From Andrew Urevig at National Geogaphic:
Contradicting some previous accounts, the team argues that this new evidence appears to show that the common ancestor of all panarthropods did not have a complex three-part brain—and neither did the common ancestor of invertebrate panarthropods and vertebrates.
…
That structure can be traced back through the fossil record. Kerygmachela’s relatively simple brain, preserved as thin films of carbon, includes only the foremost of the three segments present in living arthropods.
The researchers are relying on the remarkably hardy tardigrade (water bear) as a surviving example. Not everyone agrees:
Tardigrade brains may or may not develop based on segments at all, says Nicholas Strausfeld, a neuroscientist at the University of Arizona who was not involved in the study.
It’s not clear that tardigrades have a brain, in the usual sense; the relevant work may be done by a nerve ring around their mouths.
Vinther finds that perspective interesting. Whatever the case, he says, both ideas point to simpler ancestral nervous systems—and thus an evolutionary history in which animals’ brains evolved complex three-part structures multiple independent times. More.
If it is true that there is “an evolutionary history in which animals’ brains evolved complex three-part structures multiple independent times,” it wasn’t natural selection acting on random mutations (Darwinism). We are looking at convergent evolution instead.
See also: Cambrian fossil shows parent caring for young
Does intelligence depend on a specific type of brain?
Genomic analysis sheds more light on amazing, indestructible tardigrade (water bear)
and
Evolution appears to converge on goals—but in Darwinian terms, is that possible?