The Australian Capital Territory has native floral, bird and mammal emblems. During September and October 2020, the public voted on five candidates to make the ACT the fourth state/territory in Australia to have a fossil emblem. The fossil emblem embodies the concept of deep time and evolutionary transition, and the importance of understanding its natural history. The A.C.T. has a remarkable array of candidates for its emblem, each with its own story.
Meet Atrypa duntroonensis, a brachiopod from the A.C.T. Brachiopods are a group of marine invertebrates characterised by having two shells (valves) of different sizes. The word "brachiopod" is from the Ancient Greek brachion ("arm") and podos ("foot"). This refers to their built-in stalk (pedicle), used to anchor themselves to the ocean floor, preventing them from being tossed around by ocean currents. They first appeared in the Early Cambrian (approximately 545 million years ago).
Brachiopods are prolific throughout the fossil record, with about 30,000 extinct species and over 300 living species, making them one of the most diverse animal groups to have ever appeared. Their numbers dwindled in the most catastrophic extinction event in Earth’s history (approximately 250 million years ago) that wiped out 95% of all life on the planet. This is known as the Permo-Triassic (P/T) extinction event.
Reverend William B. Clarke
The Reverend William B. Clarke discovered the fossil site Woolshed Creek in 1844. He was an English geologist, headmaster of the King's School in Parramatta, a trustee of the Australian Museum and the vice-president of the Royal Society of New South Wales. He is often described as the "Father of Australian Geology". He recognised the fossils at Woolshed Creek as being Silurian in age and the oldest known rocks in Australia at the time. He published these findings in 1848. These rocks are now known to be 430 million years old.
Woolshed Creek, ACT
The Woolshed Creek rocks are composed of mudstone and are part of the Canberra Formation. These rocks were deposited in a tropical, shallow marine environment. Sediments dumped on sea floor communities by storm events resulted in multiple layers of densely packed fossils. In 2017 the Geological Society of Australia (A.C.T. Division) together with the A.C.T. Government, restored and upgraded the site ensuring its preservation for future generations.
Atrypa duntroonensis 3D model, courtesy ANU CT LabsGeoscience Australia
Monograptus exiguus belongs to an extinct group of animals called graptolites. They were tiny and lived in colonies that shared the same skeleton, as modern corals do today. Unlike corals, graptolites floated near the surface and did not attach themselves to a substrate. The little tooth-like structures (best seen in the next image) are the animal's living chambers and are attached to the branch. Graptolites used tiny hairs called cilia to filter food from the water. Did you know that "graptolite" means “writing on the rock”? When they were first discovered, it was thought they were "pictures" resembling fossils, rather than fossils themselves.
Graptolites first appeared in the Ordovician (approximately 480 million years ago) and went extinct in the Early Devonian (415 million years ago). These guys had a world wide distribution and evolved very rapidly. This makes them valuable for correlating the age of rocks across the world. Monograptus exiguus was first described in the Silurian rocks of England. It is not only important to palaeontologists and geologists, but Canberrans as well. This species was used to date the State Circle Shale as Silurian (It is the most common graptolite found in this rock formation). This marine rock unit underlies the Australian Parliament House on Capital Hill, therefore if Parliament house existed back then, it would have been under water!
State Circle Shale
The State Circle Shale is dated at 434 million years ago, making the graptolite slightly older than the other A.C.T. fossil emblem candidates. They drifted in the open ocean back then and were buried in deep-water sediments, in contrast to the other fossil candidates which lived on the seafloor in shallow water.
State Circle Shale - Angular Uncomformity
This magnificent exposure clearly shows the unconformable contact between the older State Circle Shale (bottom) and the multilayered Camp Hill Sandstone (top). The State Circle Shale comprises the wavy white band of siltstone running through the middle of the picture and the very fine reddish shale below it. These have been strongly contorted by folding, faulting and slumping. Excellent examples of slump rolls can be seen in the sandstone.
Gravicalymene coppinsensis is a trilobite found only in the Canberra region. Trilobites are an extinct group of arthropods (same group as spiders, scorpions, insects, crustaceans, and horseshoe crabs) that first appeared in seas of the Cambrian period (540 million years ago), and went extinct at the end of the Permian (250 million years ago). Since trilobite fossils are found all over the world, limited to a particular geological time frame, easily recognisable, and preserve very well, they are extremely useful for relatively dating the rock.
Originating from Coppins Crossing and named accordingly, Gravicalymene coppinsensis is most commonly found as fragments although there are a few near-complete specimens. At ~6cm long, this species is slightly larger and more robust than Batocara, however both trilobites would have had a similar lifestyle, sifting through the sea floor looking for food. The "calymene" part of the name means “beautiful crescent”, referring to the shape of its head. Parts of the site have been covered over by the Lower Molonglo wastewater treatment infrastructure and are no longer accessible. This species of trilobite has recently undergone taxonomic revision by scientists. When it was first described in 1980, it was named Apocalymene coppinsensis, then later that year was allocated to the genus, Sthenocalymene. It remained there until 2020, when palaeontologists assigned it to Gravicalymene.
Gravicalymene coppinsensis 3D model, courtesy of ANU Ct labsGeoscience Australia
Retziella capricornae is a brachiopod from the A.C.T., N.S.W and QLD. Brachiopods are a group of marine invertebrates characterised by having two shells (valves) of different sizes. The word "brachiopod" is from the Ancient Greek brachion ("arm") and podos ("foot"). This refers to their built-in stalk (pedicle), used to anchor themselves to the ocean floor, preventing them from being tossed around by ocean currents. They first appeared in the Early Cambrian (approximately 545 million years ago).
Retziella capricornae is a small and beautiful brachiopod species. First discovered near Rockhampton, Queensland, and later in N.S.W. and the A.C.T., it allows comparison with other Silurian aged rocks in Eastern Australia. The genus Retziella has also been found in South China and Kazakhstan indicating that these three landmasses were once close together. Canberra's Retziella capricornae is form the Yarralumla Formation, which makes it the youngest of the A.C.T. fossil candidates. Though smaller than Atrypa duntroonensis, Retziella possess strong radial ribs which gave its shell much greater strength and resistance to damage from waves generated by storms.
The Deakin Anticline (upward folding of rocks) is a distinct geological feature of interest that is part of the Yarralumla Formation in the Canberra region. Just like these fossil candidates, the rock formations are also Silurian in age.Retziella capricornae was found in the nearby Yarralumla brick-pits which is now inaccessible. The Deakin Anticline does not contain fossils.
Retziella capricornae 3D model, courtesy of ANU Ct labsGeoscience Australia
Batocara mitchelli belongs to one of the most popular fossil groups to have appeared in the fossil record, trilobites! They are an extinct group of arthropods (same group as spiders, scorpions, insects, crustaceans, and horseshoe crabs) that first appeared in seas of the Cambrian period (540 million years ago), and went extinct at the end of the Permian (250 million years ago). Trilobites were one of the earliest-known groups of arthropods.
The name trilobite comes from their three lobed exoskeleton, two lateral lobes and one central lobe. Trilobites occupied a wide array of different environments from tropical shallows and reef systems, to deeper ocean floors. It is believed that the huge diversity of body shapes seen in trilobites is related to their specific habitats and lifestyles. Palaeontologists can use this information to infer the ecology of these long extinct arthropods.
Batocara mitchelli is the most common trilobite in the A.C.T., but it is nearly always found as fragments. The species name honors school teacher John Mitchell who discovered it near Yass in the 1880s. An interesting feature about this trilobite is that the head (cephalon) and tail (pygidium) are covered by small round knobs. These are distinctive for the species but their function is unknown.
Batocara mitchelli 3D model, courtesy of ANU Ct labsGeoscience Australia
Results of the A.C.T Fossil Emblem election
On the 21st October 2020, an event was held at Geoscience Australia, Canberra where the winner was announced live on our Facebook page. Minister Mick Gentleman and our Chief Scientist, Dr. Steve Hill, proudly announced the winner of the election. With 30% of the 1135 votes, the community selected...
Want to learn more about fossils in the A.C.T?
The National Mineral and Fossil Collection, Geoscience Australia, Canberra.
Errol Fries (Fossil photographs) and Steven Petkovski (Field photographs).
Artists: Molly Kamenz (Batocara and Atrypa) Sebastian Wong (Gravicalymene, Monograptus and Retziella).
Geological Society of Australia (ACT branch), Geoscience Australia, Australian Marine Sciences Association, Australian National University, and the A.C.T. Government.
Computed Tomography (CT) Scans and models generated at CTLab - National Laboratory for X-Ray Micro Computed Tomography, Research School of Physics, The Australian National University (ANU), Canberra.
Exhibit created by Joshua White and the Collections team at Geoscience Australia.