To be able to see Ammonites the size of an adult human being, one has to go back in time about 80 million years across the Earth’s oceans, and today, their fossils are found all over the world, but the largest of all was recovered in Germany in 1895and it was an absolute success.
Belonging to the family of Parapuzosia seppenradensis –thought to be the largest species of ammonite–, the fossil discovered in 1895 it stretched 1.8 meters (6 feet), but was incomplete as is often the case with large fossils (the Patagotitan at the Natural History Museum in London is actually based on the remains of six individuals).
In life, the largest ammonites would have a diameter between 2.5 and 3.5 meters (8 to 11 feet), which brought them roughly the size of the world’s heaviest bony fish: the bizarre giant sunfish.
Ocean sunfish are especially interesting because they start life as a tiny speck of popcorn and then grow randomly into one of the behemoths of the sea. As the episode recently demonstrated Oceans Of prehistoric planetthe ammonites were somewhat similar: adorable baby ammonites struggle by the thousands to complete a treacherous journey through rock pools in the episode, and it’s likely early life would have been no different for the monstrous P. seppenradensis.
What we know, to date, about the various species of ammonites
Species of ammonites ranged tremendously in size from mini to mega, but most of the larger species evolved from the Late Jurassic onwards. Perhaps one of the most bizarre known to science was Diplomoceras maximum, which lived about 68 million years ago. Remarkable for having a life expectancy of around 200 years, it is also very memorable for its bizarre paperclip-like shape.
D. maximum was also a giant that stretched up to 1.5 meters (5 ft), but P. seppenradensis was unlikely to have a distinctively long, slender design. As such, the largest ammonite fossil ever found dwarfs the most complete remains we have for D. maximum because P. seppenradensis was a girthy unit for an ammonite.
The nautilus that lives in our oceans today probably most closely resembles the extinct ammonites, but curiously it is not their closest relative. Ammonites are actually more closely related to the Coleoidea subclass, which includes octopuses, squids, and cuttlefish.
Since the largest ammonite fossil was found more than a century ago, we haven’t discovered many large ammonites that could compete in size. Research into why one might decide to review the findings to see what they might establish about the distribution of these oceanic giants.
What they found is that if you hope to hunt down some of the largest ammonite fossils on Earth, it turns out you can have luck on both sides of the Atlantic. Both England and Mexico were found to have unusually high concentrations of adult shells, which look very different from ammonites when young, which may indicate that these were mating or hatching sites.
Like living squid and cuttlefish, ammonites may have migrated to these places to complete their life cycle before dying soon after, leaving their corpse tractor wheels strewn across the seabed.
Marine predators could explain why some species got so big, like when you’re a slow-moving ammonite you have little defense against giant mosasaurs. It’s possible that the large size made it more difficult for these predatory reptiles to fit ammonites into their mouths, meaning the larger ammonites were more likely to survive long enough to pass on their genes.
Even the largest ammonites, however, had a limit, as they peaked and began to shrink even at a time when the mosasaurs continued to get bigger. They eventually faded out of existence as part of the mass extinction event that occurred after an asteroid collided with Earth at the end of the Cretaceous, but there are plenty of opportunities to learn about these amazing animals as we uncover easter eggs academics who are their fossils.
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