STL Science Center

STL Science Center

01 July 2014


A lot of the discussion this week has concerned dinosaurs and mammals and expeditions led by Dr. Kielan-Jaworowska. Almost the first 20 years of her career focused on invertebrates though, and they have not been mentioned at all. In fact, in the history of this blog, invertebrates have been sparse at best. The main invertebrate group that Kielan-Jaworowska studied, and that I want to present today is the trilobites. Studying trilobites was no simple task, despite their supposedly simple anatomy and the similarities of their bodies. Trilobite fossils date from approximately 540 million years ago up to the end of the Permian around 250 million years ago. Trilobites are a class separated into 10 orders and many families. Global distribution of trilobites attests to their success as a group of organisms and in part, the simplicity of their body plan allowed for that success; their body plan certainly aided in the fossilization of dead trilobites. Some members did get fairly ostentatious with their appendages whereas others retained rather simplistic appearing body plans. Regardless, all trilobites have the latitudinal cephalon, thorax, and pygidium (head, chest, tail) body  sections with three longitudinal (axial and right and left pleural) lobes that are the origin of the class' name: trilobites are literally a trilobate class of animal. Trilobites can be extremely diverse within these basic guidelines. The thorax, for example, can consist of anywhere from 2 to 103 articulated exoskeleton fragments. That means, with two legs per segment, trilobites could have had anywhere from 4 to 206 legs! Segmented exoskeletons apparently allowed trilobites to roll themselves into balls, like extant pillbugs, as some fossils have been discovered rolled up. That brings me to the fun part of today. Dr. Kielan-Jaworowska studied this animals seriously for many years and probably has seen, held, and perhaps even owned reproductions of many trilobites. Thanks to the Earth Science Club of Northern Illinois, you can make your own today:

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