15 Million-Year-Old Fossil Shells Reveal Traces of Colour Patterns in South Australia
Image: 15 million-year-old mollusc shells from the Murray Basin recently discovered to preserve their original patterns by exposure to UV light. Fergusen, Reed & Garcia-Bellido 2025
When we think of seashells, we often picture their colours and striking patterns. When those shells are millions of years old, the colour is usually long gone. Fossilised shells are often pale, stripped of the pigments that once made them shine.
That’s what makes a new study from South Australia so exciting. Researchers have revealed hidden traces of colour in 15-million-year-old mollusc shells from the Murray Basin, using a surprising tool: ultraviolet (UV) light.
A Miocene Ocean World
Around 15 million years ago, during the Miocene epoch, the Murray region looked very different. Instead of the familiar River Murray, the landscape was covered by a shallow, warm sea. In the soft, marly rocks found along the river today, there is evidence of a vast and diverse ocean community in the form of invertebrate fossils and a few vertebrates, including sharks and whales. Living upon this marine seafloor were sea urchins (echinoderms), brachiopods, lace-corals, arthropods, and more, but the most common and diverse were the molluscs, including bivalves, snails (gastropods), tusk shells (scaphopods), and nautiloids (cephalopods).
The fossils of these creatures, preserved in the Murbko Marl formation, are unusually complete. Unlike many other sites in Southern Australia, where snail shells have dissolved away, here the original shells have survived. However, their colour and patterns were unknown.
Image: Significant gastropod shells from the Murray Basin under natural, UV and UV-inverted light, Fergusen, Reed & García-Bellido (2025)
Finding Lost Patterns with UV Light
Pigments break down quickly after death, which is why fossil shells usually look plain. However, under UV light, some shells fluoresce, revealing ghostly patterns that hint at their original colours.
In the first full study of Southern Hemisphere material, University of Adelaide PhD candidate Mahala Fergusen, together with Environment Institute members Dr Liz Reed and Assoc. Prof. Diego García-Bellido, examined fossil shells from the Murbko Marl. What they found was remarkable: 18 different species responded to UV light, displaying stripes, bands, and chevrons that had been hidden for millions of years.
One of the most striking examples was Lophiotoma murrayana . The discovery of its chevron pattern helped confirm its reassignment to the genus Lophiotoma, a significant taxonomic update, since the genus it was once placed in is known for species without pigmentation.
Image: Specimen of Maoricolpus murrayanus in situ, showing the preserved pattern on its shell, under UV light, Fergusen, Reed & García-Bellido (2025)
More Than Just Pretty Shells
While it’s easy to marvel at the beauty of these rediscovered patterns, the real scientific value lies in what they tell us. Pigmentation patterns can be crucial in identifying species, especially when shells look almost identical in size and shape. These hidden clues give palaeontologists new ways to solve old mysteries about classification and evolution.
The researchers also wanted to understand how these pigments and their fluorescence work. They compared a fossil snail, Maoricolpus murrayanus, with its living relative, Maoricolpus roseus, using Energy-dispersive X-ray spectroscopy (EDX). The goal was to find a chemical link to either the pigment or the fluorescence. The outcome? No clear answers. This suggests that fossil mollusc pigmentation is still a scientific puzzle waiting to be solved.
Image: UofA PhD candidate Miss Mahala Fergusen collecting data in the field (Murray Basin, 2024), Fergusen, Reed & García-Bellido (2025)
A Glimpse Into the Past
This study shows that fossils can still surprise us, even after millions of years. By using UV light, scientists have unlocked hidden details of Miocene life, giving us not only a better understanding of molluscs but also a vivid reminder of South Australia’s oceanic past.
These shells are more than just relics, they’re storytellers, preserving snapshots of an ancient sea that once covered the Murray region. Thanks to modern techniques, we can now appreciate them not just as fossils, but as windows into a world long vanished.
Read the full paper here: [Palaeontologia Electronica]
We acknowledge that this fossil material originates from the land of the First Peoples of the Murray River and Mallee Region. The research was carried out at the South Australian Museum and the material is reposited in the SA Museum’s Palaeontological Collections.
Connect with the Researchers
Dr Liz Reed
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Assoc. Prof. Diego C. García-Bellido
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Upcoming event featuring Associate Professor Diego Garcia-Bellido
Latest discoveries on Cambrian fossil arthropods from Australia and the world
When: Tuesday 7th of October 2025, from 5.30pm
Where: Goodman Building, Botanic Gardens (entry from Hackney Road)
Assoc. Prof. Diego C. García-Bellido
University of Adelaide & South Australian Museum
Abstract: Arthropods have been the most diverse phylum in the planet from the beginning of animal evolution over 500 million years ago. Unfortunately, most of its clades are not mineralised, so the best information on their early diversity, external morphology, anatomy, and life cycles comes from Cambrian Konservat Lagerstätte like the Burgess Shale in Canada, Chengjiang in China, and our very own Emu Bay Shale in Kangaroo Island. In this talk, we will look into what we have learnt in the last few decades about early arthropod evolution from the amazing range of fossils found in these internationally renowned sites.
Bio: Diego was born, raised, and graduated in Spain, where he got his BSc in Zoology (1997) and PhD in Palaeontology (2002) from the Complutense University in Madrid. Diego settled in Australia in 2012 but has previously carried out long research stays in Los Angeles, Toronto, Cambridge, and London. He studies the early evolution of animals during the Ediacaran and Cambrian, more than half a billion years ago, particularly in the Flinders Ranges and Kangaroo Island, but also the Canadian Rockies, the Andes, and the Atlas. His expertise focuses on exceptional preservation of trilobites and other arthropods, molluscs, echinoderms, worms, sponges… and has published on fossils from Australia, Canada, Spain, Portugal, Morocco, China, Argentina, and Peru. Diego has written over 100 research papers (including 3 in the journal Nature), book chapters and popular articles, presented over 80 international conference communications, and has led research projects totalling over $4 Million in funding, from organisations like Australian Research Council, NASA, Spanish Research Council and National Geographic Society.
Members and visitors are invited to attend this FREE lecture, but, for catering purposes, please indicate your attendance by email to the address below. There will be a ruffle of plants propagated by the FBGA.
Enquiries: (08) 8222 9367, friendsabg@internode.on.net
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