Amniote Dental Histology, Development, and Variation: Perspectives From the Fossil Record

Fossil teeth provide a wealth of taxonomic and dietary information for palaeontologists, but the evolution and development of the suite of tissues that attach teeth to the jaws in amniotes remain virtually undocumented. This contrasts strongly with the plethora of studies that have documented the development of the tooth attachment tissues (the periodontium) in modern mammals and crocodilians. The literary consensus is that mammals and crocodilians possess the most complex forms of tooth attachment, because each tooth is housed within a well-defined tooth socket and is suspended by a soft ligament. By comparison, nearly all other amniotes supposedly possess teeth that are fused to the jaws by a single bone tissue. To date, however, the homologues of the dental attachment tissues across Amniota remain unresolved. This thesis represents the first large-scale, comparative study of amniote tooth histology and development. By comparing histological sections of a large sample of modern and extinct amniotes, I establish tooth tissue homology across several major amniote groups and show that even the earliest amniotes possessed the same attachment tissues as those in mammals and crocodilians, but over millions of years, evolutionary changes in the timing of tooth tissue development have produced novel ways in which teeth can be attached to the jaws. Moreover, I show that studying dental batteries and the teeth of key fossil taxa can provide new insights into our understanding of the evolution and development of teeth.Ph.D