1. SHARKS

2. 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

3. Classification of Chondrichthyes
Class Chondrichthyes (~850 spp.)
Subclass Elasmobranchi (~820 spp.)
sharks, skates and rays
Subclass Holocephali (~30 spp.)
chimaeras, ratfishes

4. 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

5. 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

6. 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

7. 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

8. Heterodontiformes - horn sharks

9. Orectolobiformes - whale sharks
Rhincodon typus

10. Orectolobiformes –
nurse sharks
Ginglymostoma cirratum

11. Lamniformes - mackerel, mako, white sharks
Great White
Mako
Isurus oxyrinchus
Mako
Great White, Carcharodon carcharias

12. Carcharhiniformes - requiem sharks (blacktip)
Carcharhinus limbatus
blacktip shark

13. Carcharhiniformes - requiem sharks (whitetip)
Triaenodon obesus

14. Carchariniformes – bull sharks
Carcharhinus leucas
copyright FLMNH

15. Carchariniformes – tiger sharks
Galeocerdo cuvier

16. Carchariniformes – basking sharks
Cetorhinus maximus

17. Superorder Squatinomorphi Squatiniformes-angel sharks
bottom-oriented, enlarged pelvic fins, spike-like teeth
Atlantic Angel Shark, Squatina dumeril

18. 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

19. Squaliformes dogfish sharks Spiny dogfish-Squalus acanthus
Adipose spine

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