Fossil crustaceans

Dr Neale Monks (UK) The crustaceans are the second biggest group of arthropods after the insects and have a good fossil record, but, for one reason or another, they are not as familiar to fossil collectors as the trilobites. It may be because they’re a bit harder to identify, with many of the most diverse groups being essentially microscopic, while the bigger ones like shrimps and crabs – arely get preserved in their entirety. But even if they’re difficult to identify, crustacean fossils are interesting and often make very attractive specimens. So that’s the theme of this article really – to draw your attention to these fossils and allow you to think a bit more deeply about what they were like and how t hey w ere all related to each other. Fig. 1. While most crustaceans are marine, a large number of crayfish live in freshwater, including crayfish. Crustacean origins The earliest crustaceans are known from Cambrian sediments including the well known Burgess Shale fauna. These primitive crustaceans are essentially worm-like in shape, but they do have many of the key features of crustaceans visible even on modern types such as shrimps. Their body is segmented, but the dorsal (back) part of each segmented was hardened into a thick, protective plate. Most segments bore a pair of appendages, one pair of legs and one pair of gills. This ‘biramous’ condition has been used to contrast the crustaceans (and also the trilobites) with the ‘uniramous’ insects and spiders that normally only … Read More