Speaker
Prof.
Philip Donoghue
(University of Bristol, UK)
Description
Most living vertebrates are jawed vertebrates (gnathostomes), and the living jawless vertebrates (cyclostomes) provide scarce information about the profound reorganization of the vertebrate head during the evolutionary origin of jaws. The extinct bony jawless vertebrates (ostracoderms) are regarded as precursors of jawed vertebrates, providing insight into this formative episode in vertebrate evolution. Using synchrotron radiation X-ray tomography, we describe the cranial anatomy of galeaspids, a 435–370 Ma ‘ostracoderm’ group from China and Vietnam. The paired nasal sacs of galeaspids are located anterolaterally in the braincase, and the hypophyseal duct opens anteriorly towards the oral cavity. These structures were thus already independent of each other, like in gnathostomes and unlike in cyclostomes and osteostracans and, therefore, have the condition that current developmental models regard as prerequisites for the development of jaws. Thus, reorganization of vertebrate head was not driven deterministically by the evolutionary origin of jaws but occurred stepwise, ultimately allowing the rostral growth of ectomesenchyme that now characterizes gnathostome head development.
Please specify the session
plenary
Please specify poster or talk
talk
Primary author
Prof.
Philip Donoghue
(University of Bristol, UK)
Co-authors
Prof.
Marco Stampanoni
(PSI)
Dr
Min Zhu
(IVPP)
Prof.
Philippe Janvier
(MNHN, Paris)
Mr
Zhi-kun Gai
(University of Bristol)
