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    Teeth outside the mouth? Evolution and development of the sawfish and sawshark rostral dentitions (Elasmobranchii; Chondrichthyes)

    Welton, M. and Smith, M.M. and Underwood, Charlie J. and Johanson, Z. (2015) Teeth outside the mouth? Evolution and development of the sawfish and sawshark rostral dentitions (Elasmobranchii; Chondrichthyes). Royal Society Open Science 2 , ISSN 2054-5703.

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    Origins of the vertebrate dentition, as a patterned, functional unit associated with the jaws, remain contentious. Hypotheses suggest dentitions evolved from external placoid scales, or alternatively, from denticles within the oropharyngeal cavity, with no input from external dermal structures. The latter hypothesis suggests that oral dentitions and scales derive from separate developmental systems, while the former suggests they share a common developmental system. The latter hypothesis implies that oral dentitions are restricted to the oropharygeal cavity, while the former implies heterotopic migration of dermal structures into the mouth. To test these hypotheses, we examined the elongate rostrum (‘saw’) and associated oral dentitions in three chondrichthyan groups: Pristiophoridae (Selachii), Pristidae (Batoidea) and the fossil Sclerorhynchoidea (Batoidea). The rostrum saw of adult and embryonic individuals was investigated via 3D-rendered, volume density models from x-ray computed tomography, revealing data on topographic position, series size differences, growth stages, progressive mineralization, timing and mode of replacement of the tooth-like structures, all co-located with mineralized embayments of prismatic rostral cartilage. We suggest these structures lack the patterning and replacement characteristic of oral dentitions and instead represent dermally-derived neomorphic structures on the rostrum modified from placoid scales, independent of oral teeth.


    Item Type: Article
    Keyword(s) / Subject(s): chondrichthyes, dermal denticles, rostrum denticles, evolution of teeth, regeneration
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
    Depositing User: Charles Underwood
    Date Deposited: 31 May 2016 12:55
    Last Modified: 02 Aug 2023 17:24


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