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Unique damage-related, gap-filling tooth replacement in pycnodont fishes Project ID: 0000C1154 Public
6 Media · 6 Specimens · Creator: Collins, Sally, Underwood, Charlie · Managed by: Sally Collins, Natural History Museum, London - Division of Fossil Fish

Most jawed vertebrates (gnathostomes) replace their teeth throughout life, ‘polyphyodonty’, and there is currently great interest in its molecular and cellular basis, particularly in fish. While much has still to be elucidated, it appears that whichever tooth replacement mechanism is used, only one tooth replaces one predecessor, at any one time. Here we present fossil crushing dentitions of two extinct pycnodont fishes, Pycnodus zeaformis and Pycnodus maliensis. Their surface features and X-ray micro-CT virtual sections show no evidence of one-for-one replacement. Instead, individual large teeth were replaced by multiple small teeth, for which, as far as we could ascertain, there is no known mechanism. This occurred where underlying dentigerous bone was damaged. Small teeth also developed where parts of large teeth had broken off, and in gaps between large teeth created by the geometry of their close alignment in rows. We compared the virtual sections to those of functionally analogous crushing dentitions of three modern fishes. Contrasting greatly to the pycnodonts, each showed an orderly, one-for-one replacement, typical of osteicthyans. We propose that the pycnodont specimens exhibit a gap-filling tooth addition hitherto unseen in gnathostomes, and that the oral epithelium retained an initiatory competence throughout life, with a programming of ‘if there is a gap, fill it’. This would also have facilitated the addition of large teeth in rows, in space provided by ontogenetic growth. We hypothesise that gaps were registered as an absence of pressure at the crushing surface, initiating tooth development, as in the modern cichlid Astatoreochromis alluaudi.

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  ID Part Object Taxonomy Type Date Added Publication Status  
000519038 Part of left prearticular nhmuk:pv p:7437 Mesodon nicoleti CT Image Series 2023-04-28 Open Download  
000166477 16-bits tiff stack nhmuk:pal:PV P 60915 Pycnodus zeaformis CT Image Series 2020-11-06 Open Download  
000166520 tomograms of the complete specimen nhmuk:zoo:2017.5.22.1 Labrus bergylta CT Image Series 2020-11-09 Open Download  
000166519 tomograms of the complete specimen nhmuk:pal:PV P 75894 Pycnodus maliensis CT Image Series 2020-11-09 Open Download  
000166521 raw tomograms of Pogonias_cromis_lower_pharyngeal_jaw_BMNH 2019.11.8.1 nhmuk:zoo:2019.11.8.1 Pogonias cromis CT Image Series 2020-11-09 Open Download  
000166523 tomograms of the complete specimen nhmuk:zoo:2016.9.23.1 incertae sedis indet. CT Image Series 2020-11-09 Open Download  
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