Download pdf - Class Chondrichthyes - the cartilaginous fisheswwn.inhs.illinois.edu/~chrisp/Lower Vert/IB 496 lec 5.pdf · 1 A monophyletic group! Class Chondrichthyes - the cartilaginous fishes

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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


2. Prismatic calcified cartilage

• Skeleton entirely cartilaginous

• Calcification present in jaws and vertebrae (strengthens cartilage)


3. Skull (chondrocranium) lacks sutures

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4. Soft fin rays unsegmented

• Epidermal origin


5. Fins are tribasic

• Supported by three skeletal elements


6. Teeth not fused to jaws

• Replaced serially in whorls

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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

Elasmobranchii

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Order Lamniformes (mackerel sharks)

• Seven families, 16 species

• Sand tigers, Goblin sharks, Thresher sharks Basking sharks


•goblin shark


• megamouth shark

• discovered 1976!

• Known from only 9 specimens

• Feeds on pelagic krill

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• Family Alopidae (thresher sharks)• Extended caudal fin, used to corral prey• Strong swimmer, will jump out of water


• 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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• Family Carcharhinidae (requiem sharks)

Great white shark Bull shark

People Eaters!

Oceanic white tip shark


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

• Flattened bodies


• Family Rajidae - true skates

• lack caudal spine

• snout usally more pointed


• Families Myliobatidae, Dasyatidae, Potamotrygonidae

• wide range in size

• caudal spine

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• Family Torpedinidae - electric rays

• pelvic fins separate

• possess electrocytes


• Family Torpedinidae - electric rays


• Family Pristidae- sawfish

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Subclass HolocephaliRatfishes, rabbitfishes, or chimeras

Order Chimaeriformes (58 species)

Subclass HolocephaliRatfishes, rabbitfishes, or chimeras

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Subclass Holocephali

• lacking gill slits

• Upper jaw fused to cranium

• skin is naked in adults

• Males have cephalic claspers, tentaculum

Differ from sharks and rays by:

Order Chimaeriformes

Ecology, Life History

• Reproduction, oviparous (egg-laying), internal fertilization

• Benthic, deep sea (80 to 2600 m), around the world

• Nocturnal

• Feed mainly on benthic invertebrates