A Lagerstätte (plural Lagerstätten) is exactly that: a deposit of exceptionally preserved fossils, often with soft tissue impressions. Soft tissues such as skin, organs, and muscles often do not preserve in the fossil record. This is due to their low preservation potential - meaning, these parts decay quickly whereas the harder material such as teeth, bones, and shells has a greater probability of preserving in the fossil record.
The Big Hill Lagerstätte was discovered in the forested Stonington Peninsula of the Upper Peninsula of Michigan. If we could travel back to the Ordovician Period (~430 million years ago), Michigan was a tropical shallow sea with thriving aquatic life. Protected by the Canadian Shield (a high plateau at this time), this area was likely not very affected by waves and the environment was probably similar to a lagoon. This snapshot into the Ordovician of Michigan shows scientists what was going on in a very specific and protected area of the world ~430 million years ago.
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.
Although this blog focused mostly on arthropod finds, there were over 40 species found in the Big Hill fauna, including brachiopods, ostracods, gastropods, nautiloids, bryozoans, algae, jellyfish, and other organisms.
Check out this YouTube video made by Ron Meyer and others documenting the site and interviewing experts (including Dr. James Lamsdell mentioned above) on the fossil material: https://www.youtube.com/watch?v=xakfqiwX1Fc&feature=youtu.be
Interested in reading more? Here are publications on the Big Hill fauna, one is freely accessible online and the other requires a subscription, but if you are interested in reading the article contact the corresponding author and they will send you the publication.
● Lamsdell, J.C., Gunderson, G.O., and Meyer, R.C. 2019. A common arthropod from the Late Ordovician Big Hill Lagerstätte (Michigan) reveals an unexpected ecological diversity within Chasmataspidida, vol. 19, no. 8. Open Access.
● Lamsdell, J.C., LoDuca, S.T., Gunderson, G.O., Meyer, R.C., and Briggs, D.E.G. 2017. A new Lagerstätte from the Late Ordovician Big Hill Formation, Upper Peninsula, Michigan. Journal of the Geological Society, vol. 174, p. 18-22. Not Open Access.