The University of Michigan has an interesting post about a new Lagerstatte, which was discovered in the Upper Peninsula of Michigan back in 2013. This fossil deposit dates to the Silurian Period about 430 million years ago. Over 40 species of animals have been discovered at the locality, including soft bodied animals like Jellyfish. Jellyfish are exceedingly rare in the fossil record. Another animal found there is a strange arthropod called chasmataspids, which are related to sea scorpions. The Youtube video provides a good explanation of the site.
The fossil collection adventures began in the fall of 2013 and the team started finding many fossils that they thought were eurypterids - sea scorpions - but they turned out to be an even stranger group of arthropods called the chasmataspids.The Big Hill fauna completely changed our understanding of the chasmataspids, documenting large variation in size and species and the first complete specimens. Previously, there had only been fragmented fossils found. However, the Big Hill fauna added 50 complete specimens! So, what were all of these chasmataspids doing in Michigan ~430 million years ago? Well, just like other arthropods, chasmataspids molted or shed their exoskeleton as they grew. This is a very difficult process, as it leaves the animal very vulnerable. Dr. James Lamsdell of West Virginia University thinks that these animals were coming to the shallow seas of Michigan to molt in a more protected lagoonal environment.
Why are these strange arthropods so important? These creatures are related to spiders, mites, and horseshoe crabs - things we know and can find on Earth today. The evolutionary histories of these groups are less well understood. When did they make the transition out of the sea? Where and when did the groups we see today originate in the arthropod tree of life? The Big Hill fauna helps paleontologists better understand many of these questions.
Jellyfish were the other really important find at this location - the number of fossil sites containing jellyfish are low. Jellyfish contain no hard parts, so their ability to fossilize is very slim. Over 100 fossil jellyfish have been found in the Big Hill fauna, which is an unprecedented number for a fossil deposit.
