Monograptus exiguus belongs to an extinct group of animals called Graptolites. These particular groups of extinct animals are 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 attached themselves to a substrate. Graptolites means “writing on the rocks” and when graptolites were first discovered, it was thought that these were ‘pictures’ resembling fossils, rather than been fossils themselves. The little spikes are actually the living chambers and these chambers are attached to the branch. Additionally, graptolites would have used their tiny hairs called cilia and to filter food through the water.
Graptolites first appeared in the Ordovician (approximately 480 million years ago) and went extinct in the Early Devonian (415 million years ago). These guys are found all over the world and have an incredibly rapid evolution, this makes them valuable for correlating the age of similar rock formations 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 is because this particular species of graptolite is used to date the State Circle Shale that surrounds Parliament house on Capital Hill. Additionally, it is the most common of the graptolites found in this particular rock formation, making it easy to identify. It is dated at 434 million years ago, this places the rocks that support Parliament house at a geological time period called the Early Silurian.