Uncoupling morphological and molecular evolution: deep deuterostome origins of the vertebrate head developmental program

Ariel Pani^1,2,  Sebastien Darras⁴ , Stephen Green¹ , Marcin Wlizla¹ , Marc Kirschner⁵ , John Gerhart³ , Christopher J. Lowe^1,2

¹ University of Chicago, Chicago, IL USA , ² Stanford University, Hopkins Marine Station, Pacific Grove, CA USA , ³ MCB, University of California, Berkeley, CA, USA , ⁴ Luminy, CNRS, Marseilles, France, ⁵ System Biology, Harvard Medical School, Boston, MA, USA

Much of what we understand about the evolution of the vertebrate head has been derived from classical morphological studies on the diversity of living chordates, both complex and simple, and their early fossil record. The closest phyla to chordates have generally thought to have morphological structures that are too divergent to be informative as a comparative outgroup to reconstruct the early evolution of chordates, and the innovations that lead to the emergence of the vertebrate head. Recent research in vertebrate molecular genetics has identified much of the developmental program responsible for setting up the vertebrate head. Our work suggests that hemichordates, which are closely related to chordates, but with their own unique morphologies, possess much of the early genetic program that was thought to have evolved in association with the complex structural innovations of the vertebrate head. We explore the implications of this work for our understanding of morphological evolution and why sampling animal diversity is key to understanding the early evolutionary origins of animal form and function.