Earth's ancient 'sea'crets exposed, thanks to a geologist's 462 million-year-old find

As a point of reference, it's worth noting that the Middle Ordovician refers to a specific period of Earth's history, encompassing roughly 470 to 458 million years ago. It was a time of significant geological and biological developments.

During this period, the continents of Earth were merging to form a supercontinent known as Gondwana, which included landmasses that we recognize today as South America, Africa, Australia, and Antarctica. The Middle Ordovician is also renowned for its flourishing marine life.

What is the Burgess Shale, and why is it so significant in the study of animal evolution?

The Burgess Shale is one of the most important fossil sites on Earth, located high in the Rocky Mountains of British Columbia (Canada). 

Dating from the Cambrian (508 million years), it is thought to have preserved virtually everything living on the sea floor at the time of burial, [containing] flattened films of carbon with mudstone, but often retaining details like internal organs. 

Since its discovery, many other similar (but mostly less good) Cambrian faunas have been found, leading to the term "Burgess Shale-type faunas." These include other iconic locations like Chengjiang in China. 

The Burgess itself is still one of the best. Still, this suite of faunas gives us an unparalleled view into how life was evolving in the open seas during a particular time interval. It also happens to be during the initial diversification of animal life, giving us immense insights into the evolution of the major groups of animals and the earliest development of animal-dominated ecosystems. 

How did you first discover the new Burgess Shale-type fauna in Wales, and what techniques were used to extract the fossils?

Lucy Muir and I are a married couple living in Llandrindod and researching paleontology largely as a hobby. We are Honorary Research Fellows at the Amgueddfa Cymru--National Museum Wales, but make a living in other ways.

We found the quarry we called Castle Bank in 2013 while out on a walk (we can hardly ignore a new pile of rock, after all). We soon found that the site contained quite a few new species of sponges but not much else. As a result, we gradually collected the site over quite a few years, building up a collection in order to publish the fauna. 

When the lockdown happened in 2020, I decided to have one more day of fieldwork and then write it all up. That day was mainly about tying up loose ends, which resulted in me trying to split some difficult layers that had been largely ignored until then.

As a result, out popped a tiny tube with tentacles sticking out... which suddenly made it obvious that this site was *much* more important than we'd realized.

How do these new fossils differ from those found in the original Burgess Shale in Canada? What new insights do they provide into animal evolution?

The site is some 50 million years younger than the Burgess Shale itself, from the Middle of the GOBE (Great Ordovician Biodiversification Event).

As a result, it's a combination of leftover Cambrian-like animals (including some groups not previously known to have survived past the Cambrian, like wiwaxids) and much more advanced-looking creatures like barnacles and possible cephalocarids. 

There are also a large number of currently problematic animals that have no obvious counterpart in the fossil record or in the modern world. It's expected that most of the species in a new site like this would be new (and they are), but many of the entirely new groups of fossils seen here were unexpected. 

For a new Cambrian fauna, we have all the other Burgess Shale-type faunas to compare with, so you'd expect to see a lot of familiar groups. For the Middle Ordovician, we simply didn't know what was there... and the answer is a lot of things we couldn't have anticipated. 

What types of soft tissues have been preserved in these fossils? How can this help us better understand the anatomy and physiology of ancient animals?

The soft tissues at Castle Bank include virtually all the external tissues, no matter how fine and fragile (e.g., incredibly delicate filter-feeding arrays), and a range of internal organs from guts in several groups to neural tissue in a small arthropod. 

There may well be other tissues as well, like muscles, but these need to be confirmed in future work. 

What implications do these new discoveries have for our understanding of the origins of complex life on Earth?

Not a lot! The origin of complex life was much further back. Still, it does provide a lot of new insights in two areas:

i) The evolution of early animal groups. There are lots of new species at Castle Bank that will give us critical new insights into the evolution of particular phyla.

 ii) The evolution of ecosystems during the Ordovician, which was a revolutionary time for community ecology. Of course, it can only tell us about this community because the Ordovician was marked by increasingly extreme ecological heterogeneity. But that in itself is a lot more than we had before. 

How might these new findings be used to inform future research in paleontology, and what other areas of animal evolution might benefit from this analysis?

Castle Bank provides an entirely new angle for understanding the transition from the relatively homogeneous Cambrian faunas. [This is the time] when animals had diversified into their major groups (phyla and some classes) to the later faunas when diversification of orders, families, and species dominated the evolutionary history. 

Before there, we had a very large hole in our knowledge, but Castle Bank allows us to start to connect evolution across that gap. 

One of the most surprising aspects is how modern some unexpected groups appear, such as cephalocarids, barnacles, and rossellid sponges. 

This might suggest that the origins of many modern families go back further than expected, which (if confirmed) will start to change our expectations of what we expect to see through the Palaeozoic.

Aside from anything else, many of these must have survived the catastrophic end-Ordovician Mass Extinction rather than evolving afterward. It's another indication that the standard fossil record (shells, etc.) can be extremely misleading when it comes to the actual living communities. 

The Q&A has been slightly edited for flow.