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

Squaliformes dogfish sharks Spiny dogfish-Squalus acanthus Adipose spine

Hexanchiformes - six & seven-gill sharks (cow sharks) Sevengill Shark Heptranchias perlo Hexanchiformes - six & seven-gill sharks (cow sharks)