This is a nice mass mortality of extinct carpoids.
Castericystis vali? (UBAGHS and R. A. ROBISON 1985)
Middle Cambrian
Wheeler Shale, Millard County, Utah
USA
 
These  strange fossil creatures had spiny tails, flat long heads and were covered with hard calcitic plates. They are closer to modern echinoderms such as starfish, crinoids , seaurchin and so on. Carpoids are distinct from all other fossils echinoderms because of their complete asymmetry. They are super well prepared and detailed.
 
GEORGES UBAGHS and R. A. ROBISON 1985. A New Homoiostelean and a new eocrinoid from  the middle cambrian of Utah.The University of Kansas Paleontological contribution. Paper 115