Ch. 11-12 - Early Jawed Fishes & Chondrichthyans

True or False: No clear intermediate fossils between jawed and jawless fishes have been found.

True

What are defining features of Gnathostoma?

• JAWS 🙂 - derived from gill arches

• Paired limbs with skeletal support

• 3 semicircular canals

• Dentine-based teeth

What are defining features of the placoderms?

• Bony plated skin

• Craniovertebral joint - hinge behind the head between the braincase and cervical vertebrae that allowed jaw to open + larger gape

• Dermal bony plate “teeth” attached to jaw cartilage - no replacement dentition

Carcharhiniformes, commonly called _______ or ________ sharks, make up more than half of known shark species and are particularly diverse in tropical and subtropical nearshore habitats.

ground / requiem

Offshore, pelagic sharks include _______ species like the mako, basking, thresher, and great white.

lamniform

________ dogfish sharks are most successful in deep sea regions of the North Pacific and North Atlantic.

Squaliform

Compare and contrast skates versus stingrays.

Skates

• Deep water + high latitudes

• 1-2 dorsal fins

• Long, slender claspers depressed at distal end

Stingrays

• Tropical inshore waters

• Serrated tail spines

• No dorsal fins

• Short, stout claspers that are cylindrical or moderately depressed

The batoids are concentrated into which FOUR orders?

1. Torpediniformes - torpedo rays

2. Rhinopristiformes - sawfishes, guitarfishes, banjo rays

3. Rajiformes - skates

4. Myliobatiformes - stingrays, eagle rays

True or False: Sharks that give birth to smaller young often have larger litters and/or shorter intervals between reproduction.

True

True or False: Sharks that give birth in offshore or beachfront areas (which are frequented by larger sharks and predators) tend to have faster growth rates than those born inshore or in nurseries.

True

All elasmobranchs practice (internal/external) fertilization aided by the rolled edges of the male’s pelvic fin, known as claspers.

internal

Oviparity

egg-laying

• skates, chimaeras, and some shark species

• can take between 6-9 months to hatch

Ovoviviparity

eggs hatch within the mother → live birth

• certain species will remain in the uterus for a time and feed off of unfertilized eggs - oophagy

Viviparity

live birth

• same method used by mammals

• pups are born independent and have to fend for themselves

True or False: At least 90% of sharks exceed 30cm in length, but only around 20% exceed 2m.

True

How are certain species of sharks and sawfishes able to move between salt and freshwater?

Adjusting the osmotic concentration of their blood

Salt water = salt accumulates, water loss

Fresh water = less salt, water gain

To accommodate extra fresh water coming in due to osmotic pressure, urine production also increases.

What is the apparent function of a shark’s placoid scales or dermal denticles?

Streamlining - reduces drag in the water

How does having an oily liver rather than a gas bladder benefit sharks?

Oil provides constant buoyancy no matter the depth and pressure, so the shark can move freely without having to adjust their buoyancy control mechanisms

What are defining features of Family Rhincodontidae?

• Migratory, returns to sites annually

• Numerous small, scale-like teeth

• Feed upon plankton and nektonic prey via filtration (special sieve-like gill raker mods)

• Ovoviviparous (litter sizes over and up to 300 pups)

What are defining features of Family Ginglymostomatidae?

• Blunt head with inferior mouths and barbels in between nostrils

• Found commonly on the sea floors of continental and insular shelves

• Solitary and sluggish

• Nocturnal

• Feeds on bottom-dwelling invertebrates and fish

• Ovoviviparous

What are defining features of Family Odontaspididae?

• Littoral, found inshore past the surf zone or in shallow bays

• Only sharks known to gulp and store air in stomach to maintain buoyancy

• Feeds on bony fishes, invertebrates, rays, and other small sharks

• Ovoviviparous (uterine cannibalism)

• Poleward migration in the summer, equatorial migration in autumn and winter

What are defining features of Family Alopiidae?

• Coastal > continental, often epipelagic far offshore

• Feeds on schooling fishes, octopi, squid, and pelagic crustaceans

• Ovoviviparous (uterine cannibalism)

• Uses long caudal fin to herd and stun prey

What are defining features of Family Lamnidae?

• Primarily coastal and offshore, may also occur near oceanic islands

• Solitary or in pairs, may aggregate to feed (does not form schools)

• Feeds on bony fishes, sharks, rays, carrion, octopi, squid, sea birds, and oceanic mammals (seals, whales, and dolphins)

• Ovoviviparous (uterine cannibalism)

• True max length is unknown (possibly 6.5m+)

What are defining features of Family Sphyrnidae?

• Coastal-pelagic, semi-oceanic; often approaches inshore and enters enclosed estuaries and bays

• Solitary or in schools

• Feeds on teleost fishes, cephalopods, invertebrates, and other smaller sharks and rays

• Viviparous

What are defining features of Family Carcharhinidae?

• Coastal and brackish dwelling, capable of entering freshwater

• Will eat just about anything

• Viviparous

• Thought to have some of the highest testosterone levels found in sharks, which may be linked to their aggressive and territorial behaviors

What are defining features of Family Squalidae?

• Demersal, mainly epibenthopelagic in coastal or oceanic waters

• Prefers specific water temperatures (7-15 degrees Celsius) and will migrate to accommodate

• Opportunistic feeders

• Ovoviviparous

• Livers once used as a source of oil for lamps in the Nanaimo region