A miniature marine environment from the Middle Ordovician discovered in Castle Bank, Wales.

The well-preserved ‘marine dwarf world’ of 462 million years ago was found in Castlebank, Wales by a team led by the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS). The site includes more than 150 species, many with miniature body sizes. It is one of the most unexpected excavation sites in the world.

The study has been published in nature and its evolution on May 1.

Castle Bank, in Powys, is one of the very rare sites where soft tissues and whole organisms are preserved, providing unparalleled insight into the evolution of life. Among the best of these sites are Burgess Shale fauna, named after the classic fossil-bearing Burgess Shale deposit in Canada.

Many of these sites are found in rocks from the Cambrian period (542-485 million years ago), when known animal fossils first appeared. However, almost none of them occurred in Postcambrian rocks. As a result, paleontologists know a great deal about Cambrian marine life, but little about how it evolved in the periods immediately after.

Castle Bank dates to the middle of the Post-Ordovician period, about 462 million years ago, and rivals the best Cambrian deposits in fossil diversity and exceptional levels of preservation.

The fascinating new group was discovered in 2020 by Dr. Joe Botting and Dr. Lucy Muir, co-authors of this study, near Llandrindodd, central Wales.

To date, more than 150 species have been recovered, almost all of them new. Many of the animals are very small, only 1-3 mm long, but they retain fine details. They range from arthropods such as crustaceans and horseshoe crabs to various types of worms, sponges, starfish and many more. In some animals, internal organs such as the digestive system and even nerves are preserved, along with fine arthropod limbs and fine filter-feeding tentacles. This remarkable detail is best known from the Cambrian fauna, but not from the Ordovician.

The Castle Bank fauna represents a community of diverse marine organisms from the Middle Ordovician period, and many shell fossils were natural to these rocks.

In addition, the fossil collection also includes many unusual finds, from unexpectedly late examples of Cambrian fauna that look like opabiniids (a strange arthropod with a long proboscis) and wiwaxiids (mollusk-like molluscs armored with scales), to tantalizing, at the time Unexpectedly early fossils that resemble modern geese, cephalocharid shrimp (which have no fossil record at all) and perhaps even a close relative of marine insects.

The Cambrian period witnessed the origin of major animal groups. The Ordovician was a critical time in the history of life, too, with an extraordinary diversity of animals that produced hard skeletons and abundant fossils. In addition, familiar ecosystems such as coral reefs appeared at the end of the Ordovician period. So far, however, there is a large “gap” between these two evolutionary events.

New Burgess Shale fauna from the middle of this interval will help fill this gap by answering questions about the transition of fauna from the Cambrian to the Paleozoic and about the shift in ecosystems from the Cambrian type (which was similar across much of the world) to the The most diverse we see today.

A few papers have been published describing sponges and one about a primitive relative of modern arthropods called Mieridduryn based on these animals. Many more papers will follow and the collections will continue. According to Dr. Muir, “Most fossil deposits of this importance have been studied for many decades, and this likely wouldn’t be any different.”

Joseph Botting and two NIGPAS collaborators (YD Zhang, JY Ma) are collaborating at the Ordovician Konservat-Lagerstätte, and parts of this work, including the observation and analysis of some samples and reconstructions, are being completed at NIGPAS under support from CAS.

The Castle Bank fauna has important implications for the evolution of sponges, especially Hexactinellida, and is considered a transitional period between Cambrian sponges and that of Anji fauna, another Burgess-Shale animal from Zhejiang, China, that researchers have dedicated themselves to for years.