Archimedes screws 350 million years before Archimedes?
Fossile d'Archimedes des collections de Paléontologie. Photo ©Martine Lambricht
Bryozoans are small aquatic animals, ranging in size from less than a millimetre to a few centimetres. As with corals, from which they are nevertheless very different, the basic individual, called a zoid, almost always lives in the company of numerous similar animals, grouped together in a colony called a zoarium, which can adopt a wide variety of shapes: rod, disk... Most of the time, the colony is attached to a rock or shell, which it covers in the same way as undergrowth mosses, hence their name: bryozoan means "moss-animal". Bryozoans, or ectoprocts, have a long evolutionary history, and have been around for almost 500 million years!
Bryozoan Membranipora © Ryab Hodnett, Wikimedia commons
In the seas that covered part of the USA during the Carboniferous period, colonies of bryozoans took on an even more distinctive form. This was the genus Archimedes, in which the bryozoan colony formed an endless screw - or Archimedes screw - which could then form a large helical sail. This arrangement enabled each zoid to optimally filter the nutrients present in the water, while taking up very little space! The veil was often broken when the colony died or fossilized. As is the case here, only the more solid central "screw" remains.
Archimedes fossil from the Paleontology collections. Photo ©Martine Lambricht
3D model of anArchimedes specimen from the Université de Liège collections
