The Nautilus and the Ammonite

Ken Brooks (UK) This article was inspired by a poem in which an ammonite and a nautilus travel the world’s oceans for millions of years, until they are finally separated by extinction, and is based on a talk I gave on HDGS Members Day, on 18 July 2010. The nautilus and the ammonite The Nautilus and the Ammonite were launch’d in storm and strife; Each sent to float, in its tiny boat on the wide, wide sea of life. They roam’d all day, through creek and bay, and travers’d the ocean deep; And at night they sank on a coral bank, in its fairy bowers to sleep. And the monsters vast, of ages past, they beheld in their ocean caves; And saw them ride, in their power and pride, and sink in their deep sea graves. Thus hand in hand, from strand to strand, they sail’d in mirth and glee; Those fairy shells, with their crystal cells, twin creatures of the sea. But they came at last, to a sea long past, and as they reach’d its shore, The Almighty’s breath spake out in death – and the Ammonite liv’d no more. And the Nautilus now, in its shelly prow, as over the deep it strays, Still seems to seek, in bay and creek, its companion of other days. And thus do we, in life’s stormy sea, as we roam from shore to shore; While tempest-tost, we seek the lost – but find them on earth no more! GF Richardson … Read More

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Monster nautiluses of the Palaeozoic

Neale Monks (UK) The handful of nautilus species found in seas today are small, retiring animals that scavenge about at night, foraging for carrion and crustacean moults. However, nautiluses were not always so insignificant and, during the first half of the Palaeozoic Era especially, nautiluses were major predators, occupying the same niches in Ordovician and Silurian seas as sharks do today. The first nautiluses Compared to their cousins, the ammonites, the Palaeozoic nautiluses are relatively unfamiliar animals. That is a shame, because they are truly remarkable, in all likelihood being the first really big predators to evolve on Earth. But, to understand how they reached the top so quickly, we need to look back at their ancestors, the floating ‘snails’ of the Cambrian. Nautiluses are the most primitive of all the cephalopods, the group of molluscs that also includes squids, octopuses, cuttlefishes, ammonites and belemnites. Nautiluses appeared during the Late Cambrian, about 500Ma, but what their ancestors might have been remains uncertain. The traditional explanation is that the first nautiluses, such as Plectronoceras exile, were derived from monoplacophorans. These are snail-like molluscs today, limited to a few species only found in relatively deep water, but in the past they were quite diverse. Although they look a lot like a limpet, their internal anatomy is distinctive, with unusual features such as serial repetition of the gills, kidneys and reproductive organs along the body. At least some monoplacophorans had chambered shells. The Late Cambrian animal, Knightoconus antarcticus was one such species, but, … Read More

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