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Showing results for tags 'Medusoid'.
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Red Flag on "Medusoid" fossils from the Ediacaran of Namibia
connorp posted a topic in Is It Real? How to Recognize Fossil Fabrications
For those interested in Ediacaran fossils, you may have seen a lot of supposed medusoids coming out of sandstones/quartzites in Namibia. They are usually labeled as unidentified medusoids, but sometimes as the enigmatic genus Namacalathus to command a higher price. At first glance, some specimens do bear resemblance to a top-down cross section of Namacalathus (such as the specimen below), however note that Namacalathus are preserved as calcite skeletons, not as molds in sandstone. A thread discussing these was posted several years ago, without a definitive conclusion. As far as I can find, there have been no published articles on these so called fossils, and perhaps rightly so. After a recent trip to the Field Museum, I am fairly confident that all of these specimens are simply the result of weathering in sandstone. Here is the specimen at the Field Museum that piqued my interest. A quick scan of our favorite auction site will reveal a number of nearly identical specimens listed as medusoid fossils. These holes are likely what are known as tafoni, defined by Wikipedia as "small (less than 1 cm (0.39 in)) to large (greater than 1 meter (3.3 ft)) cave-like features that develop in either natural or manmade, vertical to steeply sloping, exposures of granular rock (i.e., granite, sandstone) with smooth concave walls, and often round rims and openings." They have various methods of formation, but the more "Namacalathus"-looking specimens look (at least to me) to be the result of iron nodules rusting out. They may also be several tafoni that overlapped. Here is an image of tafoni in sandstone from Namibia. (image credit Wikipedia) Regardless of the exact process of formation, I am confident in saying that these are not fossils. There are plenty of other Ediacaran fossils out there for purchase, and given the high price tag these pseudofossils seem to command, I hope this post helps collectors avoid wasting money.