Id: Is This A Prehistoric Worm Trail Imprint?

[EnglishGrace]

Hello
Please could you tell me what made these tracks? They are imprinted in the rock and on close inspection the track is a continuous line with horizontal lines rather like a worm has on its body. The imprinted trail meanders randomly across one square metre of rock. You can see the width of it compared with my finger in the image. It is on the Northumberland coast in England on a beach that has remains of petrified trees from prehistory. If the tracks were made by a type of prehistoric worm - what is the name of it, when would it have lived and what would its environment have been like? Thank you very much.

[TqB]

I think they're modern limpet tracks - they're quite often mistaken for fossils! (Try Googling "limpet track" - one of the top image results is from Seahouses.)

[Auspex]

Are they actually incised into the rock, and not just a surface scraping? If not, then I believe that modern limpet feeding-traces is correct.

[Herb]

Mollusc trails living or dead.

[EnglishGrace]

I've had a good look at many images of limpet trails and none of them look like what I found and also they don't look like my image either. All the limpet trail images are made through a layer of sand, or otherwise if on rock they bear no resemblance to the impression I found. So I don't believe this is a limpet trail. If you look at my full size image you'll see that barnicles and old growths on the rock are on top of the incised trail, which means it's been there far longer than a transient limpet trail. As for it being a "mollusc trail" - it's 100% not a mollusc trail.

I have said in my original posting that the trail has horizontal lines like the segments of an earthworm, so it is not simply a white line; and it does not rub off the rock.

After seeing some images of millipede tracks I'm starting to wonder now whether my trail was made by a type of ancient millipede as the tracks are pretty much identical to some large modern millipedes. Did millipedes live in England in prehistory; when? I found a pic of a millipede track on a rock from Wales - it looks very similar to my trail. Thanks.

Here are some limpet trail pics, plus millipede trails:

[Auspex]

One observation that gives me pause about their antiquity is that they follow the topography of the rock as it is now, and are not restricted to a discrete sedimentary bedding plane: they were made after the rock assumed its current form.

[TqB]

I agree with Auspex, they're not fossils I'm afraid.

They look like modern gastropod trails that have been abandoned for a while (often due to mortality - even a few cold nights can kill off limpets).

The tracks cut through the red and blue micro-algae patches on the surface of the rock, clear evidence of fairly recent feeding.

The colour difference will survive for long enough for overgrowth by barnacles (a barnacle can reach 3mm or more in less than a month.) And the track won't rub off!

There are older, fainter tracks visible where the algae have started to return.

The tracks aren't fresh so you won't necessarily see clear radula marks but I guess enough of the structure has survived to produce the parallel worm-like lines you're seeing. The clarity of the pattern will also depend on the type and thickness of the of algal film being grazed.

Limpet trails (and periwinkle to some extent) are often habitual rather than transient. The mucus they leave behind causes entrapment and growth of some of the microalgae that they feed on - so they are, in effect, farmers. Also, if the mucus dries out too much between tides, it doesn't rehydrate properly and can last quite a long time - that might be contributing to the pale colour but I don't know if it would rub off easily or not.

Limpet tracks with barnacle and seaweed overgrowth:

http://www.geograph.org.uk/photo/2245648

Edited May 4, 2015 by TqB

[EnglishGrace]

The tracks cut through the red and blue micro-algae patches on the surface of the rock, clear evidence of fairly recent feeding.

The colour difference will survive for long enough for overgrowth by barnacles (a barnacle can reach 3mm or more in less than a month.) And the track won't rub off!

There are older, fainter tracks visible where the algae have started to return.

The tracks aren't fresh so you won't necessarily see clear radula marks but I guess enough of the structure has survived to produce the parallel worm-like lines you're seeing. The clarity of the pattern will also depend on the type and thickness of the of algal film being grazed.

Limpet trails (and periwinkle to some extent) are often habitual rather than transient. The mucus they leave behind causes entrapment and growth of some of the microalgae that they feed on - so they are, in effect, farmers. Also, if the mucus dries out too much between tides, it doesn't rehydrate properly and can last quite a long time - that might be contributing to the pale colour but I don't know if it would rub off easily or not.

THANK YOU TARQUIN

I really appreciate the time you've taken to analyse the image and think about creating such a valid reply. It's such a good answer that I can't disagree with! I'm willing to be wrong when my view is so thoroughly and thoughtfully unravelled.

[TqB]

Thank you for your very kind response! Glad I was some help, keep the specimens coming.