SHARKS Sharks the beginningor the end Existence of
SHARKS
Sharks: the beginning…or the end? ? © Existence of elasmobranchs with little change is a testament to their evolutionary success and durability © Appear in fossil record in late Devonian, 500 mybp (perhaps earlier) © Last class of fishes to appear in fossil record Elasmobranch… plate or strap gill
Classification of Chondrichthyes ©Class Chondrichthyes (~850 spp. ) – Subclass Elasmobranchi (~820 spp. ) • sharks, skates and rays – Subclass Holocephali (~30 spp. ) • chimaeras, ratfishes
Distinguishing Elasmobranch Traits © cartilaginous skeleton © absence of swim bladder © heterocercal tail © placoid denticles - scales and teeth © spiracle present with 5 -7 gill slits (no operculum) © urea retained for osmoregulation © spiral valve in intestine © males have clasper organs for internal fertilization © embryonic development with physiological care © oviparous, ovoviviparous, viviparous © jaw hyostylic (single connection of upper jaw to neurocranium - adds protrusibility) or amphistylic (two connection points - anterior and posterior) © teeth in rows, are constantly replaced © eyes small
Holocephali: traits ©jaw holostylic (= autostylic = fused to neurocranium) ©spiracle absent; gills covered by single operculum ©all oviparous ©cloaca lacking - separate urogenital pore ©skin lacking scales; placoid spines ©males with head claspers ©teeth are plate-like, non-deciduous ©eyes large
Chondrichthian success story? © Buoyancy control: fatty liver, no swim bladder and no energy required © Swimming adaptations: rigid fins instead of rays © Body covering: placoid scales, reduce drag (see Helfman, fig. 12. 3) © Osmoregulation adaptations © Reproductive adaptations: self-sufficient young © Feeding adaptations © Sensory system: tapetum lucetum, ampullae of Lorenzini © Respiration effectiveness
Elasmobranch classification ©Superorder Galeomorphi • large, pelagic predators, blade-like teeth – Heterodontiformes - horn sharks – Orectolobiformes - nurse sharks, whale sharks – Lamniformes - mackerel, mako, white sharks – Carcharhiniformes - requiem sharks (blacktip, whitetip, reef, bull), tiger sharks, basking sharks
Heterodontiformes - horn sharks
Orectolobiformes - whale sharks Rhincodon typus
Orectolobiformes – nurse sharks Ginglymostoma cirratum
Lamniformes - mackerel, mako, white sharks Great White Mako Isurus oxyrinchus Mako Great White, Carcharodon carcharias
Carcharhiniformes requiem sharks (blacktip) Carcharhinus limbatus blacktip shark
Carcharhiniformes - requiem sharks (whitetip) Triaenodon obesus
Carchariniformes – bull sharks Carcharhinus leucas copyright FLMNH
Carchariniformes – tiger sharks Galeocerdo cuvier
Carchariniformes – basking sharks Cetorhinus maximus
©Superorder Squatinomorphi – Squatiniformes-angel sharks • bottom-oriented, enlarged pelvic fins, spike -like teeth Atlantic Angel Shark, Squatina dumeril
©Superorder Squalomorphi • smaller, pelagic and benthic sharks, feed on smaller prey, some with pointed teeth, some with pavement teeth – Squaliformes - dogfish sharks – Hexanchiformes - six & seven-gill sharks (cow sharks) – Pristiophoriformes - saw sharks
Spiny dogfish-Squalus acanthus ©Squaliformes dogfish sharks Adipose spine
Sevengill Shark Heptranchias perlo Hexanchiformes - six & seven-gill sharks (cow sharks)
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