File

Class Chondrichthyes:
cartilaginous fishes
 The
class Chondrichthyes has two
subclasses:

Elasmobranchii: sharks, rays, skates.

Holocephali: chimaeras
sharks
rays
chimaera
Figure 24.01
16.1
Figure 24.02
16.2
Class Chondrichthyes

The Chondrichthyes’ well-developed jaws, highly
developed sense organs, powerful swimming ability and
streamlined shape have enabled them to thrive as
marine predators for more than 350 million years,
as other groups have come and gone.

There are just under 1,000 living species, all of which
have cartilaginous skeletons, even though they are
descended from ancestors that had bone.
Fossil history of Chondrichtyes
 One
of the best known extinct genera is
Cladoselache a pelagic marine predator
from the Devonian (416-360 mya).
Cladoselache picture
Cladoselache
http://www.dinosoria.com/poissons/cladoselache_03.jpg
Cladoselache lacked the rostrum (snout) of modern
sharks
Evolution of Chondrichthyes

By the Jurassic (200-146 mya) sharks of modern
appearance had evolved. Several genera from that era
are still extant.

The most distinctive feature of modern sharks is the
rostrum or snout that overhangs the mouth.

Finally, the teeth are covered with thicker more complex
enamel than in earlier sharks.
Megalodon
 Megalodon
(Carcharodon megalodon) is
another extinct shark species that is the
largest predatory shark known.
 Megalodon
occurred from 28-1.5 mya and
at approximately 16m long (and with a
mass estimated at 47 metrics tons) it
resembled a massive great white shark
and was the top ocean predator of its era.
“Megalodon (gray and red) with the whale shark (violet), great white shark
(green), and a human (blue) for scale. Note: The maximum size attained
by C. megalodon is indicated by the 20 m scale.” From Wikipedia.
http://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Megalodon_scale
1.png/220px-Megalodon_scale1.png
http://upload.wikimedia.org/wikipedia/com
mons/thumb/7/7a/Megalodon_shark_jaws_
museum_of_natural_history_068.jpg/300px
Megalodon_shark_jaws_museum_of_natur
al_history_068.jpg
http://upload.wikimedia.org/wikipedia/com
mons/thumb/7/71/Megalodon_tooth_ruler.j
pg/220px-Megalodon_tooth_ruler.jpg
http://upload.wikimedia.org/wikipedia/com
mons/thumb/1/1f/Carcharodon_megalodon
.jpg/220px-Carcharodon_megalodon.jpg
Megalodon
 Megalodon
preyed on anything it wanted
including pinnipeds, sea turtles, and
frequently whales.
 Fossil
whale skeletons contemporaneous
with Megalodon show bite damage clearly
inflicted by Megalodon.
Megalodon
 Megalodon’s
bite force:
10x that of a great white shark
5x that of a Tyrannosaurus rex
Figure 24.07
Diversity of sharks
Sharks
A
typical shark is about 2m long, but they
range in size from a few miniature forms
that are 25 cm long up to perhaps 18m in
length.
 Despite
their range of sizes all modern
sharks share a suite of characteristics.
Figure 24.co
Hammerhead
Shark
Basking Shark
http://oursurprisingworld.com/wp-content/uploads/
2008/02/disgusting_fishes_7-basking-shark.jpg
Whale shark
http://animals.nationalgeographic.com/
staticfiles/NGS/
Shared/StaticFiles/animals/images/
primary/whale-shark-with-fish.jpg
Spiny dogfish
http://elasmodiver.com/Sharkive%20images/Spiny%20dogfish%20059.jpg
Figure 24.08
16.6
Character Traits of
Cartilaginous Fish

Skeleton made of cartilage

Placoid scales (small tooth-like structures)

Claspers

Electroreception
Figure 24.18
16.15
Shark teeth

The placoid scales are modified in the mouth to produce
the rows of replaceable teeth characteristic of sharks.

Each tooth in a shark can be rapidly replaced as it
becomes worn or damaged. Teeth are not embedded in
the jaw but arranged on a spiral or whorl shaped
cartilaginous band in which replacement teeth are
always developing behind the functional tooth.

Teeth in young sharks may be replaced as often as once
every 8 days.
Figure 24.08
16.6
http://www.sharkattackphotos.com/Shark_Miscellaneous.htm
Figure 24.09
Sand tiger shark (note multiple rows of teeth)
Variation in tooth structure
 The
type of teeth a shark possesses is
dictated by the prey it eats.
 Sharks that feed on crustaceans, mollusks
and similar hard shelled prey have dense
arrays of flattened teeth designed for
crushing.
 Fish feeders have long pointed needle-like
teeth for gripping.
Porbeagle shark’s (a fish eater) teeth
http://www.elasmodiver.com/Sharkive%20images/PorbeagleSharkTeeth001.jpg
Variation in tooth structure
 Sharks
that feed on large prey such as
mammals have pointed lower teeth and
triangular serrated upper teeth for cutting.
 Plankton
feeders such as basking sharks
have small non functional teeth.
Blue shark upper (top) and
lower jaws (bottom)
http://www.marinebiodiversity.ca
/shark/english/teeth.htm
Shark Jaws

A shark’s jaws can open in a variety of different
positions depending on the prey.

The upper jaw is attached flexibly in two
locations (front and back), both of which can
move.
Shark Jaws
 Protrusion
of the upper jaw moves the
mouth away from the head and allows a
bigger bite to be taken than would be
possible if the upper jaw was immobile.
Great White Shark
http://img.dailymail.co.uk/i/pix/2007/07_03/19sharkDM_468x591.jpg
Biting
 The
head movements from side to side
saw off a large chunk of flesh, which
results in massive bleeding.
 Great
Whites kill large prey, such as sea
lions, by taking a big bite and then waiting
for the victim to bleed to death.
Shark Eating
 http://www.youtube.com/watch?v=oIy_eYj
20_0
Prey detection
 Smell
is used to detect prey from a
distance
 Vibrations
(lateral line system)
 Electroreception
 Good
vision up close