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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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