Were magnetic teeth the first sat nav system?

A LITTLE less than a year ago, I wrote of a long-dead character from my boyhood called Guthrie Neilson (who, incidentally, was married to Maisie Cumming from Embo) and how he taught me much about the flora, fauna and natural history of the Tain area.

In doing so he once took me to the rocky foreshore south and west of the village of Shandwick, and showed me an outcrop of limestone accessible at low tide where particularly fine ammonites (curly shelled fossil cousins of cuttlefish) could be found.

Oho! – we could indeed see ammonite shapes on a couple of large pieces of limestone – and having prized these free, we laboriously carried them along the beach to where Guthrie’s ancient MG was parked, and thence they continued to Tain.

That night, in my bedroom, and with "FOSSILS – a guide to prehistoric life – 481 illustrations in colour" I studied my two rocks with great interest.

Yes they were ammonites, definitely, two of them, one on each rock, and as I turned the rocks over and moved the table lamp closer, I wondered what might lie within. That would not be known until I got going with a hammer and chisel.

But what was this? In the brighter light something small and oval caught my eye. I could hardly believe my luck – it could be only one thing, and I knew it from FOSSILS, it was a small and perfectly formed trilobite.

It read: "Trilobites (meaning ‘three lobes’) are a well-known fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods…"

And as I turned the pages of FOSSILS, I could see quite clearly that this was a late ammonite, and very probably Cummingella belisama, one of the Proetidae family of trilobites, the last family of trilobites before they too became extinct and trilobites vanished from the face of the Earth.

I could see that my small find, about half an inch long, was Cummingella because it was non-spiny (unlike earlier trilobites) and was smooth and segmented, rather like what we call a "slater" in the Highlands, a woodlouse. I retired to bed rather pleased with my scholarship.

The next day, in the bright sunshine of my window ledge, further examination revealed that in fact there were no less than six Cummingella fossils evident on the surface of my rocks. By now highly delighted by these discoveries, I took the point of my geometry compass and gently scraped away a bit of dirt next to one of the Cummingella – whereupon, to my horror, it promptly fell off my rock and lay on its back showing a wet-looking underneath. When I bent forward and peered closely, I caught a distinct smell – rotten fish!

Now, gentle readers, you might be forgiven for thinking that I had mistaken ordinary limpets for my imagined trilobites, but I wasn’t quite as thick as that.

In fact after a further consultation, this time in my seashore and rockpool book, I eventually established that these increasingly dead and smelly wee things were "chitons", marine molluscs distantly related to limpets, but with jointed shells that they can roll up like a woodlouse should they be dislodged from their host subsea rocks.

Of course, with the wisdom of hindsight, I can now see that I should have checked my dates – because the trilobites died out in a mass extinction towards the end of the Permian geological age, roughly 100 million years before the age of the rocks containing ammonites that I had found at Shandwick.

It was a bit of a boo-boo.

Why the name Cummingella? This one puzzles me, and at this stage the internet doesn’t seem to provide the answer. But I guess that a person called Cumming had something to do with it. Who knows, maybe there was even an Embo connection.

One final point – and it is about my smelly wee chitons. For a mollusc, a chiton has a truly remarkable sense of direction.

For lunch, a chiton prefers algae scraped off subsea rocks with its special teeth (unique in the animal kingdom) made of magnetite, the iron oxide that is the most naturally magnetic mineral in the world.

Off trundles our chiton for his lunch, on a nice fresh patch of algae, and then when he has finished he trundles back home to the exact same spot that he came from. And he does this again and again, back to the very same spot. So how does he do it, how does he remember the way? Even today scientists are not sure.

Some say that he can remember the topography of the rock he has trundled over, and thus know how to retrace his steps. Others say that he leaves a chemical or slime trail that he can double back on. And the most bold of all suggest that his magnetic teeth act like a compass that he navigates with using the earth’s natural magnetic field.

It’s quite a thought, all these little fellows trundling about, and then finding their way home again with their junior satnavs. They date back to the Cambrian period, the era that followed the dawn of life on earth, and trundling about today they have outlived both the trilobites and the ammonites.

It had to be the special magnetic teeth wot did it.

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