[b]Huge Jurassic Heteromorph Ammonite From France[/b]

Feb 26, 2004
Here is a very nice, VERY large heteromorph ammonite plate from France. The large specimen is almost 1 meter in size. They quite often refer to specimens such as this as "marine cemeteries", due to the mass mortality evident on the plates. there are several differnt genus of ammonites represented here, as well as other inverts. We recently sold the sister specimen to this....whose large specimen measured about 3/4 the size of this one. This is most likely the single finest specimen of this type of ammonite (not to mention the killer association!!) known to science. I will also include another photo of the one that we just sold. The smaller of the two took almost an entire year to prepare, and is displayed exactly as it was found. The matrix is essentially a diatamecious mud, so preparation of matrix specimens is time consuming.

Here's the info:

Genre : Emericeras emerci ( big one)
hamulina ( like a saxophone...Hamulina clintoni !!!)
Acrioceras ( little like the big)
lilltle no unrouled Costidiscus
espèce :
Age : Barrémian
localité : Alpes de Hautes Provence
Fantastic specimens Michael. Thankyou for posting them.

I wondered if there have been any studies completed on the angle of orientation on heteromorph ammonites such as the Emericeras you have shown us here. Do you have any information on how such an animal would have been suspended in the water?

I would imagine that the smaller ammonite, Hamulina, would have had several changes in orientation as it grew as the shell curved and looped back on itself.

Very strange indeed!
Huge Jurassic Heteromorph Ammonite From France


Haven't stopped by for a while -- but glad I did, what an amazing fossil. Truly world class.

Anyway, as for orientation, it depends on the mass distribution of the animal in the shell. Traditionally, the assumption has been that the animal more or less filled the living chamber (as with Nautilus today) with the result that the shell of these heteromorphs tends to point upwards rather than forwards. This only makes sense if these animals were planktonic, there's no way they could have swam.

Trueman A. E. 1941. The ammonite body-chamber, with special reference to the buoyancy and mode of life of the living ammonite. Quarterly Journal of the Geological Society of London, 384: 339-383.

Two scientists from the former USSR suggested an alternative, that these animals could manipulate the balance of gas and water in the shell, and thus change their orientation. They draw on the example of the modern cuttlefish, which although it doesn't change orientation, can change its overall density in this sort of way. If they could do this, then heteromorphs could point the aperture either upwards or forwards.

Kakabadze M. V, and Sharikadze M. Z. 1993. On the mode of life of heteromorph ammonites heterocone, ancyclocone, ptychocone), p. 209-215. In S. Elmi, C. Mangold and Y. Almeras (eds.), 3-eme Symposium international sur le Cephalopodes actuels et fossiles. Geobios Memoire Special 15.

However, Jeremy Young and myself suggested a similar result using a simpler mechanism. If the animal was smaller, like a snail, then moving around in the long body chamber would cause the same thing to happen. If the animal was at the front, the aperture would point forwards and down, if the animal pulled back, then the aperture would tip upwards.


There are QuickTime movies at this site that explain all three of these hypotheses.

I favour the small body in a long body chamber for several reasons. One is that it would be easier to venitlate the mantle. If the body was long and narrow, then the head (or whatever) would have to pump in and out much more deeply to clear fresh water over the gills. Secondly, the long body chamber would be an effective defence. Heteromorphs are often found with "scars" indicative of attack by benthic, peeling predators such as crabs. These don't smash the shell, but peel it back bit by bit. It's very distinctive. Anyway, the long body chamber reinforced by ribs makes sense as a defence against this.

Monks N. 2000. Mid Cretaceous heteromorph ammonite shell damage. Journal of Molluscan Studies, 66, 283-285.



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