The other worlds beneath our feet

Welcome to the weird and wonderful world of the Burgess Shale Biota

By Mia Wroe

11 hours round hike from the nearest town, isolated deep in the Canadian Rockies of British Columbia, sits one of the most important scientific sites in the world. The Walcott Quarry is known for producing Burgess Shale; an extremely fossiliferous rock that is between 505 and 510 million years old (for context, the dinosaurs went extinct a mere 66 million years ago). This is a ‘Konservat-Lagerstätten’ - or ‘site of exceptional preservation,’ meaning that soft tissues have been fossilised here.

The organisms represented by the Burgess Shale offer an insight into a period of time known as the Cambrian explosion, when we see the sudden appearance of most of the major animal phyla we still see today. Life before the radiation consisted mainly of colonies of cells and primitive multicellular animals, but the rapid diversification of the Cambrian brought with it life that would look somewhat more recognisable as what we would call ‘animals’ today. Colourful sponges and corals lay on the seafloor beside odd worms and primitive mollusc burrows. Higher in the water column, early arthropods, like the iconic trilobite, became some of the first actively swimming predators and scavengers and stalked the seafloor, on the lookout of their next meal.

Whole books have been dedicated to the fauna of the Burgess Shale and its array of unusual organisms from deep time. One specimen from the Burgess Shale clearly shows an arthropod whose new cuticle had not hardened quick enough after its last moult to protect it from a cluster of carnivorous (and affectionately named) penis worms. Others are less recognisable, like Anomalocaris; an early arthropod whose body parts had been incorrectly identified as three separate and unrelated species until Harry B. Whittington corrected the error in 1985. Now we know that the mysterious ‘headless shrimp’ were attached to the ‘jellyfish’ mouth of this metre-long top predator.

Perhaps the most famous mystery that arose from the Burgess Shale was that of Hallucigenia. When it was first fully described by Simon Conway Morris in 1977, it was reconstructed upside down, walking on what we now believe to be two sets of spines that actually run along its top. Hallucigenia was placed in the rather broad phylum Lobopodia, classifying it simply as “worm with legs.”

Anomalocaris canadensis by Jack Mayer Wood

The Burgess Shale is the site most people think of when they hear ‘exceptional preservation.’ But is it not unique. Fifty minutes on the number X8 bus from Broad Street towards Wolverhampton will take you to another quarry; Wren’s Nest. Here, you can find the Wenlock Limestone Formation, Dudley’s own site of exceptional preservation. Head to ‘Fossil Trench’ (you can recognise it by the steep rock face with massive, distinct ripples) and you can collect your own fossils. The site is an SSSI so hammering is not permitted, but plenty of weathering means that you can pick up almost any loose rock there and find it full of fossilised Silurian corals, bryozoans, brachiopods and, if you’re lucky, a trilobite or two.

From Issue 17