1 A monophyletic group! Class Chondrichthyes - the cartilaginous fishes Class Chondrichthyes • Two major monophyletic lineages • Subclass Holocephali • Subclass Elasmobranchii Class Chondrichthyes • Most are marine • Fossil Record • Scales and denticles, Ordovician 455 mya • Teeth, Devonian 418 mya • Skeleton, Devonian 394 mya
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A monophyleticgroup!
Class Chondrichthyes - the cartilaginous fishes
Class Chondrichthyes
• Two major monophyletic lineages
• Subclass Holocephali
• Subclass Elasmobranchii
Class Chondrichthyes
• Most are marine
• Fossil Record
• Scales and denticles, Ordovician 455 mya
• Teeth, Devonian 418 mya
• Skeleton, Devonian 394 mya
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Devonian “Age of Fishes”
Elasmobranchii
• Sharks, skates, and rays (820 species)
• Seven synapomorphies define Elasmobranchs
Elasmobranch synapomorphies
1. Pelvic claspers • Derived from the margin of the pelvic fin
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Shark Reproduction
1) Ovipary - egg laying
2) Yolk-sac viviparity - live born young attached yolk sacs
3) Placental viviparity - embryos nourished through umbilical cord
4) Uterine viviparity - nutrients in uterine milk absorbed through mouth and skin
Elasmobranch synapomorphies
2. Prismatic calcified cartilage
• Skeleton entirely cartilaginous
• Calcification present in jaws and vertebrae (strengthens cartilage)
Elasmobranch synapomorphies
3. Skull (chondrocranium) lacks sutures
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Elasmobranch synapomorphies
4. Soft fin rays unsegmented
• Epidermal origin
Elasmobranch synapomorphies
5. Fins are tribasic
• Supported by three skeletal elements
Elasmobranch synapomorphies
6. Teeth not fused to jaws
• Replaced serially in whorls
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Elasmobranch synapomorphies
Elasmobranch synapomorphies
7. Placoid scales
Elasmobranchii
• Sharks, skates, and rays (820 species)
• Nine orders
• Typically predators, rely on smell
• Most inhabit near shore waters
• Only 28 of 820 species freshwater
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Elasmobranchii
• Most truly freshwater species are stingrays that occur in larger tropical rivers.
Elasmobranchii
Several species of sharks in family Carcharhinidaewill enter freshwaters periodically
• Family Alopidae (thresher sharks)• Extended caudal fin, used to corral prey• Strong swimmer, will jump out of water
Order Lamniformes (mackerel sharks)
• Family Cetorhinidae (basking shark)
• Pasive filter feeder on zooplankton, reach large size (20-25 feet)
• Gill rakers serve as filter, shed in winter
Order Heterodontiformes (horn sharks)
• One family, 8 species
• Dorsal spines present
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Order Hexanchiformes
• Two families, 5 species - frill sharks and cow sharks• thought to be relict species, teeth and body plan similar to Devonian sharks
Order Pristiophoriformes (saw sharks)
• One family, 5 species
• pointed snout used to thrash and incapacitate small fishes
Order Orectolobiformes (carpet sharks)
• Seven families, 31 species
• Carpet sharks, nurse sharks, whale sharks
• Nocturnal hunters, rest during day in groups
• Flattened bodies
• Most are bottom dwellers, sensory barbels above mouth
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Order Orectolobiformes
• Family Rhinocodontidae (whale shark)• one species• Largest living fish, 20 m (59 ft), 40 tons!• Thought to live 100-150 years• Active filter feeding on zooplankton, small inverts., and small fishes
Order Squaliformes - dogfish sharks2nd most diverse Order - 4 families, 74 species
Order Squatiniformes - angle sharks - 1 family, 12 species
Order Carcharhiniformes (ground sharks)
• Family Carcharhinidae (requiem sharks) Largest Order - 8 families, 210 species
Tiger shark Hammerhead shark
People Eaters!
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Order Carcharhiniformes (ground sharks)
• Family Carcharhinidae (requiem sharks)
Great white shark Bull shark
People Eaters!
Oceanic white tip shark
Order Carcharhiniformes (ground sharks)
Why are sharks the ultimate predators?
• Well developed sense of smell
• Well developed sense of hearing
• Excellent eye sight
• Well developed lateral line
• Ampullae of Lorenzini
• Nicitating eye lids
Shark attacks on humans
• 35 to 55 unprovoked attacks each year
• 6 to 11 fatalities per year
• 54% of attacks on surfers/windsurfers 38% on swimmers/waders 6% on divers/snorkelers
Regions with most shark attacks:
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Order Rajiformes (skates, rays, guitarfishes)
•13 families, 465 species
• Differ from sharks in having gill slits in ventral position and pectoral fins continuous with head