Hello Amos,

on your picture you show the pellets and, nearby a funnel structure. Are they connected? Can you provide a picture of the excavated spiral?

From your description and the dimension of the burrows, it sounds like scorpion burrows, known also from Urodacus yaschenkoi in sandy terrestrial environments in Australia:

http://www.thedailylink.com/thespiralburrow/features/burrow03.jpg

http://www.thedailylink.com/thespiralburrow/features/burrow05.jpg

Terrestrial annelids can be ruled out because of the burrows dimensions (from my poor knowledge, there is no species which can make burrows of this dimension in Spain)

Greetings to Be'er Sheva!

Johannes

edit:

http://www.thedailylink.com/thespiralburrow/features/burrow01.html

and maybe: Koch 1978: A comparative study of the structure, function and adaption to different habitats of burrows in the scorpion genus Urodacus (Scorpionida, Scorpionidae) Rec.West.Aust.Mus. 6(2):119-146.; I think it is available for free, if you search for the article via google.

This looks very much like a pit-mound-structure (the ones I'm familiar with) created by marine worms (like Arenicola marina, see e.g. this link: http://www.arkive.org/lugworm/arenicola-marina/image-A23909.html).

However, as this isn't a marine environment I would guess it is some terrestrial worm species endemous to the area ;)

I hope this helps?

My guess (but just a guess with this limited information) would be castings from an invertebrate such as an annelid or a crustacean; it looks more like annelid t me, but there are lots of variations.  Of course, large nemerteans are also a possibility with this sort of casting.  These castings doe appear to be derived from passage through the digestive tract.  Are these near the salt water, with saline sand underneath, or is the water fresh?  Since you are near the Mediterranean Coastal and estuarine areas at this location, it may be that the animal lives in the saline saturated environment deep down, but if somewhat euryhaline can more toward the surface during rainfalls.

@ Klaus - There are earthworms in that area, but I haven't heard of giant earthworm that would make such thick casts in Donana. But I will ask around.

@ Johannes - The funnel structure is an antlion pit, but there is no association between the two. It just happen to be next to this mound, but all the other dozens of mounds didn't have an antlion pit near them. I may have a photo of the excavation, I will have to dig among my photos from that trip, but it was with a larger diameter and didn't look like the scorpions tunnels you directed me to. I have actually excavated many scorpions tunnels in the Negev Desert, and this one in Donana definitely looked different.

@ David - There are brackish/salty lakes in the area, but all the mounds I have seen were in stable sands too far and much too high above the underground water level. When I looked at the mounds, my impression was that it was wet sand pushed out of the tunnel opening, and not a cast, but I may have been mistaken. 

Anybody is familiar with the excavating habits of Blanus cinereus (Iberian worm lizards)? These Amphisbaenid reptiles are known to occur in Donana reserve and are subterranean. I read that " It is often found in moist, sandy soils that are easy to burrow in and have a high level of humus". But no mention to mounds nor to pushing sand out of the tunnel.  http://www.iucnredlist.org/details/61469/0

I agree with David. Based on the photo's these castings doe appear to be derived from passage through the digestive tract. Thus some annelid (worm) species seems most likely to have caused them.

Hi,

sorry for the additional questions (I'm very interested in traces, and I come from field of palaeontology, and there is a somewhat different approach):

1. From my knowledge, such "outbursted" material can originate, for sure, from a diggestive tract, but the appearance is nearly identical when it came over outpressure via a burrow with some kind of (organic) lining. How do you can exclude this from the pictures?

2. From my point of view, structure and dimension of the burrow is more indicative than the "outbursted" pellets. There are some papers about continental setting's trace assemblages, an interresting one is

Hasiotis, S.T. and Bourke, M.C. 2006. Continental trace fossils and museum exhibits: displaying burrows as organism behaviour frozen in time. The Geological Curator, 8(5):211-226. see link below.

There are some more from the same autor, and some of I.A. Buatois. Because I did not know: Do You know some kind of earthworm (or other annelid) burrows with the spiral structure described above? I never see similar complex burrows from the annelids I know (and most of them prefer a somekind different sedimentary facies).

And the third question: as far as I know, large ("giant" earthworms are restricted to Africa and SE Asia. Are there comparable species known from Spain?

Best regards (and thanks for upcoming answers)

Johannes

@ Amos: you may also include topics like "Trace fossils", "Ichnology" and "Palaeoichnology" to your question, there are a lot of related specialists in this community...

www.geocurator.org/arch/Curator/Vol8No5.pdf

from additional interest is maybe

Platt et al. 2010: USE OF LOW-COST MULTISTRIPE LASER TRIANGULATION (MLT) SCANNING TECHNOLOGY FOR THREE-DIMENSIONAL, QUANTITATIVE PALEOICHNOLOGICAL AND NEOICHNOLOGICAL  STUDIES. - Journal of Sedimentary Research, v. 80, 590–610.

especially the scannings from the supplementary material.

Best regards

A suspect has been apprehended in one of the tunnels and has been named: Ceratophyus_hoffmannseggi. It is a dung beetle (Coleoptera: Scarabaeidae) (see photos attached). I happened to be back in the field when it rained again, and soon after additional rains the mounds collapse and apparently the constructors clears them. So I chose a mound that was in the process of being renovated, a couple of hours after the rain, excavated it, and found that beetle. So it must be sand pushed through the tunnel, and not through the digestive track. That beetle is an amazing excavator - as you can see in the second photo, as soon as the beetle is left on the ground for a few seconds, it immediately tries to excavate into the sand again.

Thanks to all who responded and posted suggestions.