1. Class Amphibia – Focus on the Mudpuppy
Vertebrate Anatomy

2. Chordate Lineage Leading to Amphibians
The evolutionary path that leads to the amphibians is also closely related to the taxonomy that we assign amphibians
The best classification/taxonomy does reflect evolutionary history of organisms

3. Kingdom Animalia
All animals (even the most primitive) possess certain characteristics
Eukaryotic cells
No cell walls
heterotrophic
Some ancient member of the animal kingdom gave rise to…

4. Phylum Chordata
All chordates possess the characteristics found in all animals, PLUS
Dorsal hollow nerve cord
Notochord
Pharyngeal gill slits
Post anal tail
Some ancient Chordate gave rise to…

5. Subphylum Vertebrata
All vertebrates possess the characteristics found in all animals and in all chordates, PLUS
A backbone
Note that no animals up to and including this INITIAL vertebrate had jaws…
Some ancient vertebrate then gave rise to…

6. Superclass Gnathostomata
All gnathostomes possess all the characteristics found in all animals, all chordates AND in all vertebrates PLUS
Jaws
Some ancient gnathostome then gave rise to…

7. Classes Chondrichthyes and Osteichthyes
The first gnathostome that arose was most likely a bony fish (osteichthyes). It is thought that sharks (chondrichthyes) arose from an extinct group of bony fish (placoderms) and that their cartilaginous skeletons are a later development.
At any rate, the chondrichthyes line, though quite successful (there are lots of sharks, skates and rays) is a “dead end” in that it does not give rise to any higher vertebrates
The bony fish have two very important subclasse. These are…

8. Subclass Actinopterygii and Subclass Sarcopterygii
The Actinopterygii you learned about when we did the perch. These are the ray-finned fish
This is a hugely important group as it includes the vast number of bony fish HOWEVER…
It is NOT the group of bony fish that gave rise to the amphibians
The Sarcopterygii is a very important group
NOT because it has lots of members – actually few
It is thought that some member within this group gave rise to amphibians (and thus ALL tetrapods)

10. Subclass Sarcopterygii
The important characteristic of this group is their fleshy-fins
Their fins are thick and fleshy, not thin like those of the ray-finned fish
It is this group of fish that is believed to have given rise to the amphibians
Their limbs were substantial and muscular enough to act like very primitive “legs” allowing the first amphibian-like ancestors to “walk/crawl” over short spans of land
Presumably to escape predators in the water and/or
move from one small pool to another to exploit food resources

12. Class Amphibia
At this point, we discuss all vertebrates (those arising beyond the fishes) as tetrapods
Means 4 limbs
These are the LAND vertebrates
So… the vertebrate group basically consists of two major groups (note that these are NOT formal levels of classification)
Fishes – water dwelling
Tetrapods – land dwelling (mostly)

13. What are the advantages of land living?
Less competition for food and other resources (at least at first)
Escape predators chasing you in the water
Not near as many predators on land (at least at first)
Lots of unexploited resources on land (at least at first)

14. Problems aquatic animals had to overcome in order to live on land
Movement on land
Breathing
Water loss from tissues
Reproduction
Get sperm to egg
Prevent drying of fertilized eggs and embryos
Energy
It takes more energy to move on land
It takes more energy to maintain body temperature on land because temperatures are less stable on land

15. Even though amphibians can live on land, the transition is incomplete…
Most amphibians have external fertilization and development
Skin must be kept moist because it is used as a breathing organ
Thus drying of tissues is still a problem
Though lungs are found in most adults, gills are still present in juvenile forms.

16. Generalized Characteristics of Amphibians
Aquatic as juveniles; terrestrial as adults
Of course there are always exceptions
Aquatic characteristics
Gills
Lateral line
Tail fin
No limbs
Algae eaters
Terrestrial Characteristics
4 limbs (and no fins)
Lungs
carniverous

17. The Amphibian Heart – an organ in transition
Amphibians possess a 3 chambered heart
2 atria and 1 ventricle
Atria receive blood
Ventricle pumps blood

18. The Amphibian Heart – an organ in transition
It is in this heart that we first see a “double loop” circulation pattern
Remember the single loop in fish
Drawback – blood slows down a LOT after passing through the capillary beds of the gills AND the body
In amphibians:
Blood is sent in one loop to the lungs/skin
Blood is sent in a second loop to the organs of the body
Efficiency of the double loop
After going to the lungs/skin (or gills) the blood is returned to the heart for another PUMP
THEN the blood goes off the the body
TWO pumping events prevent the blood from slowing down so much as it returns to the heart

19. The Amphibian Heart – an organ in transition
Drawbacks of the amphibian heart
Separation of oxygenated blood coming from lungs/skin and deoxygenated blood coming from the body organs is INCOMPLETE
There is some MIXING of oxygenated and deoxygenated blood in the VENTRICLE
Thus making this circulatory arrangement NOT as efficient as would be ideal.

22. The Mudpuppy Heart
We need to remember that the mudpuppy is a bit odd in that it’s lungs are essentially useless as respiratory organs, so the circulation path of the blood is not benefiting so much from oxygen from the lungs.

23. Classification of Modern Amphibians – 3 Orders
                                    
Order Caudata – the salamanders
4 limbs
Long tail (used for propulsion in swimming)
Crawling and/or swimming
Many actually have internal fertilization through the use of a spermatophore, but development is external
Neoteny in some (sexual maturity as juveniles)

24. Classification of Modern Amphibians – 3 Orders
Order Anura – the frogs and toads
Jumping (adults)
No tails (except juveniles)
Both fertilization and development are external
COMPLETE metamorphosis

25. Classification of Modern Amphibians – 3 Orders
Order Apoda – the “legless salamanders”