From The Conversation:
If all jawed vertebrates, including humans, are nothing more than highly evolved placoderms, then key features of ourselves should be traceable to structures that first appeared in our fishy placoderm ancestors. This would include particular jaw and skull bones and the proportions of our face and brain.
But our new evolutionary tree challenges the idea that placoderms gave rise to all other jawed vertebrates.
Instead, we suggest they are a side branch in vertebrate evolution – diverse and successful in their day but ultimately all destined for extinction. If correct, this alternative tree would require a radical rethink of many aspects of vertebrate evolution.More.
If evolution takes place by a number of means other than Darwinian descent, as now seems the case, the whole concept of a tree of life is passé. That doesn’t mean it’ll die out; only that it will hang around and confuse people. See, for example, the non-trees of life.
See also: Cichlid speciation attributed to “plasticity” now : What’s interesting about this account is the relatively relaxed (thus more correct) attitude to speciation, an oblique sign of weakening Darwinism. Darwinism depends on the concept of speciation. When speciation just isn’t very clear, Darwinism just isn’t very clear.
What the fossils told us in their own words
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The traditional view (artwork):