A part of evolution is strange little animals –

Evolutionary events during the Cambrian period, 539 to 485 million years ago, led to the dynamic and vibrant planet we have today.

The so-called Cambrian explosion can be best understood by examining well-preserved fossil sites such as the well-known Burgess Shale in Canada, where animal remains are preserved as thin carbon imprints in the sediments.

The findings provide snapshots of early life and help paleontologists track the evolution of animal groups over time. But this type of protection stopped at the beginning of the Ordovician period, 485 million years ago. This has created a gap in the knowledge of how Ordovician animals evolved from Cambrian animals.

New Small Fossil Discoveries

Now a new discovery site has been discovered at Castle Bank in Wales, England. It is also the site of discoveries of organic remains similar to those found in the Burgess Shale in Canada.

But there is one decisive difference, namely that the size of a new fossil rarely exceeds a few millimeters.

Very well preserved animal tissues

Uppsala University researchers can submerge fossils from the new discovery site in an acid solution to separate the brittle fossils from the rocks in which they are embedded. Then they examined the details with powerful microscopes.

In this way, the researchers found many well-preserved animal tissues. This confirms the presence of Burgess Shale-type fossils, such as those found in Canada, of late Ordovician age.

Among the variety of animal remains found in the rock are marine worms and various crustaceans similar to today’s animals, but including species from groups that no longer exist, various fungi, and enigmatic arthropod predators called opapinids.

Miniaturization is a big phenomenon

The small size ranges of these fossils, compared to their Cambrian counterparts, suggests an evolutionary process known as miniaturization. This means that under certain conditions smaller organisms have an advantage over larger ones, so they become increasingly common.

Many of the animal groups identified at the new site in Wales still have very small representatives today. Everything indicates that it was a significant and widespread phenomenon when animals became smaller.

An untapped source of information

If small animals became common in the oceans at this time, after the Cambrian period, the analytical methods used could provide more insight into the origin of the small species appearing at this time. An acid-based laboratory technique can be used in the analysis of fine-grained sedimentary rocks, revealing microfossils even when their larger counterparts are undetectable to the naked eye. This method was previously mainly used in Cambrian paleontology.

– The technology we use for microfossil analysis really contributes to our understanding of early life, says Elise Wallett, PhD student at Uppsala University’s Department of Geosciences.

Scientific Article:

A Middle Ordovician Burgess Shale fauna from Castlebank, Wales (UK), Natural Ecology and Evolution.

Contact:

Elise Vallet is a PhD student in paleobiology at Uppsala University
[email protected]