Abstract
The origin of jawed vertebrates did not just involve the evolution of jaws but also the reshaping of the whole face and anterior part of the brain. Jawless vertebrates have a median nasohypophysial duct; jawed vertebrates have separate nasal sacs opening externally, and a palatal hypophysis. In jawless vertebrates the forebrain is much shorter than in jawed vertebrates and the hypophysis is relatively anterior. It is not easy to understand how the transition between these two contrasting architectures was accomplished, but recent research has shown that a series of fossil intermediates, including both jawless and jawed members of the jawed vertebrate stem group, bridge the gap and give a surprisingly detailed picture of the transformation. I will present a summary of this research, with focus on the anatomy and evolutionary significance of the early placoderm Romundina.
Per Ahlberg
EBC – Evolutionary Biology Centre
Uppsala University