Download File - Ms Nickel`s Biology 11H

Biology 11
Higher Chordata:
Subphylum Vertebrata:
The Fishys
Phylum Chordata is typically divided into four subphyla:
Higher Chordates
 We are going to spend the next few classes talking
about the Subphylum Vertebrata (AKA: the higher
chordates!)
Higher Chordata Objectives: Vertebrata
 Describe the 3 Classes and an example
animal
 Anatomy of the Perch
Subphylum Vertebrata
Characteristics:
1. Endoskeleton of bone or cartilage which
surround the dorsal nerve cord (a
backbone or vertebral column)
2. Notochord absent or reduced in adult
3. Pronounced cephalization
4. A closed circulatory system
Class Agnatha
Jawless fishes
 Much more dominant in the early oceans
where they were mud suckers or filter feeders
– no articulating jaws
 Evolved gills to improve oxygen uptake and
thus increased activity levels
 No paired appendages
 Represented today by Lamprey and Hagfish
Class Chondrichthyes
Cartilagenous Fishes
 Skeleton is made of cartilage not bone
(secondarily evolved)
 Evolved articulating jaws by modification of
anterior two pairs of gill slits
 Have no operculum or air bladder
 Very streamlined body with paired fins for
steering
Class Chondrichthyes
 Have well developed senses, especially smell
 Are almost all predators
 Developed internal fertilization and carry eggs
internally (no nutritional connection) as young
must swim when born
 Much more dominant in early oceans
 They are: sharks, skates, and rays
Hammerhead
Shark
Tiger Shark
Skates:
- Rounded shape
- Thicker heavier tails
- No spines on tail
- Thorns on tail and back
- Elongated nose
- Smaller
- Lay eggs
Rays:
- Kite shaped
- Thin barbed tails
- Spines on tail
- No thorns on tail
and back
- Larger
- Give birth to live young
Class Osteichthyes
The Bony Fishes
 Have a calcified skeleton - are dominant water
vertebrate
 Have an operculum and air bladder (formed as
a pocket off the pharynx)
 Developed the structure that evolution would
select for in moving the vertebrates to land
Class Osteichthyes
1. Circulatory System
 Have a two chambered heart that pumps
blood to the gills then the rest of the body
2. Nervous system
 Have the basic organization of a vertebrate
brain and well developed senses
 Behaviours begin
Class Osteichthyes
3. Reproduction
 Have external fertilization and development
with little if any post natal care
 Young are born able to swim and feed and
must fend for themselves
4. Excretory System
 Have a dorsal kidney that excretes mainly
ammonia as nitrogen waste
Class Osteichthyes
 There are two main groups
of fish seen today:
1. Teleosts:
 true fish with ray finned
appendages
 Evolved in fresh water then
moved back to the oceans
 Most common fish today
(salmon, trout etc)
Class Osteichthyes
2. Lung fish and Lobe-finned fish
 These two fish evolved in fresh water at a time
when periodic and severe droughts occurred
 Lung fish seen today in Africa and South
America
 Use their crude lungs to gulp air to assist gills
(usually live in stagnant water)
Class Osteichthyes
 Lobe-finned fish were mostly bottom dwellers and
used their more sturdy fins to grope along the bottom
of the swamps and to occasionally move about the
muddy shores
 Both of these fish are well represented in the fossil
record
Evolution to Land
Vertebrates faced many problems moving onto
land
Problems:
1. Gas exchange (moist membrane problem)
2. Movement: loss of buoyancy
3. Obtaining food - must adapt to new food
especially tough plants
Evolution to Land
4. Dessication
5. Reproduction: with motile sperm
6. Development: all animal embryos develop in
water
7. Senses: land is much more transparent than
water - can be seen easier - much more to
detect and react to
8. Adaptation: to rapid, severe climate changes
Evolution to Land
On to Land!
 The bony fish evolved from the cartilagenous
fishes, probably in fresh water
 During the Devonian, the land became much
hotter and drier
 Water habitats both shrank and became
stagnant
Evolution to Land
 Shallow pools of water would dry up most
quickly - problem for fish
 Competition for food and space also
intensified as the habitat shrunk
 If your pond is drying out, to survive you need
to get to another pool of water
 Nature would select for any structure that
would aid short term movement on land
Evolution to Land
 Fleshy, sturdy fins would allow the fish to
“steer” a course between water holes using
the muscular tail for propulsion
 This is very energetically costly: crude lungs
were already developing as the stagnant water
had too little oxygen (which evolved into air
bladders in water fish)
 Nature would select for better lungs
Evolution to Land
 One advantage they would discover while in
transit was unlimited food (no other major
animals on land)
 This would encourage them to stay longer on
land
 The end result would be a lobe finned, lung
fish capable of limited movement on land
A Coelocanth, a lobe-finned fish!