Why dinosaurs lived much more complex lives than we thought

Everything we collectively think about dinosaurs is built on information imbibed over the past decades from a variety of places – from reputable books and documentaries to Hollywood movies that don’t let science get in the way of a good story. But many of the characteristics of these long-lost animals in the public consciousness are most probably wrong, says palaeontologist Dave Hone at Queen Mary University of London.

Hone, who literally wrote the book on dinosaur behaviour and has also described several new species of pterosaurs, is on a mission to correct the record. He describes himself as a zoologist of dead animals and uses modern-day comparisons to bring dinosaurs to life.

Did Velociraptor really hunt in packs? How did predatory dinosaurs bring down huge herbivores? What were the elaborate frills of Triceratops for? And why did pterosaurs get so much bigger than birds? He spoke to New Scientist about what we know – and don’t know – about these extraordinary creatures.

Michael Le Page: Let’s jump straight in. Everyone remembers the pack of Velociraptor hunting the kids in Jurassic Park. But you question whether dinosaurs really hunted in packs.

Dave Hone: One thing to say whenever we talk about “Did dinosaurs do X?” is that dinosaurs lived on every continent, in just about every ecosystem, and for 160, 170 million years. It would be weird if they didn’t do any given behaviour. But what evidence have we got for cooperative group hunting in the theropods, the carnivorous dinosaurs? Basically, almost none.

There is a famous set of multiple fossils of Deinonychus, a close relative of Velociraptor, found in association with a large herbivore called Tenontosaurus. That was inferred to be a group of them hunting Tenontosaurus. But lions don’t normally keel over when five of them bring down a buffalo. Reanalyses have questioned that interpretation, although I do still think it’s at least plausible.

But then, how do you transfer that? Lions hunt in groups. If you apply the same logic people apply to dinosaurs, that would mean all the other big cats hunt in groups. None of them do. So, you’ve got to be incredibly careful.

We have also found tyrannosaurs in groups. Maybe that does mean they lived in groups, but that doesn’t mean they hunted in groups.

But there is evidence for herbivorous dinosaurs living in groups?

Yes, we do have very large numbers of herbivores captured in groups. But some of these groups are preserved in things like floodwaters. A modern analogy for this is the Masai Mara migration, where millions of wildebeest cross the river. In 100 million years from now, you could dig up thousands of wildebeest and conclude they live in herds of tens of thousands. But they mostly live in small groups.

We’ve also found groups of fossils of juvenile dinosaurs, haven’t we?

Yes, that’s a really interesting thing. The average clutch of dinosaur eggs might be 20 or 50. Some are probably laying multiple clutches in a year. So, you should have dozens of juveniles for every adult, and instead we have dozens of adults for every juvenile.

Juveniles are very rare, about 5 per cent of all finds. But if you find a group of dinosaurs, about half of them are of juveniles. So juveniles are getting together in groups when adults aren’t. And of course, there’s an extremely good reason for that, which is to avoid being eaten. If you’re a young dinosaur, you need to eat a lot. And every time you’ve got your head in a bush, you’re not looking for a predator. Whereas, if there’s a group of you, someone is very likely to spot it.

So while dinosaurs may not have hunted in packs, they were vicious predators.

Yes, we’ve got a bunch of what we think are predation or failed predation attempts by theropods. There’s often bites on the tail [bones], which makes sense. Biting the tail is a brilliant way of crippling a dinosaur because they have these enormous leg muscles that go from about halfway down the tail to the back of the thigh. That is the single biggest source of power for these animals. And they’ve got enormous blood vessels and things running through it. So if you want to cripple or kill something quickly, that’s a very good way of doing it.

But these big predatory dinosaurs did fight each other, didn’t they?

We’ve found lots of fossils with injuries, in particular on the faces. It’s particularly common in tyrannosaurs. In some cases, there are these enormous score marks all across the face. I described one with Darren Tanke where a chunk of the back of the skull was bitten off and you can see it’s healed. So these were pretty tough animals getting into serious scraps.

And we’re talking about predatory dinosaurs, but there’s also evidence that herbivores like the ankylosaurs may have fought with each other.

Yes, ankylosaurs are famous for their club tails and armoured heads and bodies, and the assumption has been this is to fight off potential predators. But work by Victoria Arbour shows that this armour is particularly good at resisting heavy impacts. Well, that’s not a bite, and what might have a big heavy thing that’s trying to hit you? So it’s looking increasingly like they’re fighting each other.

Now, that doesn’t mean they’re not fighting theropods with their club tails, but that’s not why they evolved. It’s often overlooked that these things can be multifunctional. The example I give for this is elephant tusks. They fight with them, dig with them and strip bark off trees with them. But when tusks first evolved, they weren’t very good for any of these things. The initial selection for them could well have been sexual.

It’s often assumed that the armour and frills of ceratopsians like Tricerotops were there for these herbivorous dinosaurs to defend themselves against predators. But you think they could be a result of sexual selection, don’t you?

Features that are used for sexual display tend to grow fast when these animals hit sexual maturity. We looked at this in Protoceratops because we have lots of fossils of various ages – about 80 specimens – and that is exactly what we found. The growth trajectory of their frill is slow until they get to about half adult size, and then suddenly it gets very quick.

You study the flying reptiles known as pterosaurs as well as dinosaurs. Were these animals really able to hatch out of an egg and fly straight away?

The idea they might be precocial, as it’s known, has been around for a while, but it’s only relatively recently, with the discovery of pterosaur embryos, that we’ve had good data that supports it.

If you look at birds inside eggs, they have well-developed feet, but they don’t have well-developed wings. Before pterosaurs have hatched, they’ve got long wings with strong bones, almost identical to the adult condition. That immediately points to the idea that they might be flying straight out of the egg.

Does this mean pterosaurs didn’t have parental care? Were they fending for themselves?

It has been suggested that they don’t have parental care. Growth rates in pterosaurs are incredibly hard to work out, but what data we have suggests pterosaurs had very slow growth.

That fits with the idea that they are precocial, because flying has a high energy demand and if you need to eat lots just to move about to find more food, you can’t put a lot into growth. That said, there are precocial animals that also get parental care – lots of antelope and deer can walk and even run hours after being born.

There are also the living groups that are very close relatives of the animals that came before and after dinosaurs. The living crocodilians are the nearest to non-living dinosaurs that we have. And then birds are literally dinosaurs. All crocodilians look after the eggs and the babies after hatching. So do almost all the 11,000 species of bird. So parental care should be the starting hypothesis for pterosaurs and dinosaurs, and then you need to look for evidence that would contradict it. With dinosaurs, the sauropods [the biggest, long-necked dinosaurs] are the only ones that appear to dump the eggs and then move off.

This idea of pterosaurs being able to fly from hatching, but also having parental care, is conjuring up a vision of a mother pterosaur flying through the air with a trail of little pterosaurs behind her.

I’ve not thought of it, but it’s certainly not impossible. There are Arctic ducks that jump off a cliff after their parent almost immediately after hatching, though it’s not flying.

Many pterosaurs also had extraordinary head crests. Do we know why?

More pterosaurs than not have some kind of cranial crest. Indeed, soft tissue crests have been found in some exceptionally well-preserved fossils, so quite a few species not thought to have them might well have done. In some species, such as such as tapejarids, the head crests were enormous and extravagant. There’s good evidence this is sexual selection. These crests are bigger in older animals, and they’re not obviously functional. It’s been suggested they help steering, but I don’t think any of those papers have been convincing.

I did a study with my PhD student, Ross Elgin, that showed the long spikes of Pteranodon didn’t help them steer. Looking more broadly, all the head crests are all different. If you look at flippers, turtles and dolphins and penguins and plesiosaurs all evolved similar flippers because there is one good way of making a flipper. If there were some massive selection pressure to help you steer in the air, we’d expect pterosaur head crests to all end up looking the same, too.

Pterosaurs evolved into the largest flying animals that ever lived, with wingspans of around 10 metres. Why have no birds reached these sizes?

I’m going to annoy every ornithologist, but birds aren’t actually very good at flying compared to pterosaurs. My go-to analogy is the Yak-38, the Soviet attempt at making a vertical take-off plane like the Harrier jump jet. But while the Harrier has only one engine, they put three engines in the Yak-38, two to take off vertically and one to move it horizontally. The problem is, when you’re moving horizontally, you’re now carrying all the weight of the extra engines. So it’s not an efficient design.

This is true of birds, too. They jump into the air with their legs and run with them on the ground, so they need big, heavy legs. But when they’re flying with their wings, the legs are just dead weight. Whereas pterosaurs walk and run with the enormous flight muscles on the front limbs. They walk on all fours, but their hind legs are really skinny. And when they come to launch, they’re jumping with the giant flight muscles they need to fly.

The other advantage they have is they’re not feathered. Bird feathers are quite heavy and, as birds get bigger, they need more feathers to create the airfoil to keep them up. Pterosaurs have their membranous wings, which are very thin and wouldn’t have weighed much. They do have a filamentous body covering, but it’s quite different to what we see in birds. This probably explains why we’ve got four or five lineages of pterosaur that got to more than 8 metres in wingspan.

What is one thing you would like people to realise about dinosaur behaviour?

Dinosaurs were real living animals, and we should think of them in that context. They are superlative animals. We should absolutely get excited that titanosaurs were 50, 60 tonnes and Tyrannosaurus was 5, 6 tonnes or whatever the current estimates put it at. And Triceratops had metre-long horns, and Stegosaurus had these enormous plates.

And they are wondrous, wonderful, fascinating animals, as are pandas and lions and centipedes and jellyfish and everything else. So let’s sit them within that pantheon and treat them as real animals, and not focus on the hyperbole of their size and weirdness.

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