ordovician period

In this week’s Trilobite Tuesday, we present a brief history of the ebb and flow of trilobite evolution. These amazing arthropods existed for nearly 300 million years of earth history, during which time they produced over 25,000 different scientifically recognized species. But the fact is that after presenting a dizzying array of species during the Cambrian, Ordovician and Silurian periods, by thetime the trilobite line reached the Devonian some 400 million years ago, their species count had dwindled down to a precious few. And by the time the Mississippian began, their was ostensibly only one order of trilobites left—the Proetids. Here is an attractive example of a “double” Ameropiltonia lauradanae from the Mississippian-age shale of Missouri. These proetids were among the last survivors of the noble trilobite lineage.

Learn much more on the Museum’s trilobite website

It’s time for an alien-looking Trilobite Tuesday! 

By the Ordovician time period, approximately 460 million years ago, trilobite eyes had developed into an almost dizzying array of sizes and shapes. Some, like those attached to species such as Asaphus kowalewski (pictured) and Cybele panderi, sat atop spindly “stalks” up to three inches long. This feature presumably allowed the trilobite a better view of the world around it, even when it may have been lurking under a thick layer of silt or mud along the sea bottom. Other trilobites of the time period, such as the aptly named Cyclopyge bohemica, developed huge wrap-around holochroal eyes featuring over a thousand small, tightly packed lenses that allowed a virtually uninterrupted view of the ocean surrounding it.

Meet many more trilobites on the Museum’s website.