This is Throwback Thursday #125. In these, we look back into the past at ESCONI specifically and Earth Science in general. If you have any contributions, (science, pictures, stories, etc ...), please sent them to [email protected]. Thanks!
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Who's ready to get back to ESCONI meetings? We have the September 2022 General Meeting coming up on September 9th, 2022 at the College of DuPage. The very first ESCONI General Meeting at the College of DuPage occurred on Friday, September 9th, 1983. This was announced in the July/August 1983 edition of the ESCONI newsletter. Previously, most General Meetings were held at the Hummer Park Field House in Downers Grove.
The topic of that meeting was "Post Glacial Fish from the Lake Michigan Drainage in Milwaukee, Wisconsin" given by Susan Teller-Marshall of the Lincoln Park Zoo.
The October 1983 newsletter had a summary of her presentation by Recording Secretary Kathy Dedina.
Tonight's speaker is Susan Teller-Marshall of the Lincoln Park Zoo. Her program is on the post glacial fishes of the Milwaukee drainage. Susan is a vertebrate paleontologist not a geologist. She did her master's on material collected by amateurs along the gulf coast of Texas. Without the amateurs, her thesis would not have been possible. The area yields too little to devote a season to collecting there. The work on the post-glacial fishes was done at the University of Illinois and formed the basis for a series of papers. I hope to show you that you can reconstruct a fossil from only parts of the animal. The paper on the fishes of the Milwaukee drainage is available from the Milwaukee Museum.
The first site studied was at Michigan City, Indiana. Someone brought a fossil fish to the Field Museum. The museum called Dr. Bardack, my adviser. The fish was a pike. We collected in the Michigan City area to get more material. We found quite a few fossils. When a group of fossils are found together, there are several ways to test if they actually occurred together--1) Would you expect these to occur together answer yes for Michigan City fossils; 2) Was the geological feature long or short lived - short-lived for Michigan City. The shorter-lived the feature, the more likely the fossils occurred together; 3) Sedimentation study is done; 4) Radiocarbon dating gives approximate age. Fish are more particular where they live since they have a more limited tolerance.
The animals found at Michigan City were: long-nosed gar fish, northern pike, northern brown bullhead, blue gill, large-mouthed bass, sauger, painted turtle and red-throated loon. Each of these animals could be separated from related species by distinctive skeletal features. As an example, the northern pike has a long, flat head with a distinctive top headbone. The lower jaw and tooth pattern separate the northern pike from the related muskie. The northern brown bullhead was determined from the pectoral spine. Only the brown or yellow bullhead has serrated teeth at the base of the spine. By measuring the depth to length of spines, we found each species has a size range that did not overlap. I was particularly pleased with the sauger because it was my find. The specimen was a complete fish head. The distinctive features of a sauger are found in the head. The turtle was studied by an expert at the University of Illinois. We took his word for the identification. Loons have much longer braincase than other birds with more primitive features. The skull was too small for a common loon. The bill and distribution determined it to be a red-throated loon.
We charted the habitats these animals live in. One animal specie may live in a variety of habitats. All the animals we found at Michigan City occur in a warm shallow marsh. The fossils were radiocarbon dated to 6350 B.P. Was the climate at that time warmer than the climate of today? Some literature say that the climate then was not the same as now. 22,000 years ago, the Wisconsin glacier reached its peak; 14000 years ago, ice receded north of Chicago; 9,000 years ago Lake Michigan water was at its lowest lever; 4,000 years ago, it approached its present stage. The Michigan City fossil location was quite a ways from the shore of the lake. 10,000 years ago, the climate warmed and reached its peak 4,000-6,000 years ago then it cooled. This climatic data is based on pollen data. Some geologists didn't think the climate was significantly different after the receding of the last glacier than today.
Since one community doesn't tell much, we looked into the literature for other locations. We found one other community, Fenton Lake in Michigan, dated about 1,000-3000 B.P. The Fenton Lake fossils included lake trout, lake whitefish, suckers, walleye, silver red horse, and muskellunge. The Fenton Lake fishes were colder water fishes than those of Michigan City. We envision that the Michigan City community was a marsh or shallow pond that warmed up in the warmer weather. Fenton Lake was deeper and stayed cooler. A number of the Michigan City fish ranged further south than those of Fenton Lake. The difference in species at the two locations may represent differences in habitat rather than climate. Caution should be used in determining climate on the basis of pollen data only. The period of 4,000-6,000 B.P. was very dry. Many areas were drained. Some fishes may have been kept out of an area by changes in water or river patterns rather than climatic cooling.
A fossil which turned out to be a mudminnow was given to us for study by the Milwaukee Museum. We found that the museum had a whole room full of material from the mudminnow location. The fossils were found during sewer works. The fossils found at the Milwaukee location were: central mudminnow, black bullhead, small-mouth bass, pike, muskellunge, green sunfish and pumpkinseed. The radiocarbon date was 7,750 B.P. The fossils of Milwaukee represent a different community than the fossils of the Michigan City location. Milwaukee was a slow-moving cooler stream or river. Since our papers, there has been a turnaround in how post-glacial fossils are viewed. Factors other than climate are being considered when studying the distribution of fossils.
Kathy Dedina, Recording Secretary
Sander canadensis - AKA Sauger
