![]() The ancient Egyptian god Amun (“Ammon” in Greek) was often depicted with a ram’s head & horns. The living chambered nautilus also has a squid-in-a-coiled-shell body plan, but ammonites are a different group.Īmmonites get their name from the coiled shell shape being reminiscent of a ram’s horn. Ammonites are an extinct group of cephalopods - they’re basically squids in coiled shells. This genus is considered by some to be a junior subjective synonym of Didymoceras.Īmmonites are common & conspicuous fossils in Mesozoic marine sedimentary rocks. fossil ammonite (CM 33061, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA) (fossil heteromorph ammonite) (Late Cretaceous)Įmperoceras sp. Journal of Molluscan Studies, 66, 283-285.Emperoceras sp. Mid Cretaceous heteromorph ammonite shell damage. Anyway, the long body chamber reinforced by ribs makes sense as a defence against this. These don't smash the shell, but peel it back bit by bit. Heteromorphs are often found with "scars" indicative of attack by benthic, peeling predators such as crabs. Secondly, the long body chamber would be an effective defence. 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. One is that it would be easier to venitlate the mantle. I favour the small body in a long body chamber for several reasons. ![]() There are QuickTime movies at this site that explain all three of these hypotheses. 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. If the animal was smaller, like a snail, then moving around in the long body chamber would cause the same thing to happen. However, Jeremy Young and myself suggested a similar result using a simpler mechanism. Almeras (eds.), 3-eme Symposium international sur le Cephalopodes actuels et fossiles. On the mode of life of heteromorph ammonites heterocone, ancyclocone, ptychocone), p. If they could do this, then heteromorphs could point the aperture either upwards or forwards. 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. 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. Quarterly Journal of the Geological Society of London, 384: 339-383. The ammonite body-chamber, with special reference to the buoyancy and mode of life of the living ammonite. This only makes sense if these animals were planktonic, there's no way they could have swam. 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. Truly world class.Īnyway, as for orientation, it depends on the mass distribution of the animal in the shell. Haven't stopped by for a while - but glad I did, what an amazing fossil. Huge Jurassic Heteromorph Ammonite From France Hamulina ( like a saxophone.Hamulina clintoni !!!) The matrix is essentially a diatamecious mud, so preparation of matrix specimens is time consuming. The smaller of the two took almost an entire year to prepare, and is displayed exactly as it was found. I will also include another photo of the one that we just sold. This is most likely the single finest specimen of this type of ammonite (not to mention the killer association!!) known to science. We recently sold the sister specimen to this.whose large specimen measured about 3/4 the size of this one. there are several differnt genus of ammonites represented here, as well as other inverts. They quite often refer to specimens such as this as "marine cemeteries", due to the mass mortality evident on the plates. The large specimen is almost 1 meter in size. Here is a very nice, VERY large heteromorph ammonite plate from France.
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