• Eating animals, large and small
• Some eat blue whales (80 feet long, largest living animal)
• Some eat plankton, measured in 1/10’s of an inch
• Sharks don’t eat vegetables

• Find prey
• Catch prey
• Eat prey

• Lateral lines of neuromast cells sense vibrations
• Olfactory pits on underside of snout
• Ampullae of Lorenzini sense others’ electric fields
• Brain of smell - 1/3 to 2/3 of brain dedicated to smell
• Eyes - large in deepwater sharks
• Eyes - mirror-like reflective membranes enhance light gathering

• Streamlined bodies
• Boat-hull-like scales
• Shark teeth are specialized scaled
• Scales and teeth may be remnant of ancestors’ exoskeleton
• Powerful and/or precise swimmers (bodies and tails specialized for environment)
• Disguises/camouflage (coloration, shape, habit)
• Teeth - especially the spike-like ones
• Also sawfish teeth

• Spike teeth better for catching
• Triangular teeth better for cutting
• Serrated
• Thick-based if for chopping, too
• Flat teeth for grinding, crushing
• Plankton eaters have modified gills
• Conveyor-belt teeth
• 5 to 15 rows of teeth
• May lose 1000 teeth in a year

• Disguises/camouflage
• Dermal spines/placoid scales--armor
• Spines on fins (e.g. horn shark)
• Live birth or tough egg cases

The characteristics of each species of shark tell us where and how that shark lives.

There are about 900 species of sharks, rays, skates and a few intermediate groups vs. 40,000 bony fish (teleosts). Only a few fish eat sharks, but sharks eat almost all kinds of bony fish.

• Scales (rounded, bone-like vs. teeth)
• Gills (one, covered by bony operculum vs 5-7, no cover)
• Air bladder (yes vs. no)
• Skulls (sutured bone vs cartilage)
• Teeth (in sockets in bony jaws vs. loosely attached to cartilaginous jaws)
• Mouth (at end of body vs. under head)
• Tail (symmetrical vs asymmetrical)
• Vertebrae (stop at tail vs. present in upper lobe of tail)
• Fins (moveable, rigid w/ rays/spines vs. flipper-like, flexible, but relatively immobile)
• Skeleton (bony vs. cartilage, some w/ calcium in places)

Sharks have been finding, catching and eating, and doing it well, for a long time.

The oldest shark fossils are 390MY old, from the Devonian period. Obviously shark-like, and sharp-toothed.

• Like modern heterodontus (port jackson shark and horn shark)
• Features tell us where and how it lived/lives
• Two kinds of teeth - sharp middle teeth for fish. Flat side teeth for mollusks and crustaceans
• Flat-bottom, less streamlined body with non-specialized tail
• Irregular brownish coloration for camouflage

• Bottom-dwelling fish-eaters mud sharks
• Teeth have narrow cusps
• Body shape, tail for maneuverability

The settings already mentioned - ocean bottom, eating mollusks, crustaceans, and small fish - not too exciting

• Vast spaces
• No concealment for predators (or prey)
• Speed vs. maneuverability

Is there a shark built for this job?

• Open ocean
• spear-like teeth
• Powerful body w/ stiff skeleton (by shark standards)
• Symmetric tail
• Tail and body resemble tuna’s
• Darker above and lighter below
• Warm blooded
• Older/larger makos have more triangular anterior teeth
• Ancient makos nearer shore; broader (more triangular) teeth for eating marine mammals; ancient makos were up to 20’ long

• Open Ocean and near-shore
• Darker above and lighter below
• Mako-like, but with broader, serrated teeth (different prey)
• As big as the ancient makos (perhaps a little larger)

• Huge!
• Triangular teeth
• Axe-like, for mega-prey (e.g. whales)
• Over-specialized? (Mother Nature pushing the envelope)

Let’s calm down and consider some sharks that are a bit more sedate but, in their own ways, just as effective

• Basking Shark
• Whale Shark (50’ long largest living fish)
• Megamouth Shark
• Open Ocean, but slow (like plankton)
• Modified gills with gill rakers
• Big mouths
• Tiny teeth
• Dermal spines many, sharp (defensive)

• Coastal areas and fishing banks
• Swarming feeding style - flexible body, tail for maneuverability
• Were a major problem for fishermen, they’re so numerous and efficient (when they’re around you don’t catch anything else), until they were discovered to be great as fish and chips
• Spines in front of dorsal fins - arch their backs and sting accurately!

• Another bottom-feeder (shape)
• Teeth are compound and pointy (remember 6-gill?)
• Skin covered with defensive brambles

• Slimmer (less muscular) than open ocean shark, with maneuverability tail (like a scaled-up dogfish)
• Mostly shallow ocean and reef
• Teeth compound - broadly triangular, but with long, spikey points, and thick at base--these sharks eat anything! They’ll chase fish around reefs or prey on seals and other marine mammals.

• King of maneuverability
• Herds fish near-shore
• Smacks fish and even sea birds or surfers with huge upper lobe of tail
• Smallish sharp teeth and weak-ish jaws

• Reasonably trim - nearshore, shallow water, bays and estuaries
• Novel approach to the catch phase - Sneak up to a school of fish Shake that wild thang!
• Sawteeth are dermal spines (fossil varieties loosely attached, but modern ones are set firmly into the cartilage)

• Bottom-feeder (shape, coloration) in kelp forest
• Fish-eater (pointy teeth, but small, indicating it’s not aggressively pursuing larger prey)

• And, shallow water or deep
• Tight nearshore spaces or open ocean
• Surface, middle or bottom

If you’re an animal in the ocean there’s a shark that can find you can catch you and can eat you, whether you are - mammal, bird, fish, crustacean, shellfish or plankton. Sharks are designed and built for the job, with the:

• Senses to find you
• The body to get to you
• And the means to catch and eat you!

The Life and Times of Long Dead Sharks
This website provides a broad overview of the Western North Atantic's selachian fauna from the Cretaceous to Present. This site has a Web Page about Sharktooth Hill.
http://www.elasmo.com/

Sharks Live
Live Cams, species guide and more.
http://www.oregonlive.com/sharks/

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