The fossils include many soft-bodied creatures found in rocks which are hundreds of millions of years old.

They were discovered near Llandrindod Wells, Powys, in mid Wales.

The rocks were laid down under the sea over 460 million years ago when mid Wales was covered by an ocean.

Researchers at Amgueddfa Cymru - Museum Wales made the discovery in 2020 during the COVID-19 lockdown.

Over 170 species were discovered at a secret location on private land.

Experts and Llandrindod residents Dr Joseph Botting and Dr Lucy Muir said the site was rare as it had preserved soft tissue and complete organisms, not just shells and bones.

The site, referred to as Castle Bank by researchers, dates from the Middle Ordovician, some 50 million years after almost all previously known examples of the same type which date back to the Cambrian Period (538 to 485 million years ago).

The discovery is important as it gives a fresh insight into how life evolved in this period, according to Dr Muir.

"It coincides with the 'Great Ordovician Biodiversification Event', when animals with hard skeletons were evolving rapidly," she said.

"For the first time, we will be able to see what the rest of the ecosystem was doing as well."

The fossils found at Castle Bank include different types of worms, sponges, barnacles, starfish and a creature that may be distantly related to insects.

The site was also home to the youngest known examples of unusual groups of animals that include opabiniids, creatures that had a proboscis that looks like a vacuum cleaner tube.

Another creature they found was the wiwaxiid, a strange oval-shaped mollusc with a soft underbelly and a back covered with rows of leaf-shaped scales and long spines.

Places where soft-bodied fossils can be found are extremely rare and only one other site from the period in Morocco preserves them to this level of detail.