Identifying Ormsaigbeg's Fossils

Ormsaigbeg's 'Jurassic Coast' boasts some magnificent Cephalopod fossils, the Cephalopods being the class that includes the modern octopus and squid.  What makes the Ormsaigbeg specimens so unusual is their size - there are several which are around 300mm in diameter, which means their full size when they were alive some 130 million years ago might have been twice that.

This is one of the ammonites. There are several good specimens, and they all look much the same, so they're probably all the same species - but identifying it is the devil's own job.

Researching the internet didn't produce much, but the Geological Survey's 'Regional Guide' to the area - my copy is dated 1961 - states that the Ormsaigbeg rocks belong to the Inferior Oolite, and the zone fossil is....

.... Ludwigia murchisoni, an ammonite that might well be the one we see. This is a better specimen from the Museo Caffi di Bergamo. Unfortunately, the 'Guide' states that another common fossil in this area is Graphoceras concavum which also looks very like the Ormsaigbeg ammonites.

The ammonites became extinct at the same time as the dinosaurs, but other the Cephalopod along this coastline is a nautilus - in this case, neatly cut in half so that we can compare it with....

....a modern example of Nautilus pompilius.

Here, the only clue to our nautilus' identity is that a similar beast is found in rocks of the same age in Skye, and this is Cenoceras cf striatum.

All of which leaves us a little, but not much further forward. If anyone has a friend who is a professor of palaeontology with a particular interest in Jurassic cephalopods, perhaps he/she might be able to help.

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