Chancelloria eros scleritome (7.1 cm tall) from the Middle Cambrian of western Utah, USA.

Cambrian rocks frequently produce some of the oddest-looking organisms anywhere in the fossil record. One distinctive group of fossil organisms long known from Cambrian rocks is the chancelloriids. Chancelloriids have bag-shaped bodies covered with multirayed sclerites. They are often perceived as representing fossil sponges (Porifera), but ultrastructural studies on chancelloriid skeletal components show that they are a separate group.

This is a commercially prepared, complete scleritome of Chancelloria eros Walcott, 1920 (Animalia, Coeloscleritophora, Chancelloriidae) in hard, gray, slightly calcareous mudshale. It comes from the “deep Wheeler Lagerstätte” (sensu Robison, 1991 in The Early Evolution of Metazoa and the Significance of Problematic Taxa), one of several famous soft-bodied fossil deposits in Utah. Most chancelloriid fossils are isolated sclerites, typically collected from acid residues of Cambrian limestones.

Stratigraphy: Wheeler Formation, upper Ptychagnostus atavus Interval-zone (= lower Bolaspidella Assemblage-zone), upper Middle Cambrian.