This week’s image is of a trilobite (acadoparodoxides mureroensis), found in Morocco but on display at the Houston Museum of Natural Science:
The trilobites (“three lobed”) were a class of arthropods that roamed the oceans hundreds of millions of years ago. The taxonomy of trilobites is uncertain, but divided into nine orders (or maybe ten, depending on the source you’re looking at) — at least for the time being. All of these orders (with one possible exception) appeared during the Cambrian period around 520-540 million years ago, and the last of them died out during the mass extinction at the end of the Permian about 250 million years ago.
During their 300 million years on earth, the trilobites busily diversified into some 17,000 distinct species filling a variety of roles in marine ecosystems. Since they were so successful in their day, and wound up populating essentially all marine environments of their time, trilobites have left fossils across the globe — and in the process played a role in a number of biological and geological discoveries. Trilobite fossil data has been used as evidence in discussions of punctuated equilibrium as a mechanism of evolution, as supporting evidence for the theory of continental drift, and for understanding the Cambrian Explosion. They are also the state fossils of Ohio , Wisconsin, and Pennsylvania in the U.S.