Lizzy - good photos (scale, cropping, sharpness, lighting, background) - that helps a lot; thanks.
However, I can't quite 'see', or not with confidence...
Do some of these marks continue around the stone to some extent, perhaps even joining up to form a continuous loop? I'm asking because I'd like to know if they are manifestations of structures that go through the rock or if they are just on its surface.
I may have some suggestions depending on your answer.
There are one or two faint markings on the sides of the stone, where it seems to go around but it's hard to tell because the edges are smooth, so the marks could of been eroded away.
It looks as though their just on the surface.
Thanks for replying!
OK Lizzy, thanks.
Some bivalves can make holes in rock, either by chemical corrosion or physical abrasion. Some other creatures have a holdfast (byssus) that uses chemical corrosion to make holes in the rock.
These are moden effects, unrelated to the rock's geological history.
I have a hypothesis:
1. Your rock was part of an outcrop on a beach, where it was colonized by rock-boring bivalves or some other creature (as above). Those animals detected weaknesses in the rock and preferred to do their hole-making there. Such weaknesses arise by differences in the nature of the rock. Those weaknesses may be in planes or curved surfaces or in irregular pockets or fossils. In your case, I think the weaknesses were fairly irregular but still with some structure. Consequently, your 'strings of pockets' follow the same layout.
2. At some point, your rock broke off the outcrop. As it was rolled around on the beach, the hole-making creatures were killed and knocked off.
3. With continued erosion of the rock's surface, over decades or more, most of the strings-of-pockets became shallower.
4. You found the rock!
There are some problems with this hypothesis:
- in some places, the pockets can be seen to be almost completely enclosed (holes rather than pockets)
- the 'walls' separating the pockets are rather regular in thickness
- I have not found any examples like yours
So I am open to other suggestions.
- Boring bivalves - http://www.answers.com/topic/boring-bivalves
- Lithophaga - http://www.biolib.cz/en/image/id10845/ (note the irregular arrangement of the burrows - not like yours)
Thank you for your hypothosis! I don't really know much about fossils so it's very interesting to an hear educated idea.
I searched on bivalves and this is the closest I could find to my example, though obviously the pockets are not indented here.
God for you for looking, Lizzy.
There is a superficial similarity, but the marks you found are where regularly-spaced lumps on the surface of a bivalve have become worn down. Neither that, not the impressions such lumps might make, explains your strings-of-pockets.
These traces remind me of something I found some time ago. Take a look and see if you agree. I didn't really get to the bottom of what my find was.
Rhys - well done for remembering and finding that; thanks.
There is definite similarity. It is a shame a definite ID was not obtained.
It is interesting that example occurs on a bedding plane. If that and structures in the current specimen are closely related, it makes me lean towards a flexible lumpily-tubular structure, which could be deposited on the sea floor and/or buried within a layer of sediment. If the latter, its presence in the rock millions of years later could influence the way the rock breaks - accounting for this specimen happening to have these structures largely at its surface.
I wonder about strings of eggs, perhaps encased in a collagenous/calcareous sheath. By way of an approximate example of what I have in mind - a string of (toad) eggs -
http://www.terrariet.dk/Pedostibes_hosii_UK.html (2nd image down on the right).
In 'Trace Fossils: Concepts, Problems, Prospects' (edited by William Miller III; Elsevier, Oct 13, 2011), p.511 -
there is a description of 'spheres arranged in a string of beads'
Also, on on P.452, there are 'strings of sausages'
That describes a sediment-consuming animal (Parastichopus californicus, giant california sea cucumber) enclosing the sediment as mucous-wrapped parcels in their gut, and excreting the materials still in that state. Rows of beads are said to be produced in a similar way (Capitella, a polychaete worm).
(Yes, you would think the likelihood for preservation of such material to be very low.)
I don't have access to the real book (only the Google Books incarnation), and I can't see the figures referred-to - so I can't tell how similar those things are.
- Nudibranch eggs, photographed by Igor Bartolucci
But I have found no photos of fossils of Nudibranch eggs
Perhaps it will give somebody else a line of research to follow...
I agree with Mike, I have a load of these from when I have been on holiday, none of which were fossils. I have heard sea urchins also do something alike if I remember right.
Just for reference, an interesting specimen has come-up for ID
...Which turns out to be the bleached remains of a calcareous seaweed, Corallina officinalis.
Morphologically, it would appear to be a candidate for a/the explanation of the string-of-beads conundrum
Thanks for the thought, but I don't think so.
I don't know of a sponge with suitable morphology.
Chain corals can have a superficial resemblance in 2D, ie. on a flatt(ish)surface
But in 3D they are like fences
The string-of-beads specimens commonly wrap around curved surfaces (eg. of a pebble), and retain the same appearance irrespective of the orientation of the surface. If they were chain corals, the marks would become more elongate around the curvature of the surface. (Easier to see than to explain.)
Also, the chain corals have walls (ie. they are hollow in the middle), whereas the beads in the string-of-beads seem solid. OK, the beads may be moulds, but I have yet to see one where either the fossil itself is present or there is a cast loose within the mould (the latter would obviously require a mould visible through only a little window - else the cast would fall out).
Just for future reference...
Another vague possibility is something like Catellocaula vallata; see:
- http://woostergeologists.scotblogs.wooster.edu/tag/ichnology/page/2/ (search for 'Catellocaula ').
That's thought to be due to a soft-bodied parasite, such as an ascidian tunicate [sea squirt] like the modern Botryllus (paraphrasing). ...Which means it requires the presence of a bryozoan. ...Which is unlike the specimen at the start of this discussion.