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Is it extinct? Is it alive? What is the difference between the ammonite and the nautilus? Did Kate get the two confused her whole life until a few months ago and thought they were both extinct? Maybe.\n\nA fossilized ammonite shell:\n\n\n\nAnother fossilized ammonite shell of a different shape:\n\n\n\nA third fossilized ammonite shell of a yet different shape:\n\n\n\nA gigantic fossilized ammonite shell:\n\n\n\nA fossilized ammonite shell of gem quality, called an ammolite:\n\n\n\nThis is what an ammonite might have looked like when it was alive. I drew this myself IN MS PAINT because I couldn't find anything online I liked. There's 15 minutes of my life I won't get back:\n\n\n\nThis is an alive and not extinct nautilus:\n\n\n\nAnother alive and not extinct nautilus:\n\n\n\nThe slimy or crusty nautilus. Look, I don't make these names up:\n\n\n\nA nautilus tucked up in its shell and peeking out to see if that diver is going to eat it:\n\n\n\nYou can contribute to helping conserve the nautilus:\n\nSave the Nautilus\n\nShow transcript:\n\nWelcome to Strange Animals Podcast. I\u2019m your host, Kate Shaw.\n\nThis week let\u2019s learn about two groups of mollusks, ammonoids and nautiloids. One group is extinct, one is still around\u2026but they both look a lot alike, and they\u2019re way more interesting than the word mollusk makes them sound!\n\nWe\u2019ll start with ammonoids, specifically ammonites. Ammonites first appear in the fossil record around 409 million years ago, but they died out at the same time as the dinosaurs, around 66 million years ago. Many ammonite fossils look like snail shells, but the shell contains sections inside called chambers. The largest chamber, at the end of the shell, was for the ammonite\u2019s body, except for a thin tube that extended through the smaller inner chambers, which allowed the animal to pump water or air into and out of the chambers in order to make itself more or less buoyant in the water. Some ammonites lived at the bottom of the ocean in shallow water, but many swam or floated throughout the ocean.\n\nComparing ammonites to snail shells may not give you the right idea about ammonites, though. Even big snails are pretty small. While many ammonites were no larger than modern snails, many others were bigger than your hand, sometimes twice the size of your hand even if you have really big hands. But during the Jurassic and part of the Cretaceous, some ammonites got even bigger. One species grew almost two feet across, or 53 cm, another grew some 4 \xbd feet across, or 137 cm, and one species grew as much as 6 \xbd feet across, or 2 meters. It was found in Germany in 1895 and dates to about 78 million years ago. And it wasn\u2019t actually a complete fossil. Researchers estimate that in life it would have been something like eight and a half feet across, or 2.55 meters.\n\nWe have a lot of ammonite fossils, and many of them are beautifully preserved. Some still show a mother-of-pearl layer, a lustrous, iridescent layer of shell that modern molluscs still form. Some ammonite fossils are so lustrous that they\u2019re considered gems, called ammolites. Ammolites are usually polished and made into jewelry. In the olden days people thought ammonites were petrified snakes, and would sometimes even carve the end of the ammonite shell into a snake\u2019s head.\n\nMany fossil ammonites aren\u2019t fossils of the actual shell. When an ammonite died, its empty shell would fill with sediment. Frequently the shell itself wasn\u2019t preserved, but the sediment inside was. That gives us elaborate casts of the insides of ammonite shells, in such good condition that researchers can determine the internal anatomy of the shell. We know mosasaurs frequently ate ammonites because we have fossils with tooth marks that match mosasaur teeth.\n\nThere are so many ammonite fossils that paleontologists can date layers of rock by examining which species of ammonite appear in it, called index fossils. Different species frequently had much different shells, some smooth,