How To Find Dinosaur Fossils

Thursday, July 25, 2019

The tail of a sauropod dinosaur found in the Sahara Desert in Niger. These bones were discovered on a joint expedition by the Museum and Kingston Polytechnic (now Kingston University) from 1987 to 1988.

For palaeontologists in the field, few techniques have changed much since the early days of dinosaur hunting. 

Many of us associate science with high-tech undertakings. But when it comes to digging up dinosaurs, methods are far more humble, with palaeontologists in the field typically armed with shovels, brushes and the occasional power tool. 

Where do you find a dinosaur?

Prof Paul Barrett is a dinosaur researcher at the Museum and has taken part in many a dig, most recently the Mission Jurassic dig in Wyoming, USA. When it comes to knowing where to look, he says, 'We don't just go to any site and start digging. It's an educated guess.

'When we go out, we're looking for rocks of the right age that we know might have dinosaur fossils in them. So that's rocks from the Mesozoic Era - from the Triassic, Jurassic or Cretaceous periods.

'We look at geological maps to see where these types of rocks are appearing. Then when we go to those places, there should be some chance of finding a dinosaur.'

Palaeontologists don't always have to dig to find evidence of dinosaurs. Rocks can naturally weather away to reveal bones that have been hidden for millions of years.

Topographic maps can also be useful in the hunt for fossils. These show vertical depth as well as man-made structures such as roads, and can indicate how accessible a site will be.

What do fossils look like?

'Before we get digging, Paul says, 'we want some indication that there is a dinosaur in the ground. It does come down to luck: the dinosaur fossils have to have been eroded out at the surface so that you can see at least a little bit of it poking out.

'We spend a lot of time walking around, looking at the floor.'

Finding isolated fragments of bone, sometimes called float, are an indication that there may be more fossils nearby.

This bone was found naturally eroding out of the surrounding sandstone during the Mission Jurassic dig in Wyoming. Fragments like this indicate there may be more bones nearby.

You can figure out whether it's a fossil with a trained eye and a hand lens, but there is another way to quickly tell bone from stone in the field - although it's not particularly pleasant.

'In some cases, rock and bone look very similar, but fossils still have the structure of the living bone tissue that it once was. It will have a pattern of microscopic, honeycomb-like structures running through it,' explains Paul.

'Rock doesn't have this, so one quick way to tell the difference is to lick it.

'The tiny tubes in the bone draw moisture out of your tongue. So if it sticks to your tongue, it's probably bone, and if it doesn't it's probably rock.'

In some cases, bone (L) can look very different to the surrounding rock (R). The difference really depends on the type of rocks it's embedded in.

Scientists have trialled methods such as ground-penetrating radar to locate bones underground. But so far they haven't been effective enough, which suggests that for now the traditional approach to dinosaur hunting works best.

Digging for dinosaurs

Once you've selected a spot where there may be bones below the surface, getting a dinosaur out of the ground often requires a lot of digging.

'It's rare that you'll find a whole dinosaur bone, and even rarer, a whole skeleton waiting at the surface to be discovered,' explains Paul.

Mark Graham, a fossil preparator at the Museum, works to excavate fossils from the Morrison Formation

In places where there is a lot of overburden (the rocks overlying the material you're trying to dig up), palaeontologists may use heavy machinery to remove it and gain access to the fossils below. Early fossil hunters sometimes resorted to dynamite to blast the rocks apart to get to the bones.

Once closer to the bone bed, palaeontologists switch to smaller tools such as trowels, brushes and utility knives. It can take days or even weeks of painstakingly working around a bone to be able to remove it from the ground with minimal damage. 

Excavating dinosaur bones

Dinosaur bones can be very fragile. Even those that appear large and heavy can't always support their own weight when lifted out of the ground, as they may have fractures running through them.

Even the largest dinosaur bones can be fragile and fracture. These sauropod bones were found in the Sahara Desert in the 1980s.

Fossils can break during the excavation process. Paul says, 'It's actually quite common. When you're taking a bone out of the ground, you aren't exactly sure where the ends of it are or where it starts going into the ground.

'Often you first find the bone by accidentally digging into it, so it's very common to take a little nick off. We just keep the little pieces and they get stuck back on. We take really good care of them. We're very good with glue and we can usually make the bones right again.'

To protect the bones during transport, palaeontologists use field jackets. This involves using plaster of Paris and burlap to create a cast around a bone, similar to the casts doctors use to stabilise a broken arm or leg.

A sauropod bone in the Sahara Desert is wrapped in plaster and burlap in a process known as jacketing

'We don't just pull the bones out of the ground, because they tend to break on the way back to the lab,' Paul says. 'We keep them embedded in at least some of the rock to make that transportation process as safe as possible, and then the hard work of getting them out of the rock happens back at the lab.'

In the lab, a fossil preparator will remove the plaster jacket, then the rocks surrounding the bone, and will fix any fractures to stabilise the bone.

Understanding ancient environments

Fossilised dinosaur bones aren't always the only things found during an excavation. Other scientifically valuable information and specimens can be uncovered, such as evidence of early mammals and invertebrates, as well as trace fossils such as coprolites or trackways.

Usually a dig isn't just spent getting the dinosaurs out of the ground. Scientists will also take the time to study the rocks and excavate other fossils they find along the way.

Palaeontologists may use other techniques, too, such as screen washing.

On the Mission Jurassic excavation, scientific associate and microvertebrate expert David Ward led a team to engineer a sieving machine in the field, which was affectionately known as Hank

'We take big bags of sediment and we wash them down with water to look for the tiny fossils within them. We're looking for things like the teeth of mammals and dinosaurs, the tiny vertebrae of lizards and snakes, and other things like that,' explains Paul.

By looking at both animals that lived alongside the dinosaurs and fossilised plants, palaeontologists can build up a more complete picture of what kind of environment the dinosaurs were living in millions of years ago, and how it changed.

Understanding environmental changes in the past could help us understand more about how they affect our planet today.