The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Thursday, March 20, 2014

March 20. Ordovician trilobites

Ordovician trilobite
Are you familiar with pill bugs? Roll-up bugs? I haven’t seen one in decades – maybe they don’t live here in the arid west, or heaven forbid, maybe I’ve lost my curiosity at what might be under a rock. If that’s it I’ll have to remedy that. But I recall well as a child in Michigan finding these little gray multi-legged critters in the garden. If you touched them, they’d roll up into a tight little ball. Their soft underbellies were protected by their relatively hard carapaces.

Pill bugs are arthropods like insects, centipedes, and spiders, but they aren’t closely related to them. They are actually crustaceans, isopods, more closely related to shrimp and lobsters. And of course, trilobites were arthropods too, and they shared with pill bugs the ability to roll themselves up into a defensive posture.

Flexicalymene, enrolled
Trilobites may have actually peaked during the Cambrian Period, but they certainly participated in the Ordovician diversification, with lots of new species appearing. They seem to get a little fancier in their ornamentation and development of spines and they clearly became adept at enrolling. Trilobites could definitely roll themselves into tight defensive balls early in the Cambrian, but for some time it was thought that the earliest trilobites couldn’t do it. But in 2013, a team from the University of Cambridge described some olenellids – early trilobites – from about 510 or so million years ago that could and did enroll themselves. So this is not strictly an Ordovician trilobite thing. But some Ordovician trilobites, such as Felexicalymene from the Ordovician of Ohio, Kentucky, and Indiana, made themselves famous by doing it.
—Richard I. Gibson

Ordovician trilobite photo by Vassil, under GNU free documentation license. Flexicalymene photo by Steve Henderson, used by permission.

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