Happy Friday! I’ve returned to my home base, the Michigan State University Museum. Today we’re taking a prehistoric trip back in time via the Hall of Evolution. Our first stop is the Paleozoic Era (542 to 251 million years ago) a span of time so vast it is divided into six lengthy periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.
The Paleozoic Era took place long before the great dinosaurs. Animal and plant life flourished and the mighty trilobite ruled the sea. These ancient, disk-shaped creatures were named for their three-lobed bodies: the cephalon or head, thorax, and pygidium (think: tail). Trilobites scavenged for food along the ocean floor, and like a porcupine or 3-banded armadillo, curled into a ball when predators swam near.
Like their modern day arthropod ancestors (lobsters, crabs, crayfish), trilobites had a hard exoskeleton that was periodically shed. In fact, many trilobite fossils are cast off exoskeletons. Trilobite fossils have been found on every continent, and there are approximately 20,000 different types, ranging in size from almost three feet to less than an inch long.
Unfortunately, the trilobite was a victim of the Great Dying or 5th mass extinction. This catastrophic loss of life at the end of the Paleozoic Era killed off 96% of the species living at that time. Marine animals were particularly hard hit. There are many theories, but no clear evidence of what caused the Great Dying (drop in oxygen levels, an asteroid, fluctuations in sea level, or some combination). What is clear, is that the intrepid trilobite survived almost 300 million years and today you can view their fossilized remains in museums worldwide.
Next week we’ll continue our trip through the Hall of Evolution by taking a closer look at the Mesozoic Era or Age of the Dinosaurs.
Fun Fossil Fact: Trilobites have been selected as the state fossil (yes, that’s a thing) in Wisconsin (yay Cheeseheads!), Ohio and Pennsylvania. If you’d like to geek out on all things arthropod, check out Understanding Evolution by the University of California Museum of Paleontology.
Palaeontologyonline.com, (2013) Mark Bell, Fossil Focus: Trilobites, Vol. 3, Article 5, 1-9.
National Geographic News (2009) Christine Dell’Amore
The Atlantic, The Weird Stories Behind America’s Official State Fossils by E. Yong (Mar 2016)