Tyrannosaurus

Tyrannosaurus (/tɪˌrænəˈsɔːrəs, taɪ-/) is a genus of large theropod dinosaur. The type species Tyrannosaurus rex (rex meaning 'king' in Latin), often shortened to T. rex or colloquially t-rex, is one of the best-known theropods. It lived in what is now western North America, on an island continent called Laramidia. Tyrannosaurus had a wider range than other tyrannosaurids. We find its fossils in many geological formations from the late Maastrichtian age of the late Cretaceous period, 69 to 66 million years ago. It was one of the last known members of the tyrannosaurids and among the last non-avian dinosaurs before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal meat-eater with a big skull balanced by a long, heavy tail. Its front legs were short but strong, with two claws. The biggest known Tyrannosaurus measured about 12.3–12.4 m (40–41 ft) long. Some think it could have been even bigger — up to 13 m (43 ft) long, 3.7–4 m (12–13 ft) tall, and weighed about 8.8 t (8.7 long tons; 9.7 short tons). Although some other theropods may have been just as big, Tyrannosaurus is still one of the largest land predators known. It was probably the top hunter in its world, catching animals like hadrosaurs, young armored plant-eaters such as ceratopsians and ankylosaurs, and maybe even sauropods.

Tyrannosaurus has been one of the most famous dinosaurs since the early 1900s. Science writer Riley Black called it the "ultimate dinosaur". Its fossils are popular in museums, and it has appeared in media like Jurassic Park.

History of research

The search for Tyrannosaurus began in the late 1800s. One of the earliest discoveries was a tooth found in Colorado in 1874. Later, in the 1890s, more bones were uncovered in Wyoming, though they were first thought to be from another dinosaur.

The most famous discovery happened in 1900 when Barnum Brown found the first partial skeleton in Wyoming. Another skeleton was found in Montana in 1902, and it was named Tyrannosaurus rex in 1905 by Henry Fairfield Osborn. The name means "tyrant lizard king," showing how strong it was.

Since then, many more Tyrannosaurus skeletons have been found across western North America. Notable discoveries include Sue, one of the most complete and largest Tyrannosaurus skeletons, found in 1990, and Stan, another very complete specimen found in 1992. These fossils have helped scientists learn more about how Tyrannosaurus lived and grew.

Description

Tyrannosaurus rex, often called T. rex, was one of the largest land meat-eaters ever. One famous example named Sue is at the Field Museum of Natural History in Chicago. Sue measured about 12.3–12.8 metres (40–42 feet) long and stood nearly 4 metres (13 feet) tall.

Tyrannosaurus had a strong skull up to about 1.5 metres (5 feet) long, with teeth made for biting through tough meat. Its eyes helped it see well while hunting. The dinosaur's body was heavy but had hollow bones to stay a lighter weight. Its arms were very short, with only two fingers, while its legs were long and strong for moving quickly.

Classification

Tyrannosaurus is the main genus of the superfamily Tyrannosauroidea, the family Tyrannosauridae, and the subfamily Tyrannosaurinae. It helps scientists decide which other species belong in the same group. Other members of the tyrannosaurine subfamily include the North American Daspletosaurus and the Asian Tarbosaurus.

Tyrannosaurids were once thought to come from earlier large theropods like megalosaurs and carnosaurs, but are now grouped with smaller coelurosaurs. The earliest tyrannosaur group was the crested proceratosaurids, with later members in the Pantyrannosauria. Tyrannosaurs started small but grew larger by the Early Cretaceous. They became more common after other dinosaur groups declined in the Late Cretaceous.

Tyrannosauroids have fused nasals and a special tooth arrangement. Pantyrannosaurs have unique hip features and a large opening in the quadrate bone. Some developed an arctometatarsus, and eutyrannosaurs have a rough texture on their nasal bones. Tyrannosaurids do not have kinetic skulls or special crests on their nasal bones. They have a distinctive process on their lacrimal bone and a smaller interfenestral strut than the maxillary fenestra.

Paleobiology

Life history

Scientists have found young T. rex fossils, which help us learn about how they grew. A young T. rex weighed about 30 kg, while the biggest adults weighed about 5,650 kg. One young T. rex died when it was just 2 years old. The famous T. rex named Sue was about 27 to 33 years old when it died.

Young T. rex stayed under 1,800 kg until they were about 14 years old. After that, they grew very fast, adding about 600 kg each year for four years. Their growth slowed down around 18 years old. T. rex could also change how fast they grew depending on how much food they had.

Skin and possible filamentous feathering

We found feathers on some dinosaurs, which makes us wonder if Tyrannosaurus had feathers too. Small early relatives of Tyrannosaurus had filamentous structures, which are like the first steps to feathers. But skin from bigger tyrannosaurids, including Tyrannosaurus, shows scales. This means any feathers Tyrannosaurus might have had were probably only on some parts of its body.

Studies also suggest that Tyrannosaurus may have had lips covering its teeth, instead of showing its teeth like a kangaroo. This idea comes from comparing T. rex to modern lizards and looking at how its teeth wore down.

Sexual dimorphism

As scientists found more T. rex fossils, they looked at differences between them. Some thought there were two body types, one stronger and one thinner. The stronger one was sometimes thought to be female, maybe because it had a wider pelvis that could help with laying eggs.

But newer evidence makes this less certain. For example, a big bone was found on a strong T. rex, showing that this feature could not be used to tell sexes apart. Differences between fossils might be because of where they lived or how old they were.

Posture

Tyrannosaurus was once shown with its body at a 45-degree angle and a dragging tail, like a kangaroo. But scientists later found this posture would hurt its joints. Now, we think T. rex held its body close to the ground and used its tail for balance. This is how it is shown in museums and movies today.

Arms

When T. rex was first found, only the humerus (upper arm bone) was known. Early pictures gave it longer arms with three fingers. But later finds showed that T. rex actually had short arms with two fingers, about 1 meter long.

Even though their arms were small, the bones show areas where strong muscle would have been. Some think the arms could have helped in mating, getting up from lying down, or holding prey while biting. But others think the arms were too small for these jobs.

Thermoregulation

Tyrannosaurus was long thought to have a "cold-blooded" metabolism. But evidence suggests it might have had a faster metabolism, maybe like warm-blooded animals.

Studies of growth rates, oxygen in bones, and spectroscopy of tissue suggest T. rex could control its body temperature. Its metabolism was probably higher than reptiles but maybe not as high as birds. Some think its big size alone (gigantothermy) helped it keep a steady temperature.

Soft tissue

In 2005, researchers found soft tissue in a T. rex leg bone. The tissue had flexible blood vessels and things that looked like blood cells.

This discovery challenged the idea that fossils only turn to minerals. If true, these proteins could tell us more about dinosaur genetics. But some think the tissue might be biofilm made by bacteria, though this is still being discussed.

Speed

Ideas about how fast T. rex could run differ a lot, from 16–24 km/h to as high as 72 km/h, though the higher number is unlikely.

Tyrannosaurus was a big meat-eater and probably could not run as fast as smaller meat-eaters. Studies suggest it could run up to around 27 km/h, but would get tired quickly. T. rex was also a good walker, using a steady step to save energy, and could run short distances when needed.

Possible footprints

Two fossil footprints might belong to T. rex. The first was found in New Mexico and is 83 cm long by 71 cm wide. The second, found in Montana, is 72 cm long.

While these tracks look promising, we are not sure if they were made by Tyrannosaurus, as it is the only big theropod known from these areas. More footprints found in Wyoming and Colorado are also thought to be from Tyrannosaurus or close relatives, helping us learn about how they walked.

Brain and senses

Studies show that Tyrannosaurus had very good senses. Its eyes were placed to give it excellent binocular vision, better than modern hawks, which would help it track prey.

Tyrannosaurus also had a very good sense of smell, with some of the largest smell-related parts in its brain compared to other non-avian dinosaurs. Its cochlea (part of the inner ear) was long, meaning it could hear well, especially low sounds. Its nose was also very sensitive, possibly helping it feel temperature differences, touch eggs and young, or talk with others.

Social behavior

Some scientists think Tyrannosaurus may have hunted in groups, based on finding several fossils close together and comparing them to related species like Tarbosaurus and Albertosaurus.

But this idea is debated. Some think these groups might have come together because of drought or flooding, rather than working together. Others suggest tyrannosaurs might have gathered at dead animals like modern Komodo dragons, instead of hunting together. Injuries on T. rex fossils, like bite marks, have also been used to suggest that they interacted with each other.

Diet and feeding behavior

Most scientists think Tyrannosaurus was both a hunter and a scavenger. As the biggest meat-eater around, it probably hunted large plant-eaters like hadrosaurs and ceratopsians.

Tyrannosaurus had one of the strongest bites of any land animal, able to crush bones. There is debate about whether it was mainly a hunter or a scavenger, with some saying its short arms made hunting hard, while others point to its good senses and vision as tools for hunting. Evidence includes healed injuries on prey animals and tooth marks on other Tyrannosaurus fossils, suggesting both hunting and eating others of its kind.

Parenting

We do not have much direct proof of Tyrannosaurus taking care of its young because we rarely find young fossils or nests. But some scientists think, like its modern relatives birds and crocodiles, Tyrannosaurus may have protected and cared for its young.

Evidence from other dinosaurs, like building nests and feeding young, supports the idea that theropods might have done similar things. But without direct fossil proof, this is still just a guess.

Pathology

Studies of Tyrannosaurus fossils show signs of stress fractures and tendon avulsions, showing an active life. Stress fractures, caused by repeated injury, suggest regular activity instead of one event.

Tendon avulsions, where tendons pull away from bones, have been found in Tyrannosaurus and Allosaurus, giving clues about their muscles and behavior. Injuries like healed fractures and scars from bites also suggest fighting and a diet that included hunting instead of just scavenging.

Paleoecology

Tyrannosaurus lived during the Lancian faunal stage at the end of the Late Cretaceous period. It lived in areas ranging from Canada in the north to New Mexico in the south, on what was known as Laramidia. Important fossils of Tyrannosaurus have been found in the Hell Creek Formation, which had a warm and humid climate with many different kinds of plants and animals.

In addition to Tyrannosaurus, this area was home to other dinosaurs such as Triceratops, Ankylosaurus, and Edmontosaurus annectens. Another place where Tyrannosaurus fossils have been found is the Lance Formation in Wyoming, which looked like a bayou environment.

Cultural significance

Tyrannosaurus is the most famous dinosaur in popular culture. Since it was named in 1905, this big meat-eating dinosaur has captured people's imaginations. Movies like Jurassic Park and King Kong use it, and many museums show models and skeletons of T. rex. People often know its full scientific name, making T. rex a well-known symbol in the world of dinosaurs.