A Who's Who of Devonian Invertebrates
In addition to helping unlock the mysteries of evolution, past climate, paleobiology, and a multitude of other uses, fossil invertebrates are an invaluable tool for dating rocks. Many groups of organisms have well established age ranges for when certain species existed. When coupled with radiometric dating techniques, stratigraphers can use these groups as tools to finely divide the geologic time scale into "relative ages". One of the most useful groups of fossils are the brachiopods. These shelled organisms were abundant in the well-lit shallow seas of the Devonian of North America. In fact, it was during the Devonian that this phylum reached its peak of diversity.
This peak in speciation is likely related to the preferred habitat of many brachiopods. The Devonian epeiric seas would have been produced abundant primary producers, those organisms at the bottom of the food chain. Brachiopods feed with a soft structure termed a lophophore. The lophophore is a sort-of siphon through which water is pumped. The interior is lined with cilia which act to filter out organic matter from the water. These likely included microscopic organisms as well as detritus suspended in the water column. It may seem like a slim meal to a human, but to a brachiopod the Devonian seas were one giant feast!