![]() ![]() ![]() One of the most amazing images revealed by the scans shows fragments of planktonic, or floating, crustacean stuck between the teeth of one of the ammonite fossils. X-rays create virtual slices of the specimen, which are then stitched together into a three-dimensional image by computer software. The technology is much like a very detailed CT scan. So the research team turned to a new technology, synchrotron X-ray microtomography. Even if you were willing to slice up a specimen for examination, the process is likely to destroy the very structures you're trying to study, Landman said. It was one of these long-shelled groups, the baculites, that Landman and his colleagues examined.īecause baculite jaws are small and delicate, it's difficult to examine them without destroying the fossil specimen. Other species had shells shaped like unicorn horns. Some species' shells were spirals, much like that of their closest-living look-alike, the nautilus. Unlike today's squid and octopus, ammonites had external shells. Ammonite fossils are common, especially in South Dakota where Landman and his colleagues found their specimens. They roamed the seas from 407 million to 65 million years ago, when they went extinct. Like the squid and the octopus, ammonites were cephalopods, a type of mollusk, but that's about as far as the similarities go. And for that, sharp, pointed teeth are ideal.There's nothing in today's world quite like an ammonite. Since ammonites could not withdraw entirely into their shells for self-defence, it would then just be a question of dragging the creature out of its chamber in order to eat it. ![]() Even a small puncture to the shell, which a pointed tooth would be well able to deliver, would let the water in and cause that control to vanish. Ammonites' manoeuvrability would have depended crucially on their buoyancy control. But second thoughts provide a possible explanation. That a shark with teeth like this would try to make a meal of an ammonite is, at first sight, odd. In a modern predator, that would indicate the habit of eating fish. The teeth of Planohybodus, in contrast, were slender and pointed-the sort usually associated with grasping and tearing at flesh. Those modern sharks that eat shelled animals have robust teeth for crunching through hard exteriors. The tooth belongs to a species called Planohybodus. Based on comparisons with modern evacua, these are probably from sharks.īut which sharks? Dr Vullo's ammonite nails one culprit. On top of that, coprolites, as palaeontologists politely describe fossil faeces, have turned up with ammonite shells in them. And some seem to have been bitten by sharks. Some appear to have been attacked by the beaks of other cephalopods. Some ammonite fossils have tooth marks that look as though they were made by huge reptilian predators called mosasaurs. But what ate ammonites has never been shown in such an unambiguous manner. What ammonites-or, at least, some of them-ate became clear earlier this year when an X-ray showed a small crustacean in the jaws of a species called Baculites. Modern pearly nautiluses, whose relationship to ammonites is much debated, have a similar arrangement. The result had neutral buoyancy, allowing the animal to move (like squid) by jet propulsion. ![]() These shells were divided internally into gas-filled chambers. Unlike squid, though, they had protective shells. Like squid, they were swimming tentacled molluscs-a group called the cephalopods. They occupied a position in the Mesozoic oceans similar to that of modern squid. ![]()
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