A Treasury of Trilobites
Trilobita is one of the most recognizable and successful groups of animals of all time. UAlberta has over 15,000 trilobite fossils, most of which are in the UAlberta Museums Invertebrate Paleontology Collection. Nearly all of the fossils were collected by UAlberta researchers and students. Over 150 species of trilobites have been named by the research group led by Professor Emeritus Dr. Brian Chatterton, who worked in the Department of Earth and Atmospheric Sciences from 1970 – 2010. The UAlberta Museums Invertebrate Paleontology Collection has the finest collection of Devonian trilobites from Morocco in the world.
By exploring the UAlberta Paleontology Museum virtual tour and this website, you can experience our trilobite displays from wherever you are.
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Trilobita is an extinct group of three-lobed arthropods that lived in ancient oceans. Arthropoda is the group of animals with jointed and segmented exoskeletons made of the organic material chitin. Insects, shrimps, crabs, spiders, and millipedes are examples of arthropods.
The trilobite exoskeleton was built of the mineral calcite underlain by chitin. Trilobites were the first group of animals to have compound eyes, the same kind of eyes that crustaceans and insects have. Most trilobite body parts were underneath the back part of the exoskeleton, just like those of a horseshoe crab.
Image credit: https://uwm.edu/field-station/horseshoe-crab/
Trilobites had multiple lifestyles and feeding habits. Some adults lived on the sea floor whereas others had adaptations to swim in the water column. Trilobites would either hunt and eat worms or other invertebrates, scavenge and eat bits of edible material on the ocean floor, or filter food from the water. Paleontologists interpret what trilobites ate by looking at parts of the exoskeleton that could be used for feeding.
Trilobites procreated via sexual reproduction. They developed and grew through metamorphosis and moulting, much like lobsters and grasshoppers.
It is thought that trilobites had at least four different lifecycles. One involved all stages, from eggs to adult, living on the sea floor. In another lifecycle, eggs were spawned into the water column, early larval stages swam, and later larvae and adults lived on the ocean floor. Fossil evidence also suggests that eggs were sometimes brooded externally underneath the cephalon, like in horseshoe crabs.
The youngest adult form of a trilobite was small enough to fit on the end of a piece of spaghetti. As the soft body parts of the adult grew, the exoskeleton would become too small. It would crack along suture lines between parts of the cephalon so that the soft bodied animal could escape. The old exoskeleton was shed, and a new one formed. Most trilobite fossils are incomplete moulted exoskeletons.
Explore trilobite lifecycles (ontogeny)
Over 21,000 species of trilobite have been described. It is impossible to estimate the number of individuals of any species that has lived because the fossil record preserves only a tiny number. Plus, only a fraction of the rock record is accessible to paleontologists for study.
At times, trilobites lived in oceans around all ancient continents. By 485 million years ago, trilobites reached their peak number of species and were most abundant. Long lived, diverse, everywhere. There is no doubt that trilobites were one of the most successful groups of animals of all time.
Note: Genera is the first word of a species name. For example, "Homo" is the genus for the name "Homo sapiens," our species.
Trilobites lived in the oceans from 521 million years ago to 250 million years ago. Trilobites existed more than 100 million years longer than the dinosaurs which lived from about 245 million years ago to 66 million years ago. Humans have been around for the last 2.5 million years, a mere geologic wink.
The diversity and geographic range of Trilobita was impacted by five mass extinction events. The most significant occurring 375 million years ago. After which, only one type of trilobites remained. Trilobites went extinct by 250 million years ago during the biggest die off in Earth’s history when 96% of the species on the planet were lost. It is no wonder this event is called "The Great Dying."
Mass extinctions are caused by dramatic and persistent changes to the environment. The following Earth processes may contribute to extinctions: volcanism, shifts in tectonic plate positions, altered ocean circulation, atmospheric and climate changes, meteorite impacts, and new predators or competitors.
Fanciful Forms
The images below illustrate the breadth of trilobite form. The head end of the trilobite is to the left. The size and shape of the parts of the exoskeleton vary greatly. Some lack ornamentation, whereas others are decorated with spines, or bumps. The Huntoniatonia fossil shows spots of white which may be the actual colour pattern of the exoskeleton.
Acanthopyge (Lobopyge), 395 million years old, Morocco, 2.2 cm