This is Mazon Monday post #244. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Arthropleura cristata was described by Eurgene Richardson, Jr. in 1956 in "Pennsylvanian invertebrates of the Mazon Creek area, Illinois. Trilobitomorpha: Arthropleurida" in Fieldiana Geology 12(4): 76-76. He based this work on specimens he collected with George Langford in 1952 and a specimen collected by John L. McLuckie in 1953.
Fig No. 1: Arthopleura fossil found by Eugene Richardson and GL in 1952.
Fig No. 2: Arthropleura fossil found by Mr. and Mrs. John L. McLuckie in 1953.
There is a small report of the finds by Geoege Langford on George's Basement.
ARTHROPLEURA
An account of this arthropod was published in the May 1954 Chicago Natural History Bulletin by Eugene S. Richardson Jr, Curator of Fossil Invertebrates.
In the summer of 1952, while the two of us were on collecting trip we found two specimens Fig. 1 and 2 We were impressed by the fact that they were exactly alike in general form and in the shapes of the five areas defined by grooves. The surfaces of these areas were pitted and mottled. They resembled a specimen described and illustrated by Pierre Provost in 1919 from a deposit in France. It was part of a Crustacean hitherto unknown in this country.
In 1953 Mr. and Mrs. John L. McLuckie of Coal City, lll, found a specimen Fig. 3 which I attempted to draw as a complete arthropod but found great difficulty in so doing becauce the specimen lacked symmetry right a left on on the longitudinal median line. It was unequilateral, After lthorough investigation, Richardson discovered that the supposed crustacean Fig 3 was merely a leg of one, and that Figs 1 and 2 were plates joining the lags to the crustacean's body., whose length Fig 4 might have been as much as five feet. This is by far the largest animal ever found in our Wilmington deposit.
My drawing is taken from the above. Richardson's illustration which is copied from a drawing ny Professor Waterlot, University of Lille, France, where numerous fragments of the animal were collected from the coal deposits.
George Langford mentions an article by Eugene S. Richardson in the May 1954 edition of the Chicago Natural History Bulletin. Here is that article.
SMALL CLUES SOLVE 'CASE OF THE INCONSPICUOUS GIANT'
BY EUGENE 3. RICHARDSON, JR
CURATOR of FOSSIL, INVERTEBRATES
THE INVERTEBRATES are, on the whole, rather inconspicuous animals, probably because they live on the wrong side of the tracks and don't have backbones like all the respectable vertebrates that we commonly associate with. If you ask a friend to mention a lot of animal names, he'll undoubtedly run through cows, tigers, wombats, elephants, mice, and such familiar creatures before he'll shift gears and even think of mentioning the mosquitoes, clams, amoebas, earthworms, or shrimps that actually far outnumber them.
Thus it is likely to come as a surprise to find that in some times and places the invertebrates have included in their ranks animals larger than the contemporary vertebrates. Of course, this was the case in the early part of the Paleooic era before there were any vertebrates at all. But the invertebrates won that round by default and we won't even mention it. Also, there are tales and shreds of evidence of the mysterious Kraken of today's oceans, a squid that may be larger than a whale. But we won't mention that either because we aren't very sure of it.
But another giant invertebrate has recently turned up in our own back yard, among the familiar fossil ferns and crab-like animals of the strip mines near Chicago. These strip mines, in Will and Grundy counties, are only about fifty miles from the heart of the city and have for years attracted not only Museum staff members but also hundreds of other collectors from near and far. The fossils lie in the heaps of clay, or spoil, removed from the mines when the coal was scooped out, and collecting fossils is simply a matter of walking around and picking them up. People have been collecting them from the strip mines since the early 20's, and from the banks of Manon Creek, where the same bed is exposed along the stream, since 1857, almost a century.
In spite of the long and intense interest in these areas and in spite of the thousands of fossils that have been removed and examined, every collecting season yields some hitherto unknown fossil forms. Thus, during the summer of 1952, when I was collecting fossils with George Langford, Curator of Fossil Plants, we were not surprised to find two specimens that looked like something new (see Figure 1).
Figure 1. An unknown organ—is it plant or animal? Museum fossil-hunters found two of these one day and started on the trail of an inconspicuous giant.
We tucked them into our collecting bags and brought them back to the Museum, where Curator Langford washed them and carefully cleaned off a small amount of mineral deposit. Then we examined them and tried to think what they could be. At first glance the pattern of triangular bosses reminded us of the leg-bases of ancient spider-like arachnids that we sometimes find in the spoil heaps. But these specimens were far bigger than any arachnids that we had ever encountered, and, more important, they lacked a right-left symmetry that arachnids must have. We remarked on the texture of the surface of the triangular bones, closely resembling the texture of an arthropod shell.
If you examine the shell of a crayfish or crab with a magnifying glass, you can easily see the irregularly spaced pits, pores, and bumps that almost all arthropod shells have. But, again, all arthropods have a right-left symmetry. Although we were ready to admit that these might be arthropod specimens, we couldn't think of any Coal Age arthropod large enough to use these pieces and still have room for a matching piece on the other side to make up the symmetry. Neither could we recognize these pieces as resembling any known arthropod by itself.
At that point, Curator Langford brought out some specimens of seed-fern fruits from the same deposits. Although the new unknowns didn't look just like any of his fruit specimens, the resemblance was close enough in some respects that we decided that we had picked up some unknown plant parts. So we agreed that they should be put in the fossil plant collection, in a drawer with other unknowns waiting for further information. They might well have stayed there for some time to come, for new information. would have to be in the form of new and more complete specimens, as we could be sure that Curator Langford had not over looked any published pictures of fossil plants that might resemble them.
NEW EVIDENCE FOUND
But they stayed tucked away for less than a year. In 1953, Mr. and Mrs. John McLuckie, of Coal City, were collecting fossils in the spoil heaps when, at the end of the day, Mrs. McLuckie picked up "one more for luck" and found what seemed to be a complete shrimp about six inches long. more than twice the size of any of the shrimp-like animals commonly found in the strip mine deposits (see Figure 2). Mrs. McLuckie very kindly allowed us to bring her specimen to the Museum to be photographed and studied, and in it we found the answer to the two specimens among the unknown plants.
Figure 2. The leg of an unknown giant animal, with duplicate of unknown organ joined to inner end.
The supposed shrimp had what seemed to be a perfectly good jointed abdomen with little legs projecting from each segment, but the front end didn't fit with any shrimp that ever lived. Rising like a comb from its back, where there should have been just a rounded armored thorax, was a duplicate of one of those unknown organs with the triangular bumps.
Mrs. McLuckie's "shrimp" thus brought the two unknown specimens out of the plant drawer again and into my hands, for the task of comparing them with other fomil invertebrates was within my province.
Examining the new large specimen under the microscope, I noted that the supposed legs projecting from the joints of the ab domen were actually spines attached to those joints. But since the specimen was clearly some kind of arthropod, with the typical surface texture and with a jointed armor, it became clear that the entire specimen was not an animal, but merely the leg of an animal. But what a tremendous animal it must have been, compared with our ordinary fossils from that locality! An arthropod with a leg six inches long must have had a body several feet long.
FIRST AMERICAN SPECIMEN
Now, the procedure of identifying fossils depends, first of all, on looking at pictures published in various journals. So I disappeared into the Museum's fine research library and soon found that our specimens were from a large but primitive creature called Arthropleura, never before found in North America, though not uncommon in some of the European coal basins.
Unfortunately, no complete specimen of an Arthropleura has ever been discovered, but enough specimens of various pieces have been found so that Professor Waterlot, of the University of Lille in France, has been able to make a drawing of what it must have looked like (see Figure 3).
Figure 3. This is the newly identified animal itself, Arthropleura by name, as reconstructed from frag- ments found in the Saar Basin in Europe.
In life, our inconspicuous giant must have been about five feet long. Compared with the other invertebrates among which it lived, it was an imposing monster, but it is surprising to find that it was also tremendously larger than the little vertebrates that are occasionally found in the spoil heaps. Those were less than a foot in length, though in the same Coal Age there were larger vertebrates, approaching the length of Arthropleura, in other places.
And the organ with the triangular bosses on it? Professor Waterlot, who has seen a good many specimens, including some with several legs, reports that it is an attachment organ, which holds the leg flexibly but tightly to the body.
