Retziella capricornae is one of five candidates for the ACT state fossil emblem. The ACT will be the fourth state to have chosen a state fossil emblem. All candidates embodies the concept of deep time and evolutionary transition as being important to understanding the natural history of the particular state.
Retziella capricornae a member of the group, Brachiopoda discovered in the ACT. Brachiopods are a group of marine invertebrates that are characterized by two shells (valves) of different sizes. The word "brachiopod" is from the Ancient Greek brachion ("arm") and podos ("foot"). They first appeared as a group in the Early Cambrian (approximately 545 million years ago). These guys are absolutely prolific throughout the fossil record, with approximately 30,000 different extinct species and over 300 modern species, making them one of the oldest groups of animals to have ever appeared. Their numbers have dwindled since because of the most catastrophic extinction event (Permo-Triassic extinction event) that wiped about approximately 95% of all life on the planet, approximately 250 million years ago.
Retziella capricornae is a wonderful and small brachiopod specimen. This fossil is found in QLD, NSW and in the ACT, allowing comparison with other Silurian sites in Eastern Australia. First discovered near Rockhampton, Queensland, Retizella is found in Canberra’s Yarralumla Formation which is slightly younger than the Canberra Formation, at about 428 million years ago. Despite been smaller than its other brachiopod candidate, Atrypa duntroonensis, Retziella possess strong radial ribs which in turn gives its shell much greater strength and resistance to damage and environmental forces such as waves generated by storms. During the Silurian period, South China and Australia were pretty close together, this means that Retziella capricornae has close cousins that are be found in China. Comparing closely related species helps scientists understand how species have changed over time in response to the dynamic nature of their environment.