What Were Dinosaurs Really Like? The Newer Science

If you learned your dinosaurs from older books and films, you probably carry a picture of large, scaly, greenish-brown reptiles, slow in the head and slow on their feet. Most of that picture has been redrawn. Not by opinion, but by particular fossils found in particular places, and by new ways of reading them.

This article goes through the main changes, and is honest about the parts that are still argued over. The quotations are from my book Dinosaurs, which follows the evidence one discovery at a time.

A dinosaur is a family tree, and it is still alive

The first correction is to the word itself. A dinosaur is not simply any large, extinct reptile. To a palaeontologist the word names a single family tree: the last common ancestor of Triceratops and the house sparrow, plus all of its descendants. That tree took root on the Triassic plains of Pangaea around 233 million years ago, and one branch of it is still singing in your garden.

This is meant literally. There are around 11,000 species of birds alive today, nearly twice the number of mammal species, and every one of them is a dinosaur. Not a descendant of dinosaurs in a loose sense, but a member of the group, in the same way that bats are mammals. Birds are theropods, the branch that also includes Tyrannosaurus and Velociraptor.

One consequence is easy to remember:

Tyrannosaurus was more closely related to a sparrow than it was to Stegosaurus.

Birds did not appear suddenly, either. The features we think of as belonging only to birds, from feathers and wishbones to hollow bones and folding wings, accumulated one by one in dinosaurs over more than 100 million years. A 2014 study by Michael Lee and colleagues found that the theropod line leading to birds shrank steadily for some 50 million years, from animals of around 160 kg to under 1 kg.

Many had feathers, and we know some of their colours

In August 1996 a farmer named Li Yumin split a slab of grey shale near the village of Sihetun in Liaoning, north-east China, and found a small skeleton lying in a curl. Along its neck, back and tail ran a dark fringe of fine filaments. It was named Sinosauropteryx prima, "first Chinese dragon feather", and photographs passed around a scientific meeting in New York that autumn caused a sensation.

For a decade afterwards, feathered dinosaurs were small: turkey-sized hunters, crow-sized gliders. Big predators, it was assumed, would overheat in a coat and must have been scaly. Then in 2012 Xu Xing and colleagues described Yutyrannus huali, a tyrannosauroid about 9 m long and the largest animal known with direct evidence of feathers. The assumption fell over.

The film star needs correcting too. The real Velociraptor was a feathered, turkey-sized hunter from the Gobi, about 2 m long. The raptors of Jurassic Park were modelled on the larger Deinonychus.

It would be neat to say that everything was fluffy. The evidence does not allow it. Skin impressions from Tyrannosaurus rex, described in 2017, show small scales on the neck, hip and tail, so the giant may have lost much of the coat its ancestors wore.

Colour is the other half of the new look. For most of the history of palaeontology, the colours of dinosaurs were pure guesswork. Artists painted them green or brown like lizards, and textbooks said plainly that colour would never be known.

That changed in 2008, when Jakob Vinther, then a graduate student at Yale, looked at a striped Cretaceous fossil feather from Brazil under a scanning electron microscope. The dark bands were packed with tiny sausage-shaped bodies. The pale bands had none. They were melanosomes, the structures that hold the pigment melanin, and they can survive in fossils.

The results are specific:

Anchiornis was the first dinosaur to have its entire plumage colour-mapped, and it looks rather like a black-and-white woodpecker with a red cap.

Sinosauropteryx turns out to have been banded in ginger. Pigment maps from one Chinese fossil of Psittacosaurus reveal a countershaded animal of the forest floor. And in 2017 Jasmina Wiemann and colleagues detected pigments in the eggshell of the oviraptorid Heyuannia, suggesting its eggs were blue-green like an emu's.

They grew fast, nested and looked after eggs

The older view of dinosaurs as sluggish reptiles began to break in the 1960s. In August 1964 John Ostrom of Yale University and his assistant Grant Meyer found a large, curved claw weathering out of a hillside near Bridger, Montana. In 1969 Ostrom named the wolf-sized predator Deinonychus antirrhopus, and his monograph quietly set off a revolution. Here was an animal built for an active life.

Then came the evidence about families. Maiasaura, the "good mother lizard", is the dinosaur that made parental care a serious scientific question. At Egg Mountain in Montana its mound nests sit in a colony, spaced about one adult length apart.

One famous name records a mistake. In 1923 a toothless, parrot-faced skeleton was found lying on top of a clutch of eggs at the Flaming Cliffs of Mongolia. The eggs were assumed to belong to another dinosaur, the obvious story was a crime caught in the act, and the animal was named Oviraptor, "egg seizer". It was really a parent brooding its own eggs. The name misled for seventy years.

Growth was quick and childhood was dangerous. A sauropod hatchling weighing a few kilograms could become an adult of 50 tonnes or more, a ten-thousand-fold increase. Young Maiasaura grew so fast that most of their adult size was reached in a few years, yet Holly Woodward's growth study found that around nine in ten died in their first year.

What is still argued over

A fair account of the newer science has to include its open questions. There are plenty.

Start with speed. In Jurassic Park a Tyrannosaurus keeps pace with a speeding jeep. According to nearly every study since, that is physically impossible. An African elephant, the closest living animal to an adult T. rex in weight, reaches about 25 km/h and never gets all four feet off the ground at the same time.

Then pack hunting. Ostrom found Deinonychus teeth and bones alongside skeletons of a plant-eater, which suggested pack hunting, but the finds are still debated.

Then soft tissue. In 2005 Mary Schweitzer reported flexible, vessel-like structures inside a T. rex thigh bone from Montana, a claim that still divides palaeontologists.

Then whole animals. Few dinosaurs have been rebuilt as often as Spinosaurus. At around 14 m it was probably the longest meat-eating dinosaur known, yet for most of the 20th century almost nobody had seen a bone of it.

Even names move. Brontosaurus was officially sunk in 1903 and raised again by data in 2015.

Why the picture keeps changing

For most of its history palaeontology meant hammers, brushes and a good eye for anatomy. Those still matter, but since the 1990s a new tool kit has transformed what a fossil can reveal.

The same bone that once gave a name and a length can now yield growth rates, brain shapes, colours, body temperatures and a place on a family tree tested by computer.

And sometimes the rock simply hands over more than anyone hoped. On 21 March 2011 a heavy-equipment operator named Shawn Funk struck something hard in an oil sands mine in Alberta. It was the front half of an armoured dinosaur, preserved in three dimensions with its skin and armour still in place. A technician spent more than five years and around 7,000 hours freeing it from the rock. Its last meal survives in its gut: mostly fern leaves, with about 6 per cent charcoal, suggesting it browsed regrowth after a forest fire.

That is the level of detail now on offer. Not a monster, but an animal with a diet and a season.

What to take from this

• "Dinosaur" names a family tree, and birds are a living branch of it.
• Feathers were widespread among theropods, including some large ones, but adult T. rex skin shows scales.
• Fossil pigment structures have given real colours for a few species.
• Dinosaurs nested in colonies, brooded eggs and grew quickly.
• Speed, pack hunting and soft-tissue claims are still debated, and good sources say so.
• The picture changes because the methods improve and new specimens keep turning up.

If you would like to follow the evidence one discovery at a time, Dinosaurs, No. 10 in The Visual Encyclopaedia, covers the real specimens, sites and people in 100 chapters with 100 detailed plates. It is a 302-page PDF and EPUB, and it costs £9 on Gumroad: matsiems.gumroad.com/l/dinosaurs.