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, within the Cambrian period, contains a missing chapter. Palaeontologists refer to it as the “Furongian gap”. It is 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 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 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 is a reminder of how incomplete our understanding of Earth’s history remains.
We describe a new 500-million-year-old arthropod from Québec, Canada. Arthropods are animals with exoskeletons. 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.
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. 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.
The specimen was originally collected in 1962 during geological mapping near SainteAnne-de-la-Pocatière in Québec. It came from mudstones within the Rivière-duLoup Formation, deposited in relatively deep marine slope environments during the late Cambrian. 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 an important aspect of palaeontology: major discoveries do not always emerge directly from fieldwork. Museum collections contain enormous quantities of under-studied material collected over the past century. Revisiting these collections can reshape the understanding of ancient ecosystems.
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. 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.
The Conversation