206 — Brain and eyes of Kerygmachela reveal protocerebral ancestry of the panarthropod head

Park et al (10.1038/s41467-018-03464-w)

Read on 14 March 2018
#neuroscience  #nervous-system  #fossil  #protocerebrum  #panarthropod  #euarthropod  #arthropod  #brain  #eye  #x-ray  #Cambrian  #Buen-formation 

I saw Rebecca Gelernter’s illustrations and was inspired to read this paper.

The past few days have been a tour of the deep sea, and today’s paper continues that pattern. And much like yesterday’s paper, which looked far back in the fossil record to watch the origins of tetrapody, today’s paper looks even further back (by a handful of millions of years) to watch the birth of the arthropod centralized nervous system.

The authors of this paper discovered fifteen Kerygmachela specimens from which they were able to identify fossilized neural tissue (an extremely rare occurrence). Like the eyes of fossilized arthropods from the Burgess Shale, the Kerygmachela eyes from the Buen Formation are highly reflective.

Arthropods’ centralized brains are stored in their heads, and I don’t think it’s necessarily clear how strange that is. So many relatives of the arthropods have highly distributed nervous systems. What was the impetus to centralize into a single brain? Euarthropodian brains are admittedly tripartite, but the pieces are colocated and interconnected, which means that they may have been derived from the Kerygmachela unipartite protocerebral structure. And while conventional wisdom has suggested that the common ancestor of vertebrates and arthropods had a tripartite brain, it seems more likely based upon these findings that the ancestral brain was unipartite instead.

These findings help to anchor our understanding of arthropodian and vertebrate evolution: The complex arthropod brain and eye structures may have arisen from simple precursor eye structures rather than from modified limbs (as was also previously hypothesized).