Gnathostome dental pattern and the evolution of chondrichthyan dentitions

One of the most significant vertebrate innovations was the evolution of jaws, and on these jaws, teeth arranged into functional dentitions. These dentitions allowed vertebrates to radiate into a number of major groups, including sharks (Chondrichthyes) and bony fishes (Osteichthyes). Along with these are a variety of fossil groups whose dentitions have been difficult to understand and interpret. Because these fossil groups are closer to the origin of jaws and teeth, it is crucial that we try to better understand how their dentitions evolved.

One way to do this is to study how the dentitions of living groups developed and then apply these observations, as far as possible, to the development of dentitions in fossil taxa. The group Osteichthyes includes well-known fish such as the tuna, salmon, seahorse, coelacanth, lungfish and also tetrapods. Osteichthyan dentitions have been intensely studied in recent years, and we even understand what genes are involved in producing these dentitions. Despite this, even within this group we know nothing about tooth development of more primitive osteichthyans, such as the paddlefish and gar. As well, and perhaps somewhat surprisingly, we know very little about how genes control development of shark and ray dentitions. The goal of our project is to study development in a broad range of chondrichthyans to find common developmental characters of these dentitions that can be compared to osteichthyan dentitions and in the future, to the more primitive, problematic fossil taxa.

Shark teeth are plentiful in the fossil record and features they show are important in identifying different species. Chondrichthyans show a wide variety of dentitions, ranging from large numbers of almost microscopic teeth along the jaw (in filter-feeding sharks such as Rhincodon, the Whale shark), to the pavement-like dentition in rays, to a dentition in which teeth change along the jaw from biting to crushing (Heterodontus, the Port Jackson shark). This diversity has made it difficult to find common patterns of dentition development that could be used to compare to the problematic fossil vertebrates mentioned above. Sharks and rays also possess other 'tooth-like' structures such as the gill rakers in the filter-feeding basking shark Cetorhinus and 'teeth' along the rostrum of sawfish and sawsharks.

Our project will study specimens of a wide range of modern sharks and rays of different growth stages in order to investigate the patterns of tooth development within the jaws and changes in the number and shape of teeth during growth. A number of exceptionally well-preserved fossils will also be studied in order to place the modern forms within a wider context within the Chondrichthyes. Additionally, we will study embryos of a shark, ray and a basal bony fish and will record the genes controlling their tooth development that will allow us to compare underlying mechanisms of the formation of teeth in all vertebrates.

1) Academic Beneficiaries: see 'Academic Beneficiaries' page.
2) Citizen Scientists: Shark teeth/dentitions have a high degree of interest among amateur collectors/researchers. In the fossil fish collections at the Natural History Museum, London (NHM), shark teeth represent a large portion of donations to the collection, and general enquiries. This is due to the easy availability of relevant shark-bearing geological formations outside London. Our work will be of interest to these citizen scientists as it will provide new characters to help them identify and classify their fossil finds, and illustrate a new aspect to their fossils (ontogeny, or how teeth/dentitions develop through growth) that they may not have considered. In this way, our project will contribute to increasing public awareness and understanding of scientific issues. We will develop an outreach/learning packet that can be modified to meet the needs of these beneficiaries; our team members will use these and each plan to attend one internal (e.g., NHM Nature Live), and two external UK events per year of the grant, to better disseminate our research and increase the impact of our work (see role of 'virtual palaeontology', below). We can also reach citizen scientists via NHM websites such as 'Nature Plus' (http://www.nhm.ac.uk/natureplus/index.jspa) and KEEmu, where we can blog project progress, including strong visuals such as reconstructed CT-scans, histological images, gene expression results, etc.
3) Students (schools) and adult education: These beneficiaries will overlap with 'citizen scientists', but we will modify our outreach events to maximize our impact with these beneficiaries. After initial discussions, we could tailor our outreach packet for individual schools and curricula. For example, we would be more specimen-oriented (Recent shark jaws, histological slides, cleared and stained specimens) for a biology class. For a class interested in the technological side of our research, we could focus on CT-scanning (using images and videos on a portable laptop) and 3-D rapid prototyping (both aspects of outreach and education via 'virtual palaeontology', Rahman et al., 2012. Evo Edu Outreach DOI 10.1007/s12052-012-0458-2). By disseminating our results in this flexible, adaptive way, we will contribute to the scientific culture in the UK and Europe. Students could also access websites as above.
4) Museums, galleries and aquaria: Given the wide public interest in shark teeth/dentitions, our work will be beneficial to museums and galleries that may be able to incorporate our results into exhibitions or for use in museum talks or public engagement. For example, PI Johanson regularly contributes to NHM public engagement via 'Nature Live', 'Science Uncovered' and 'A-levels' schools programme. Project Partner Sansom has already liaised with the Sea Life Centre in Birmingham such that we will provide them a version of our outreach to use. The Sea Life Centre has a network throughout Europe providing opportunities for outreach in continental Europe as well (targeting facilities in Germany).
5) Staff working on this project: Staff will acquire important skills from either CT-scanning (NHM, KCL), including using the software needed to structurally render this data, or, analysis of gene expression patterns via in situ hybridization. These are highly mature technologies and used in a wide variety of research programs involving both fossil and extant specimens. In this way, our project will train and deliver highly skilled researchers and technicians. Additionally, the PDRA (Sheffield) will travel to the lab of Project Partner Marcus Davis (Kennesaw State University), having the opportunity to develop their skills and interact in a new lab environment. Our timeline suggests these benefits acrue within the first year with respect to the CT-scanning, and within the first two years for the molecular work.