Jump to content
connorp

Red Flag on "Medusoid" fossils from the Ediacaran of Namibia

Recommended Posts

connorp

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.

 

large.5a1e0ac57cb3f_Problematikum1598aNamacalathushermanastesEdiacariumFishRiverCanyonNamibia182642001641Problematikum1598a.thumb.jpg.67d6465ee1d88752b0e09ddab04c592a.jpg

 

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.

 

IMG_5357.thumb.jpg.f3771fc8ed19b69d0c5a37cf1fe9d7a4.jpg

 

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.

 

640px-Tafoni_at_Twyfelfontein_(Namibia).jpg.12c2513c2451dd70d100d5fe1a821e95.jpg

(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.

 

Share this post


Link to post
Share on other sites
Fossildude19

Moved to "Is it Real"  ;) 

Share this post


Link to post
Share on other sites
oilshale
2 hours ago, connorp said:

…... 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....

 

 

 

 

Better specimens: I don't know if it's really Namalacanthus, but the structures don't suggest it's just weathered sandstone. I suspect that the calcite skeleton is weathered out and only a sandstone imprint remains.

 

 

Namalacanthus.JPG.895d0138fb95e3d8a1659a217f8c8eaf.JPG

Share this post


Link to post
Share on other sites
oilshale
20 minutes ago, Pemphix said:

Remark: Ediacara fossils (for example from Farm Aar) are part of the national heritage of namibia and therefore banned from export/import....

 

You are right! No matter if this is Namalacanthus, any other fossil or just a weathered sandstone - for this reason you should refrain from buying these "fossils".

Share this post


Link to post
Share on other sites
oilshale

This is a paper from Zhuravlev et al.: Ediacaran skeletal metazoan interpreted as a lophophorate.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4650157/pdf/rspb20151860.pdf

Have a look at Fig 1b and 1h. Not identical but - I think - comparable structures.

 

 

Share this post


Link to post
Share on other sites
oilshale
5 hours ago, connorp said:

 

 

large.5a1e0ac57cb3f_Problematikum1598aNamacalathushermanastesEdiacariumFishRiverCanyonNamibia182642001641Problematikum1598a.thumb.jpg.67d6465ee1d88752b0e09ddab04c592a.jpg

 

By the way, I have published this picture in Steinkern.de, the German speaking equivalent of TFF. This "fossil" is in my possession.

Share this post


Link to post
Share on other sites
connorp
2 minutes ago, oilshale said:

By the way, this is a paper from Zhuravlev et al.: Ediacaran skeletal metazoan interpreted as a lophophorate.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4650157/pdf/rspb20151860.pdf

Have a look at Fig 1b and 1h. Not identical but - I think - comparable structures.

They certainly are similar looking. However, Namacalathus are usually found in dense assemblages, and almost always associated with SSFs such as Cloudina. Most "specimens" for sale are presented in very smooth pieces of sandstone/quartzite, yet I have never seen evidence of any SSFs in these pieces. As quoted below (from Penny et al. 2016), isolated Namacalathus can be found, but are certainly not the norm. Perhaps if these specimens are Namacalathus, they have all been collected from a low-ramp setting where isolated individuals are found. But Namibia is the primary source of Namacalathus specimens, and it would seem strange to me that no specimens available have been collected from more abundant reef settings.

 

"Namacalathus commonly occurs in densely aggregated assemblages, which range from decimetre to metre scale. In the inner ramp setting, some in situ Namacalathus occur as isolated individuals (Fig. 4A,C), but most are found in aggregations of up to 0.5 m diameter (Fig. 4B). In mid- ramp reefs, small (<0.5 m) aggregations are associated with thrombolite heads. These close- packed aggregations contain individ-uals of up to 35 mm cup diameter, although a range of individual sizes occurs (Fig. 5A,B,F). Some of these large individuals also have external spines, although the sample contains too few individuals with this feature to statistically analyse its occurrence (Fig. 5B). On open surfaces in mid- ramp reefs, Namacalathus aggregates to form sheets of up to 5 m in diameter (Fig. 5D,G), and also intergrows with extensive (>20 m in diameter) thickets of Cloudina riemkeae (Fig. 5E,D; Wood & Curtis, 2015)."

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

×