The Deep Secrets of the Nautilus
There was a time when the most fearsome ocean predators included enormous squid relatives encased in spiral shells. Around 485 to 444 million years ago (or the beginning of the Paleozoic era), these “nautiloids” were very abundant and diverse. Because some species survived the late Cretaceous extinction, nautiloids persist on Earth today, reminders of ancient ocean ecosystems, and researchers have long wondered whether these “living fossils” still use marine habitats like their ancestors.
To that end, a new study led by Peter D. Ward of the University of Washington, a Nautilus collaborator, with a team of researchers from Australia, Papua New Guinea, Samoa and Switzerland, documented evidence that modern nautiloids, notably Nautilus spp. And Allonautilus spp.have habits distinct from those of their long-extinct cousins.
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Researchers tracked the nautiloids with transmitters equipped with temperature sensors to study their daily behavior and indicate the depths where hatching, juvenile growth and sexual maturity occurred. During their lifetime, nautiloids changed the water depth by up to 200 meters. Concurrently, isotopic analysis of modern and fossil nautiloid shells provided a growth profile relative to water temperature. The results showed that the extinct nautiloid species matured in much warmer waters than today’s nautiloids.
Ocean temperatures were warmer from the Cretaceous to the Miocene, but modern nautiloids also live in deeper waters than their ancestors. “Extant species of both living genera appear to live deeper and grow in colder waters than any extinct species,” the researchers wrote. They hypothesized that modern nautiloids evolved to find food using chemoreception in the darkest ocean depths instead of vision. The shells of modern nautiloids also appear to have thickened, a potential adaptation to withstand higher water pressures at depth.
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Surprisingly, these modern nautiloids were far more abundant than any fish species, which the study authors attribute to fishing pressures at these sites. Similarly, nautiloids could benefit from reduced populations of their main predators: sharks and other bony fish. They may also adapt better than other species to environmental changes in ocean temperature and chemistry, thanks to their low metabolism.
It is therefore fair to say that today’s nautiloids are not so much “living fossils” as species that are resistant to environmental changes.
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Main image: farbkombinat / Adobe Stock
