RARE Polychaete Worm Fossil from Cambrian Utah
From a Burgess Shale-like Laggerstatt

Description: The Polychaeta (Bristleworms) can trace their ancestry back to the Cambrian Explosion. The segmented bodies of the Polychaeta have paired lobes called parapodia which have a function in locomotion or respiration. The parapodia bear numerous bristles which are the source of the name of the class (Polychaeta means many bristles). Modern members of the family prey upon sponges; perhaps this one did as well . This one is a species of Burgessochaeta, a taxon known from the Burgess Shale of Canada. It is not related to any extant bristleworms, and as such has been assigned its own family: Burgessochaetidae. Intact specimens are known to possess at least 24 trunk segments, and range in size from 20 mm – 50 mm insize, so this example would have been the Goliath of all. It is the FIRST and ONLY example I have ever seen from the Weeks Formation.

The House Range of Utah has several formations that exhibit Burgess Shale-like preservation of soft tissues, and yield fossils of creatures closely allied with the Burgess Shale biota. Interestingly, the formations are normally found in alternating biofacies. Some are rich in trilobites lacking soft bodied organisms, while adjacent ones lack trilobites but preserve soft bodied organisms in the form of kerogenized carbon films. Gaines (2004) has studied the taphonomy of House Range soft tissue preservation, hypothesizing a taphonomic pathway much like the Burgess Shale with delayed decay facilitating rapid diagenesis in an anoxic zone lacking benthic bioturbators. While soft bodied organisms are far rarer and generally not so exquisitely preserved as in the Burgess Shale, some scientists believe the House Range biota might be even more diverse. Many fossils found are enigmatic as to their taxonomic placement. Unfortunately, the numerous sites are much understudied, while mining operations are resulting in wholesale destruction of a potentially rich portion of the Cambrian fossil record.

References:

• Briggs D.E.G., and R.A. Robison. 1984. Exceptionally preserved non trilobite arthropods and Anomalocaris from the Middle Cambrian of Utah. University of Kansas Paleontological Contributions, Paper 111:1-24.
• Gaines, Robert R.; Kennedy, Martin J. Droser, Mary L. 2004. A new hypothesis for organic preservation of Burgess Shale taxa in the middle Cambrian Wheeler Formation, House Range, Utah. Palaeo, 220:193-205.
• House Range Fossils: Wheeler Shale, Marjum Formation, and Weeks Formation, The Virtual Fossil Museum (www.fossilmuseum.net).