Museum PhD student Simon Wills has spent the last five years searching for a needle in a haystack, or rather, tiny teeth in tonnes of clay deposit. What he's found dramatically changes the picture we have of the Middle Jurassic ecosystem in what is now Britain, and the dinosaurs that lived here.

Simon's discoveries include the world's earliest examples of the group of meat-eating dinosaurs that evolved to include Velociraptor.

It's back-breaking work. 'At one site we dug out around seven or eight tonnes of clay by hand,' explains Simon. That's equivalent to the weight of about one and a half Asian elephants. It's a lot of clay to search through for dinosaur teeth that in some cases are less than a millimetre in size. So why is Simon looking for such small fossils, when dinosaurs are some of the largest land animals ever to have existed? The Middle Jurassic: a time of dinosaur diversification Simon's research focuses on the Bathonian, a period of time about 168-166 million years ago, which forms part of the Middle Jurassic Period. Back then, Britain was a series of small tropical islands, like the Bahamas are today. The climate was hot and humid. Low-lying land was covered in swamps, marshy areas and river deltas.

Roaming among these habitats were meat-eating theropod dinosaurs such as Megalosaurus, Proceratosaurus and Eustreptospondylus. There were also plant-eaters including sauropods such as Cetiosaurus, stegosaurs such as Loricatosaurus, and ornithopods such as Callovosaurus.

'The Middle Jurassic was a significant time for dinosaurs,' says Simon. 'They diversified quite rapidly during this geological epoch. 'But in Britain (and elsewhere around the world too) we don't have many dinosaur remains from this time, simply because of a lack of appropriate-age terrestrial rocks. This means we have an incomplete picture of what dinosaurs were living here then.' What we do have are thin layers from the Bathonian containing miniscule fossils, or microvertebrates. What are microvertebrates? Microvertebrates are the tiny remains of small vertebrates - not just dinosaurs but other animals such as lizards, crocodiles and mammals. The fossil bones and teeth are so small they have to be studied under a microscope.

'Microvertebrates tend to be found in clay deposits,' explains Simon, 'because what you're looking at was once an old pond, small lake or what we call an overbank deposit - where a river or stream flooded its banks. Simon clarifies, 'It's not that dinosaurs were living in the pond - they're not aquatic. But they'll have lived and died nearby. 'As with a pond in your garden, debris tends to get swept in from the surrounding area and concentrates there.'

Simon was looking at material from three quarry sites: Woodeaton and Kirtlington near Oxford, and Hornsleasow in Gloucestershire. Simon adds, 'The sediment layers here are really quite small in extent, a few metres to tens of metres in size, which is typical of terrestrial microvertebrate deposits. 'But they are rich in small bits of bone and teeth, as these gradually accumulated.' Lots of teeth Microvertebrate deposits tend to be full of teeth, because teeth preserve well - enamel is very hard and doesn't break down.

The teeth from Kirtlington and Hornsleasow were collected in the 1980s and 1990s by other researchers, mostly from University College London and the University of Bristol. Many of these were entered into the Museum's collection but hadn't been fully described and identified. 'It shows the value of collections,' says Simon. 'We were able to go back and look at this material, carry out further analysis and include it in our study.' The other teeth used in the study were dug out from Woodeaton Quarry by Simon, working alongside Museum colleagues Emma Bernard, David Ward and Pip Brewer, who were interested in fish and mammal microvertebrate fossils.

Discovering new dinosaurs While small dinosaur teeth have been known about for years, they've been largely overlooked. Simon's work shows the great potential for making important discoveries from these tiny specimens. He says, 'I measured the size and shape of the teeth and compared them to known dinosaurs from that period. Some we were able to identify as small variants of known groups - theropods, for example. 'But what was particularly exciting was that some of the teeth didn't match any of the groups currently established as living in the UK at that time. Instead, we found that they matched dinosaurs known elsewhere (but not from that particular time) and suspected here: a group of dinosaurs called maniraptorans, specifically dromaeosaurs.'

Simon adds, 'In dinosaur exploration, people tend to be seduced by the bigger stuff. It's considered more exciting and makes more of an impact when put on display. But this means microvertebrate fossils are often overlooked. Yet these can fill in lots of the gaps in our knowledge about ancient ecosystems and they can even reveal the presence of dinosaurs we wouldn't otherwise know about.' What were dromaeosaurs like? Dromaeosaurs were a family of small to medium-sized carnivores that thrived in the Cretaceous Period. Known species range from 70 centimetres to around six metres long. 'It seems that we identified some of the earliest examples of dromaeosaurs worldwide,' says Simon. These slender, agile predators walked on just their back legs. They had long arms, large hands and three clawed fingers. Some, if not all, were covered in feathers.

One of their most distinctive features was a large, curved claw on their second toe. Probably the most famous example is Velociraptor, a Late Cretaceous dromaeosaur species from Mongolia. Tiny teeth, big challenges The teeth that Simon works on are extremely small, some less than a millimetre in size. Some were probably from baby dinosaurs, while others were likely from small-bodied adult dinosaurs. According to Simon it's hard to know which is the case, because dinosaur teeth do not change much as the animal gets older - they grow, but the shape and characteristics remain the same.

Why was there an absence of larger teeth? Simon explains, 'It is probably down to the environment. The small ponds and lakes where the microvertebrate deposits formed would naturally have attracted small creatures, like such habitats do these days.' Handling such tiny teeth was one of the most difficult parts of the entire operation, says Simon. 'When you've got several hundred miniscule teeth, it's quite hard. 'They're easy to lose and although they are quite robust - they've survived millions of years, after all - they're also surprisingly easy to destroy. A painstaking process After multiple rounds of washing and drying the many tonnes of clay, Simon was left with a residue of concentrated material. The next step was to sort through this to pick out the teeth by hand, under a microscope. A bucket's worth of sediment could contain anything from zero to 20 teeth.

'I've sat for many, many hours with my eyes glued to a little box of stuff under my microscope,' says Simon, 'using tweezers and a tiny paintbrush to separate out bits of bone and teeth into small tubes.' Once he'd accomplished this, Simon needed to image the teeth. This could involve taking a straightforward photograph, a scanning electron microscope image or - most useful in this case - a CT scan, which is used to create a 3D digital model.

'Digitisation is important,' asserts Simon. 'I hardly ever look at the teeth themselves. I look at the digital models I've built of the teeth.' Models are much easier to manipulate than fragile, fiddly teeth. Simon explains, 'I can easily spin a 3D model around on my computer, measure it and even zoom in to see features more clearly.'

But imaging hundreds of teeth is itself a challenge. Simon says, 'I had to develop a process where I could easily scan more than one tooth at a time. He did this by working with colleague Dr Charlotte Brassey, who is now based at Manchester Metropolitan University. 'We 3D-printed some little trays, each divided into nine little holders, or 36 for smaller teeth. We stacked six trays vertically and CT-scanned the entire block in one go. We then wrote a little computer programme to cut out each block of tooth data.' Using this process, Simon was able to scan 54 or 216 teeth at once, then create models of the individual teeth.