On the trail of the evolution of mammals

Woman sitting on top of a large, layered rock formation

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.

Wareolestes rex is a Middle Jurassic mammal, illustrated here by Elsa Panciroli

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?

The Rock Hyrax (Procavia capensis) is a terrestrial mammal native to Africa and the Middle East

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.

Follow Elsa on Twitter at twitter.com/gssciencelady.

Drawn to life

A set of illustrated cartoons of the heads of eleven people with their names handwritten underneath

By Rachel Simpson

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.

Barma Booties used on the rocks at Mistaken Point, and my first drawing of the series.

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.

Annelid worms drawn with Tombow brush pens.

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.

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!

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.

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 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.

Two images of coloured drawings of extinct marine creatures side by side
Comparison between week 2, Luke Parry’s talk (left), and Week 9, Derek Briggs’ talk (right): What a difference 16 weeks of drawing practice makes!

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.

To see more of Rachel’s illustrations visit www.rachelerinillustration.co.uk.

High-tech insect origami

By Dr Ricardo Pérez-de la Fuente, Research Fellow

Earwigs are fascinating creatures. Belonging to the order Dermaptera, these insects can be easily recognised by their rear pincers, which are used for hunting, defence, or mating. But perhaps the most striking feature of earwigs is usually hidden – most can fly with wings that are folded to become 15 times smaller than their original surface area, and tucked away under small leathery forewings.

With protected wings and fully mobile abdomens, these insects can wriggle into the soil and other narrow spaces while maintaining the ability to fly. This is a combination very few insects achieve.

I have been working on research led by Dr Kazuya Saito from Kyushu University in Japan, which presents a geometrical method to design earwig wing-inspired fans. These fans could be used in many practical applications, from daily use articles such as fans or umbrellas, to mechanical engineering or aerospace structures such as drone wings, antennae reflectors or energy-absorbing panels!

Dr Saito came to Oxford last year for a six-month research stay at Prof Zhong You’s lab, in the Department of Engineering Science at the University of Oxford. He introduced me to biomimetics, an ever-growing field aiming to replicate nature for a wide range of applications.

Biological structures have been optimised by the pressures of natural selection over tens of millions of years, so there is much to learn from them. Dr Saito had previously worked on the wing folding of beetles, but now he wanted to tackle the insect group that folds its wings most compactly – the earwigs.

He was developing a design method and an associated software to re-create and customise the wing folding of the earwig hind wing, in order to use it in highly compact structures which can be efficiently transported and deployed. Earwigs were required!

Here at the Museum we provided access to our insect collections, including earwig specimens from different species having their hind wings pinned unfolded. These were useful to inform the geometrical method that Saito had been devising.

Dr Saito was also interested in learning about the evolution of earwigs and finding out when in deep time their characteristic crease pattern established. Some fossils of Jurassic earwigs show hints of possessing the same wing structure and folding pattern of their relatives today.

However, distant earwig relatives that lived about 280 million years ago during the Permian, the protelytropterans, possessed a different – yet related – wing shape and folding pattern. That provided the chance to test the potential and reliability of Saito’s geometrical method, as all earwigs have very similar wings due to their specialised function.

The geometrical method turned out to be successful at reconstructing the wing folding pattern of protelytropterans as well, revealing that both this extinct group and today’s earwigs have been constrained during evolution by the same geometrical rules that underpin the new geometrical design method devised by Dr Saito. In other words, the fossils were able to inform state-of-the-art applications: palaeontology is not only the science of the past, but can also be a science of the future!

We were also able to hypothesise intermediate extinct forms – somewhere between protelytropterans and living earwigs – assuming that earwigs evolved from a form closely resembling the protelytropterans.

As a collaboration between engineers and palaeobiologists, this research is a great example of the benefits of a multidisciplinary approach in science and technology. It also demonstrates how even a minute portion of the wealth of data held in natural history collections can be used for cutting-edge research, and why it is so important to keep preserving it for future generations.

Soon these earwig-inspired deployable structures might be inside your backpacks or used in satellites orbiting around the Earth. Nature continues to be our greatest source of inspiration.

Original paper:  Saito et al. (2020). Earwig fan designing: biomimetic and evolutionary biology applications. Proceedings of the National Academy of Sciences of the United States of America.

When life got hard

By Dr Duncan Murdock, Research Fellow

Whether you’re a great white shark with a deadly conveyor belt of teeth, a deep sea snail with a coat of armour or a coral building the Great Barrier Reef one polyp at a time, mineralized skeletons are a crucial part of many animals’ way of life. These hard skeletons – shells, teeth, spines, plates and bones – are all around us.

The fossil record is full of the remains of the skeletons of long-extinct critters, so much so that entire layers of rocks can be composed almost completely of them. But this has not always been the case…

A piece of 425 million year old sea floor containing the skeletons of trilobites, brachiopods, bryozons, corals and gastropods preserved as limestone

Travel back some 570 million years to a time known as the Ediacaran and the picture is very different. Although there were large-bodied creatures that were possibly animals, they were entirely soft-bodied. Then, right at the end of the Ediacaran Period, the first animals with hard skeletons evolved, creating strange tubes, stacked cones, and other bizarre forms such as Namacalathus, which resembles a baby’s rattle!

Some of the first animals with skeletons, Cloudina and Namacalathus alongside the soft-bodied Ediacaran fauna. Reconstruction based on rocks from Namibia, Southwest Africa, from 543 million years ago. Image: Mighty Fossils.

 

In the following few tens of millions of years, in the early part of the Cambrian Period, a whole host of animals burst onto the scene baring their ‘teeth’, hiding in their shells, and bristling their spines. In fact, we can trace the origin of almost every kind of animal skeleton to this relatively short window of the Earth’s past.

In my research, I have compiled the evidence for how and when these skeletons first appear. Three key observations have emerged. First, skeletons evolved independently many times in different animal groups. Second, there is both direct and indirect evidence, such as exceptionally preserved fossils and trace fossils, for entirely soft-bodied examples of animal groups that later evolved skeletons. And lastly, the first animal skeletons are less complex and more variable than later examples.

Added to what we know about how living animals build their skeletons, this all points to one explanation: Animal skeletons evolved independently in different groups by utilising a common ‘toolkit’ of genes, inherited from their common ancestor but used in different ways in different skeletons.

In other words, the soft-bodied ancestors of animals with hard parts had inherited all they needed to build simple skeletons that were then honed into the array of shells, teeth, spines, plates and bones we see today. For these skeletal pioneers, armed with their genetic ‘toolkit’, the environmental and ecological pressures of the early Cambrian prompted the evolution of similar, but independent, responses to their changing world – when life got hard.

Murdock, DJE. 2020. The ‘biomineralization toolkit’ and the origin of animal skeletons, Biological Reviews, is available for free here.

Top image: Tiny fragments of early skeletons, shells and spines, from around 510-515 million years ago.

 

A grasp of the past

by Ricardo Perez-De-La Fuente, research fellow

Few creatures look weirder – or are cooler, in my opinion – than mantidflies. There are around 400 species of these small predatory insects known worldwide – a scarce diversity by insect standards.

Like praying mantises, mantidflies have long ‘necks’ and forelegs armed with powerful spines and other structures used to hunt their prey with a sudden lethal grasp. The unfortunate victims become immobilised until they are meticulously eaten alive – not the best way to spend your last minutes on Earth!

Mantidflies belong to the Neuroptera order of insects and so aren’t actually related to praying mantises, but to insects such as lacewings and antlions.

A new paper that a colleague and I have published presents a new fossil mantidfly from Spanish amber that is important in understanding the evolution of their gripping – or raptorial – forelegs. The finding is presented in the open access journal Scientific Reports today.

Although the discovery has just been published, we excavated the new fossil during the scorching summer of 2010 in Teruel, northeastern Spain.

Amber excavations are very romantic – while they take place we carefully store the amber, piece by piece, into muddy plastic bags, remaining oblivious of what creatures are being unearthed because the amber surfaces have become opaque during fossilisation. Later, in the laboratory, the surfaces of the amber pieces are polished and screened for inclusions. Then a first glimpse is gained into what has remained frozen in time for millions of years.

It is only when the amber inclusions are carefully examined and studied that the implications of the specimens that were dug up years earlier start to be revealed. In this case, a specimen that was preserved in fragments, nothing spectacular at first look, ended up being truly exceptional.

Foreleg of Aragomantispa lacerata, showing powerful spines and other structures adapted to strike and hold prey.

Extinct true mantidflies, particularly those preserved in amber, are extremely rare. Our new fossil, pictured above at the top of the article, is 105 million years old, from the Cretaceous period. It currently stands as the oldest true mantidfly known in amber. The new extinct species, named Aragomantispa lacerata, has allowed us to compare the structures of the raptorial forelegs between extinct and extant mantidflies with an unprecedented detail.

Comparison between the foreleg spine-like structures of the new fossil mantidfly (up), with those from a close modern species (bottom).

Present-day mantidflies have forelegs with spines that bear minute cones at their tip. These cones are sensory organs that elicit the striking reflex and feel the prey’s movements once captured and restrained by the mantidfly’s tight embrace.

The forelegs of Aragomantispa lack these cones at the spines’ tip, instead having larger, icicle-shaped tips. We do not know how sensitive the mantidfly forelegs were in the Cretaceous, but the spines of at least some of these insects seem to be not as specialised as those from their present-day relatives.

Some mantidflies have smaller, reclined hair-like structures forming an edge on the leg’s surface opposing the spines. These reinforced edges create a scissor effect that stuns prey when the forelegs strike. Although Aragomatispa has these structures on the forelegs, they are also different in shape to those found on extant mantidflies.

Reconstruction of Aragomantispa lacerata striking at a hypothetical prey on a fern in the Cretaceous Spanish forest.

The fossil record offers the only direct means to assess when and how the traits characteristic of a given animal group originated in time. However, this kind of fossil evidence appears very occasionally. Our discovery shows that the foreleg spine-like structures of recent mantidflies were not fully developed in at least some of their Cretaceous ancestors.

The most exciting part is to think that this story and literally thousands more lie waiting to be discovered – or otherwise forgotten forever – buried underground.

How the sea cucumber lost its armour

By Imran Rahman, Research Fellow

You have probably heard of sea cucumbers. If you’re lucky, you might have seen one, if not in the wild, then perhaps in a nature documentary like Blue Planet or the children’s cartoon Octonauts. If you’re less lucky, you might have eaten one – they are most commonly described as slippery and bland in taste!

Despite their appearance, sea cucumbers are actually marine animals most closely related to sea urchins, rather than to worms or slugs. Over the past century palaeontologists have uncovered a range of ancient fossil relatives of modern sea cucumbers that allow us to piece together the story of how they evolved from armoured ‘tanks’ into the naked slug-like forms we see today. One such fossil is described in a new paper by my colleagues and I, just published in the journal Proceedings of the Royal Society B.

The fossil in question is 430-million-years-old, and it comes from a site of exceptionally-preserved fossils in England called the Herefordshire Lagerstätte. Herefordshire has produced many exciting discoveries over the years, from prehistoric parasites to an ancient ‘kite runner’. The new fossil is the first of its kind from this deposit.

Like all fossils from Herefordshire, the specimen was preserved in an egg-shaped nodule of rock. Because the rock has the same chemical composition as the fossil, it could not be studied with modern imaging methods such as CT scanning. Instead, it had to be studied by painstakingly grinding away the fossil, a few hundredths of a millimetre as a time, with photographs taken of each exposed surface using a digital camera. This allowed us to build up a dataset of hundreds of slice images through the fossil, which were digitally reconstructed as a 3-D ‘virtual fossil’ on a computer.

The 3D computer reconstruction revealed a very peculiar animal, about 3 cm wide, with 45 tentacle-like ‘tube feet’ and a large mouth surrounded by five teeth. The animal had a skeleton made up of numerous hard plates, which were composed of the mineral calcite. After studying this fossil and comparing it to other similar ones from the same time period, we were able to identify it as a species new to science. We named the species Sollasina cthulhu, for its resemblance to monsters from the Cthulhu universe created by author H.P. Lovecraft.

One of the most useful things about our 3D computer reconstruction was that it enabled us to study the inner features of the fossil, as well as the parts visible on the outer surface. This revealed internal soft parts that had never previously been described in this group of fossils. In particular, it allowed us to see an internal ring-like structure within the main body cavity.

3D reconstruction of Sollasina cthulhu. Left-hand image shows part of lower surface. Right-hand image shows same view with outer surface partly transparent to reveal inner ring (in red). Credit: Imran Rahman, Oxford University Museum of Natural History

We interpreted this inner ring as part of the water vascular system – the system of fluid-filled canals used for feeding and movement in modern sea cucumbers and their relatives, such as sea urchins and starfish. In life, the ring was connected to the large tube feet, which were filled with seawater. Most of these tube feet were used for crawling over the seafloor, with those nearest the mouth used for capturing food. The teeth could cut and crush food items, which were then eaten by the animal.

Life reconstruction of Sollasina cthulhu. Credit: Elissa Martin, Yale Peabody Museum of Natural History

To work out the evolutionary relationships of Sollasina cthulhu, we assembled a list of characteristics for various fossil and modern sea cucumbers and sea urchins. We analysed this matrix using several computational methods to determine how these different animals were related to one another. The results confirmed that Sollasina cthulhu and closely-related forms were ancient relatives of modern sea cucumbers. This allowed us to reconstruct the early evolution of sea cucumbers, back to their shared common ancestor with sea urchins, over 450 million years ago. Our study demonstrates this was a story of loss, with fossil sea cucumbers becoming progressively less armoured as they evolved into modern forms.

This discovery has greatly improved our understanding of sea cucumber evolution, but several questions remain. One intriguing question is when and how did sea cucumbers lose their teeth, and did these evolve into any features seen in living sea cucumbers? Future study of existing and new fossil sea cucumbers and sea urchins will help to answer this and other intriguing questions.