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

Description: This fine example is a member of the genus Leanchoilia. Several were figured in the article by Briggs and Robison as being similar to Leanchoilia superlata from the Burgess Shale. Like those examples, the great appendages are not preserved, but all the other diagnostic features are present. Briggs and Robison believed it to be a new species, which to my knowledge has yet to be described. Whatever the precise taxonomic status, this is a most unusual and highly desirable specimen, and the FIRST I have seen with such detail.

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).