Sharkcetera Trivia Quiz

Answer: Between 360-450 million years

Shark skeletons are made of cartilage not bone so their fossil record is poor but not unknown. Early shark fossil records are based mostly on teeth and scales. However, whilst some of these fossil remnants are 480 million years old, the oldest complete shark fossil is only about 360 million years old. This means that the first sharks appeared around 200 million years before the first dinosaurs.

Due to the lack of fossil records, conventional scientific thinking documented that shark anatomy was believed to be a primitive condition in vertebrate evolution compared to all other fishes and land animals, which both had ossified (hardened with minerals) bony skeletons.

Answer: True

In 2015, in a peer-reviewed scientific journal, the paleontology world was shocked when a paper by Long and Burrow et al. revealed that an extinct shark, Gogoselachus lynbeazleyae, fossil found in Western Australia showed that the shark's skeleton contained both bone and cartilage. Further studies have shown that sharks probably evolved from ancestors with far more bone in the skeleton than present-day sharks.

Modern sharks have evolved with lighter cartilaginous skeletons to become swifter swimmers, escape predators and quickly catch their prey. This means that the cartilaginous skeleton is not a primitive precursor of the bony skeleton but quite the reverse - it is a positive evolutionary process.

Cartilage is flexible, durable and yet has half the density of bone. This facilitates speed through the water. The cartilage flexibility allows sharks to bend much more easily than bony fish. This elasticity is important giving them more speed as their tails can move faster to propel them through the water. Coupled with a body tapered at both ends (fusiform shape), skeletal flexibility and lightness some sharks have evolved into very fast swimmers, an essential trait in an animal that needs to swim faster than its prey.

Answer: Rough: contains denticles (tooth-like) projections to increase speed

Sharks and rays have specialised placoid scales, which are called dermal denticles (dermal - skin, denticle - tooth). Denticles have the same structure as a tooth, which has three layers: an outer layer of enamel, dentine, and a pulp cavity. The rough denticles are arranged in a regular pattern to increase hydrodynamics. These denticles have projections that point backward, which also increases hydrodynamics. Unlike other types of scales, denticles do not get larger as the fish grows. Instead, the fish increases its scale production.

Answer: False

Shark teeth are comprised of enamel (calcium, phosphorus/protein complexes). Tooth shape is determined by the shark's diet.

Some species, like the great white shark, are born with many rows of sharp, pointed and serrated teeth in the lower jaw and strong, triangular-shaped teeth in the upper jaw. This enables the great white to cut large prey into smaller pieces to facilitate swallowing. These teeth are replaced every two weeks (approximately) and up to 40,000 can be lost over a shark's lifetime.

Close relatives of the great white are the bull shark and blue shark. Both have needle teeth that are long, sharp and pointed and are suited for grabbing and then holding tightly onto prey. This type of tooth is very useful for prey that have narrow bodies, such as smallish fish. Bull sharks typically feed in murky water with low visibility making it important for them to be able to hang onto their prey as soon as they seize it.

Nurse sharks, angel sharks, and other bottom-feeder sharks have densely-packed flattened teeth to enable them to feed on crabs, crustaceans, snails and other hard-shelled animals found on the sea bed.

Three species of sharks (basking, megamouth, and whale sharks) don't use their teeth at all (which are flat, only 5-6 millimetres (1/4 inch)long} because they are filter feeders eating tiny organisms like plankton. These sharks eat by swimming towards their prey with open mouths They then filter the water through their gills retaining the food inside their mouths. Their prey is then swallowed, not chewed, with no need for their teeth at all.

Answer: Gills

All sharks have gills. In its simplest form, water containing oxygen passes through the gills where oxygen is extracted and passed into the bloodstream. Most sharks have five gill slits on either side of the head. Cow sharks, a primitive shark species that lives at great depths, have six or seven gill slits.

Atmospheric air contains around 21% oxygen. In water, oxygen content is obtained via photosynthesis outside the water environment. Surface water, up to 100m / 300 feet, contains around 1% oxygen, much less at greater depths. Humans only need about a quarter of the 21% oxygen available from the atmosphere. Sharks need 8/10 of the 1% available to them. Mako and great white sharks require speed, so they stick close to the surface where the oxygen concentration is greatest. Constant forward movement of the shark causes water to flow through the gill slits all the time. This is called ram ventilation. Some sharks, like the whale shark, shortfin mako and great white, will die if they become motionless as they have no backup system to ram ventilation. Other sharks, such as nurse sharks, wobbegongs, catsharks and sand tigers, can stay in one place and still breathe. As they are slower sharks, they need to be able to catch prey at slow speeds so they will hide or camouflage themselves, waiting motionless for unsuspecting prey to move past them. In these situations, they suck water into the mouth which is then washed over the gills and carbon dioxide passes out.

In some species, spiracles (openings behind the eyes) provide oxygenated blood directly to the eye and brain through a separate blood vessel, which is absent or very much smaller in fast-moving sharks.

Answer: 2

The shark, like most fish, has a two-chamber heart. The ventricle pumps unoxygenated blood through the gills, where it picks up oxygen, which then is circulated, dissolved in the blood, to organs and tissues, returning to the heart via the atrium. In the next beat, the atrium fills the ventricle and the process repeats itself. The great white shark has a resting heart rate of about 30 beats per minute, which is less than half that of a normal resting human heart.

The two-chambered heart is not that efficient. A bottleneck in circulation occurs when the blood reaches the gills. To maximise oxygen absorption, there are many tiny capillaries needed which slows circulation. The average blood pressure for a sand shark is 33/23 (human 120/80). Because of low blood pressure sharks, needs to constantly swim, relying on muscle movement to circulate blood effectively.

Answer: Yes, they can warm blood to higher than water temperature

White sharks are endotherms, which means they can regulate their body temperature up to 25 degrees F/14 degrees C above water temperature.

Sharks have two types of muscles: White (which predominates) and a smaller amount of red muscle. White muscle is used for fast, sudden bursts of speed, while red muscle is slow-muscle action for 'routine' movement. These red muscles have a network of veins covering them, Because these types of sharks need to swim to be able to breathe, they always move the red muscles alternately. These contractions cause the tail to flick sideways, causing the shark to swim. Red muscles give off heat, which passes into the veins (because of the continuous movement) and the warmer blood flows to the rest of the body. This increased body heat means these sharks can swim at higher speeds.

Answer: No

For a fish to be buoyant, or float, it must displace an equal or greater amount of water than its own body mass. The trick is the swim bladder, which is basically like an air-inflated balloon that can expand and contract depending on how much gas is inside. When the swim bladder expands it will increase in volume and therefore displace more water. This increases the fish's buoyancy and it will float upward. When the swim bladder deflates, the fish's buoyancy decreases and the fish will sink as it displaces less water.

Sharks have no such organ. Instead, they have huge livers that may take up to 90% of the space inside the body cavity and 25% of its weight. The liver is bi-lobed and is oily. It is used for energy storage, buoyancy and, unlike mammalian livers, has a role in waste removal. The shark's liver has a huge quantity of low-density lipids along with squalene, a cholesterol type of fat that is very low in density, much less than water. Because of this difference, buoyancy is maintained. Consider these statistics from post-mortem shark studies:

*A basking shark liver weighing 940 kg (2,072 lb.) contained 2,270 litres (545 gallons) of oil
* A great white shark weighing 3,310 kg (7,300 lb.) had a liver 455 kg (1,002 lb.) in weight

Answer: Electroreception

Sharks have good vision and a good ability to see in dim light. Shark eyes have a large proportion of rods, which makes them highly sensitive to changes in light intensity, facilitating sensitivity to contrasts of light and shadow. Shark eyes have cone cells, indicating that sharks have some degree of colour vision. A shark's pupil can dilate and contract, unlike other fishes. As a result, some sharks are very sensitive to direct sunlight. Puffadder shysharks (Haploblepharus edwardsii) curl their tails back to cover their eyes if they are caught and fished out of the water.

While sharks, like most fishes, have no outer ear, they nevertheless have an acute sense of hearing which can detect sound, acceleration, and gravity. Hearing is used to detect prey, primarily. In addition to ears, most sharks have a lateral line which is a series of fluid-filled canals underneath the skin of the head and alongside the body. Each canal is open to the environment through tiny pores. The line senses low-frequency vibrations, distance perception and directional water flow.

Sharks have an acute sense of smell. It is well known they can detect minute quantities of substances (eg blood) in the water. They have paired external nostrils which lead to ventral olfactory organs. These are blind sacs that are not connected to the mouth nor play any role in respiration.

Sharks have a complex and extensive sensory system around their heads called the ampullae of Lorenzini. They have external pores over the surface of the head. Each pore leads to a gelatinous substance-filled canal which then leads to a membranous sac called an ampulla which contains sensory cells and nerve fibres within the wall of the ampulla. As all living creatures produce electrical fields, the ampullae can detect the fields at short distances. The shark uses this sense to hunt prey in the final stage of hunting when vision is poor or the prey is hiding under sand on the seabed. Electroreception is also used for navigation. Electroreception is not specific to sharks. It is found in other fish and mammals, such as bats. However, it is finely tuned and used extensively by sharks.

Answer: Pectoral

Fins are rigid structures connected to the body by cartilaginous rods.

The caudal fin is considered the tail of the shark. As it moves back and forth, it propels the shark forward and downward. The paired pectoral fins located on the sides act in a similar manner to aeroplane wings to compensate for this downward motion and provide lift. These are usually the largest fins on a shark.

The dorsal fin is perhaps the most well-known of a shark's fins as its appearance has been exploited in movies as it breaks the surface of the water. This fin is used to stabilise the shark and to change direction. Most sharks have a second smaller dorsal fin located along the back close to the tail. Most, but not all, sharks have paired pelvic fins for stabilisation. Some species have a small anal fin for stability.