Around 120 years ago, William Sollas, Professor of Geology at the University of Oxford, developed a special technique for grinding down and imaging certain kinds of fossils. Sollas was based at the Museum at the time, and the process he pioneered is still used here today, as our PalaeobiologyTechnician Carolyn Lewis explains to mark the anniversary of Sollas’ birthday on 30 May.
Here at the Museum, I work on a collection of exceptionally well-preserved fossils from the Silurian Herefordshire Lagerstätte. They were deposited on the seabed 430 million years ago when the animals were buried by a volcanic ash flow. The fossils range in size from less than a millimetre up to a few centimetres, and represent a diverse collection of marine invertebrates that includes sponges, echinoderms, brachiopods, worms, molluscs and a wide variety of arthropods.
These Herefordshire Lagerstätte fossils are unusual in that many of them have preserved soft tissues in remarkable detail, including eyes, legs, gill filaments, and even spines and antennae only a few microns in diameter. The key to this extraordinary preservation is that as the fossils developed, calcium carbonate nodules formed around them, protecting and preserving the fossils since the Silurian Period.
Usually, only the hard parts of fossil invertebrates are preserved – the carapace of trilobites or the shells of brachiopods, for example – so the Herefordshire material provides us with a great opportunity to work out the detailed anatomy of these early sea creatures.
But the problem we face is how to extract the specimen from the rock nodule without losing the information it contains. The fossils cannot be separated from the surrounding rock by dissolution, because both fossil and nodule are made mainly of calcium carbonate, so would dissolve together. And they are too delicate to be extracted mechanically by cutting and scraping away the surrounding nodule. Even high resolution CT scans cannot, at present, adequately distinguish between the fossils and the surrounding rock material.
To get round this problem we use a method of serial grinding and photography based on the technique developed by William Sollas in the late 19th century. We grind the fossils in increments of 20 microns then photograph each newly ground surface using a camera mounted on top of a light microscope. This generates hundreds of digital images of cross sections through the specimen.
Then, using specially developed software we convert the stack of two-dimensional images into a 3D digital model that can be viewed and manipulated on screen to reveal the detailed form of the animal. These 3D models are artificially coloured to highlight different anatomical structures and can be rotated through 360o, virtually dissected on screen, and viewed stereoscopically or in anaglyph 3D.
Although our method of serial grinding is still fairly labour intensive, it is far less laborious and time-consuming than the process used by William and his daughter Igerna Sollas. Compared to the photographic methods of the early 20th century, where each photographic plate required long exposure and development times, digital photography is almost instant, enabling us to grind several specimens simultaneously.
Computer software also allows us to create 3D virtual models rather than building up physical models from layers of wax. Yet despite our modern adaptations, we are using essentially the same technique that William Sollas developed here at the Museum 120 years ago. And using this technique to study the fossils of the Silurian Herefordshire Lagerstätte has yielded a wealth of new information that opens up a unique window into the evolution and diversification of early life in our oceans.
To mark Plant Appreciation Day today, Lauren Baker and Chris Thorogood of the University of Oxford Botanic Garden and Arboretum take us on a quick tour of the evolution of plants: from primitive water-dwelling algae to the colonisation of land, and the eventual success of angiosperms – the flowering plants.
The Earth formed around 4.6 billion years ago, and around 2.7 billion years ago the very first plants evolved. These were the algae, a diverse group that live mainly in water. The ancestor of all modern algae – and the first organisms to photosynthesise – were cyanobacteria. Green algae evolved from these cyanobacteria and are the ancestors to all modern plants.
We owe the air we breathe to plants. With the production of oxygen through photosynthesis came a drastic climatic shift around 2.4-2.0 billion years ago. Known as the Great Oxygenation Event, it dramatically increased oxygen and decreased carbon dioxide in the atmosphere.
Jump ahead 1.5 billion years and the evolution of plants really takes off. To leave the water, plants needed to develop protection from drying out. The group that colonised the land is called the bryophytes, and includes the liverworts, hornworts and mosses.
Bryophytes are simple plants that lack true roots or ‘plumbing’ vascular tissue such as xylem or phloem. Bryophytes may have evolved from green algae in shallow, fresh water and developed the ability to survive on land when these pools dried out: 470 million years on, you can still see many bryophytes growing in damp habitats today.
The first vascular plants appear around 430 million years ago. One of the earliest examples was Cooksonia, consisting of a simple branching stalk without leaves.
Lycophytes, which evolved around 350 million years ago, also have vascular systems that enable water and nutrients to be moved around the plant. This drove the evolution of more complex, multicellular plants.
The ability to pump water allowed lycophytes to grow to heights of 45 m and they formed vast forests. Their remains also make up the coal, oil, and natural gas we use for energy today. More than 1,200 species of lycophytes exist now, grouped into three orders: the club mosses, quillworts and spike mosses.
A ‘living fossil’ that can be seen growing at the Botanic Garden is Equisetum, commonly called the horsetail. Horsetails evolved around 350 million and although the species alive today are herbaceous, extinct horsetails such as Calamites once formed large trees. The fossilised remains of Calamites in the collections of the Museum show the vascular tissues that would have carried water and nutrients up the vast trunk of the tree.
Cycads also evolved around the same time as the lycophytes and horsetails. They could easily be confused with palms, but unlike palms they are not flowering plants. Cycads belong to a group of plants called the gymnosperms, a name that literally means ‘naked seed’, and refers to the plants’ reproduction with seeds that are not encased in an ovary. Cycads can survive for over 1,000 years and are very slow growing. Today, the majority of the 200 surviving species are threatened with extinction.
Another ancient and unusual group of gymnosperms that evolved alongside cycads and lycophytes are Gnetophytes, which include plants such as Ephedra, Welwitschia, and Gnetum. There are about 40 living species of Gnetum, and they are tropical evergreen trees, shrubs and lianas. Before DNA sequencing technology, they were believed to be the closest living relatives of flowering plants due to the sugary sap they produce to attract pollinating insects, like the nectar produced by flowers.
Fossils of Ephedra date back as long as 120 million years ago. They are pollinated by both wind and insects, and are found across all continents except for Australia. With small, scale-like leaves they are highly adapted to arid environments, growing in sandy soils with direct sun exposure.
But perhaps the most familiar gymnosperms are the conifers. Conifers include the world’s oldest tree, the bristlecone pine, and the world’s largest tree, the giant Sequoia. There are over 615 species of conifers, most belonging to the pine family, Pinaceae.
The evolution of flowering plants – the angiosperms – 125 million years ago, was the start of a global botanical competition with gymnosperms, and it changed the appearance of our planet forever. The fossil record shows the earliest flowering plants bloomed alongside the dinosaurs, and probably looked something like a magnolia.
Unlike the gymnosperms, the angiosperms reproduce with flowers and their seeds are contained within protective ovaries. Despite their relatively late emergence, the diversity of flowering plant species was accelerated by their evolution alongside insect pollinators. Today, of the roughly 350,000 known plant species, 325,000 are flowering plants.
This week my colleagues and I announced the discovery of a new species of mammal from the time of dinosaurs. It is one of two rare skeletons we’re studying from the Isle of Skye in Scotland. These mouse-like animals lived in the Middle Jurassic (166 million years ago), and tell us about the evolution of mammals in the time of dinosaurs.
The two fossils belong to Borealestes serendipitous and Borealestes cuillinensis. B. serendipitous was the first Jurassic mammal ever found in Scotland, known originally from pieces of fossil jaw found on Skye in 1971. In our new paper, we describe the skull of a partial skeleton of this species, found in 1972 by the original discoverer of the site, Dr Michael Waldman and his colleague Prof Robert Savage. But this exceptional fossil lay unstudied for over 40 years. Only now is it giving up its secrets thanks to powerful synchrotron X-ray scans, which reveal the anatomy in incredible detail.
The other fossil skeleton was found in 2018 by my colleague Prof Richard Butler. After taking it back to the lab and CT-scanning it, we realised it was a new species. We named it Borealestes cuillinensis in honour of the Cuillin mountain range on Skye (Gaelic: An Cuiltheann), a stunningly jagged set of peaks that overlooks where the discovery was made.
Most ancient mammals are only known from a few teeth and jaws, so these skeletons are exceptionally rare. They are currently the most complete Jurassic mammals described from the UK.
The Middle Jurassic is an important time in animal evolution, because it marks an increase in the diversity of lots of different groups. Just afterwards, in the Late Jurassic, there are many new species of mammals, amphibians, small reptiles and dinosaurs, which flourish into the Cretaceous period. All of this diversity began in the Middle Jurassic, but fossils from that time are rare, making it difficult to unpick the causes of these changes. This means that any material from that time period is extremely important to our understanding of the course of evolution, and the drivers of animal diversity.
Our team have been carrying out fieldwork and research on Skye for the last decade. It includes researchers from National Museums Scotland and the universities of Oxford and Birmingham. We are working on many more exciting fossils from the island, so keep an eye out for the next discovery!
Read the paper ‘New species of mammaliaform and the cranium of Borealestes (Mammaliformes: Docodonta) from the Middle Jurassic of the British Isles’ published today in the Zoological Journal of the Linnean Society.
Top image: Digital reconstruction of two Jurassic mammal skulls. (c) Matt Humpage
Elsa Panciroli recently joined the Museum research team as an Early Career Leverhulme Research Fellow. Elsa is a Scottish palaeontologist, whose studies focus on the early evolutionary origins of mammals, working extensively on fossils from the Isle of Skye. Here she tells us how her work will combine studies of mammal evolution with stunning new fossil finds from Scotland.
We are mammals. This means we share a common ancestor with creatures as different as hippos, opossums and platypuses. All of us are united in one taxonomic group by a suite of characteristics in our bodies, but principally, that we feed our young on milk. Every mammal from a baboon to a blue whale produces milk for their offspring, and this makes us unique among animals alive on Earth today.
But not all mammals bring their young up in the same way; raising a kitten is nothing like raising a kangaroo or a platypus. Kittens are born stumbling around with their eyes closed, while platypus babies are laid in eggs – yes eggs – and when they hatch they look like little scampi. Both are underdeveloped at birth or hatching, but that’s nothing compared to kangaroos. They leave the womb only millimetres in length, and wriggle their way like living jellybeans toward a teat in the marsupial pouch, where they latch on. Only after two months of milk-drinking are they able to hop for themselves and leave the pouch.
The different ways that mammals are born and grow is a huge area of scientific research. But there are still some major questions to answer about the evolution of these growth patterns. When did the ancestors of mammals stop laying eggs? Were they born defenceless, or able to fend for themselves? How quickly did they grow up and how long did they live?
Over the next three years at the Museum, I’ll be looking for evidence in the fossil record to help us try and answer some of these questions. I’ll study living mammals to understand how they are born and grow, combining this information with data from some of the amazing fossils being found on the Isle of Skye. With collaborators in South Africa I’ll try and work out how the ancestors of mammals developed, and what this means for the bigger picture of the origin of mammals as a group.
Alongside my main research I hope to share lots of stories about our fossil past through the museum’s fantastic public engagement programme. I’m also very active on social media, and I write about science for online and in print publications. So if you see me on your next visit to the building, or find me online, feel free to ask about my research! I look forward to seeing you, and sharing more about the elusive and exciting origins of mammals – and ourselves.
When the campaign to build the Museum was launched, science at Oxford was understood as natural theology. By the time the Museum opened in 1860, a new secular approach to science was on the rise.
In this last episode of the Temple of Science podcast series we see how the art and science of the Museum responded to the challenge posed by Charles Darwin’s theories of evolution and natural selection, and the scientific naturalism that they epitomised.
Worms, fish and … Greenland? Hugely different topics which all have one thing in common – the Museum’s First Animals exhibition online lecture series. Running every other Wednesday from May until September 2020, this series provided a fantastic insight into a wide range of topics about how the first animals lived, died, and are studied. And illustrator Rachel Simpson tells us how she drew her way through them all…
I came across this lecture series just before the first talk and I knew I had to sign up. Drawing along to lectures is a hobby I seem to have developed in the past few months as we went into lockdown and didn’t have much to do. It’s the perfect combination for me – an opportunity to listen to interesting topics and brush up on my live drawing skills at the same time. There’s no pause button, there’s no asking the webinar speaker to just go back a few slides and hold on a minute whilst I draw; it’s fast paced, it’s inspiring and it’s a great way to just create art.
I’ve done some illustration work with the Museum before so I knew that it was going to be fun. In 2018, I worked with Dr Jack Matthews illustrating Ediacaran Fossils as part of a collaborative university project between the University of Plymouth and the Museum. I was also lucky enough to be able to go to Newfoundland and see some of the fossils myself, again with Jack. This was such an incredible opportunity and opened up a whole new world of science/art collaborative work which I didn’t know about before.
The First Animals series kicked off with Jack’s talk titled Don’t walk on the rocks! – an interesting insight into how protective “Barma Booties” (some rather funky socks worn to protect fossil sites such as Mistaken Point, Newfoundland) might actually be damaging to the fossils they’re meant to be protecting. Having been to Mistaken Point myself and worn these socks, it was interesting to hear about their possible impact and to learn about the experiments conducted to prove this fact.
Of course, at the same time as Jack was talking, I was scribbling away in my sketchbook trying to form some sort of visual response to the talk. At the end of the hour I’d managed a portrait of Jack and a family of Barma-Booted tourists trampling on the fossil site. It was a start. The beginning of my lecture drawings and a point at which I can retrospectively say started a new hobby.
Over the following weeks we heard about worms from Dr Luke Parry; 3D reconstruction from Dr Imran Rahman; The Chronicles of Charnia by Dr Frankie Dunn; and the first animal skeletons from Dr Duncan Murdock. Luckily for me, all the speakers kindly included photos and descriptions of the topics they were discussing which meant that I was never short of visual inspiration for my drawings. After all, it’s hard to try and draw an annelid worm if you’ve never seen one before.
I love to look at the fossils being discussed and then try to draw a little character or creature inspired by them. They’re not scientifically accurate, nor are they always anatomically correct, but they have character and begin to bring to life the essence of something that’s been dead for many millennia. The fossils are obviously stone-coloured so I take as many liberties as possible when it comes to colour. I like to make them as vibrant and colourful as I can, so although they probably didn’t look like that, that’s how I like to think they looked.
Some fun little beasties from Dr. Imran Rahman’s talk.
Charnias galore! They come in all different shapes and sizes.
Small filaments which could have joined all those Charnia together.
Shells, bones and teeth from Dr. Duncan Murdock’s talk drawn in Tombow brush pen and Posca Pen.
Within my wider practice I like to use stamps as the basis of my illustrations. These however, are time consuming to make and therefore not very suitable for when I’m drawing along to lectures. As a result I’ve found myself using brush pens and pencils to make my lecture illustrations. If you’re interested in art, or thinking about getting into art, brush pens will be your best purchase. They create a wonderful quality of line and are quick and easy to use. Whereas a ballpoint pen will give you one line of a certain weight and thickness, brush pens are versatile and depending on the pressure applied, the line quality will change.
For the first few lectures I only used brush pens, but later on I decided to use coloured pencils as well, to add depth to the drawings. As I got more used to drawing in lectures I found that I was making more illustrations per talk. Early on, I managed to finish maybe a double page in my sketchbook but towards the end of the series I was filling four double pages! It’s amazing what a little bit of practice can do.
As the weeks went by the talks continued and we heard about the evolutionary origin of animals from Museum director Professor Paul Smith; an introduction to taphonomy, the study of fossilisation, by Professor Sarah Gabbott; and how the first animals moved by Professor Shuhai Xiao.
During this time I became a lot more confident drawing the specimens; looking back I can see that this was the period in which my work developed the most. My drawings began to have more character and life. The landscape drawings were slowly becoming more realistic and detailed. This was great news for me as this whole endeavour began as a way to practice my drawing skills in a timed environment.
Paul Smith’s lecture has to be my favourite of them all. He gave a wonderful talk all about the Evolutionary Origin of Animals and talked us through his fieldwork expedition to Greenland. How I would have loved to have been on that trip!
How I would have loved to have been on this trip! Drawings of Professor Paul Smith’s fieldwork to Greenland.
Some of the weird and wonderful fossils Professor Paul Smith found on his trip.
One of my favourite drawing from the lecture series! Drawn with Tombow brush pens and Polychromo pencils.
It was during Paul’s talk that I made one of my favourite drawings from the series – the plane –and coincidentally it was also at this point that I bought myself some new polychromo pencils. I started using these pencils in my illustrations on top of the Tombow brush pens. The pencils added a softer layer on top of the solid base colour from the brush pens and meant that I could add more details, shading and most importantly, the characterful eyes I love to add to my drawings.
Fish and animal studies from Professor Sarah Gabbott’s introduction to taphonomy, the study of the processes of fossilisation.
Imagine being the owner of this house and being told there were found fossils on your roof! Drawing from Professor Shuhai Xiao’s talk.
Buoyed by this development in my drawings, and some lovely responses to my work on Instagram and Twitter, I raced through the next few weeks of talks and made twelve pages of drawings over the next four talks. Professor Derek Briggs told us all about extraordinary soft-bodied fossils; Professor Gabriela Mángano told us about the trace fossil record; and Professor Rachel Wood gave us her thoughts about what triggered the Cambrian Explosion.
Another favourite drawings from the series, drawn from Professor Derek Briggs’ talk.
Close up of drawing from Professor Derek Briggs’ talk.
Trace fossil studies drawn in Tombow brush pens and Polychromo pencils.
The last drawings from the series from Professor Rachel Wood’s talk.
Another of my favourite drawings from the series was from Derek Briggs talk about extraordinary soft-bodied fossils. Here, I made a small series of drawings based on some of the animals mentioned in the talk and as soon as I’d finished drawing them I wished that they were real and that I could pop them in a fish tank and keep them as pets. These drawings got the best response on social media too and it’s wonderful now to look back and compare these drawings to the work I was creating at the beginning of the series.
The First Animals series may be over but keep your Wednesday evenings free because there are more talks to come! The next series, “Visions of Nature”, starts on 8 October so make sure you join us then! A huge thank you to all the speakers, to Jack for hosting and to the Museum for running the events.