This is Mazon Monday post #271. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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We have a bonus Mazon Monday this week—though since this second post falls on a Tuesday, we’ll call it Mazon Tuesday. On Monday, May 26th, the Chicago Tribune published an article highlighting Mazon Creek, the Field Museum, and ESCONI—a combination we’re proud to see featured. The article is titled "The world’s best-preserved fossils are right outside Chicago. But there are no dinosaur bones at Mazon Creek." Earlier in May, on a beautiful spring day, Dr. Arjan Mann brought members of his lab and the Field Museum’s PR team to the Braceville spoil pile to meet with several ESCONI members. The visit focused on discussing Mazon Creek science and exploring how professional paleontologists can collaborate with amateur collectors to help revitalize research in this important fossil locality. Oh... and to collect a few concretions!
Sixty-five miles southwest of Chicago, a small hill that looks like a prop from an Indiana Jones movie breaks up the flat, monotone landscape. Consisting of shale, sandstone and rocks from an old coal mine, the waste pile — located on a massive river delta from another era — is an unremarkable remnant from the region’s once-thriving coal industry.
Except it contains many of the world’s best-preserved, most diverse fossils.
The defunct mine’s location in Grundy County is one of several sites spanning six counties that belong to the Mazon Creek fossil beds, a time capsule dating back some 309 million years — way before the age of dinosaurs — to the Carboniferous period, when large coal deposits formed around the world and terrestrial ecosystems developed. At the time, this area was swampy and tropical, and home to various organisms like the Illinois state fossil, the peculiar Tully monster, which has been found only here — a cigar-shaped vertebrate creature up to a foot long with eyes that protruded sideways, a long snout and a toothy mouth.
“You get everything from insects, millipedes, plants, jellyfish, all the way to early tetrapods, big animals like embolomeri, as well as larval forms,” said Arjan Mann, who recently joined the museum as an assistant curator of fossil fishes and early tetrapods, or four-limbed animals, such as the crocodile-like and predatory embolomeri. “This makes Mazon Creek the most complete record of a Paleozoic ecosystem” — an era that contained six periods and spanned from 541 million to 252 million years ago.
Despite their uniqueness, these sites remain relatively unknown to many outside paleontology circles. Maybe because no dinosaur bones have ever been found in this area or the rest of Illinois, and those tend to draw the most attention.
