Roughly 500 million years ago, a strange event in the evolution of life on Earth seems to have taken place.
The known fossil record from this time, which falls within the Cambrian period, contains a missing chapter. Palaeontologists refer to it as the “Furongian gap”. And it’s striking because there is an explosion of biodiversity within the fossil record both immediately before and after it.
This decline has been considered evidence for a real biological crisis – one driven by environmental instability, changing ocean chemistry, cooling climates, a lack of oxygen in ancient seas, or a combination of these factors.
Our new study, published in the journal BMC Biology, provides new evidence for an alternative idea. The Furongian may not represent a true collapse in biodiversity, but rather a gap in where scientists have looked and what kinds of rocks have been studied.
It’s a reminder of how incomplete our understanding of Earth’s history remains.
A rare group of fossils
We describe a new 500-million-year-old arthropod from Québec, Canada. Arthropods are animals with exoskeletons – that is, skeletons on the exterior of their bodies.
The fossil belongs to a rare group of early arthropods related to the lineage leading to spiders and scorpions. Importantly, it comes from a geological setting that scientists have not previously recognised as being notable for preserving fossils at this time in Earth’s history.
The fossil itself is named Magnicornaspis garwoodi. The animal belongs to the corcoraniids – an enigmatic group of early arthropods that have broad head shields, segmented bodies, and defensive spines.
Corcoraniids remain exceptionally rare globally. Only a handful of species are known from the Cambrian and Ordovician periods.
Our specimen is unique for its two large forward-projecting spines extending from the head. These exaggerated spines distinguish the species from previously known relatives. They suggest defensive adaptations within the group evolved earlier than previously recognised.
Thomas Turner
Sitting in a museum drawer for decades
The specimen was originally collected in 1962 during geological mapping near Sainte-Anne-de-la-Pocatière in Québec. It came from mudstones within the Rivière-du-Loup Formation. This formation was deposited in relatively deep marine slope environments during the late Cambrian.
This represents quieter offshore conditions where fine mud settled through the water column. These rocks have received relatively little palaeontological attention, making them ideal for reassessment.
The specimen sat largely overlooked within the collections of the Smithsonian National Museum of Natural History in Washington DC for decades. This highlights one of the most important aspects of palaeontology: major discoveries do not always emerge directly from fieldwork.
Museum collections contain enormous quantities of under-studied material collected during geological surveys and expeditions over the past century. Revisiting these collections with modern techniques can fundamentally reshape understanding of ancient ecosystems.
Ajay Suresh, CC BY
More treasures awaiting discovery
Our discovery adds to a growing body of evidence that challenges the notion of a barren late Cambrian world.
Studies from China and Sweden have documented other well-preserved fossils from about 497–485 million years ago.
Together, these discoveries suggest ecosystems may have remained diverse and ecologically complex during this time.
The new Québec fossil expands this picture geographically. Our specimen demonstrates the ancient Appalachian margin of eastern Laurentia, the ancient continent that included much of present-day North America and Greenland, was a site of excellent fossil preservation.
This broadens the known distribution of soft-bodied fossil preservation during the interval. It also hints that comparable deposits may await discovery elsewhere.
The Furongian gap therefore may not represent a biological collapse at all. Instead, it may partly reflect an “anthropogenic bias” in the fossil record – a distortion introduced by where humans have searched, collected, and studied fossils.
Each newly discovered Furongian exceptional fossil site narrows this supposed gap. They reveal increasingly sophisticated ecosystems thriving during the late Cambrian.
Entire groups of organisms – and possibly even ecosystems – may still await discovery within museum drawers or poorly studied rock formations. The late Cambrian lasted millions of years across vast ancient oceans. Yet only a tiny fraction of its environments have been systematically explored for soft-bodied preservation.
The next major fossil discovery may not come from a newly discovered outcrop in a remote desert. It may already exist, inside a museum cabinet, collected decades ago and waiting for someone to recognise its significance.
