When: Carboniferous (~315 to 300 million years ago)
Where: at least North America and Europe, possibly worldwide
What: Archimylacris is a 3 inch (~8cm) long ‘roachoid’. This over 300 million year old fossil insect and its kin have been commonly referred to as ‘ancient cockroaches’, but studies have revealed they are ancestral to all of the Dictyoptera (roaches, termites, and mantises). Fossils of Archimylacris are fairly common in the Carboniferous, but most of the specimens are fragmentary with isolated wings being the most numerous component recovered by far. Specimens such as the one shown above are found in nodules (a solid blob with mineral composition different from the surrounded rocks). These specimens revealed much more of the animal’s morphology, as the whole specimen is present, but what is available for study is greatly limited to the fracture plane that is broken open. A fairly recent study microCAT scanned the specimen, revealing the complete morphology in intricate detail, and generating a cgi model as a reconstruction. This study revealed that Archimylacris lived much like modern roaches do, in dense forests eating detritus and capable of fast scurrying, possibly rearing up on their hind legs as they ran. It is easy to see how Archimylacris and other fossils that we now identify as stem Dictyoptera were first thought to be ancestral to only roaches; the roach body plan is one that has been conserved for hundreds of millions of years. Modern roaches retain many primitive features, whereas termites and especially mantises have greatly transformed over millions of generations.
For a cool movie of the reconstruction, and a bit more details as to how it was accomplished, visit: http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_14-4-2010-15-39-48