Eigg Dino Paper: non-technical version

I’ve had a few requests for a non-technical summary of the paper describing the recent discovery from the Isle of Eigg. Our paper, titled First dinosaur from the Isle of Eigg (Valtos Sandstone Foration, Middle Jurassic) Scotland, was published in the scientific journal Earth and Environmental Science Transactions of the Royal Society of Edinburgh in August 2020. There are 13 co-authors, each bringing their own specialism to the mix, with myself as lead author. 

But scientific papers are often a bit opaque for non-specialists. So below I've written a walkthrough of the science, written for the general public. In it, I tease out the details of our discovery and research for everyone to enjoy. If you have any Qs, please ask!

Introduction

The Middle Jurassic (174-164 million years ago) is a special time in the evolution of life on Earth. Many groups appeared at this time or shortly before, and they split into lots of new families, and exploited new ways of life. This evolutionary pattern is also true for dinosaurs. However, scientists struggle to understand how and why this happened because fossils from the Middle Jurassic are so rare. Almost five times as many fossils are known from the Late Jurassic as the Middle! As a result, every Middle Jurassic fossil is a vital clue to life at this time, and scientifically significant.

Although dinosaurs have been found in Scotland already, all of them have come from the Isle of Skye. This is because there are fossil-rich Jurassic rocks on the island dating to around 166 million years ago. As well as dinosaur limb bones, teeth, and footprints, scientists have found fossil crocodiles, turtles, pterosaurs, mammals and marine reptiles, as well as invertebrate fossils like ammonites and belemnites.

The Isle of Eigg, which lies south of Skye in the Inner Hebrides (west coast of Scotland), is also known for its Jurassic fossils. However, these are all from marine animals and mainly comprise reptiles (like plesiosaurs), fish, and sea-living invertebrates. Fossils have been found on Eigg since the early 19^th century, but in 200 years of searching no-one had ever found terrestrial animal fossils.

Our paper describes the first dinosaur bone found on Eigg, which I discovered during National Geographic funded fieldwork by the University of Edinburgh in 2017. Our small team was given permission to work on the Island by the Isle of Eigg Heritage Trust. Eigg is owned by the residents, so we had to seek their permission to work there. We found the bone on the shore where there are a series of rocks called the Great Estuarine Group. This is the same group that yields fossils on Skye. It includes many different layers formed under different conditions: some when the Inner Hebrides was a shallow sea, and others from lagoons and deltas when the land was just above sea-level. The Eigg dinosaur was in a layer called the Valtos Sandstone Formation, which was formed on an ancient Middle Jurassic shore where rivers met the sea, perhaps in a brackish (mixed salt and fresh water) lagoon.

The stratigraphy of the Great Estuarine Group, and location of the Isle of Eigg.

The Fossil

The dinosaur bone is now part of the collections at National Museums Scotland (specimen number NMS G.2020.10.1). It was removed from the shoreline using rock saws, and the bone carefully extracted from the remaining rock by expert preparator, Nigel Larkin. The Eigg bone is half a metre long, and each end is missing, which makes it hard to identify what it is. There are tooth marks on the surface, which tells us it was scavenged after death. Nigel used a kind of glue to reinforce the bone and prevent it from breaking further. There was a section of the bone missing in the middle, so Nigel used the indent in the rock as a cast, reconstructing this missing part. 

The Eigg bone, NMS G.2020.10.1. A) the bone within the rock, partly excavated, and B-C) the bone reconstructed and removed from the rock.

Matthew Humpage photographed the fossil so that we could use the pictures for the paper, then he made a photogrammetry model of the bone, which is online and free to access on a site called Sketchfab. The fossil was also studied by thin-section, allowing us to look at the internal structure. This was done by Gregory Funston, who cut a thin slice through the bone in cross-section. He ground and polished this slice down to make it thin enough to pass light through, then examined it with a microscope. We used the information about the bone structure, along with comparisons with dinosaur bones from across the UK and rest of the world, to work out what kind of animal it belonged to.

Bite marks in the Eigg Dino Bone.

Identity of the Eigg Dinosaur

Our team had to work together to figure out what animal the Eigg bone belonged to, and which bone it could be. Because there have been many marine reptile fossils found on Eigg, marine reptile expert Davide Foffa compared it to these extinct ocean-going creatures. Swimming animals have special adaptations in their bones for their way of life, including having very short, wide limb bones, and thickened internal bone structure. Not only was the Eigg bone not the same shape as a marine reptile bone - it was too long and slender – it was not thickened like a marine animal bone. This meant we could be sure it wasn’t a marine reptile, and must be some kind of dinosaur.

Next we compared the bone to the three main groups of dinosaurs: theropods, sauropods, and ornithiscians. Co-authors Stephen Brusatte, Femke Holwerda, and Susannah Maidment are all dinosaur experts, and so were able to work systematically through all the possible identifications, narrowing it down. Because it was badly damaged, the Eigg bone didn’t have any diagnostic features (features that help identify the species) to guide us. Instead, we had to use detective work to narrow down the possibilities. It didn’t match the shape of theropod bones, but bore some resemblance to sauropod fibulae – the smaller of the two lower hind leg bones. It was also similar to a sauropod femur, but it would have to have been a particularly small, slender sauropod. Overall, the Eigg bone bore the closest resemblance to an ornithiscian fibulae, having the same length and width, and similar shape in cross-section. Ornithiscians include Stegosaurus and other armoured dinosaurs, which are already known from the Jurassic of the Northern Hemisphere, including sites in England.

Top) the skeleton of a Stegosaurus (from Natural History Museum London) showing the lower hind leg bones. Bottom) the cross-section of the Eigg Dino Bone, used to study the microscopic structure.

Greg’s cross section of the bone gave us the final clues we needed to identify it. He could tell from the fine detail of the bone structure that it was most likely an ornithischian – specifically a thyreophoran, which includes animals like Stegosaurus. The holes left behind by blood vessels told us that it had a relatively slow growth rate – unlike sauropods which grow very quickly to large sizes. There was a lot of secondary remodelling in the bone, which is when the bone alters as the animal grows. Very similar patterns are seen in stegosaurs like Hesperosaurus, Kentrosaurus and Stegosaurus.

Another thing Greg could see in the bone structure were lines that accumulate as the animal matures. These are known as LAGs (lines of arrested growth), and are found not only in bones, but also in teeth. The Eigg bone had a single LAG, which tells us it was older than one year in age, perhaps just a few years older – a youngster by dino standards. There was no sign that growth had stopped, so it was probably still actively growing before it died.

Conclusions

Putting all of this information together, we can tell that this is a limb bone from a stegosaur-like dinosaur. It is most likely a fibula, or hind lower leg bone. The animal was only young when it died, and was washed into a lagoon by the sea, or perhaps just off-shore, where it was chewed-on by marine reptiles.

Although dinosaur fossils in Scotland are few, and much less complete than those found in more famous Jurassic exposures in England, they are equally important. They add data to our Spartan picture of this time period. The bone from Eigg is also significant for Scotland as the first dinosaur fossil outside of Skye, and the first belonging to a stegosaur-like, thyreophoran dinosaur. It backs up the suggestion made recently by Paige dePolo and her co-authors that fossil trackways found on Skye belonged to thyreophorans.

It has taken 200 years of searching to find this dinosaur fossil on Eigg, but hopefully it won’t take as long to find the next one! Our team is grateful to our sponsors and the people of Eigg for their support – hopefully there are many more fossil discoveries to be made in the Inner Hebrides to enrich our understanding of life in the time of dinosaurs.

On Finding a Dinosaur

They tell me I’m good at finding things. Word searches, jigsaw puzzles - they are unintentional brain-training to isolate patterns in chaos. When looking for fossils it takes a few attempts to recognise what you’re seeking. Then they say you ‘get your eye in’, or that you ‘have the eye’ for it. I tell them, I have two.

I found my first dinosaur on a glorious sunny day in the Inner Hebrides. I leapt from boulder to boulder across the foreshore of the Isle of Eigg, sprinting like a mountain goat back to my teammates. With each jump I looked down to place my feet securely on dry Jurassic sandstone, which Velcro-gripped the soles of my tattered hiking boots. The stench of sulphur was making me dizzy – a nearby pool choked in marine algae was festering in the hot May sunshine. To avoid it, I moved up shore. As I flew down from a high platform into a small shingle inlet, I saw a silhouette. Long, with a bulbous end. Pattern recognition. 

Shoreline on Isle of Eigg, with Isle of Rum in the distance.

Momentum carried me several steps further along the clattering shingle before I fully registered what I’d seen. I skidded and turned back. The shape was nestled in a boulder tucked below the sandstone outcrops. I crouched down and reached out, running my fingertips across the rough surface. The electric-thrill formed a Bifröst to the ancient past.

Most fossils are not worth collecting, and that’s where scientific knowledge comes in. It was my fourth palaeontological expedition with teams working in my home-country of Scotland. That day in 2017 I recognised the black splodge on the rocks of the foreshore as the remains of a limb bone. It looked like burnt charcoal, the surface cracked as though oven-baked. Where the bone was damaged I saw the tell-tale honeycomb of a structure once-living; the strut of biological architecture, nature’s engineering exposed. A portion of the long mid-shaft was gone, leaving a ghostly indent in the rock. A million frozen grains of sand encased one end of the bone, reluctant to let it go. This stone had carried it for 166 million years like a time-capsule. It was a dinosaur limb bone. I took photographs, then turned and sped South again. 

The Eigg dinosaur bone, or StEiggosaurus, moments after I found it.

When I found my team mates I told them I’d found something. What is it? they asked. I knew how disappointing it was when your ‘fossil’ find turned out to be a bit of driftwood, or a splatter of solidified tar, so I replied that I wasn’t sure, but maybe a limb bone... What kind of limb bone? They pressed. I sheepishly mentioned some possibilities, non-commitally mumbling dinosaur.

I led them back along the shore. When they caught up and saw it, their faces exploded like grin-grenades. They knelt and examined it, agreeing it was indeed a dinosaur limb bone. The first dinosaur I’d found, and the first dinosaur ever found on the Isle of Eigg.

We took photographs and notes, planning how it could be collected. In the following weeks a team arrived by boat to slice through the shore and cut out its dinosaur heart. This bone - which had drifted offshore in the Jurassic sea and come to rest in a sandy bed for a geological nap - now drifted once again, southwards to the lab of our colleague, Nigel Larkin. He carefully removed the surrounding sandstone, exposing the limb bone for us to study.

My artwork showing the kind of dinosaur the Eigg bone belonged to. It may have died crossed a river or delta, and been washed out to sea.

It was scarred by scavengers, and the ceaseless surf of Eigg had made off more than half the evidence, one granule at a time. To figure out to which animal it belonged, I worked with palaeontologists who specialise in different groups of extinct reptile: Femke Holwerda (sauropod-lover), Susannah Maidment (queen of stegosaurs), Davide Foffa (marine reptile chaser), Stephen Brusatte (theropod enthuser). With so little of the bone left to study, we turned to the tell-tale biological structure for further clues. Gregory Funston examined the microscopic structure of the bone, a codex for an animal’s growth. The evidence combined to tell us that this was the leg bone of a stegosaurian dinosaur, a plate-backed herbivore of the Jurassic. An early resident of Eigg, now at rest in the National Museum of Scotland in Edinburgh.

By the time the whole team had assembled to look at the discovery on the shoreline that Summer’s day, I was already elsewhere. I’m restless as a wave, prefering movement. Hopefully life will always find me leaping along fermenting shorelines and shuffling below cliffs. I revel in zenful hours squinting at glinting surfaces, with salt spray scratching my lips and flaying my fingertips, sifting through ancient sands for fragments of Jurassic Scotland. 

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Panciroli, E., Funston, G. F., Holwerda, F., Maidment, S. C. R., Foffa, D., Larkin, N., Challands, T., dePolo, P., Goldberg, D., Humpage, M., Ross, D., Wilkinson, M., Brusatte, S. L. 2020. First dinosaur from the Isle of Eigg (Valtos Sandstone Formation, Middle Jurassic), Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 1-16.