The material is probably Cretaceous chert (or jasper? - in the picture on the right there are probably intrusions of agate) from the contact with submarine volcanic rocks from the Flysch Zone of Western Carpathians (Moravia, Czech Republic). But they have been found as artefacts on a Magdalenian site nearby...My idea is that the material is the result of silica intruding flysch sediments with fossils...
Your photos have no scale. If these are microscopic, then they bear some resemblance to crustacean microcoprolites, some of which are cylindrical with longitudinal "canals" in characteristic arrangements.
Dear Andrew, thanks for the estimation. There is a micrometric scale (barely visible, I admit) at the margins of the photos. The coprolites would then be of ca 1-2 mm in length.
Best wishes,
Martin
Sorry! Well, the scale is compatible with microcoprolites, which, after all, represent the interior diameter of the crustacean's gut. The internal structure is created by long processes within the gut that direct any coarse material to the center of the fecal mass. Many ichnospecies have been named in ichnogenera Favreina, Parafavreina, Palaxius, Helicerina, and others, and they can be useful as index fossils. For a lengthy bibliography, see the FAVRIS section of Joachim Blau's website (https://www.staff.uni-giessen.de/~gg13/VON_MIR/JOACHIM.HTM). Another current researcher in this area is Diego A. Kietzmann. Together with David Kopaska-Merkel, I have written a single article on a Jurassic (Oxfordian) ichnospecies of Parafavreina.
David Buchs at Cardiff University, UK, has found similar microcoprolites associated with submarine volcanics, so your material might another example of this sort of occurrence.
Thanks to both of you, I will go through the articles. It is good to hear the volcanism hypothesis might be correct.
Martin
The two photos on the left are almost certainly of fecal pellets of the burrowing shrimp, Calianassa, i.e. "crustacean coprolites." That may be too specific, but they are dead ringers for the modern examples. They were once graced with the generic name, Favreina, on the misconception that they were dascyclad algae, from the Upper Jurassic of the Jura mountains, as I recall. They have since been reported from rocks of many ages, some as old as late Devonian. A lot of references are available on the internet.
BTW: Burrowing crustaceans, possibly Calianassa, have also been honored with a generic name for one type of distinctive burrow: Ophimorpha, especially common in the Cretaceous. The distinctive external lumps that define this ichnogenus are probably mud lumps or fecal pellets packed against the burrow wall to stabilize it.
These critters deserve to be recognized as the Michaelangelos of the invertebrate world for their excellence in both sculpture (of their feces) and architecture.
Dear Paul, thanks for the exact estimation. As I mentioned above, I do not know the exact age of the fossils but intensive volcanism only occured in that part of the Flysch Belt of Western Carpathians in the Lower Cretaceous, and it was probably the source of silica that composed these cherts...
Not all crustacean microcoprolites can be traced to Callianassa. Callianassa is merely one genus of many crustaceans that make these fecal pellets; they include, for instance, galatheid crabs as well as ghost shrimp. Most of the species whose pellets have been described have since been removed from this genus; e.g., the well-known Callianassa major of the Georgia coast has been reassigned to Callichirus. The best paper that I know of describing the modern fecal pellets is a classic by the late Wayne Pryor:
Pryor, W.A., 1975. Biogenic sedimentation and alteration of argillaceous sediments in shallow marine environments. Geological Society of America Bulletin, 86(9), pp.1244-1254.
The shrimp usually expel the fecal pellets from the burrow, in such great numbers that they form biogenic muds in places. They are not pressed into the walls of Ophiomorpha to form the lining; those are pellets of sediment, not feces.
Thanks for the update on Callianassa nomenclature and the reference by Wayne Pryor, whom I greatly respect. Bob Folk, whose fixation on fecal pellets suggests anal retention, likes to cite a treatise by Rev, William Buckland (1784-1856) as the best thing ever written on fecal pellets, at least prior to Pryor.
I certainly overstated the case for Callianassa, as I lamely cautioned ("too specific"). In addition to expelling pellets with their excavated sediment, they may also pack them in some of the dead-end side tunnels in their complex burrows in muddy sediment, as shown by Gene Shinn's burrow casts:
Shinn, E.A., 1968, Burrowing in recent lime sediments of Florida and the Bahamas: Jour. Paleontology, v. 42, p. 879-894. (see p. 884)
Also illustrated in: Enos, Paul and Perkins, R.D., 1977, Quaternary sedimentation in south Florida: Geol. Soc. America, Mem 147, p. 1-130 (see p. 71)
Their advanced architecture included latrines.
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