Evolutionary paths and relationships

For example, the comparison of the sclerites of the early Cambrian creature halkieria and the later wiwaxia show a remarkable resemblance to each other. Not only that, the sclerites also show a relationship with the chaeta of annelid worms. Therefore wiwaxia can be considered as a transitional form between halkieria and annelida (Ref 1.)

The shells of halkieria also show a close resemblance to brachiopoda shells and it is hypothesised that over time the creatures shortened and folded over joining their two shells together for increased protection. Note that although they look like bivalve mollusc their shells are formed differently. Bivalves molluscs have two symmetrical shells which grow joined at a hinge whereas brachiopods have two separate, differently shaped shells which form at the ends of the embryo and come together only because of folding (Ref 2.)

The lobopods appear to have evolved from predatory priapulid worms while changing from a burrowing to a crawling lifestyle (Ref 3). These are thought to have gone on to evolve into the incredibly diverse arthropods, including arachnids, crustaceans, insects and the extinct trilobites. Reinforcing this hypothesis is the recent discovery of the fossil remains of a creature called Miraluolishania which appears to have features of both lobopods and arthropods (Ref 4.)

Although not complete nor beyond controversy, these proposed relationships allow us to sketch out a general picture of connections between the groups of creatures. Note that it's hard to separate ancestors from sister groups purely from fossils. For example, the anomalocarids may actually be a sister group to the ancestors of arthropods rather than being direct ancestors themselves.