early life – More Than A Dodo

Cambrian creation

by Abigail Harris

Over the past few months our researchers have been working with University of Plymouth illustration student Abigail Harris, who has delved into the weird and wonderful world of some of the earliest animals. Here, Abigail tells us about the process that led to the creation of her Cambrian artwork, inspired by our First Animals exhibition.

I first visited the Museum in April this year when I was given the opportunity to collaborate with scientists as part of a module in my BA in at the University of Plymouth. Things kicked off with a short talk about the Ediacaran and Cambrian geological periods, when Earth’s first animal life started to appear.

I quickly narrowed my interest down to fossils from the Cambrian period which are more complex life forms, more similar to life today. A collection of small fossils from the Chengjiang fossil site in Yunnan province, China was the inspiration for some initial observational drawings.

Abigail Harris - sketches for artwork showing reconstruction of Cambrian ocean animal life — A sketchbook page showing initial sketches and observations of *Onychodictyon*

After returning to Plymouth University, I began to develop these initial sketches and observations, continuing to research the Chengjiang material and learning more about the characteristics of some of the creatures preserved as fossils.

I wanted to create an under-the-sea ecology reconstruction showing a diversity of life forms, focusing on Onychodictyon, Cotyledion, Cricocosmia, Luolishania, and Paradiagoniella.

A five-step process was used for each reconstruction. Initially, I would sketch the fossil as I saw it, then I would research the characteristics and features of that animal, making a list of things to include in my drawing. A second drawing would then include all of these characteristics, not just what was initially visible in the fossil.

These rough sketches were then sent to the scientists for feedback, helping me to redraw and paint the illustrations with watercolour, before scanning and digitally editing each painting. Lastly, I created a background and added my illustrations.

Initial under under the sea ecology reconstruction.

Although the reconstructions were not completely finished by the time of my project deadline, I returned to the Museum in July and was given a tour of the First Animals exhibition by Deputy Head of Research Imran Rahman, as well as the opportunity to discuss how to improve my artworks for accuracy.

Another round of sketching and painting led to the final piece, shown at the start of this article, complete with an added digital background of the seafloor, and darkened to reflect the murky world of a Cambrian ocean, 50 metres below the surface.

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.