Monsters Storm The Field

Invertebrate paleontologists aren’t afraid of anything, so when Collections Manager Paul Mayer was offered a chance to add hundreds of monsters to The Field’s collections, he jumped at the opportunity. The monsters in question, Tully monsters, are just a small part of the enormous donation of Thomas V. Testa’s collection of Mazon Creek fossils that The Field Museum just received from Field Associate Jack Wittry.  

Mazon Creek, an area about 50 miles southwest of Chicago, is one of the richest fossil sites in the world. It was once the swampy coastline of a warm sea that covered much of North America—the landscape was a little like Louisiana today. When animals died there, they sunk into the mud and were rapidly buried before they got a chance to rot, forming fossils inside hard nodules of rock. The fossils in this area were first discovered in the 1800s, but it wasn’t until the area was strip-mined for coal in the 20th century that large numbers of fossils were collected.

Mazon Creek fossils are some of the best in the world—they’re plentiful, they’re extremely well-preserved, and they represent lots of animals that don’t normally fossilize very well, including soft-bodied animals like worms.

The Field Museum has been collecting Mazon Creek fossils for nearly 100 years, and we have one of the world’s strongest collections. Wittry’s donation of 7,000 Mazon Creek fossils brings our total to over 50,000.

 “This is probably the largest private Mazon Creek collection, and certainly the best,” said Mayer. “We need collections large enough to study the diversity of the living things at Mazon Creek and the variation that occurs within individual species and the whole ecosystem.” But Testa’s collection, which he carefully amassed over decades, doesn’t just contain a large number of fossils—they’re also very high quality, because Testa was picky about which fossils he actually added to his collections.

The Testa fossils range from shrimp to fish to amphibians to worms. “Plus, there’s a lot of diversity among all these species represented. For example, with different kinds of worms, a roundworm is as different from a spoon worm as a jellyfish is from a wolf,” said Mayer.

So what’d we get?

So many. Of everything. The donation includes some 7,000 Mazon Creek fossils, and right now they’re sitting in cardboard beer flats, taking up seven huge metal lockers in our collections. But here are some cool ones:

Tully monster

Tully monsters are a mystery—nobody knows exactly what kind of animal they are. “Maybe they’re worms, or leaches, or a mollusk like a snail with no shell. Maybe they’re a kind of cephalopod, like a cuttlefish or octopus with only one tentacle,” mused Mayer. “People are still investigating what they are—that’s part of what makes Mazon Creek so neat.” As best as we can tell, they’re soft-bodied invertebrates, maybe around a foot long, with stalk eyes and a long snout with a toothy mouth at the end. Maybe the 416 new Tully monsters will help scientists figure out what the heck they are.

Horseshoe crab

Horseshoe crabs aren’t really crabs. (Nor are they horseshoes. Naming fail.) Instead, they’re in a group of arthropods that are more closely related to spiders and scorpions. And they’ve been living in the world’s oceans for hundreds of millions of years—this specimen is from 307 million years ago, but they’re still around today.

Shark egg case

The Mazon Creek area was a shark nursery, and if that’s not metal, we don’t know what is. Sharks that lived in freshwater rivers would swim into the saltier shoreline to lay their eggs in these pinecone-looking egg cases, kind of the opposite of how ocean salmon today swim up rivers to breed and lay their eggs.

It’ll take a while for our scientists to start using all these fossils in their research—they have to go through and catalogue all of them first. “Otherwise, we’d have 7,000 fossils in a zillion boxes—how would you ever find what you wanted?” said Mayer. But in the meantime, you can see some of our Mazon Creek fossils (and even walk through a recreated coal swamp from 300 million years ago) in our Evolving Planet exhibition.

Image credits:

© The Field Museum, GEO85141c, Photographer Ron Testa and Sophia Anastasiou Wasik. © Nicole Karpus. © Thomas V. Testa. © The Field Museum, GN90846d_H25_CBPM5, Photographer Eric Manabat.