Arthropods
 
Arthropods are invertebrates with jointed legs. They make up about 75% of all animals on Earth and have a major role in maintaining ecosystems as pollinators, recyclers of nutrients, scavengers and food for other animals. They include many animals we come across in our gardens, such as spiders, ants, centipedes and slaters. Arthropods are divided into four major groups:
insects;
- myriapods (including centipedes and millipedes);
- arachnids (including spiders, mites and scorpions);
- crustaceans (including slaters, prawn and crabs).
Arthropods have been around for a long time. Their ancestors originated 530 million years ago in Cambrian oceans at a time only dimly understood by modern science. Arthropods exist today because they have successfully adapted to a range of changing environments.
While arthropods are everywhere, we do not know how the different groups are related. There are many conflicting ideas about how arthropods evolved and diversified. The Australian Museum has researchers studying the relationships between groups of arthropods. They are attempting to resolve the problem of arthropod phylogeny by re-examining available information using new technology and studying some recently discovered Cambrian fossils. The new technology used by the researchers includes electron microscopy and computer-aided phylogenetic analysis. The Australian Museum is in a unique position to tackle the problem of arthropod phylogeny because it has specialists in all major groups of arthropods.
Animals living today have a great deal of evolution behind them, so finding information about the deep-branches in the arthropod phylogenetic tree is difficult. To improve the chances of finding clues to these early branches, researchers study the phylogenies of each arthropod group and then choose only those animals that are most likely to provide information about their ancestors. Such animals include horseshoe crabs (or king crabs), scorpions, velvet worms, leptostracan 'shrimps' and wingless insects, such as silverfish.
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