Name: Tyrannosaurus rex
Name Meaning: Tyrant Lizard King
First Described: 1906
Described By: Osborn
Classification: Dinosauria, Sauirschia, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Tyrannosauroidea, Tyrannosauridae, Tyrannosaurinae, Tyrannosaurini
Tyrannosaurus rex. This is the name that everyone has associated with dinosaurs since before most readers of this blog can remember. It is the embodiment of power, terror, real-life monsters, and everyone - I mean everyone- has an opinion about it. So what can I tell you here that you do not already know? Well, I can tell you a lot, actually. And I can also tell you what you already know just for posterity’s sake. But first, two things to get off the bat here:
1. It is T. rex or Tyrannosaurus rex. t rex, T-rex, and variations thereopn are incorrect. You see, Tyrannosaurus is the genus name; rex is the species name (much as for humans it is Homo sapiens). And in phylogenetics, the genus and species names for an organism are always in italics (if possible). Furthermore, the genus name is always capitalized; the species name is not capitalized. Finally, oftentimes it is useful to shorten the name to just the genus initial and the full species name; when you do this, you put a period after the genus initial, a space, and then the species name. Hence, the hyphen of the completely incorrect T-rex is out of place, just for one example. It is Tyrannosaurus rex, Tyrannosaurus, T. rex, or nothing.
2. Based on fossil evidence, it is most likely that Tyrannosaurus had feathers, given the prevalence of feathers in its evolutionary tree and the early evolutionary position of feathers in Dinosauria. Given that, I admit that it is a valid argument to say that Tyrannosaurus might have been too big for full body feathers; however, in paleontological and biological studies of trait evolution, it is always Occam’s Razor: the simplest explanation is true. And thus, since T. rex’s ancestors definitively had feathers, it is simpler for T. rex to have had feathers than for it to have not (its more complicated to lose a trait than to keep it); furthermore, similar sized animals have been found completely with feathers, or with feathers and scales, so size isn’t much of an issue here. In short, until we have direct evidence that Tyrannosaurus rex wasn’t feathered (and right now, we do not), we must say that it was; much as we must say that early primates had fur, since mammals ancestrally have fur, even though we do not have a lot of fur fossils for early primates. I will hear no more argument on the subject, especially non-scientific (“Feathers make T. rex uncool!”) arguments.
Now that we’ve gotten that out of the way, let’s get down to business. Tyrannosaurus lived in the Maastrichtian age of the Late Cretaceous period, 68 to 66 million years ago, right up until the end of the Mesozoic Era (hence, almost ever dinosaur documentary ends with them, and there’s the classic image of T. rex against a giant asteroid falling from the sky). It has been found all over Western North America, from Colorado to Wyoming to South Dakota to Montana. It has been famous since its discovery, due to its size and relatively terrifying stature. It is also known from over 30 specimens, however these specimens are not all complete, and what we know about T. rex is based on a cross examination of all individuals. It probably reached a maximum length of 13 meters long and 4 meters tall, making it about 6.8 metric tons in weight. It was the largest carnivore in its environment, but not the largest carnivore of all time or the largest carnivorous dinosaur; Spinosaurus holds that second title. But, Spinosaurus basically only lived in the water, so it really is a silly question to ask who would win that fight. It’s comparing apples and oranges.
Tyrannosaurus, like others of its family tree, had a fairly unusual skull for a theropod. It had binocular, good vision; a deep skull, and a short snout. The nasal bones and some others were fused but had a honeycomb of tiny air spaces, making them both stronger and more flexible and light. It had, as a result, an extremely powerful bite, exerting an extreme amount of force in a wider area due to the U-shape (rather than V-shape) of its upper jaw. It is possible, as a result, that it had the strongest bite force of any terrestrial animal known, with up to 23.5 metric tons in the highest estimates. It had marked heterodonty in its teeth, with closely packed teeth at the front of the upper jaw, with serration as well as a curved shape. This would allow them to stay intact when the T. rex bit down on struggling prey. Furthermore, the back teeth were robust, more robust, and reinforced. The teeth could get up to 30 centimeters in length, the largest tooth of any carnivorous dinosaur known.
Many specimens have been found, as stated, and as such we know a lot about this dinosaur’s life history and traits. Like humans, tyrannosaurs in general grew moderately in early life and later life, with an extreme period of rapid growth in their teens. Furthermore, Tyrannosaurus, as opposed to other members of its family, had extreme growth in the teenage years, gaining an average of 600 kg a year, allowing it to go from 1,800 kg as a juvenile to 6,000 kg as an adult in just four or so years (talk about a pubescent growth spurt, am I right?) In fact, as such, as juveniles Tyrannosaurus young would have been fairly similar to other members of the tyrannosaurid family group, only distinguishing itself in size and stature after this period of rapid growth. This growth also brought about sexual maturity (woo, puberty for T. rex), though most tyrannosaur specimens known died long before this point, as many long-lived animal species show in the past and today. However, sampling bias plays a high role in age-group fossilization representation, and as such the relative mortality rates for T. rex at different life stages cannot be conclusively stated.
Sexual dimorphism has been seen in the species, given the presence of two distinct body types amongst fossils. The robust morph also had a wider pelvice, indicating that this form would have belonged to the female to allow for the passage of eggs. However, recently the evidence for dimorphism has been weakened due to the idea that certain differences could be based on location, rather than sex. One specimen, however, dubbed B-rex, was found with soft tissue, some of which identified as medullary tissue, which in modern birds is used as a source of calcium for eggshell production. This indicates that B-rex was a female and died during ovulation, and as this is not found in crocodiles, is another link between birds and dinosaurs.
T. rex is often made fun of for the size of its arms, though as long term fans of this blog know, it didn’t have the smallest arm to body ratio for dinosaur by any stretch of the imagination (remember the month of the abelisaurs? I do.) The arms of T. rex were 1 meter long (which was short compared to its body, as I’m sure you’ve figured,) and could have assisted T. rex in rising itself from a lying down position. It also could have been used to grip down on struggling prey while T. rex tried to kill it with its jaws, which has been supported by analysis of the mechanics of the arms. It would have been able to lift 199 kg in its arms without the help of other muscles, making its actual lifting power about 3.5 times as strong as a human of the same size would be. The arm did have a limited range of motion though, but that would allow the prey to hold still, aiding T. rex in finishing the kill with its crunching jaws.
It is still relatively unclear whether T. rex was warmblooded or coldblooded (endothermic or ectothermic, respecitvely). High growth rates in the animal’s youth, combined with lower growth rates as an adult, are similar to patterns in birds and mammals, indicating endothermy. Furthermore, studies have been done using the Oxgyen isotope ratios in the fossilized bone to determine the temperature of the bone when it was deposited, which can correlate with body temperature. The temperature has been found to not vary much across the body, indicating a constant internal body temperature and a metabolism somewhere between ectothermy and endothermy. This has been corroborated by similar patterns in other dinosaurs but wide variation in lizards and other, less bird-like reptiles. However, this only proves homeothermy - constant body temperature - and does not indicate if it was endothermic through metabolism or gigantothermic through the size of the animal, which can help to maintain body temperature.
The locomotive abilities of Tyrannosaurus have long been under debate, especially its maximum speed and its turning abilities (much like one’s main concerns when deciding in Mario Kart.) It was probably slow to turn, taking 1 to 2 second to go 45 degrees, an amount that humans do in about a fraction of a second. This was due to T. rex's center of mass being far away from its center of gravity, giving it terrible rotational inertia (physics, my nemesis, how are you.) The maximum speed is under considerable more debate. This is thanks to the convenient lack of running tracks for T. rex, or any theropod, making it hard to know its speeds definitively. Its been called slow (Jack Horner and Don Lessem), and its been called fast. I, and most others, spent our childhood being told practically every other year something different, so here’s a little timeline.
- Traditionally, hollow bones and other features may have kept the body of T. rex relatively light, allowing it to have long, flexible legs with high speeds; furthermore it had large thick leg muscles, giving more power to faster running up to 40-70 km per hour
- 1993 Jack Horner and Don Lessem argued that it was actually slow, because its ratio of femur to tibia length was >1, like in modern elephants, who cannot run.
- 1995 Farlow et al. argued that it would have been fatally injured when moving quickly, the torso of the animal slamming into the ground at 6 Gs (six times the acceleration due to gravity) and the arms would not have reduced the impact. However, giraffes actually face similar problems, making it possible that T. rex ran when necessary despite the risks.
- 1998 Holtz describes that the distal hindelimb components (shin, feet and toes) were much longer relative to the femur, and that inconjuction with tightly interlocked foot bones transmitted the locomotion force from the foot to the lower leg better than in earlier theropods, allowing faster speeds
- 1998 Christiansen figured that the leg bones of Tyrannosaurus were not that much stronger than those of elephants, and thus the maximum speed of T. rex was about 11 meters per second… but a lot of this was based on dubious assumptions.
- 2000 Gregory S. Paul pointed out that the flexed kneed and toes were better designed for running in T. rex than in humans or elephants, and the reduced risk of getting hurt fighting would have outweighed any risk in actually running.
- 2002 a paper in Nature used math to find that anything above 40 km/hr would have required extremely large leg muscles, up to 40-86% of the body mass, and even moderately fast speeds would have required large leg muscles. It is unsure, therefore, what the top speed was, as we do not know how big the leg muscles were.
- 2003 Snively and Russelfound that the toe bones and ligaments there could work together in a ‘tensile keyestone model’ to strengthen the foot, keeping it stable and resistant, storing the strain energy through the use of these arctometatarsals (hello physics, my old friend.) This woul dhave given it greater agility than other large theropods without this feature.
- 2007 More computer models estimated a top speed of 29 km/hr, based on solely fossil data
- 2010 Scott Persons proposed that the speed was enhanced through tail muscles, assisting in leg retraction and ehancing running ability, agility and balance. The tail was further adapted for large muscle mass growth, with the muscle that would balance the leg in question making up as much as 58% of the tail’s muscle mass, giving it a closer center of mass and gravity, improving balance and agility, and also making it less front heavy and decreasing its rotational inertia.
- 2011 Mallison proposed that it used short, rapid strides rather than long strides like modern birds and mammals in order to run faster, making it more like power-walking, lessining the need for additional muscles in the legs. This also makes it harder to calculate stride length, as it cannot be measured the same as one does in birds and mammals. However, this depends on how frequently dinosaur muscles could contract, something we don’t know much about.
- Even if T. rex could not run, it could get to about 17 km/hr, which is still faster than most hadrosaurids and ceratopsians (provided you agree that ceratopsians are slow, which is actually under debate), its main prey species. It was also much longer than the animals it hunted, further aiding in prey capture.
In short, I would pick another cart, just in case.
Tyrannosaurus rex had keen vision, with a binocular range of 55 degrees, surprising that of modern hawks, and 13 times the visual acuity of humans, allowing it to discern objects as far away as 6 kilometers. It needed this keen depth perception to figure out where the horns and spikes of armored dinosaurs, such as ankylosaurids and ceratopsians, jutted out, allowing it to get in and kill the prey in the most efficient and safe manner possible. Its visual acuity was not based on movement and honestly I have no idea how Jurassic Park got away with that. It also had an heightened sense of smell, allowing the animals to detect carcasses by scent alone across great distances, and in fact T. rex probably had the most heightened sense of smell of any known non-avian dinosaur. It also had high hearing acuity, hearing best in the low-frequency range, which probably facotred a lot in behavior. It had one of the largest brains of all adult non-avian dinosaurs with the exception of some maniraptoriforms, but still in the range of modern reptiles and lower than that of modern birds - but close to that of alligators.
You know what people like to argue about as much as they like to argue about T. rex locomotion? Its predator or prey habits. Hoo boy. Jack Horner has long been a proponent of the scavenger theory, citing the short arms that could not be used to grip prey (which, as we’ve learned, actually could grip prey,) heightened sense of smell which is common in modern day scavengers like vultures to allow for the sniffing out of carcasses, the ability for T. rex teeth to crush bone, to get more nutrition from bones in a carcass, and of course, its speed being too slow to catch prey. However, as we’ve already learned, a lot of these points aren’t very convincing, and in fact, there is also evidence for hunting behavior. Binocular vision like hawks would allow for the ability to hunt better, and in modern animals binocular vision is mainly found in predators. Furthermore, an Edmontosaurus skeleton has been found with damage healed on its tail vertebrae, indicating that the T. rex attacked it when alive. There has also been evidence found for interaction between Triceratops and Tyrannosaurus. However, if Tyrannosaurus had been a scavenger, then the smaller predators of the area would have been the apex predators (such as troodontids,) and the size of T. rex would have allowed it to steal kills from them. Like most larger carnivores, T. rex probably engaged in an opportunistic mixture of both. It may or may not have an infectious bite like Komodo dragon, but this is under debate, and it probably processed kills through lateral shakes of the head.
Source: http://luisvrey.files.wordpress.com/2012/06/t-rex-offspringb.jpg (Note: The mom should also have feathers)
There is some evidence for pack behavior in Tyrannosaurus, given finds in which multiple individuals were found together and the possibility of pack behavior in other tyrannosaurids. Given its large brain to body size ratio, it also was smart enough for complex behaviors, and groups would have worked together to take down well armored prey. Furthermore, trackway evidence in Canada has indicated that tyrannosaurs may have hunted in groups. There is not a whole lot of evidence about behavior out there, however, in the fossil record, and while there are many opponents of the pack hunter theory, their evidence is as scarce as the pro position. It might have had a sort of halfway point between pack hunting and solitary hunting, forming groups when convenient. Furthermore, little evidence is present for or against nesting behavior, which I find frustrating; while many species of dinosaurs took care of their young, many others did not. I’m inclined to think, based on their large brain size and close relationship to birds, that Tyrannosaurus did care for its young in some capacity; however, more research needs to be done before it can be scientifically analyzed.
Tyrannosaurus lived in a complex, but not very diverse community of dinosaurs. At the end of the Cretaceous, dinosaurs were already dwindling in diversity due to a complex interplay of environmental factors. This contributed, in the end, to the extinction of non-avian dinosaurs at the end of the Cretaceous; they were already significantly less diverse, and it did not take much to finish off the rest. It lived alongside Triceratops, the sauropod Alamosaurus, and other herbivores such as Torosaurus, Edmontosaurus, Ankylosaurus, Pachycephalosaurus, Thescelosaurus, and the theropods Ornithomimus and Troodon. In its southern range, it also has lived alongside Struthiomimus and Leptoceratops, Glyptodontopelta, and Quetzalcoatlus. It lived in a warm and humid suptropical climate, alongside the Wetern Interior Seaway. It can be supposed that it went extinct with the asteroid impact at the K-T boundary. As we all know, Tyrannosaurus rex is a really famous dinosaur; and as such, its reference in pop culture are practically infinite.
Shout out goes to my friend tyrannosaurslair, who requested having his favorite dino dedicated to him!