Tuesday, June 4, 2019

Mazon Creek Pennsylvanian Age Fossils and the Tully Monster

During one of our tours in the Field Museum, the guide explained that southwest of Chicago was one of the best fossil hunting areas in the world. I first Googled "Sully Monster." I was off by a letter. The famous fossil animal is Tullimonstrum gregarium or Tully monster named after Francis Tully who, in 1958, took three specimens to the Field Museum for identification.

The Tully monster was a soft-bodied, invertebrate, marine animal—an animal that has no shell and no backbone, and lived in the ocean. It had an elongate, segmented body that tapered at both ends. At the front was a long snout ending in a "jaw" with eight tiny "teeth." At the other end was a tail and two fins. Two eyes on stalks projected out sideways near the front of the body. Judging from the streamlined shape, flexible body, and maneuverable fins, it's likely the Tully monster was an active swimmer. Perhaps, like a modern squid, it hovered near the sea bottom. The Tully monsters' "jaws" and apparent swimming abilities suggest that they attacked other marine animals such as jellyfish and shrimp, perhaps piercing their prey with their "teeth" and sucking out the juices.

Although more than half of all the states have official fossils, few have one unique to their state. The Tully monster is found nowhere else in the world. Not only is it unique to Illinois, but apparently it is unique among animals.

A reconstruction of the Tully Monster as it would have looked 300 million years ago.
Credit: Sean McMahon/Yale University via EurekAlert

This is a reconstruction illustrating what Tully monster looked like.
Credit: Sean McMahon via EurekAlert

In 2016, Victoria McCoy partnered with the Field Museum to study thousands of fossils. They concluded that a line in the fossils was a notochord instead of its gut. So it was a Chordate, the ancestor of vertebrates.  "Once the researchers realized they were working with a vertebrate, many of the Tully monster’s bizarre features fell into place, especially once the team compared it to modern lampreys. Scans of the fossils showed that the creature’s teeth probably were made of keratin, just like lamprey teeth (and human fingernails)." [NationalGeographic] In 2017, a paper was published that claimed it was not a vertebrate. [FieldMuseum] But the Field Museum researchers feel the 2017 paper doesn't present enough data to cause them to change their opinion that the Tully Monster is part of the lampery lineage.

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In the following satellite image, note all of the long, skinny lakes that are close to each other. Those are the meta land scars for a lot of strip mining.
Note how this area is on the edge (coast) of an inland lake during the Pennsylvanian Age.
Will Map
The region is dotted with small towns and villages--Braidwood, Wilmington, Braceville, Carbon Hill--that sprang up around mines excavating the massive deposits of high-quality, low-sulfur coal that began to form 280 to 300 million years ago.
Back then, Illinois was deep in the interior of a supercontinent that would later separate into today's major landmasses. Near the equator the region was covered partly by vast swampy forests, partly by a huge shallow sea. To the east, rivers rushed down mountains, carrying sediment through the forests and forming muddy deltas where they emptied into the sea. The future tricounty area was on one of these deltas.
The coal bed they were mining had a layer of shale on top that was moved aside as spoil piles.
The miners dug through the shale to get to the coal seams, piling the waste rock above ground. Because the concretions were in the lowest layers of shale, just above the coal, they were deposited on the tops of these enormous "spoil" piles. As rain and wind eroded the soft shale, the concretions began poking out and rolling down to the base of the hills. Miners reportedly cracked them open on the railroad tracks and sold them to researchers, schools, and museums.
The development of earthmovers in the 1920s led to strip mining. Thousands of tons of shale were scraped off the coal seams, and huge mechanized shovels piled it in steep ridges along the troughs. By the mid-30s picking the concretions off the ridges had become a popular local pastime.
"State and federal reclamation laws passed in the 60s that required mining companies to return the land to some semblance of its original state by bulldozing flat the peaks of the spoil piles and seeding them with plants. The thick overgrowth--which teems with ticks--makes it hard to get to prime collecting spots and halts the erosion that gradually exposes the concretions." The Illinois Department of Natural Resources now has authority over what is left of Pit 11, a major source of scientifically important fossils over the decades. They care about hunters and fishermen and have been openly hostile towards collectors. [ChicagoReader]

In addition to the Tully Monster, there were many more new species found because this site preserved the soft tissue. Most were found by amateur collectors. Fortunately, for decades Eugene Richardson at the Field Museum was willing to look at what the amateurs found. In the mid-50's Peabody Coal Company was mining Pit 11. They unearthed a rich bed of fossils, and Peabody allowed collectors on the spoil piles as long as they stayed away from the mining machines. If a collector found a new species, the museum wanted the fossil donated to the museum as the "holotype." [ChicagoReader]

But many collectors were reluctant to do that because their fossil would be locked away in a museum drawer were even the collector himself would have a hard time seeing it again. I feel Richardson's management did science a great disservice by not developing a Mazon Creek display that showed all of the holotypes with information that included who discovered it. I don't buy that the museum did not have room for such a display because when I visited the museum in the 1970s, they had an entire hall with a rock display. The display was embarrassingly old and didn't have much information. I'm sure the display was built before the term "plate tectonics" was even coined. The lack of visitors in that hall indicated that others also thought the display was not worth the space it consumed. Any other museum could have done a comparable generic rocks display. But other museums could not have as easily done a Mazon Creek fossil display. If the Field had used that hall for a public display of what the collectors had found, I'm sure more of them would have been inclined to donate what they found. With a public display, they could not only take their kids to show them what they found, they could take the kid's classroom. Talk about a nice "show and tell" topic. If bullet proof glass was used, the fossils would hve be safer in the public display hall than in the lab. The ChicagoReader mentions that specimens "disappeared" from their laboratory.

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