestimated by 25-45 percent. Having a larger caudofemoralis means the center of mass would be closer to the hindquarters and hips, and would help with rotating more quickly

In 1998 Holtz said that tyrannosaurids and some close relatives had long shins and toes compared to other theropod’s femurs, and that tyrannosaurids and relatives had tightly interlocked foot bones to help with locomotion, and therefore tyrnnosaurids and close relatives were the fastest large theropods
In 2013 Holtz said that large allosaurs had shorter feet than T. rex, though they were similarly sized, and T. rex had longer, skinner, more interlocked feet, which are attributes of animals that move faster
In 2003 Eric Snively and Anthony P. Russel said that T. rex feet had a “tensile keystone model” to increase its stability and help it be more efficient and less strained
T. rex metatarsals (foot bones) are arranged as digitigrade, where they form an extension to the lower leg bones, which increases the total length of the leg area, and increases its stride (seen in animals that run after other animals)
As mentioned throughout, lots of debate over whether T. rex was a hunter or scavenger
In 1917 Lambe said T. rex was close to Gorgosaurus and therefore a scavenger, because Gorgosaurus teeth showed hardly any wear on them. However, theropods replace teeth frequently, so not many people agreed
Jack Horner has argued that T. rex was a scavenger, though not in scientific literature, and only has a tool to teach people, mostly kids, that you shouldn’t make assumptions without evidence
Jack Horner said T. rex could not be a predator because of its small eyes, small arms (couldn’t hold prey), and large legs (slow). He has said it was a scavenger because of its great sense of smell, and legs that were built for walking long distances
T. rex had a great sense of smell and could smell carcasses from far away, like vultures
In the hunter/scavenger debate, researchers said T. rex could not purely be a scavenger because modern pure scavengers, like vultures, glide to cover large areas efficiently. Others have said that T. rex’s ecosystem would have had many animals to scavenge, although T. rex may have had to be cold-blooded to get enough calories from scavenging than the calories it spent foraging. They also argued that animals during T. rex time didn’t have gliding scavengers, so there was no competition for this type of food
If T. rex was a scavenger, may have been big enough to steal food, but may have been outnumbered by smaller theropods
Some of T. rex prey could move pretty fast, so if T. rex could only walk it would probably was more likely to scavenge. However, T. rex may have been fast enough for large hadrosaurs and ceratopsians
Because T. rex teeth could crush bone, it could get to the bone marrow (very nutritious). Karen Chin and others found bone fragments in coprolites from tyrannosaurs, though they said tyrannosaur teeth were not adapted to chew bone the way modern hyenas are to get to bone marrow
T. rex eyes point forward, so it had good binocular vision (found mostly in predators), so points to hunting behavior. Jack Horner has said there’s a trend of steadily improving binocular vision in tyrannosaurs, though not clear why if tyrannosaurs were scavengers
One Edmontosaurus skeleton has been found to had damage to its tail vertebrae from a T. rex, that healed, which shows it probably survived an attack (and T. rex tried to hunt it)
Also evidence of an attack on a Triceratops, that had partially healed tyrannosaur tooth marks on its neck frill, and had a broken horn with new bone growth after the break. Unclear who initiated this fight, could have been either. Since the wounds healed, Triceratops probably survived
In 2001, Bruce Rothschild and others did a study examining evidence of stress fractures and tendon avulsions (injury to the bone where a tendon or ligament attaches to the bone) in theropods. In Tyrannosaurus and Allosaurus, they found avulsion injuries only in the forelimb and shoulder that suggests their musculature was different from birds. They suggested that the tendon avulsion in Sue the T. rex was probably from struggling prey, which is evidence for being an active predator instead of scavenging for food
Most scientists think T. rex was both a hunter and scavenger, like most large carnivores
Pete Larson found a broken and healed fibula and tail vertebrae on Sue, some scarred bones from the face, and a tooth from a different T. rex in a neck vertebra. This may mean tyrannosaurs were aggressive with each other, though not clear if it would be about food or finding a mate, or if it was cannabalistic. Later studies found these wounds were infections, or damage to the bones after Sue died, and not necessarily injuries, or that the injuries were pretty generic and not necessarily from a fight with another T. rex
Phil Currie suggested T. rex could have hunted in packs. Compared T. rex to Tarbosaurus and Albertosaurus, and mentioned three T. rex skeletons found in South Dakota near to each other. He did CT scans and said its brain was three times larger than expected for its body size, so may have been capable of that kind of complex behavior. Prey such as Triceratops and Ankylosaurus would have been armored and fast, so T. rex would need to hunt in groups. Possible that juveniles and adults worked together, with juveniles running down the prey and adults killing it
Lots of scientists don’t agree with this theory, which has not been peer-reviewed (was part of his book Dino Gangs and a TV special). It’s based on comparing T. rex to different species, and the idea of Tarbosaurus hunting in packs hasn’t been published in a peer-reviewed scientific journal yet. Other explanations for theropod skeletons ending up together could be droughts or floods
Lawrence Witmer and Ryan Ridgely found that T. rex had heightened sensory abilities (rapid eye and head movements, ability to sense low frequency sounds, and a good sense of smell)
If T. rex hunted its prey would include Triceratops, Ankylosaurus, and hadrosaurs that may have had complex social behaviors, so precision was important to get in and out
T. rex had large olfactory bulbs and nerves, so may have been able to smell carcasses from far away (comparable to modern vultures)
Could hear low frequency sounds
Had a relatively large brain for adult non-avian dinosaurs
In 2012, Karl Bates and Peter Falkingham said that T. rex had the most powerful bite of any land animal. They found an adult could have between 7,800 and 12,800 lb of force in its back teeth (some scientists have estimated higher)
Greg Erikson and Paul Gignac said in 2017 T. rex could have bite forces of 1,900 to 7.700 lb, and could crush bones
Stephan Lautenschlager and others found that T. rex could open its jaw around 80 degrees, and could have a wide range of jaw angles for biting
Tip of the upper jaw was U-shaped, which meant it could rip out more tissue and bone in one bite, though that was stressful on its front teeth
Had heterodont teeth (different shapes)
Jaws had up to 60 teeth
Teeth have been described as “like lethal bananas”
Largest tooth found so far was 12 in (30.5 cm) long, including the root when it was alive
T. rex had heterodont teeth with different functions, according to a 2012 study. The front teeth were for gripping and pulling, the side teeth were for tearing flesh, and the back teeth diced up pieces of meat. T. rex teeth were wide and a bit dull, so it could withstand force by struggling prey
T. rex may have had a septic bite. William Abler hypothesized that teeth serrations may have had pieces of meat with bacteria in them, which would make T. rex bites deadly, like Komodo dragons were thought to have. Jack Horner said T. rex serrations were more cube-like than round in shape, like a Komodo dragon’s teeth. However, all salivia could contain deadly bacteria, so may not have been a method for killing prey
T. rex had an S-shaped curved neck, that was short and muscular
In 2007, Eric Snively and Anthony Russell found that T. rex neck muscles were so strong T. rex would have been able to throw a piece of meat that weighed 110 pounds 15 feet into the air and catch it again
According to Michael Habib, T. rex had thick neck muscles to hold its skull and give it a more powerful bite force (neck muscles compete for space in the shoulder with arm muscles, and the neck is bigger than the arms). According to Habib, long arms are more easily broken and take more energy and can get disease, so short arms may have been more beneficial
A 2016 study suggested that large theropods like Tyrannosaurus had lips that covered their teeth, based on the fact that they had enamel, and enamel needs to stay hydrated
Thomas Carr and others found in 2017 that tyrannosaurs had large, flat scales on their snouts, with small keratinized patches. They suggested that tyrannosaurs had sensory neurons under the scales on their faces and may have used them to identify objects, measure the temperatures of nests, and pick up eggs and hatchlings (headlines were about mating)
Compared to the rest of its body, T. rex arms are relatively small, at about 3.3 ft (1 m) long. They have large areas for muscle attachment, so were probably very strong
Osbon said in 1906 that the forelimbs may have been used to grasp a mate while mating. Others have suggested T. rex used its arms to help it get up after falling.
Arms may have been used to hold down prey while tearing it to pieces with its jaws
Forelimb bones had thick cortical bone, which may mean it could withstand heavy loads. An adult T. rex biceps brachii muscle could life 439 lb (199 kg), and it had other muscles to make it even more powerful
Arms had a limited range of motion. Shoulder joints could only move 40 degrees and elbow joints could only move 45 degrees
All these factors may mean T. rex used its arms to hold struggling prey
One scientists, Steven Stanley, said T. rex may have used its arms for slashing prey, especially juvenile T. rex (arms grew slower in proportion to their bodies)
Earlier tyrannosaurs like Eotyrannus had proportionately longer arms than T. rex, and as tyrannosaurs got bigger over time, their arms got shorter. Some scientists therefore think this group would have eventually lost its arms, if it kept evolving. But will never know for sure
When T. rex was first found, they had only found the humerus part of the forelimb. So, Osborn mounted his T. rex in 1915 to have three fingers, like Allosaurus. Lawrence Lambe had described the two fingers of Gorgosaurus, a close relative, in 1914, but this was not confirmed for T. rex until 1989 when the Wankel rex was found with complete forelimbs (Sue also has complete forelimbs)
T. rex had many hollow bones, to help reduce weight
Had a long tail that helped balance head and body
Tail sometimes had over 40 vertebrae
Juvenile T. rex may have had feathers but adult T. rex probably had no feathers. Skin impressions found show it had a pebble-like structure
Others say: No direct evidence that T. rex had feathers, but it’s likely to have had feathers on at least parts of the body (related species had feathers)
Example: Dilong had feathers (scientists think feathers may have been related to body size, where juveniles were feathered then shed them and only had scales when they got bigger because they no longer needed the insulation, though some large tyrannosaroids had feathers covering most of the bodies, so not sure this hypothesis is true)
Another example is Yutyrannus, which was 30 ft (9 m) long and weighed up to 3,100 lb (1,400 kg), and had feathers on various parts of its body, which may mean its whole body was covered in feathers
Skin impressions of a T. rex specimen found in Montana in 2002 (nicknamed “Wyrex”) showed small patches of scales
Possible that feathers in tyrannosauroids varied based on body size, climate, or other factors
In March 2005, Mary Higby Schweitzer and others said they had found soft tissue from the marrow cavity of a T. rex leg bone, found in the Hell Creek Formation. It had blood vessel tissue and microstructures resembling blood cells, that somewhat resembled ostrich blood cells and vessels. Not clear if something strange happened to preserve these, or if the material is original. Though if it is original, it would help scientists figure out some of the DNA content of dinosaurs. It’s possible no one had found this before because they did not think it was possible, and so were not looking. Since then these tissue-like structures have been found in two more tyrannosaurs and a hadrosaur
In 2007, Asara and others found that seven traces of collagen proteins found in T. rex bone most closely matched those in chickens. Finding proteins in fossils so old changed scientists’ views of fossils. Before, it was thought fossilization replaced all living tissue with minerals
More studies in 2008 showed the close connection between T. rex and modern birds
In 2008, Thomas Kaye and others questioned the soft tissue in T. rex, saying that it was actually slimy biofilm made by bacteria. They found that what had been thought to be remnants of blood cells were actually framboids (had iron presence), which were microscopice mineral spheres with iron. The researchers had found similar spheres in other fossils from different periods, including ammonite. In the ammonite the spheres were found in a place where the iron could not have been related to the presence of blood
Schweitzer criticized the study, sayind there is no reported evidence that biofilms can produce branching, hollow tubes, like the ones she found in her study
In 2011, San Antonio, Schweitzer, and others published details on the parts of the collagen that had been recovered, which was the inner parts of the collegen coil, as expected from a long period of proten degradation
For a long time it was thought T. rex and other dinosaurs were ectothermic (cold-blooded)
In the 1960s, Bob Bakker and John Ostrom challenged this idea in the Dinosaur Renaissance
T. rex was thought to be endothermic (warm-blooded) and active
Growth rates indicate it had a high metabolism
Reese Barrick and William Showers looked at the oxygen isotope ratios in a T. rex torso vertebrae and tibia (this ratio is sometimes used to determin the temperature of the bone when it was deposited). They found very little difference in temperature (only 4 to 5 degrees C or 7 to 9 degrees F), which they said indicated that T. rex had a constant internal body temperature, known as homethermy, and had a metabolism in between ectothermic reptiles and endotermic mammals.
Some scientists said that the ratio of osygen isotopes in fossils from today do not necessarily represent the same ratio in the past, and may have changed during fossilization.
In later papers, Barrick and Showers said they found similar results in Giganotosaurus
Even if T. rex had evidence of homeothermy, does not mean it was endothermic
T. rex may have been a warm-blooded metabolism through gigantothermy, where its surface area was small compared to its volume and mass, which meant less area for heat to escape the body, which raised its base temperature
Several footprints have been found that may have been from a T. rex: one track found in 1983 in New Mexico that was 33 in (83 cm) long and 28 in (71 cm) wide, one track found in 2007 in Montana that was 28 in (72 m) long (not clear if it was T. rex), and one track found in 2016 in Wyoming that are thought to be either from a juvenil T. rex or a Nanotyrannus
Lots of different estimates for max speed, mostly 25 mph (40 kph), some as low as 11-25 mph (18-40 kph) and some as high as 45 mph (72 kph); based on tracks found but not many have been found of large theropods running
Another study in 2017 found T. rex could reach a max speed of 17 mph (27 kph)
Most recent research on T. rex locomotion suggests T. rex reached max speeds of 25 mph (40 kph), and that faster speeds were not possible because they required very big leg muscles. However, it’s unknown how large T. rex leg muscles were
In 2007, a study with computer models estimated running speeds of up to 18 mph (29 kph)
Even a max speed of 11 mph (18 kph) is faster than a lot of prey, like some hadrosaurs and ceratopsians
Lots of debates over whether T. rex could run or not
Possible that T. rex did not run
T. rex may have been slow to turn (may have taken 1 to 2 seconds to turn 45 degrees), based on its center of mass being far from its center of rotation
In 1993 Jack Horner and Don Lessem said that T. rex was slow and probably could not run, because the ratio of its femur and tibia was larger than 1, like in many other large theropods and in modern elephants
In 1998 Christiansen said the T. rex leg bones were not much stronger than elephants, and suggested a max speed of 25 mph (40 kph), but that this was based on many dubious assumptions
In 1995 Farlow and others said that T. rex, weighing between 5.4 and 7.3 metric tons (6 to 8 short tons), would have been seriously or fatally hurt if it fell while moving quickly, and its small arms could not help on impact. However, giraffes can run up to 31 mph (50 kph), though they can break a leg or fatally hurt). Could be that T. rex ran when necessary
In 2017, William Sellers and others found via a computer model that T. rex could not run because of high skeletal loads. They estimated T. rex to weigh 7 tons and the model showed that moving more than 11 mph (18 kph) would have shattered the T. rex leg bones
In 2011 Heinrich Mallison proposed that T. rex and other dinosaurs could have moved quickly by power walking (found a few similarities in dinosaurs and race-walkers, with less muscle mass in the ankles and more muscle mass in the hindquarters). However, John Hutchinson cautioned that scientists must first look into dinosaurs muscles to see how frequently they contracted
However, T. rex had hollow bones and other features to be lightweight, and other animals such as ostriches have long, flexible legs and can run fast but take slow strides as well
T. rex also had larger leg muscles than any current living animal
Gregory S. Paul said that T. rex had a large ilium bone to help support large muscles for running, and other features, and that one formula to calculate speed was not that reliable, because it was too sensitive to bone length, making long bones artificially weak. He also said the risk of being hurt while fighting may have been worth the risk for T. rex falling while running
In 2010 Scott Persons suggested that T. rex may have had strong caudofemoralis (tail) muscles to help with its speed (had certain muscle arrangements with some similarities to modern reptiles)
The caudofemoralis may have helped with running, agility, and balance
Additionally, T. rex tail muscle mass may have been underestimated by 25-45 percent. Having a larger caudofemoralis means the center of mass would be closer to the hindquarters and hips, and would help with rotating more quickly
In 1998 Holtz said that tyrannosaurids and some close relatives had long shins and toes compared to other theropod’s femurs, and that tyrannosaurids and relatives had tightly interlocked foot bones to help with locomotion, and therefore tyrnnosaurids and close relatives were the fastest large theropods
In 2013 Holtz said that large allosaurs had shorter feet than T. rex, though they were similarly sized, and T. rex had longer, skinner, more interlocked feet, which are attributes of animals that move faster
In 2003 Eric Snively and Anthony P. Russel said that T. rex feet had a “tensile keystone model” to increase its stability and help it be more efficient and less strained
T. rex metatarsals (foot bones) are arranged as digitigrade, where they form an extension to the lower leg bones, which increases the total length of the leg area, and increases its stride (seen in animals that run after other animals)
As mentioned throughout, lots of debate over whether T. rex was a hunter or scavenger
In 1917 Lambe said T. rex was close to Gorgosaurus and therefore a scavenger, because Gorgosaurus teeth showed hardly any wear on them. However, theropods replace teeth frequently, so not many people agreed
Jack Horner has argued that T. rex was a scavenger, though not in scientific literature, and only has a tool to teach people, mostly kids, that you shouldn’t make assumptions without evidence
Jack Horner said T. rex could not be a predator because of its small eyes, small arms (couldn’t hold prey), and large legs (slow). He has said it was a scavenger because of its great sense of smell, and legs that were built for walking long distances
T. rex had a great sense of smell and could smell carcasses from far away, like vultures
In the hunter/scavenger debate, researchers said T. rex could not purely be a scavenger because modern pure scavengers, like vultures, glide to cover large areas efficiently. Others have said that T. rex’s ecosystem would have had many animals to scavenge, although T. rex may have had to be cold-blooded to get enough calories from scavenging than the calories it spent foraging. They also argued that animals during T. rex time didn’t have gliding scavengers, so there was no competition for this type of food
If T. rex was a scavenger, may have been big enough to steal food, but may have been outnumbered by smaller theropods
Some of T. rex prey could move pretty fast, so if T. rex could only walk it would probably was more likely to scavenge. However, T. rex may have been fast enough for large hadrosaurs and ceratopsians
Because T. rex teeth could crush bone, it could get to the bone marrow (very nutritious). Karen Chin and others found bone fragments in coprolites from tyrannosaurs, though they said tyrannosaur teeth were not adapted to chew bone the way modern hyenas are to get to bone marrow
T. rex eyes point forward, so it had good binocular vision (found mostly in predators), so points to hunting behavior. Jack Horner has said there’s a trend of steadily improving binocular vision in tyrannosaurs, though not clear why if tyrannosaurs were scavengers
One Edmontosaurus skeleton has been found to had damage to its tail vertebrae from a T. rex, that healed, which shows it probably survived an attack (and T. rex tried to hunt it)
Also evidence of an attack on a Triceratops, that had partially healed tyrannosaur tooth marks on its neck frill, and had a broken horn with new bone growth after the break. Unclear who initiated this fight, could have been either. Since the wounds healed, Triceratops probably survived
In 2001, Bruce Rothschild and others did a study examining evidence of stress fractures and tendon avulsions (injury to the bone where a tendon or ligament attaches to the bone) in theropods. In Tyrannosaurus and Allosaurus, they found avulsion injuries only in the forelimb and shoulder that suggests their musculature was different from birds. They suggested that the tendon avulsion in Sue the T. rex was probably from struggling prey, which is evidence for being an active predator instead of scavenging for food
Most scientists think T. rex was both a hunter and scavenger, like most large carnivores
Pete Larson found a broken and healed fibula and tail vertebrae on Sue, some scarred bones from the face, and a tooth from a different T. rex in a neck vertebra. This may mean tyrannosaurs were aggressive with each other, though not clear if it would be about food or finding a mate, or if it was cannabalistic. Later studies found these wounds were infections, or damage to the bones after Sue died, and not necessarily injuries, or that the injuries were pretty generic and not necessarily from a fight with another T. rex
Phil Currie suggested T. rex could have hunted in packs. Compared T. rex to Tarbosaurus and Albertosaurus, and mentioned three T. rex skeletons found in South Dakota near to each other. He did CT scans and said its brain was three times larger than expected for its body size, so may have been capable of that kind of complex behavior. Prey such as Triceratops and Ankylosaurus would have been armored and fast, so T. rex would need to hunt in groups. Possible that juveniles and adults worked together, with juveniles running down the prey and adults killing it
Lots of scientists don’t agree with this theory, which has not been peer-reviewed (was part of his book Dino Gangs and a TV special). It’s based on comparing T. rex to different species, and the idea of Tarbosaurus hunting in packs hasn’t been published in a peer-reviewed scientific journal yet. Other explanations for theropod skeletons ending up together could be droughts or floods
Lawrence Witmer said the social behavior can’t be determined by estimated brain sizes, though T. rex may have had large enough brains for communal hunting (semi-organized behavior)
July 2014 fossilized trackways found in Canada showed that tyrannosaurids may have hunted in packs
In 2010, Currie, Horner, Erickson, and Longrich suggested T. rex could be cannabalistic. They found T. rex specimens with T. rex tooth marks on their bones (humerus, foot bones, and metatarsals), which may be evidence of opportunistic scavenging. These parts of the body didn’t have much meat, so T. rex may have been eating a carcass that had already been chewed on. Possibly that other tyrannosaurids were also cannabalistic
In 2009 a study found that holes in some Tyrannosaurus skulls that were thought to be from attacks from other Tyrannosaurus were actually from Trichomonas-like parasites that often infect avians
However, Joseph Peterson and others found evidence that Jane the juvenile T. rex was attacked by another T. rex. Her skull had healed puncture wounds on the upper jaw and snout, probably from another juvenile T. rex, and CT scans showed the wounds came from a traumatic injury and that there was some healing after. They also said Jane’s injuries were structurally different from the parasite pathologies found in Sue
T. rex used to be depicted as a “living tripod” with its tail dragging, similar to a kangaroo. Henry Fairfield Osborn posed his T. rex skelton at the American Museum of Natural History this way, and it stayed that way from 1915 until 1992 (which inspired many depictions in films and paintings, including Rudolph Zallinger’s The Age of Reptiles mural in Yale University’s Peabody Museum of Natural History)
In the 1970s scientists realized this was not the right posture and that it would have weakened or dislocated joints
Then Jurassic Park showed T. rex in a modern pose
T. rex appears in many films, ads, post stamps, and other media
Very popular dinosaur, appears in many forms of media (popular name)
Henry Fairfeld Osborn said in 1905, “I propose to make this animal the type of the new genus, Tyrannosaurus, in reference to its size, which far exceeds that of any carnivorous land animal hitherto described…This animal is in fact the ne plus ultra of the evolution of the large carnivorous dinosaurs: in brief it is entitled to the royal and high sounding group name which I have applied to it.”
Osborn considered mounting the two T. rex skeletons (known at the time) to face off over a carcass at the AMNH, but then decided to mount just one
December 30, 1905, the New York Times said T. rex was “the most formidable fighting animal of which there is any record whatever,” the “king of all kings in the domain of animal life,” “the absolute warlord of the earth,” and a “royal man-eater of the jungle”
In 1906, T. rex was called the “prize fighter of antiquity” and the “Last of the Great Reptiles and the King of Them All.”
In 1927, Charles Knight painted a mural of Tyrannosaurus and Triceratops for the Field Museum of Natural History
Can see T. rex in many films, including 1925 The Lost World, 1933 King Kong, 1918 The Ghost of Slumber Mountain (shows T. rex facing off against Triceratops)
Often depicted as having three fingers in early films, like in Fantasia (Walt Disney told Barnum Brown that “it looked better that way”)
One of the first times T. rex was portrayed in the proper posture (not tail dragging) was the 1984 short Prehistoric Beast, made by Phil Tippett with his go motion technique (stop motion animation and motion blur)
Phil Tippett also worked on Jurassic Park, which used CGI instead of stop motion (when he first learned they’d use CGI, he said, “I’ve just become extinct” and Spielberg used that line in the movie)
T. rex is also in all the Jurassic Park and Jurassic World movies, the 1960 movie Dinosaurus!, the 1966 movie One Million Years B.C., The Last Dinosaur from 1977, The Land Before Time from 1988, We’re Back! A Dinosaur’s Story from 1993, Tammy and the T-Rex from 1994, Theodore Rex 1995, Toy Story from 1995, Pooh’s Grand Adventure: The Search for Christopher Robin in 1997, Night at the Museum from 2006, Meet the Robinsons from 2007, Ice Age 3: Dawn of the Dinosaurs from 2009, The Good Dinosaur from 2015, and countless others
Godzilla is a mixture of Tyrannosaurus, Stegosaurus, and Iguanodon
Also has appeared in Japanese animated films such as You Are Umasou from 2010, The Age of the Great Dinosaurs from 1979, Magic Tree House from 2011, and Doraemon: Nobita’s Dinosaur from 1980 and 2006
T. rex has also been in many TV shows, including Barney & Friends, Dinosaur Train, The Wiggles, 1974 Doctor Who Invasion of the Dinosaurs, Dinosaurs (with the Sinclairs), and many more
T. rex has also been in the TV documentary Dinosaurs! from 1985, which used some scenes from the 1984 short Prehistoric Beast (Phil Tippett)
T. rex has also appeared in documentaries including Walking with Dinosaurs, When Dinosaurs Roamed America, Dinosaur Planet, and more
T. rex has appeared in books, including Jurassic Park and the sequel The Lost World, Primeval: Extinction Event, We’re Back! A Dinosaur’s Story, and many more
T. rex has also appeared in video games, on stamps, in comics, and as animatronics for various exhibitions
In Lake Buena Vista, Florida, you can go to T-Rex Cafe, where you eat food and hang out with life-sized dinosaurs
Marc Bolan first saw T. rex at the Natural History Museum in London and later named a band Tyrannosaurus Rex, later T. Rex (abreviated properly). It was a very influential British rock band in the 60s & 70s.

Fun Fact:

Most birds have relatively large eyes for the size of their head, and their eyes aren’t fully spherical (they’re flattened on the back) so they can’t rotate in their sockets. This means that they have to move their whole head to look at something new. Dinosaurs may have had to do the same.

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This episode is brought to you in part by TRX Dinosaurs, which makes beautiful and realistic dinosaur sculptures, puppets, and animatronics. You can see some amazing examples and works in progress on Instagram @trxdinosaurs