Raptorex' 15 minutes of fame

When first unveiled Raptorex caused quite a stir. Here was an early Tyrannosauroid that had evolved all the features of T. rex... at 1/100th of it's size.
But it wouldn't be long before these claims would be seriously challenged, ultimately reducing Raptorex to a nomen dubium.

Raptorex kriegsteini compared to a human (image by Conty, from Wikipedia)

The paradoxical arms of T. rex

The puny size of Tyrannosaurus arms is so much a part of it's iconic image there is a Tumblr dedicated to things that T. rex would have been unable to do, because of it`s short arms (T-Rex Trying). Paradoxically the arms of a T. rex are actually quite robust and would have been rather muscular in life. 
So were those puny arms merely vestiges inherited from a longer armed ancestor, or were they actively used.. and if so, what for?

T. rex head & arms (original image from Wikipedia, by user FunkMonk)

Yutyrannus, the fuzzy giant

The first definite feathered Dinosaur was found in 1996 in the Liaoning Province in China, since then many more have followed, most of them quite small. Not so Yutyrannus, at 9 meters and an estimated one-and-a-half tonnes it's a giant. And it's a Tyrannosaur to boot albeit distantly related to T. rex.

Yutyrannus dwarfing the two Beipiaosaurus in the foreground

Yutyrannus wasn't the first feathered Tyrannosaur to be found. That was Dilong a much smaller animal estimated to reach some 2 meters in size (the largest fossil found was a juvenile that was 1,6m long). Yutyrannus was a basal Tyrannosaur like Dilong, that in itself is interesting because other early Tyrannosaurs like Dilong and Guanlong were much smaller.

Nanotyrannus, the Tyrannosaur that never was?

Nanotyrannus was described in 1988 by Robbert Bakker as a species of pygmy Tyrannosaur that lived alongside T. rex in what is now Montana, but it's status as a valid species is currently disputed.

Nanotyrannus life reconstruction (image Conty/Wikipedia)

The skull that formed the basis of Bakker's Nanotyrannus has certainly had an interesting second life as a fossil. When first described in 1946 it was named as a new species of Gorgosaurus, given the specific name lancesis after the Lance Formation in Montana where it was found. Subsequently it was referred to the slightly later Tyrannosaur genus Albertosaurus.

But it's moment glory would come in 1988 when it was given it's own genus by Robbert Bakker who named it Nanotyrannus because of it's small size compared to other Cretaceous Tyrannosaurs. The total length of N. lancensis was estimated to by about 5 meters in total length, less than half the size of a mature T. rex.

The status of Nanotyrannus did not go undisputed however, and the discovery of a second specimen in 2001 seemed to bring an end to the status of Nanotyrannus as separate species.

More than just a Bone-crunching Bite

Tyrannosaurus rex had the most powerful bite of any land animal that ever lived, but recent research shows that their was more to it's bite than brute force alone.

Image via Paleoblog

That T. rex had a powerful bite had long been known, a mechanical test of it's biting strength done by Paleontologist G.M. Erickson and engineers from Stanford University built a mechanical rig to replicate the teeth marks found on fossilized T. rex victims. They found a minimum bite strength of 3.300 pounds (~16.000 Newtons).
A recent computer analysis put the bite force even higher, with a minimum bite force of 20.000N and a maximum estimated  at an astonishing 57 thousand Newtons. And it should be noted that because of the differently sized teeth of Tyrannosaurs the bite force would initially be applied only to the tallest teeth, which would punch their way into the flesh (and any bones they happened to meet) ahead of the rest.

There is however evidence that T. rex wasn't optimized for brute force alone, and it comes from yet another computer analysis of the T. rex skull.

A Tyrannosaur of a different branch

Alioramus is both very closely related too, and very different from Tyrannosaurus rex. It was found in Mongolia where it lived alongside the giant Tyrannosaur Tarbosaurus.

The fossil remains of Alioramus altus showing it's body in outline (image Conty/Wikipedia)

When discovered in 1976 Alioramus was given the specific name A. remotus because it was thought to be far removed from the large Tyrannosaurs like Tyrannosaurus and Tarbosaurus that lived at the same time. But a recently found Alioramus specimen has shed new light on this relationship.
Discovered in Mongolia in 2001 the new specimen was first described in 2009 and found to be sufficiently different to warrant it's own species name. It was given the specific name A. altai after the Altai mountains in southern Mongolia.

Tyrannosaurus growth

Dinosaurs grew very large in a relatively short period of time, and their bodies changed as they matured. This happened in T. rex too, but with a twist.

"Jane" a Juvenile Tyrannosaurus (image Wikipedia)

That Dinosaurs could grow to enormous size is common knowledge, but they were surprisingly small when they hatched. Even the largest known Dinosaur egg is no more that 25 by 30 centimetres. No T. rex egg is known, so we don't know exactly how big they were when hatching, but they were probably about the size of a chicken.

The growth pattern of Dinosaurs can be roughly summarized as a number of years of slow growth, followed by rapid growth until maturity and gradual growth until death. Depending on the size of the Dinosaur it could take anywhere from 2 years for the smallest species, to 15 years for the gigantic Sauropods to reach maturity (quite amazing if you consider the size of the largest Sauropods). 

Tyrannosaurus had a surprising twist on this pattern. Much like humans T. rex did not start its fast growth until around twelve years old, and would then grow rapidly until reaching maturity at 18 or 19 years old. Compare that to the basal Tyrannosaurid Guanlong which was found to have been mature at a mere seven years of age.

The Crowned Tyrannosaur

Tyrannosaurus Rex may have been the 'king of the Dinosaurs', but it was one of it's ancestors that wore a crown.
Found in the China this early Tyrannosaurid from the Late Jurassic was named Guanlong (Crowned Dragon) because of it's distinctive crest.

Pencil drawing of the head of Guanlong wucaii by Renato Santos

Guanlong is the oldest relative of Tyrannosaurus yet found, older even than Dilong. It is therefore a very basal Tyrannosaurid with the slender build, long arms (with three-fingered hands), and a long narrow snout common to most Coelurosaurs.
It did however have a number of specializations that put it clearly in the Tyrannosaur clade. Like T. rex and all other Tyrannosaurs Guanlong had two types of teeth, with the smaller front teeth being shaped like scrapers. The foremost bone of the jaw was also very high, giving Guanlong the relatively blunt snout common to all Tyrannosaurs.

Tyrannosaurus Teeth - The crowns of a king

The teeth of Tyrannosaurus are unlike any other, they are highly specialized for killing and eating other Dinosaurs. They are not only famously large and recurved (or "banana-shaped"), but they are also placed for maximum effect.

Teeth of Tyrannosaurus Rex

Allosaurus and T. rex (not to scale)

Tyrannosaurus did not have the hatched-shaped head common to most Theropods, rather the head of a T. rex was comparatively wide ending in a blunt snout.
The teeth of a Tyrannosaur were also different in shape from those of other Theropods. Where almost all Theropods had flat blade-like teeth for slicing through meat, Tyrannosaurs had teeth that were decidedly more rounded (in some teeth almost circular) for punching through flesh and crushing bone. Tyrannosaurus in fact had three distinct types of teeth in it's jaws.

Tyrannosaurs used their mouths to manipulate their food

Everyone knows Tyrannosaurs, especially Tyrannosaurus Rex, had tiny arms compared to the size of their bodies. Although counter-intuitive for humans who do almost all their manipulation with their hands, the Tyrannosaurs could use their mouths as an all-purpose tool for feeding.

T. rex cast, showing it's massive jaws and puny arms (Wikipedia)

Not only could they bite of chunks of meat with their powerful jaws, there is fossil evidence that shows that they used their mouths to turn over the their food to get at the rest of the meat.

From the remains of a hadrosaur that was partly eaten by a Tarbosaur (a close relative of T-rex) it is clear that the Tyrannosaur extensively manipulated the carcass with their teeth. 

Feathers on your Tyrannosaurs

Life restoration of Dilong paradoxus

Ever since Archaeopteryx was discovered 150 years ago there has been speculation about the connection between dinosaurs and birds, this relationship has now become so well established that birds are considered to be a subset of dinosaurs.
During the 1990s this was further cemented by the find of many unusually well-preserved dinosaur fossils in the Chinese province of Liaoning that showed them to have feathers. The feathered dinosaurs found were small Theropods, and among them was an early member of the Tyrannosauridea.

Dinosaur Droppings

At 12 meters tall and weighing in over 6 tonnes Tyrannosaurus rex was truly a giant, and so were it's droppings. The fossilized dinosaur droppings (known as a coprolite) in the picture are half a meter long and have a volume of two litres.

Tyrannosaur coprolite from Saskatchewan (image Wikipedia)