Separate Evolutionary Origins of Teeth from Evidence in Fossil Jawed Vertebrates
Moya Meredith Smith,1*
Zerina Johanson2
Placoderms are extinct jawed fishes of the class
Placodermi and are basal among jawed vertebrates. It is generally
thought that teeth are absent in placoderms and that the phylogenetic origin of teeth occurred after the evolution of jaws. However, we now
report the presence of tooth rows in more derived placoderms, the
arthrodires. New teeth are composed of gnathostome-type dentine and
develop at specific locations. Hence, it appears that these placoderm
teeth develop and are regulated as in other jawed vertebrates. Because
tooth development occurs only in derived forms of placoderms, we
suggest that teeth evolved at least twice, through a mechanism of
convergent evolution.
1 Craniofacial Development, Dental Institute,
King's College London, Guy's Campus, London Bridge, London SE1 9RT,
UK.
2 Palaeontology, Australian Museum, 6 College
Street, Sydney, NSW 2010, Australia.
*
To whom correspondence should be addressed. E-mail:
moya.smith{at}kcl.ac.uk
