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Dental Patterns in Myliobatid Stingrays by liwenting

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									Dental Patterns in Myliobatid
         Stingrays




         Andrew Clark
          Eco/Evo 208
       November 29, 2004
              Introduction
• Family: Myliobatidae
  – highly specialized group of batoids
    • morphology and diet
  – at least 6 genera
    • 4 durophagous genera
    • 2 planktivorous genera




                                Gonzalez-Isais & Dominguez, 2004
                 Introduction
• Family: Myliobatidae
  – Genera:
     • Myliobatis (Eagle
       rays)
     • Aetomylaeus
       (Smooth-tail eagle
       rays)
     • Aetobatus (Bonnet
       rays)
     • Rhinoptera (Cow-
       nose rays)
     • Mobula (Devil rays)
     • Manta (Manta rays)

                             Gonzalez-Isais & Dominguez, 2004
              Introduction
• Myliobatidae:
         Myliobatoids         Rhinopterids            Mobulids




                  Durophagy
                                        Planktivory
               Durophagy

• Benefits                  • Constraints
  – lower competition for     – need to produce high
    resources                   compressive loads
  – lower demand for          – risk to injury
    high-speed pursuit        – prey handling times
                                are increased
                Introduction
• Durophagous
  Myliobatids
  – flattened tooth-plates
  – fused mandibular
    symphyses
  – trabecular cartilage        Rhinoptera
    in jaws




                   Dasyatis sabina
                                             Rhinoptera

 Rhinoptera
                                                          Summers, 2000
               Introduction
   • Tooth-plates vary among genera:


                                       Aetobatus
                      Aetomylaeus




Myliobatis




                 Rhinoptera         Rhinoptera
                              Introduction
    • Durophagous Myliobatids:

              Myliobatis      Aetobatus       Aetomylaeus       Rhinoptera




Loss of hexagonal dentition



                                          Hexagonal dentition
                                     Durophagy
                 Questions
• Why does Aetobatus dental pattern differ from
  other genera of Myliobatids?
   – A more diverse diet?
   – Or a different means of tooth replacement?

• What is the significance of hexagonal dental
  patterns?
   – Crushing performance?
   – Tooth replacement?
             Hypotheses
• Dental pattern anomaly of Aetobatus
  corresponds to a more diverse diet and
  is less resistant to compressive loads

• Hexagonal patterns in Myliobatid
  dentition is the optimal design for a hard
  prey diet
      Experimental Design:
       Aetobatus dentition
• Create models of tooth-plates that
  correspond to each genus
  – equally sized models of the same material


• Apply compressive loads to models

• Record magnitude of force required to
  induce tooth breakage
           Experimental Design:
            hexagonal patterns
•   Create models of different
    dental patterns
     – equally-sized models of the
       same material
     – hexagonal patterns will be
       compared with tetragonal
       and octagonal patterns

•   Apply compressive loads to
    models

•   Record magnitude of force
    required to induce tooth
    breakage
              Possible Results
• Aetobatus experiments:
   – If Aetobatus model equally resistant to compression
       • Differences due to tooth replacement

   – If Aetobatus model less resistant to compression
       • Dental pattern corresponds to a more diverse diet

   – If Aetobatus model more resistant to compression
       • Aetobatus evolved an improved dental pattern for
         crushing hard prey
              Possible Results
• Experiments on hexagonal patterns:
   – If all models show equal response to compressive loads
       • Dental pattern is not associated with durophagy
       • Different means of tooth replacement?

   – If hexagonal models more resistant to compression
       • Hexagonal dental patterns are the optimal design for
         durophagy

   – If hexagonal models less resistant to compression
       • Dental pattern is not associated with durophagy
       • Different means of tooth replacement?
             Additional Studies
• Determine the significance of different row numbers and row
  lengths
   – Do different row numbers and row lengths relate to crushing
     performance?




• Measure bite force between genera and species of Myliobatids
   – Is there a relationship between bite force and dental
     patterns?
                 References
• Gonzalez-Isais, M. & H. Dominguez. 2004.
  Comparative anatomy of the superfamily
  Myliobatoidea (Chondrichthyes) with some comments
  on phylogeny. Journal of Morphology. 262: 517-535.

• Summers, A. 2000. Stiffening the stingray skeleton -
  an investigation of durophagy in Myliobatid stingrays
  (Chondrichthyes, Batoidea, Myliobatidae). Journal of
  Morphology. 243: 113-126.

								
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