Collecting guide: dinosaurs (and their bones, teeth and footprints)

Not every creature you think of as a dinosaur is actually a dinosaur

Dinosaurs are ancient reptiles that lived on land. Those that flew, such as Pterosaurs, or lived in water, such as Ichthyosaurs, are therefore not technically dinosaurs.

In order for a dinosaur to become fossilised, a very precise sequence of rare events needs to occur. Firstly, the carcass must become entombed in mud or ash shortly after death and before any predators can scavenge it, removing the flesh and limbs.

Then the dinosaur’s body has to sink deep into the earth, so its bones become permeated with minerals and quite literally turn to stone. Finally, the geological layer that contains the fossils must remain intact and at a stable temperature and pressure so that the fossil doesn’t disintegrate.

Dinosaurs roamed the Earth for some 175 million years — which means we live closer in time to the T. rex than it did to the Stegosaurus

The first dinosaur fossils date from around 240 million years ago, during the Triassic period, when all the continents were a single land mass known as Pangea. These are the fossils of small reptiles that flourished in the hot, dry conditions.

During the Jurassic period, 201-145 million years ago, Pangea split in two, giving dinosaurs the opportunity to evolve into a wider variety of forms. The temperature dropped and vegetation increased, leading to the evolution of huge, plant-eating dinosaurs like Stegosaurus.

In the Cretaceous period, 145-66 million years ago, the land split further into some of the continents we recognise today, causing diverse evolution. This is when some of the best-known dinosaurs, such as the Tyrannosaurus rex and Triceratops, lived.

The Cretaceous period ends with the dinosaurs’ extinction. They were most likely killed off over a period of two million years following a catastrophic asteroid collision — and the climate change that followed.

The larger the dinosaur, the less likely it is to have survived intact

Factors influencing the likelihood of finding an intact fossilised dinosaur include how common the animals were during the lifetime of their species, and their size. Enormous dinosaurs such as the Brontosaurus and Brachiosaurus are much more likely to have been discovered by scavengers or broken up in the geological strata, and are therefore much less commonly found intact.

On the other hand, a Psittacosaurus carcass, which is comparable to that of a dog, is the ideal size to float down a river and be deposited under in sediments.

Footprints are the only evidence we have that certain species existed

Dinosaur teeth are quite common, because some large, carnivorous dinosaurs regularly shed them. The enamel on the teeth also helped to preserve them.

Fossilised dinosaur eggs also exist. Most of the time, working out which species they came from involves some speculation, because they’re hardly ever preserved with the animal that produced them.

It’s a similar story for fossilised footprints. Because we don’t have a complete skeleton of every species from each period, it’s hard to say which animal made them. In fact, footprints are the only evidence we have for some species ever having existed.

Fossilised dinosaur skin is some of the rarest dinosaur material around. Imagine if a cow died in a field — the skin would be the first thing to be ripped from its carcass and eaten. And even if a dinosaur’s skin did survive the scavengers, it’s likely it would have been cooked off by geological pressure, or even destroyed during excavation.

Excavation of dinosaurs is hugely laborious, involving hundreds of hours of digging with tiny dentists’ tools and brushes. It costs around half a million dollars to get the bones of a dinosaur the size of a Stegosaurus out of the ground, cleaned, stabilised and mounted. Until recently, a skeleton wasn’t worth that much, so there was little incentive to remove entire animals.

Shipping and assembling them is also a huge task. I’ve seen dinosaurs transported in seven crates, each the size of a car, and they’re put together by experienced teams using video guides. It’s a long and costly process that requires lots of patience and space.

Collecting periods and pathologies, and the most popular dinosaurs

There are collectors who specialise in specific periods: some, for example, will only want Jurassic fossils. But they might not have the space or budget for an entire animal, so instead will buy a representation of each species, such as a leg or a horn.

Other collectors might be interested in certain pathologies, such as skeletal evidence of fighting. STAN, the T. rex sold at Christie’s in 2020, had two fused vertebrae, suggesting that at some point it had broken its neck, yet still managed to live on.

However, as with the art market, it’s often all in the name. If my phone rings and someone says, ‘James, I’d like a dinosaur’, it’s almost always followed by a request for a Tyrannosaurus or a Velociraptor. These are the species we grew up with.

Interestingly though, velociraptors all come from Mongolia, so can’t be exported. They’re also the size of a chicken. Michael Crichton, the author of Jurassic Park, based his famous predators on the much larger Deinonychus, but thought the name ‘Velociraptor’ was sexier.

Incidentally, Deinonychuses aren’t any easier to own than Velociraptors. Christie’s sold one of only three known examples in May 2022 in New York. It achieved $12.4 million.

If more than half a skeleton is found, it’s considered a big win

Most dinosaur fossils that appear at auction are primary-market material, because they’ve come straight from the ground. Historical provenance is rare, unless a museum deaccessions something. Crucially, you need to know that its excavation was authorised.

Condition can also be confusing for new collectors. Because of the disruptive nature of fossilisation, no complete skeleton exists. If more than half a skeleton is found, it’s considered a big win. But even then, there is no industry standard for determining how much of a skeleton exists. Sometimes it’s done by bone count, sometimes by weight. The missing parts will be replicated with casts.

Like an artwork, dinosaur fossils should be treated with care and respect, but you don’t have to factor in things like UV light damage, and they’re not going to start disintegrating.

Individual dinosaur bones can cost as little as a few hundred dollars

Price tends to be determined by desirability, condition and also aesthetics — the vertebra of a Triceratops, for example, has an amazing sculptural quality to it.

Small, individual bones cost as little as a few hundred dollars. They’re great gifts for dinosaur-obsessed children. At the opposite end of the market is STAN, which Christie’s sold for $31.8 million — at the time was a record price for a dinosaur.

To give you an idea of how the market is exploding, rewind to 1997 and a similar T. rex sold for $8.3 million. Prior to that, they could cost as little as $1 million. These six- and seven-figure prices tend to be paid by museums, or the benefactors of museums — and a number of celebrities also reportedly collect dinosaurs.

And yes, it is possible to go digging for your own dinosaur

The basic rule of thumb is that you need the landowner’s permission, but the laws vary country by country. Unhelpfully, there is no international standard.

Some luxury tour operators specialise in dinosaur hunts, but be prepared for baking hot sun and painstaking work.

Jurassic Icons: Allosaurus & Stegosaurus will be offered at Christie’s in London on 12 December. They are on view from 7 to 12 December

Explore art from antiquity to the 21st century at Classic Week, 26 November to 12 December 2024 at Christie’s in London. On view from 29 November