Mark Wilson June 13th, 2014
SOPOT, POLAND — This morning we had the final set of talks at Larwood 2014. Out of all the presentations, the one that struck me the most was by Paul Taylor and Andrea Waeschenbach entitled “Molecular phylogeny and the adequacy of skeletal characters in cyclostome taxonomy: The alarming case of Diaperorcia purpurascens.” Paul is shown delivering it above. This project represents the best of what these bryozoan conferences are about: the combination of biology and paleontology to further our understanding of the evolution and ecology of this large phylum. It also warned paleontologists to never be complacent about the value of morphology (shape and form) for sorting out systematic and evolutionary relationships.
Diaperoecia purpurascens is a “fixed-walled, tubuliporine” cyclostome bryozoan species common in New Zealand waters today. Molecular sequence data, though, shows it is without a doubt within the “free-walled cerioporine” cyclostome genus Heteropora. You don’t need to know why those terms actually mean to understand that the molecular work has shown that two dissimilar groups share a surprisingly close common ancestor — so close that the systematics are now fully disrupted. When we knew only the morphology of these bryozoans the differences between them were apparent at a high taxonomic level. Now that we have molecular data it is brutally clear that our reliance on shape and form to separate the groups was an illusion. Molecules trump skeletal evidence — and all paleontologists have to work with are the skeletons.
Paul and Andrea did find, though, that in the early colony growth (astogeny) of these bryozoan groups they share a common pattern of tiny pores (pseudopores) on the earliest portion of the colonial skeleton (the protoecium; see above and below). It is this morphological feature, as subtle as it is, that shows the groups share a close common ancestor.
The lesson is that paleontological systematics are always provisional. We do our best with morphology alone because that’s what we have, but we should be forever haunted by the knowledge that we lack full biological evidence.