What makes Trilobites so important?
Trilobites are among some of the earliest Arthropods that roamed earth hundreds of million years ago (Gon, 2013). They are part of an extinct class of Arthropods, which is made up of 10 orders, over 150 families, 5000 genera, and over 20 000 species (Gon, 2013). Earliest fossils were found to date back all the way into the Pre-Cambrian time period up until the end of the Permian where they were totally wiped out and became extinct (Benton and Harper, 2009). Trilobites are some of the most diverse extinct organisms and some of the most studied fossils today. Due to Trilobites being so diverse, they
Figure describing rate of speciation through the ages (Gon, 2013).
are found within all continents and individual species found within specific layers of the earth or stratigraphic ranges. This allows paleontologists to paint a picture about how the Earth looked like hundreds of millions years ago in the Paleozoic era. Trilobites are often used as index fossils. Index fossils otherwise known as zone or indicator fossils are used to define and study geological periods (Benton and Harper, 2009). Based off the Law of Superposition, rocks layers lie over one another in the order of their age. The oldest rock layers are deposited at the bottom of the earth while younger rock layers are closer to the top of the earth (Benton and Harper, 2009). Trilobite fossils are used as marker fossils or biostratigraphic indicators to date the stratigraphic layer paleontologists, and geostratigraphers are looking at (Benton and Harper, 2009). They are used to date rock layers from the Cambrian all the way to the end of the Permian (Benton and Harper, 2009). Using relative patterns of stratigraphy from the study of Trilobites, scientists, refine the geological time sale combining paleontology, geology, and radioisotope chronology to set benchmarks in time across the globe (Gon, 2013).
Trilobites also provided important evidence supporting the theory of continental drift. They were found in the Atlantic and Pacific Trilobite faunas in North America and Europe. Trilobite faunas of the continental shelfs of modern North America and Europe are different in the Ordovician period but later on in the Silurian time period, it showed a mixing of species from both sides, most likely due to the continents moving together and backing the theory of continental drift (Windley, 1996).
Figure describing the mixing of Trilobite fossils between North America and Europe (Windley, 1996).
A fun fact about the fossils of Trilobites is that most of the fossils that are found of Trilobites are made from the exoskeleton. The exoskeleton is made up of chitin and hardened with calcium carbonate which makes it very suitable to be fossilized because the exoskeleton is easily mineralized which inorganic materials is replaced with minerals such as aragonite calcite (Benton and Harper, 2009). This means that the soft parts of the Trilobite are not often found except in Lagerstätten. Lagerstätten are places where a large amount of exceptionally persevered fossils are found which allow preservation of soft parts of organisms. Lagerstätten have exceptional sedimentation needed to rapidly bury the organism and has the right amount of oxygen, temperature and pH to limit decay and produce exceptional fossils (Benton and Harper, 2009). Some examples of Lagerstätten is the Shoreline Faunas in Manitoba, producing fossils from Ordovician, and the Burgess Shale in British Columbia, producing fossils from Cambrian time periods (Benton and Harper, 2009).
Picture of the Burgess Shale in British Columbia, Canada; an example of a Lagerstätten. These Lagerstätten are places with exceptional fossil quality (Niddrie, 2011).