Urokodia aequalis, an Unusual Arthropod Fossil from Chengjiang

Description: This unusual arthropod is known as Urokodia aequalis. The species was described from only a few (~15) examples. With the discovery of the Chengjiang Biota in 1984 a window on the Cambrian Explosion in China was opened. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

The taxon bears some resemblance to the younger Burgess Shale genus Mollisonia, which has been found in the younger Kaili Biota of China as well. The species derives its name from the equivalent size and approximate appearance of both the posterior and anterior shields. It is thought to have been a bottom-dwelling animal, most likely a scavenger, but little is actually known since the only soft tissue preservation found to date is a stout antenna.