Early development of rostrum saw-teeth in a fossil ray tests classical theories of the evolution of vertebrate dentitions
- Author(s)
- Moya Meredith Smith, Alex Riley, Gareth J. Fraser, Charlie J. Underwood, Monique Welten, Jürgen Kriwet, Cathrin Pfaff, Zerina Johanson
- Abstract
In classical theory, teeth of vertebrate dentitions evolved from co-option of external skin denticles into the oral cavity. This hypothesis predicts that ordered tooth arrangement and regulated replacement in the oral dentition were also derived from skin denticles. The fossil batoid ray Schizorhiza stromeri (Chondrichthyes; Cretaceous) provides a test of this theory. Schizorhiza preserves an extended cartilaginous rostrum with closely spaced, alternating saw-teeth, different from sawfish and sawsharks today. Multiple replacement teeth reveal unique newdata frommicro-CT scanning, showing howthe ‘conein-cone’ series of ordered saw-teeth sets arrange themselves developmentally, to become enclosed by the roots of pre-existing saw-teeth. At the rostrum tip, newly developing saw-teeth are present, as mineralized crown tips within a vascular, cartilaginous furrow; these reorient via two 90° rotations then relocate laterally between previously formed roots. Saw-tooth replacement slows mid-rostrum where fewer saw-teeth are regenerated. These exceptional developmental data reveal regulated order for serial self-renewal, maintaining the saw edge with ever-increasing saw-tooth size. This mimics tooth replacement in chondrichthyans, but differs in the crown reorientation and their enclosure directly between roots of predecessor saw-teeth. Schizorhiza saw-tooth development is decoupled fromthe jawteeth and their replacement, dependent on a dental lamina. This highly specialized rostral saw, derived from diversification of skin denticles, is distinct from the dentition and demonstrates the potential developmental plasticity of skin denticles.
- Organisation(s)
- Department of Palaeontology
- External organisation(s)
- University of Sheffield, University of London, Natural History Museum London, King's College London
- Journal
- Proceedings of the Royal Society of London B: Biological Sciences
- Volume
- 282
- ISSN
- 0962-8452
- DOI
- https://doi.org/10.1098/rspb.2015.1628
- Publication date
- 09-2015
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105118 Palaeontology
- Keywords
- ASJC Scopus subject areas
- Agricultural and Biological Sciences(all), Environmental Science(all), Immunology and Microbiology(all), Biochemistry, Genetics and Molecular Biology(all)
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/early-development-of-rostrum-sawteeth-in-a-fossil-ray-tests-classical-theories-of-the-evolution-of-vertebrate-dentitions(2c839895-104c-4488-9a20-818c85f1ff3a).html