1. Higher Chordata: Subphylum Vertebrata: The Fishys
Biology 11
Higher Chordata:
Subphylum Vertebrata:
The Fishys

2. 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!)

3. Higher Chordata Objectives: Vertebrata
Describe the 3 Classes and an example animal
Anatomy of the Perch

4. 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

5. 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

8. 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

9. 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

10. Hammerhead Shark
Tiger Shark

11. Skates: Rays: Thicker heavier tails No spines on tail
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

12. 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

13. 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

14. 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

16. 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)

17. 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)

18. 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

19. 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

20. Evolution to Land 5. Reproduction: with motile sperm
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

21. 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

22. 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

23. 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

24. 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

25. A Coelocanth, a lobe-finned fish!