Predator and Prey?


Jun 25, 2004
Hello all

Its been a while since I visited the seaside and as work has been a bit tedious recently, me and my mate John decided to take last Monday off and get some serious fossiling done. Went to Port Mulgrave about 9 miles to the north of Whitby where a major landslip occured a few years ago which was a good source of dead cephs. Erosion has taken its toll and the find rate has diminished somewhat since the good old days but it still has a lot of potential. Anyway, despite monsoon like conditions (after all it is Britain and supposedly the height of Summer) I was not disappointed and came back with a handful of pieces. Attached is the find of the day - a Jet Rock nodule containing a Harpoceras sp ammonite alongside an Ichthyosaur vertabra as found lying on the beach (both approx 2inches). Also attached is a rather nice 7cm Dactylioceras commune found only a few feet away. Roll on the Winter storms!

All the best



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Hi Kevin

No, the Jet Rock is a dark grey laminated shale laid down in deep water anoxic conditions. Its fairly soft - easily hammered - but contains much harder pyrite skinned nodules which go by names like The Cannon Ball Doggers, Curling Stones, Whale Stones and Lower Pseudovertebrata. Its called the Jet Rock as it contains deposits of Jet - a hard black (jet black in fact!) fossilised wood which is still used to make jewellery and was particularly popular in the Victorian era. The local fossil and jewellery shops still make Jet pendants inlaid with local ammonites.

The shales contain large numbers of flattened ammonites and 3d examples can be found in some of the nodule horizons - usually Eleganticeras elegantulum but also Harpoceras falciferum, Harpoceras exaratum and Dactylioceras sp amongst others. It's also noted for occasional finds of marine reptiles. Its equivalent in age to the German Posidonienscheifer in which are found the famous Ichthyosaurs with skin impressions.

Lovely finds! Our local discoveries all tend to be considerably newer; smilodons, mammoths, 12,000 year-old murder victims and the like, paleolithic screenwriters, etc.
Unfortunately I suspect the Harpo doesn't have a centre. There was a second example lying on top of it (all that black gunk you can see) which also had no centre preserved and seems to have disrupted the good one slightly - I'm hoping I'm wrong though!. Also the bone is quite soft - had an exploratory clean and the slightest touch of the air pen leaves a mark so I'm going to put it on one side and have it done professionally at some point.

Jean - have a look at the Yorkshire Coast Fossils website which has a range of handmade jewellery - it does look good. I got my mum a pendant for Christmas last year and she hasn't taken it off since.

Erich - A smilodon skull would look very nice above the fire place!. The Jurassic is about the youngest stuff I visit regularly as I'm more often found hanging around the Upper Carboniferous.

Two stunning fossils there Andy, thanks for showing us them.

Do you think, just possibly, that the ichthyosaur vertebra and ammonite are in context with each other, i.e the ammonite was actually in the stomach of the reptile? Or is this a chance association?
Hi Phil

Its probably a chance association. The Icthys in Germany which have been found with stomach contents intact were fully articulated skeletons whereas this is just a single vert. Also the ammonites visible on the outside of the nod show a body chamber preserved in pyrite and poor preservation of the phragmocone which is fairly common for ammonites found fossilised in the outer skin of these nodules (if they are preserved within the nodule they are usually intact) - if they'd been the Icthy's dinner I'd have thought they'd exhibit more feeding damage unless it had swallowed them whole. My guess is that it's due to a sea floor feature where currents caused an accumulation of detritus prior to the nodule formation. Don't know what triggers the formation of the nodule though. Sometimes it can be the decomposition of organic material but most of the Jet Rock nodules seem to be blanks so that might not be the case with them. No doubt somebody out there knows the answer.

All the best


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