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I have been fortunate to hunt Mazon Creek fossils for nearly 40 years. I have collected Many tens of thousands of concretions. I have also purchased premium specimens from other collectors. In the past, I have posted many of these specimens on the forum. I have decided to start posting more in depth descriptions of some of the amazing animals that can be found in the MC deposit. All specimens that I will post are from my personal collection. The first animal that I will highlight is the holothurian or sea cucumber Achistrum sp. Sea cucumbers are a common animal in today’s oceans but quite rare in the fossil record. The Marine (Essex) portion of the Mazon Creek deposit is one of the few places in the world where complete body fossils of these animals can be collected. These worm like animals are actually a type of echinoderm and show 5 radial body elements that run the length of the animal. Well preserved specimens will show a sac like body and an oral ring preserving approximately 15 calcareous plates. Occasionally the intestinal tract and other internal features will be preserved. Just like modern sea cucumbers, Achistrum sp had a leathery body covered in “J” shaped sclerites or Sigmoid hooks. Often times, detecting these under a microscope is the best way to identity poorly preserved specimens. As the animal dried out, the skin would crack and these cracks were eventually replaced by calcite. This gives the body of Achistrum sp a septarian like appearance. While modern sea cucumbers have retractable tentacles surrounding the mouth, none have been observed in Achistrum sp. The animal can reach length of over 15 centimeters however most found average under 10 centimeters. Achistrum is relatively abundant and are occasionally found in masses of multiple individuals. Despite many thousands of specimens collected, Achistrum has never been formally described. At one time it was believed that there may be as many as a dozen different species of sea cucumber found in the Mazon Creek deposit. This has been reduced to one or possibly two different types. This first image shows an exquisite specimen that I collected at Pit 11 in 2017. it is a complete animal and preserves evidence of some unusual muscular structure in the esophagus area that I have not seen before.
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Amateur fossil find 30 years ago leads to crucial evolutionary discovery today
OutrageousFennel posted a topic in Fossil News
A family of amateur fossil hunters from Utah -- the Gunthers -- found this fascinating fossil in the Spence Gulch shale part of Utah in 1992, and shared it with Richard Robison at the University of Kansas. The mystery of what it was went unsolved for nearly 30 years, until a team at Ohio State uncovered the telltale circle that showed the creature had attached to a shelly surface via a basal disc. It's the earliest/one of the earliest known specimens of a mat-sticker making the evolutionary move to attaching to a harder surface--a leap that makes some of our modern-day echinoderms, including sea cucumbers, possible. They recently published their findings in the Bulletin of Geosciences but this discovery wouldn't have been possible if the Gunthers hadn't found the fossil in the first place. Just fascinating stuff. (story here: https://news.osu.edu/scientists-discover-evolutionary-link-to-modern-day-sea-echinoderms/),-
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Taxonomy from Fossilworks.org. Description from Südkamp 2017, p. 147:" The small holothurian has a cylindrical form consisting of a distinct oral region with surrounding tentacles, and at the other end an elongate body that is rounded distally. The lobate arrangement of the 25 plated tentacles, the large ovate madreporite plate (perforated plate for entering of water), and the weakly developed calcareous ring are primitive features among the holothurians. The ossicles of the body wall are numerous small granules underlain by small plate-like elements. In the basal part thorn-like elements are more abundant." Identified by oilshale using Südkamp 2017. References: Lehmann, W. M. (1958). Eine Holothurie zusammen mit Palaenectria devonica und einem Brachiopoden in den unterdevonischen Dachschiefern des Hunsrücks durch Röntgenstrahlen entdect. Notizblatt des Hessischen Landesamtes für Bodenforschung 86, p 81-86. Südkamp, W. (2017) Life in the Devonian. Identification book Hunsrück Slate fossils. Verlag Dr. Friedrich Pfeil, München.
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Hello, here are two purported sea cucumbers among some Mazon Creek material I purchased some time ago. The first, better preserved specimen (with counterpart) was labeled without genus, the second specimen was labeled as Achistrum sp. when I got them. Is this correct? The second one looks like some Achistrum material depicted in the net, though my specimen is small (about 2 cm) and possibly only a fragment. However, I don't see anything specific in this specimen that reminds me of a sea cucumber, but the specimens "in the net" (google picture search) are of similar "structure" (except that they are longer/more complete). The first specimen (28 mm long) is different from that material, e.g. with "undulated" distal part of the body; I can well image that this can be a sea cucumber (much more plausible than my specimen of purported "Achistrum"). However, since it's so different compared to the material of Achistrum that is usually depicted, this rises the question whether specimen 1 is another genus or if it is only another (better?) style of preservation of Achistrum? Or no sea cucumber at all? Thanks, araucaria1959
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- Achistrum
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