Tag: fossilisation

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Diving into deep time

Our current First Animals exhibition is extending its run until 1 September, and to mark the extension our Research Fellow Imran Rahman takes a look at how animal life in the ancient oceans was brought to life in our Cambrian Diver interactive installation.

One of the biggest challenges in developing the First Animals exhibition lay in visualising rare fossil specimens as ‘living’ organisms, transforming them from two-dimensional imprints in the rock into three-dimensional animated computer models.

Many of the specimens on display in First Animals were collected from sites of exceptionally well-preserved fossils called Lagerstätten. These deposits preserve the remains of soft-bodied organisms that are almost never seen in the fossil record; things such as comb jellies and worms, as well as soft tissues such as eyes, gills and muscles. Even so, most of these fossils are flattened and two-dimensional, which makes it very difficult to reconstruct what they looked like in life.

Vetulicola cuneata from the Chengjiang fossil site had a large body with triangular openings on either side and a segmented tail. Its three-dimensional shape is uncertain.

To help exhibition visitors visualise the animals in a living environment we worked closely with Martin Lisec and his team at Mighty Fossils to create a set of detailed computer models of a key set of animals. We have worked with Martin before on the video of a Jurassic sea inhabited by plesiosaurs and other marine animals for our Out of the Deep display. That was very successful, but our idea for First Animals was even more ambitious: to create a unique interactive installation called the Cambrian Diver.

The material focused on the Chengjiang animals from the Cambrian of Yunnan province, China, which provides the most complete record of an early Cambrian marine community, from approximately 518 million years ago. Using fossil evidence of the organisms thought to have lived at the time we selected 12 species that were representative of the diversity of the Chengjiang biota.

The first phase was collecting as many materials as possible to be able to create 3D models. As usual, we started with rough models, where we set basic dimensions, shapes and proportions of body parts. Once approved, we moved to very detailed models for the animations, artworks and textures for less detailed models to be used within the interactive application. – Martin Lisec, Mighty Fossils

Images showing a preliminary 3-D model of the lobopodian Onychodictyon ferox in multiple views, with annotations in yellow highlighting changes suggested by Museum researchers.

To provide two-dimensional templates for Mighty Fossils to work from we scoured the scientific literature for the most recent accurate reconstructions available for each of the species.

The predatory arthropod Amplectobelua symbrachiata is a good example. We drew heavily upon a 2017 paper by Dr Peiyun Cong and colleagues, which included a very detailed reconstruction of the head region. This reconstruction shows that the underside of the head of Amplectobelua consisted of a rod-shaped plate, a mouth made up of two rows of plates, and three pairs of flaps with spiny appendages, all details that are included in our 3D model.

Scientific reconstruction (left) and our 3D model (right) of the arthropod Amplectobelua symbrachiata. Left-hand image modified from Cong et al. (2017).

Colour and texture were another consideration. To inform these we looked at living species that are thought to have similar modes of life today. For Amplectobelua, a free-swimming predator, we examined the colouration of modern marine predators such as sharks. Many sharks have countershading, with a darker upper side of the body and a lighter underside, which acts as camouflage, hiding them from potential prey.

We reconstructed our Amplectobelua model with similar countershading camouflage, with blue and red colouration inspired by the peacock mantis shrimp, a brightly coloured predatory arthropod that lives in the Indian and Pacific oceans.

3-D model of Amplectobelua in angled upper (top) and lower (bottom) views, showing countershading.

The next vital step was establishing how the animals moved and interacted with one another. This is a major challenge because in many cases there are no modern equivalents for these extinct early animals. For Amplectobelua we inferred that the flaps on the sides of the body were used for swimming, with the tail fan helping to stabilize the animal as it moved through the water. This agrees with previous interpretations of swimming in closely related animals such as Anomalocaris.

The models were built and textured by Mighty Fossils using the 3D gaming engine Unity. The video below is an accelerated sequence showing how the elements of the model are layered together.

The finished, animated and annotated Amplectobelua model is shown below, and can be zoomed and rotated. All the models generated by Mighty Fossils for the First Animals exhibition are gathered in a collection on our Sketchfab page.

Once animated models of all 12 species were created we placed them in a realistic marine environment. Study of the rocks preserving the Chengjiang fossils suggests these animals lived in a relatively shallow, well-lit sea, perhaps 50 metres deep and characterised by a flat, muddy seafloor. A continuous shower of organic particles is thought to have filled the water column, as in modern oceans.

Reconstruction of the Cambrian seafloor with ‘marine snow’

Based on present-day marine ecosystems, we infer that the number of immobile suspension feeders would have been much greater than the number of predators. As a result, we included multiple individuals of the suspension feeders Cotyledion, Saetaspongia and Xianguangia, which were tightly grouped together, but only a small number of the active predators Amplectobelua and Onychodictyon.

This scene is now populated with animals, including two predators: Amplectobelua (swimming) and Onychodictyon (centre)

The final step involved setting up a camera and user interface to allow visitors to discover the various animals in our interactive environment. For this we worked with creative digital consultancy Fish in a Bottle to identify eight locations, each focused on a different animal.

As the video above shows, users can navigate between locations by touching an icon on the screen, and when the Cambrian Diver sub arrives at a location information about the animal, its mode of life and its closest living relatives is presented on-screen. A physical joystick allows users a 360-degree rotation to look around the scene, and explore the ancient watery world.

This project was significantly bigger than the Out of the Deep work we had done previously with the Museum, mainly because of the complicated approval procedure needed for 20 individual 3D models. Along with three large illustrations, two animations and the interactive application this was a big workload! Fortunately, we managed to finish the whole project on time for the opening of the exhibition. – Martin Lisec

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Life’s big bang?

by Harriet Drage and Scott Billings

You may have heard of the Cambrian Explosion, an ‘event’, starting roughly 540 million years ago, when all the major animal groups suddenly appear in the fossil record, an apparent explosion of life and evolution.

But was there really an evolutionary explosion of all these animal groups, or is the lack of evidence from earlier periods due to some peculiarity of the fossilisation process? The debate has rumbled on for a number of years.

Now, a new study from our research team, the University of Oxford’s Department of Zoology, and the University of Lausanne, claims that the early Cambrian saw the origins and evolution of the largest and most important animal group on Earth – the euarthropods – in a paper which challenges two major pictures of animal evolution.

Euarthropoda contains the insects, crustaceans, spiders, trilobites, and a huge diversity of other forms alive and extinct. They comprise over 80 percent of all animal species on the planet and are key components of all of Earth’s ecosystems, making them the most important group since the dawn of animals over 500 million years ago.

Exceptionally preserved soft-bodied fossils of the Cambrian predator and stem-lineage euarthropod Anomalocaris canadensis from the Burgess Shale, Canada. Top left: Frontal appendage showing segmentation similar to modern-day euarthropods. Bottom right: Full body specimen showing one pair of frontal appendages (white arrows) and mouthparts consisting of plates with teeth (black arrow) on the head. Images: A. Daley.

A team based at the museum, and now at Lausanne, conducted the most comprehensive fossil analysis ever undertaken on early euarthropods, to try and establish whether these animals really did emerge in the early Cambrian period, or whether fossilisation just didn’t occur in any earlier periods.

In an article published today in the Proceedings of the National Academy of Sciences they show that, taken together, the total fossil record does show a gradual radiation of euarthropods during the early Cambrian, 540-500 million years ago, challenging other ideas that suggest either a rapid explosion of forms, or a much slower evolution that has not been preserved in the fossil record.

Each of the major types of fossil evidence has its limitation and they are incomplete in different ways, but when taken together they are mutually illuminating
Professor Allison Daley

Reconstruction of the Cambrian predator and stem-lineage euarthropod Anomalocaris canadensis, based on fossils from the Burgess Shale, Canada. Reconstruction by Natalia Patkiewicz.

By looking at a huge range of fossil material the researchers ruled out the possibility that Pre-Cambrian rocks older than around 541 million years would not have preserved early euarthropods. The only plausible explanation left is that the origins of this huge animal group didn’t evolve until about 540 million years ago, an estimate which also matches the most recent molecular dating.

The timing of the origin of Euarthropoda is very important as it affects how we view and interpret the evolution of the group and its effects on the planet. By working out which groups developed first we can trace the evolution of physical characteristics, such as limbs.

Exploring all the evidence like this allows us to make an informed estimate about the origins of key animal groups, leading to a better understanding of the evolution of early life on Earth.

Model of the Cambrian stem lineage euarthropod Peytoia, based on fossils from the Burgess Shale. Top left: Closeup of the mouth parts and frontal appendages. Bottom right: Overall view of the body. Model and image: E. Horn.

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Is it real? – Fossils

One of the most common questions asked about our specimens, from visitors of all ages, is ‘Is it real?’. This seemingly simple question is actually many questions in one and hides a complexity of answers. 

In this FAQ mini-series we’ll unpack the ‘Is it real?’ conundrum by looking at different types of natural history specimens in turn. We’ll ask ‘Is it a real animal?’, ‘Is it real biological remains?’, ‘Is it a model?’ and many more reality-check questions.

This time: Fossils, by Duncan Murdock

Whether it’s the toothy grin of a dinosaur towering over you, an oyster shell in the paving stone beneath you, or a trilobite in your hand, fossils put the prehistory into natural history collections. Anyone who has spent a day combing beaches for ammonites, or scrabbling over rocks in a quarry will attest that fossils are ‘real’. It is the thrill of being the only person to have ever set eyes on an ancient creature that drives us fossil hounds back to rainy outcrops and dusty scree slopes. But fossils, unlike taxidermy and recent skeletons, very rarely contain any original material from living animals, so are they really ‘real’?

Megalosaurus
The Museum’s famous Megalosaurus jaw

Fossils are remains or traces of life (animals, plants and even microbes) preserved in the rock record by ‘fossilisation’.

This chemical and physical alteration makes fossils stable over very long timescales, from the most ancient glimpses of the first microbes billions of years ago to sub-fossils of dodos, mammoths and even early humans just a few thousand years old. They can be so tiny they can only be seen with the most high-powered microscopes or so huge they can only be displayed in vast exhibition halls, like our own T. rex. Among this is a spectrum of how much of the ‘real’ animal is preserved, and how much preparation and reconstruction is required to be able to display them in museums.

Trace fossils include footprint trackways like these, made by extinct reptile Chirotherium.

Generally, the more there is of the original material and anatomy, the rarer the fossils are. Among the most common fossils found are ‘trace fossils’: burrows, footprints, traces, nests, stomach contents and even droppings (known as ‘coprolites’). Most ‘body’ fossils also contain nothing of the living creature, rather they are impressions of hard parts like teeth, bones and shells.

This ammonite fossil, Titanites titan, was formed when a mould was filled with a different sediment, which later turned to rock.

When an organism is buried the soft parts quickly decay away. The hard parts decay much more slowly, and can leave space behind, creating a fossil mould. If this later gets filled with different sediment, it forms a cast.

These sediments are buried further still and eventually turned into rocks. Alternatively, the hard parts can be replaced by different minerals that are much more stable over geological time. Essentially bone becomes rock one crystal at a time.

3D reconstruction of 430 million year old fossil, Aquilonifer spinosus. Found in Herefordshire Lagerstätte, which preserves ancient remains with superb detail.

Very rarely the soft parts of an organism get preserved, but in the most exceptional cases skin, muscles, guts, eyes and even brains can be preserved. If buried quickly enough an animal can be compressed completely flat to leave behind a thin film of organic material, or even soft parts themselves can be replaced by minerals, piece-by-piece. These mineralized fossils can be exquisitely preserved in three dimensions, even down to individual cells in some cases. This is about as ‘real’ as most fossils can be, except the few special cases where the remains of an organism are preserved virtually unaltered, entombed in amber, sunk into tar pits or bogs, or frozen in permafrost. The latter push the boundaries of what can really be called a fossil.

Bambiraptor feinbergi

The final step in the process, from the unfortunate demise of a critter to its eventual study or display, involves preparation. In most cases the fossil has to be removed from the surrounding rock with hammers, chisels, dental tools and sometimes acids. This preparation can be quite subjective, a highly skilled preparator has to make judgements about what is or isn’t part of the fossil. The specimen may also need to be glued together or cracks filled in, so not everything you see is always original.

As with modern skeletons, there are often missing parts, so a fully articulated dinosaur skeleton may be a composite of several individuals, or contain replica bones. This is, of course, not a problem as long as it is clear what has been done to the fossil. This is not always the case, and there are examples of deliberately forged fossils, carved into or glued onto real rocks, or forgeries composed of several different fossils to make something ‘new’, like a ‘cut n shut’ car.

So, if you see a fossil that looks too good to be true, then it just might be worth asking, “is it real”?

Next time… Models, casts and replicas
Last time… Skeletons and bones