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Dinosaurs: A Time Team Special
30 December 2001
Time Team's Tony Robinson and Phil Harding travelled to the Rocky Mountains in Montana, USA, for this special programme on dinosaurs and the 'dinosaur hunters' who discover and dig up their fossil remains. The methods used by the dinosaur hunters turned out to be very similar to those employed by archaeologists. And although Phil found he was making more use of a hammer and chisel than his usual digger's trowel, there was much more with which he was familiar from archaeological excavations.
What have dinosaurs got to do with archaeology?
How do you dig up a dinosaur?
How fossils form
Find out more
Photo Gallery
Photos, finds and reconstructions from the dig.
What have dinosaurs got to do with archaeology?
Archaeology can be defined as the study of the material remains of past ages (structures, artefacts, bones and so on) as evidence of human life, culture and history in former times. So, since the extinction of the dinosaurs took place about 65 million years ago and modern humans emerged only within the last few hundred thousand years, strictly speaking the study of archaeology has nothing at all to do with that of dinosaurs. Most archaeologists, plagued by the impression given by old film epics placing humans and dinosaurs on the earth at the same time, have grown weary of explaining why they don't dig up dinosaurs.
But as Time Team discovered on its trip to Montana, palaeontologists involved in the excavation and study of dinosaur fossils have a great deal in common with archaeologists concerned with human remains. The methods and techniques used in each case are so similar that they could often be taught in the same courses. From the initial searches of a landscape for evidence of dinosaur fossils (comparable to fieldwalking to assess surface remains in archaeology) through the excavation, conservation and study of the bones, the same broad approach is instantly recognisable to professionals in either field.
How do you dig up a dinosaur?
Finding the bones
First, of course, you have to know where to look. Palaeontologists looking for dinosaurs focus on continental sedimentary rocks of Mesozoic age. The Mesozoic era, which lasted from 250 to 65 million years ago, consists of the Triassic, Jurassic and Cretaceous periods. Dinosaurs evolved about 230 million years ago in the middle of the Triassic period and lived in abundance (depending on definitions, there are between 900 and 1500 known species of dinosaur) until they died out at the end of the Cretaceous period 65 million years ago.
The rocks that most interest dinosaur hunters were originally laid down as mud, silt, sand or lime sediments in rivers and lakes. Over millions of years they have hardened into mudstones, siltstones, sandstones and limestones. Some of the bones of dinosaurs that died or were washed into these sediments have been mineralised and preserved as fossils.
Once a potential site has been identified, the next step is to 'prospect' for surface shards of bone, including those eroded from their original locations by rain, streams or other weathering. The process is similar to fieldwalking in archaeology, and as in archaeology the location, distribution and other information obtained from such surveys is of great importance. Tracing bones back up a slope from which they have been eroded, for example, can lead to a complete skeleton still in place in the rock.
Excavating the bones
The first dinosaur hunters in the US simply hacked out dinosaur fossils with pick axes and loaded them into horse-drawn carts like piles of logs. The labourers concerned were often railroad workers, and their approach to digging up bones was not dissimilar to their work on the trans-American railroads. Dinosaur fossils are extremely fragile, however, and can shatter easily. So when the brittle bones were transported to the palaeontologists who were interested in them, they often arrived as little better than a heap of debris and dust in the packing cases.
Techniques have changed a great deal since then and dinosaur excavations can be as careful, painstaking and time-consuming as any archaeological dig. The first step is removing what is known as the 'overburden'. Often a dinosaur skeleton will be found peeping out of a sloping rock face or buried at an angle. A full skeleton can easily extend several metres into a gully wall or rock face, requiring the removal of many tons of overburden before the excavation of the bones themselves can proceed. One of the dinosaur digs filmed by Time Team was on a near sheer rock face, where up to ten metres of overburden had to be removed in order to get at the dinosaur remains. As one cubic metre of rock typically weighs between one and two tonnes – and a dinosaur can be encased in a hundred cubic metres of rock – the volume and weight of the material that has to be removed can be enormous.
Once they have cleared the overburden, palaeontologists set to work with hammers, chisels, scrapers and brushes to begin to expose the bones. They chip the rock away carefully, aiming to stop a few centimetres from the bones themselves. Techniques for fine detail work require a needle mounted in a wooden handle. By careful probing and scraping the sediment can be loosened and is then brushed away. As the bones are exposed they are painted with a dilute preservative solution, usually some sort of synthetic glue dissolved in acetone, which soaks deep into the pores of the bone to harden it.
The objective is not usually to expose the bones completely at this point. Instead they are removed in manageable blocks of stone and transported to the museum or laboratory where the task will be completed.
Before this can be done a survey is carried out to determine the best way to get the bones out. It would be impossible to move an entire dinosaur in one go as it would weigh too much, so usually the 300 or so bones in a typical skeleton are divided into separate parcels. Trenches are dug around the marked blocks, in a process called 'pedestalling' – literally putting bones on pedestals. Then sheets of wet paper are placed over the bones to act as a separator before the bones are encased in plaster – a technique first devised in the 1880s when field workers realised that by setting a fossil bone in plaster it would be protected in just the same way as setting a broken bone in a living person. After the plaster has dried the block of stone containing the bone is undermined and carefully flipped over. As much stone as possible is removed and then this side too is plastered over. When the plaster parcel is finished it can safely be removed for transport to the museum or laboratory.
Mapping the bones
As with an archaeological site, once a dinosaur skeleton has been uncovered it must be accurately recorded. The site is gridded, usually using thin string dividing it into one-metre squares, which are then themselves subdivided further. Information on the ground is transferred to squared paper, scaling the one-metre squares to a ten-centimetre square on the paper.
Other mapping techniques involve video recordings and photographs taken from all angles. These cannot substitute for the scaled maps drawn by palaeontologists – photographs give a distorted picture due to perspective, while the fossils are often the same colour as the ground and do not show up well – so the maps are the main guide for piecing together a skeleton and interpreting how it was buried.
Transporting the bones
Many bones are too heavy to move by hand. One solution adopted by palaeontologists is to design a sledge from beams of wood and then plaster the wood into the first side of the cast. When the cast is flipped over the sledge forms its base and can then be dragged away from the site. Sometimes an excavation team will build trolleys and other strange contraptions to help them move the vast weights. In remote locations, it may even be necessary to bring in civil engineering teams to build rough tracks or bridges.
Cleaning and preserving the bones
Excavation is only the beginning of the long process of cleaning, preserving and assembling dinosaur skeletons. Often bones are stored awaiting treatment for years and museums around the world have basements full of unopened plaster casts of dinosaur bones. Each parcel of bones has to be opened carefully, ideally with a precision dental cutting wheel to avoid damage to the contents.
The initial cleaning work may be fairly rapid as the bulk of the jacket and the surrounding rock (known as the 'matrix') is chipped away. As the surface of the rock is chipped away, the fragile bone is gradually revealed and further strengthening glues are soaked in. Sometimes a vacuum chamber is used to make sure that the glue goes right into the bone. When a bone or skeleton is very small it may not have all the rock removed from it. Often it is safer to reveal just one side and make it into a kind of relief sculpture backed by the sediment it lies on.
The basic methods are the same as they were a century or more ago, but new techniques include the use of an 'airbrasive' machine – a high pressure pump that blasts air from a thin nozzle at very high pressure. Small beads of glass or another hard substance may be inserted into the machine. By moving the nozzle over the fossil bones the matrix is literally blown off the bones. It is among the safest ways of cleaning bones without damaging them but also one of the most time-consuming.
In other cases, where the sedimentary rock is made up primarily of calcium carbonate, acid treatments may be used to remove it from fossil bones. The Natural History Museum in London pioneered this process in the 1950s, when palaeontologists there discovered that by placing a bone in an acid bath for a day or two any calcium carbonate covering would be completely dissolved in the bath.
Technicians soon discovered they had to be careful, though, because the wrong mix of acid would dissolve the bone as well. This is because bone is made from calcium phosphate, which also dissolves in acid but not so quickly. The acid now used is ascetic acid (vinegar) or formic acid (as produced by ants). Bones are regularly removed from the acid and treated with hardening substances before being placed back again until they have been fully cleaned.
Identifying the bones
As the bones are cleaned and preserved they are laid out ready for inspection by experts in dinosaur anatomy. Dinosaur skeletons had the familiar structure of a skull, a backbone, arms and legs, all connected in the same logical sequence as in humans – for example, each dinosaur leg consists of a thigh bone, two shin bones, a set of ankle bones and a set of toe bones. Certain bones, such as the tibia, are regarded as 'diagnostic' – that is to say, they are distinctive to particular dinosaur groups and can be used to identify which group an individual dinosaur skeleton came from. Again, comparisons can be made with archaeological techniques dating (for example) specific types or styles of pottery to particular periods.
Having established the broad group of dinosaurs to which the excavated remains belong, palaeontologists must research all published information, references, papers, illustrations and especially monographs to establish exactly which species of dinosaur they belong to. Normally the dinosaur will have already been described in the scientific monographs or papers, but occasionally there will be something new. The skull may be a different shape, there may be extra spines or lumps on the backbone, the legs may be longer or other features may distinguish it as a previously unidentified species. In such cases, the person making the discovery gets to name it. Sadly, Time Team didn't make any new discoveries on its visit to Montana, so the world will have to wait a little longer for its first Tyrannosaurus Tony or Iguanodon Hardingensis.
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