Trilobites
Ancient arthropods that dominated Palaeozoic seas for over 270 million years — the most iconic invertebrate fossils in the world.
Overview
Trilobites were marine arthropods with a segmented, mineralised exoskeleton divided lengthwise into three lobes — hence the name. For 270 million years they crawled, swam, burrowed and rolled through Palaeozoic seas, and their robust calcite skeletons and huge species count make them the most iconic invertebrate fossils in the world.
Quick Facts
Key Characteristics
- •Exoskeleton of three longitudinal lobes and three tagmata: cephalon, thorax, pygidium
- •Calcite compound eyes — holochroal, or the lens-per-lens schizochroal eyes of phacopids
- •Grew by molting, so each animal left many potential fossils
- •Many could enroll into a defensive ball; some grew spines and eye stalks
- •Facial sutures used to classify major groups
Fossil Record
Molted exoskeletons fossilise readily in shales and limestones, making trilobites one of the most abundant Palaeozoic fossils. Complete, outstretched specimens are the collector prizes; some rare faunas (Beecher's Trilobite Bed, New York) preserve legs, antennae and gills in pyrite. Famous units include the Wheeler Shale (Utah), Burgess Shale, St Petersburg limestones (Russia), and Devonian strata of Morocco and Oklahoma.
Global Distribution
Every continent — marine Palaeozoic rocks worldwide yield trilobites, with celebrated faunas in North America, Morocco, the Czech Republic, Russia, China, the UK and Australia.
Evolutionary & Scientific Importance
Trilobites define biozones across the Cambrian through Permian, track the Cambrian explosion and the Permian extinction, and their eyes are the earliest well-documented visual systems. Their rapid evolution, global spread and excellent preservation make them ideal tools for studying paleobiogeography, predation and development.