April 26, 2016

By David Hone

We all think of tyrannosaurs and in particular the iconic Tyrannosaurus rex, as some of the largest and fearsome carnivores to have ever walked the earth, thanks to popular culture. But there are many things about these great predators that you may not know about

Leading palaeontologist and writer Dr David Hone reveals six things you might not know about the tyrannosaurs.

There is no more famous dinosaur than Tyrannosaurus, the giant carnivore that roamed North America 66 million years ago.

Thanks to endless appearances in popular culture, as well as many children's books, everyone is familiar with the giant head and small arms of the largest tyrannosaurs, but there are also major misconceptions about these amazing animals.

We perhaps know more about the tyrannosaurs than any other group of ancient dinosaur thanks to a wealth of superb fossils and a huge amount of research having been poured into them – palaeontologists like tyrannosaurs too, it’s not just the public. As a result, we have an excellent idea of how these animals looked, lived, and died in the Mesozoic world.

They were both predators and scavengers

There is a persistent myth that tyrannosaurs were either one thing or the other, which is unlikely because very few carnivores can get away with being so choosy. In any case, we have direct fossil evidence for both of these activities being carried out by tyrannosaurs.

Several fossils of herbivorous dinosaurs show that they got away from hungry tyrannosaurs, as tyrannosaur teeth have been found wedged into the healed bones of these animals, so they have must have survived a predatory attack from a tyrannosaur. We also have evidence of dinosaurs that were bitten and fed on by tyrannosaurs after they had died and were partially buried – in short, tyrannosaurs were scavenging.

Tyrannosaurs were cannibals

In many cases, tyrannosaurs were the only large carnivores in their ecosystems so it’s fairly easy to work out who was doing the biting when you find scrape marks on bones, and bits bitten off them. However, it was not just the local herbivores that tyrannosaurs fed upon, it was also each other. Several tyrannosaur specimens, including those of Tyrannosaurus, show feeding traces from other tyrannosaurs.

These animals also interacted with each other when still alive and left their mark on their bones. Numerous tyrannosaurs show healed injuries on their skulls from bites inflicted by other tyrannosaurs. It looks like these animals often fought one another and left some serious wounds, though the fact that the injuries healed tell us these were not normally fights to the death.

Not all were giants

Although Tyrannosaurus and its nearest relatives were among the largest land living carnivores of all time – reaching five tons or more, and being around 13 metres in length – not all of the tyrannosaurs were giants. Like many dinosaur groups, their earliest members like Guanlong from China were rather small – only two or three metres in length, including the tail – and they lacked the giant heads and little arms of their descendants that came 100 million years later.

These smaller tyrants were predators but clearly lacked the size and bite power and would have restricted themselves to much smaller meals, and would have been wary of becoming lunch for bigger carnivores that lived alongside them.

They travelled great distances

Some of the oldest tyrannosaurs are from the UK and China, and we have tyrannosaur fossils from various parts of North America, Asia and Europe. There are also some specimens that have been tentatively assigned to this group from Brazil and even Australia, so they clearly got around.

However, we also see various groups switching continents – especially in the later part of the Cretaceous Period – with various tyrannosaur groups appearing almost alternately in North America and Asia. They also appear to have hopped across a small land bridge (over what is now the Bering Strait) multiple times.

Tyrannosaurs had feathers

Despite the endless depictions of tyrannosaurs in popular culture as scaly animals, they were in fact feathered. Two different Chinese tyrannosaurs – Dilong and Yutyrannus are preserved with feathers and many other dinosaurs that were close relatives of the tyrannosaurs also had feathers.

Given that there are few fossil beds that can preserve feathers, it’s very likely that all tyrannosaurs had at least some feathers on them. Yutyrannus was a large dinosaur (over a ton) and appears to have been feathered from head to toe, though other species may have had a mixture of feathers and scales.

There are more than 30 species

We have now found some 30 species of tyrannosaur and there are more waiting to be described in the scientific pipeline. Some of these are known from multiple complete specimens and we have a great idea of the range of variation within species, what juveniles looked like and how they grew, and we are able to restore large parts of their anatomy with great confidence.

We know that tyrannosaurs grew very fast indeed, we can tell females from males thanks to their bone structure (though to date we have no tyrannosaur eggs), and we can see that they had both exceptional vision and a superb sense of smell. Palaeontologists are even beginning to piece together their movements with studies of the muscles and bones and things like their ability to stand, run and turn – in fact, tyrannosaurs were good long distance runners.

All of this combines with our excellent knowledge of their evolutionary relationships to each other (and to other carnivorous dinosaurs), and so we are able to track their movements from continent to continent and the changes to their biology over time; together this gives us a superb idea of how these dinosaurs were like as real living animals.

There’s a lot of hype surrounding the tyrannosaurs, but the truth is based on some very sound and thorough science and is often a lot more interesting.

http://www.bbc.com/earth/story/20160412-busting-common-misconceptions-about-tyrannosaurs