Dear Bastien,

This is an Eldonia, maybe an E. berbera (Alessandrello and Bracchi, 2003), from the Upper Ordovician of Morocco. This genus is well known from the Burgess Shale Fauna (Cambrian of Canada), the ordovician species from North Africa are the youngest members of this genus... Classification as medusae is not really clear, depending which author you will follow.

In contrast to the not very trustfull trilobite on your picture, the Eldonids and also the Scyphocrinites (Crinoid) are very well preserved specimens.

Best regards

Johannes

Thank you very much for your very interesting answer !! I am a little curious about the taphonomy of this fossil too. Do you have any idea of how a soft tissue body like that can be preserved in sandstones ?

Best regards

Bastien

Hello Bastien,

beside the trilobite (upper left), the crinoid Scyphocrinites/Camarocrinus (left), and two stromatolite specimens (upper right + right) you have (as Johannes already pointed out) three specimens of the Late Ordovician enigmatic Eldonia (E. cf. berbera) in the centre of your photograph ...

Eldonia was first described by Charles D. Walcott as an pelagic sea cucumber (Echinodermata: Holothuroidea) from the "Middle" Cambrian Burgess Shale (British Columbia) ... later (since the 1980s) the genus was also described from various localities (under different names) in Yunnan, China, from the "Early" Cambrian Maotianshan Shale ("Chengjiang fauna") ...

Eldonia is definitively not an echinoderm ... more probably a cnidarian of uncertain position ...

Concerning your suggestion "the Ediacarian Tribrachidium" (which is best known from Australia and the Russia White Sea region) ... you will need to have the typical tri-radial symmetry, which is not present in Eldonia ... also the size is much different (Tribrachidium: up to 5 cm in diameter; Eldonia: normally 10-20 cm) ...

Best wishes, Mike

@ Bastien:

Nice question. Soft tissue preservation (even in coarse grained) sandstones is often explained by deposition of the fossil on or below microbial mats. Similar shallow marine settings are generally no longer existing in our todays environments, but there are some analogues from freshwater settings (If I remember right, from the northern lakes of the US). The fossils in this particular upper ordovician geological unit from morocco contain also some other faunal elements with mineralised endo- and exoskeletons (e.g. trilobites and echinoderms), and they are also only preserved as cast/imprint with some iron oxides in between (also smaller amounts of baryte, clay minerals and sometimes some late quartz).

Because of the not very clear classification, I can imagine there was maybe some "hard" phosphatic soft tissue, stabilising the eldonids in this special setting.

If I remember right there was a book about microbial mats in clastic settings, if you are interrested I can look for the reference.

@ Pablo:

I see you have found and read the label on the picture. I guess Bastien has asked for the objects in the middle, and they are no "vanadium concretions" for sure. The objects in the right upper corner were sold as "stromatolites", but this is also not very clear and still under discussion. But from the sedimentary setting I have seen in the outcrops were they were found I would say, they are no oncoids, but maybe early diagenetic intrasedimentary structures. They are of course also no fossils (in this point you are right), if they are stromatolites they are sedimentary structures, created by the process of life from different organisms (not preserved) in the same way. The general term used for such structures is "trace fossils", even if some palaeobiologists are not completly fine with this point of view on stromatolites.  The other objects (the quartz concretion (pseudomorph after anhydrite) and the agate plate covered by the hand excluded) are fossils. The trilobite is maybe partialy faked (in my opinion some areas in the left cephalic area are suspect).

Best regards

Johannes

This is the link to the book that Johannes refers to (I suspect)

http://www.shale-mudstone-research-schieber.indiana.edu/mat-book-2007.htm

Hello Meike, Johannes, and Keith

Thank you all for your answers. I did not know any thing about this very interesting topics (taphonomy and Eldonia) ! So I can imagine that similar processes occured for the jellyfishes from Luberon (Oligocene, France).

Thank you for the explanations and the book.

Best regards

Bastien

II'm not a specialist of Ediacarian fauna. But as I know: Ediacara fauna, unique assemblage of soft-bodied organisms preserved worldwide as fossil impressions in sandstone from the Proterozoic Eon at the close of Precambrian time. (mainly Vendian).These fauna represent an important landmark in the evolution of life on Earth: they immediately predate the explosion of life-forms at the beginning of the Cambrian Period 541 million years ago. The Ediacara fauna, named for the Ediacara Hills of South Australia in which they were discovered in 1946, were the first metazoans (animals made up of more than one type of cell) that required atmospheric oxygen for their growth.

Dear Keith,

nice book (not the one I have mentioned, but thank you for the hint). The book I want suggest is

"Noffke 2010: Geobiology; Microbial Mats in Sandy Deposits from the Archean Era to Today"

Unfortunately, her paper from your suggestion is not available.

Best regards

Johannes

According to my colleague Juan Carlos Gutiérrez-Marco, a paleontologist from the Complutense University of Madrid, Spain, the discoidal fossils in your photograph are "Eldonia" berbera Alessandrello & Brachi 2003, a paropsonemid eldonioid recorded from the Tafilalt Biota of the Eastern Moroccan Anti-Atlas, which is abundant in the Bou-Nemrou locality north of the village of Tamarna, El Qaid Rami valley. Its age is not Devonian, but early Late Ordovician (earliest Sandbian). Preservation of these paropsonemid fossils, showing trace of guts in your picture (early described as "coiled sacs") occurs in medium to coarse-grained sandstones, in a style reminiscent of the soft-bodied Ediacaran fossils of the White Sea Assemblage. However, the true Eldonia is mainly known from the Burgess Shale and these paropsonemids surely not belong to this genus. In addition to "E." berbera, the Tafilalt Biota provides other large discoidal ?holdfasts, non-biomineralised cheloniellid arthropods, rare vermiform fossils and articulated skeletons of echinoderms and trilobites. Extensive soft-tissue preservation of the palaeoscolecid worms down to micron-scale, as shown by my colleague in an article recently published by him in the journal "Gondwana Research".

Well Dr Bastien, really nice question you raised here. As I am the Ediacara worker, so I would only can express you thet only in late Proterozoic the soft bodied cnederian fossils preserved in the form of mould and cast or you can say in three-dimension. It is just because, that in late Proterozoic there not enough grazers, so you would get well flourish microbial mat on the sea-floor especially in the shoal or shallow water coastal environment. In presence of microbial mat if any living entity burried and subsequently decay, then it usually engulfed by the algal mat, which makes the sediment cohesive to better preservation of living entity in three-dimension, unlike in Phenerozoic.

i would recommend you to go for Gehling 1999. Microbial mats in terminal Proterozoic siliciclastics: Ediacaran death masks. Palaios 14, 40–57.

Dont forget pyrite precipitation is really important phenomenon for preservation of fossils on sandstone even in quartzite.

best

SKP