Dental Patterns in Myliobatid Stingrays

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Dental Patterns in Myliobatid Stingrays

• Andrew Clark
• Eco/Evo 208
• November 29, 2004

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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
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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
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Introduction

• Myliobatidae

Myliobatoids
Rhinopterids
Mobulids
Durophagy
Planktivory
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Durophagy

• Benefits
• lower competition for resources
• lower demand for high-speed pursuit

• Constraints
• need to produce high compressive loads
• risk to injury
• prey handling times are increased

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Introduction

• Durophagous Myliobatids
• flattened tooth-plates
• fused mandibular symphyses
• trabecular cartilage in jaws

Rhinoptera
Dasyatis sabina
Rhinoptera
Rhinoptera
Summers, 2000
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Introduction

• Tooth-plates vary among genera

Aetobatus
Aetomylaeus
Myliobatis
Rhinoptera
Rhinoptera
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Introduction

• Durophagous Myliobatids

Rhinoptera
Aetomylaeus
Aetobatus
Myliobatis
Loss of hexagonal dentition
Hexagonal dentition
Durophagy
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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?

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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

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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

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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

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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

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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?

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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?

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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.