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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.

Hi, I was out and about today, looking for fossils near our cabin in southern Norway. There are a few sites here where you can pick through shale deposited around 700-600million years ago (biri-formation). Needless to say, with company and limited time there was meager pickkngs but i found something that might me a medusoid. Can anyone confirm?

During the last years, some presumed fossil stuff from the Kuibis quartzite from the ediacaran Nama fauna of South Africa became available (via several different fossil dealers). It looks always the same and is termed as "medusoid", "Skinnera" or "possibly Albumarid", mostly with question marks which point to the uncertain ID of these specimens. They seem to be quite common since they are not very rare on the market and not very expensive, compared to ediacaran fossils that are assigned to metazoa with a greater degree of certainty. To me, they seem to be the second common ediacaran fossils on the market (after ukrainian Nemiana simplex) and thus a clarification of their identity would be of general interest. That's why I discuss this here in length. They are impressions of globular structures, sometimes surrounded by some smaller ones. They may look like bubbles, but as some of the following pictures show, they are actually globular and not hemispherical as would be the case if they were really bubbles on a surface. The Kuibis quartzite is nearly 550.000.000 years old. They are cyclic sediments from shallow intertidal to subtidal settings (shallow-water settings). The quartzite specimens are probably from the upper part of the Kuibis Supergroup and thus from near-shore marine environments, a little more distant from terrestrial settings than the lower parts. However, though ediacaran fossils are of high interest, I found no informations about these "fossils". Even the wellknown textbook "The rise of animals" vom FEDONKIN et al. (2007) doesn't mention them, in spite of a large chapter about the Nama fauna of Southern Africa, including informations about the Kuibis Supergroup and a short fossil list about the fossils in the upper member (Ernietta, Namalia, Orthogonium, Pteridinium, Rangea), from which the specimens I show here probably come (as indicated by a picture with Rangea schneiderhoehni which seems to come from the same facies). So far, I could resolve all problems with ediacaran fossils and pseudo-fossils with the help of this textbook - except for this. Maybe that's why the textbook is about metaozoa, and the globular fossils here are not considered as metazoa? I show two different specimens. Both specimens yield only impressions (negatives); if they look like positives, it's a welcome optical illusion so there is no need to make silicone casts from them. The largest globular structures are about 9 mm in diameter. The quartzites are laminated. The third picture shows a view from an inclined angle, which demonstrates that the laminations run undisturbed through the globular structures. Thus, the globular structures are positioned within laminated sandstones, but didn't alter the laminations around them. The fourth picture shows the edge of the first specimen. There is also a globular structures with undisturbed (black) laminations at its border on the right. The black layers between the laminations seem to become a bit wider and vesicular when they get in contact with the globular structures. I interprete the thin black layers as microbial mats. (The big dark spot is text marker stain - probably a number had been overwritten). Picture Kuibis 1-h shows two very tiny structures in front of the larger holes; the tiny ones look multilobulate, the larger ones more regularily spherical. Picture Kuibis 2b shows the edge of the second specimen. There are also laminations with very thin black layers, which are suggestive of microbial mats that grew until the next sedimention cycle covered them with sand. It is clear to me that it is impossible to identify the true nature of these specimens - if they are fossils at all. I'm not sure whether they are metazoa (in fact, I doubt this very much) - they could also be large protists (as had bee suggested to occur in the ediacaran age) or colonies formed by unicellular organisms. What I'm looking for: do they have a taxonomic name? If one has such a name, one can follow the current or future discussions about the nature of these specimens. But I haven't found any mention or name for these structures in the literature or internet so far, besides the IDs that are given by the dealers, usually with question marks (Skinnera, Albumarid?), but I think that these names don't match actually. They are also different from Nemiana because of size, different position to one another (Nemiana covers bedding planes in dense populations, sometimes generating a one-layer honeycomb pattern, while the globular structures of the Kuibis are distributed more randomly across the sediments, with local clustering, but not strictly within a bedding plane; they run throughout several bedding planes = laminations; and whereas the top of the Nemiana specimens is flattened and compressed, the globular structures from Kuibis show no signs of compression). One may also consider the possibility that they are no fossils at all. However, the back stain in the reddish quartzites accounts for organic matter, at least at or upon the wall of the globular structures. The black stain of the globular structures is comparable to the small black layers of the laminations which seem to indicate microbial mats. So, if the globular structures themselves were no fossils, they must have been covered by a microbial mat or organic matter of another origin. It is difficult to image that bubbles of gas or something like that might have been preserved in such a globular form, with regard to the pressure and compactation from the layers of sediments upon them. So I think it is difficult to explain them as inorganic globular structures which became dissolved later and left these dark holes in the quartzite. But maybe someones knows more about that? Thanks! araucaria1959