1. Vertebrates

2. The Origin of Tetrapods
The first vertebrates on land were amphibians in the Devonian (400 mya)
May have arose from the rhipidistian (features).
Arose in coastal or brackish marine environment

3. Origin of Tetrapods

4. Origin of Tetrapods

5. Tetrapods Advantages of Terrestriality
An increase in metabolism and development due to higher body temperature.
Energy – An increase of 10 degrees Celsius (from 20 degrees (water temp) to 30 degrees (air temp) would allow for a doubling of their metabolic rates

6. Tetrapods
Lungs – To breath air, it required an increased vascularization of the air-filled cavity (a pouch from the posterior pharynx similar to the swim bladder), with a rich capillary network to form a lung.

7. Tetrapods Double circulatory system
Fish have a single circuit system – low blood pressure
The double circulation system allows for higher pressure with one circuit going to the lungs and another going to the body.

8. Tetrapods Nasal Openings
Bony fish have 4 external nares (2 on each side) which allows water to run across the olfactory tissue.
Tetrapods have two external and two internal nares in the palate. This allows air to be drawn in through the nose.

9. Tetrapods – General Characteristics
Body Density - Limbs
Air is 1000 times less buoyant then water
counter the effects of gravity
homologous structures (bones – humerus, ulna and radius).

10. Tetrapods – General Characteristics
Body Density - Girdles –
In fish, the pectoral girdle is attached to the skull.
Early tetrapods developed a stronger shoulder girdle, bulky limb bones and well developed muscles.
The pelvic girdle is fused to the backbone to increase the force that can be generated by the hind legs.

11. Tetrapods – General Characteristics
Body Density - Vertebrae and Ribs –
Vertebrae have developed zygapophyses.
The development of ribs can also protect the lungs.

12. Tetrapods – General Characteristics
Body Density - Skull and Neck
The skull has been shortened and the snout elongated.
The head becomes separated from the body by a neck (a cervical vertebrae) that allows the head to be lifted.
A second vertebrae was then added to allow for a side to side movement.

13. Tetrapods – Evolutionary History
Fish

14. Tetrapods – Evolutionary History
“Fishapod” – Tiktaalik (375 mya)
A fish with tetrapod features, this animal probably could not walk on land but could lift itself out of the water.
Fish Characteristics
Scales
Fins
Gills and lungs
Tetrapod Characteristics
Neck
Ribs
Fin skeleton
Flat skull
Eyes on top of skull

15. Classification Phylum: Chordata Subphylum: Vertebrata
Superclass: Gnathostomata
Class: Amphibia
Order: Urodela (Salamanders)
Order: Anurans (Frogs and Toads)
Order: Apodans (Caecilians)

16. Class: Amphibia Two lives
refers to metamorphosis of many frogs
Skin smooth, moist (cutaneous respiration), and glandular (toxins)
Three chambered heart with a double circulation system
Mesolecithal eggs with jelly-like membrane

17. Order: Urodela 400 species Salamanders Retain their tail as adults
Limbs are at right angles to the body
Carnivorous

18. Order: Anurans 3500 species Frogs and Toads Lose their tail as adults
Hind limbs are adapted for jumping
Tongue connected to front of mouth
Secrete mucus

19. Order: Apodans
150 species
Caecilians
Legless and blind

20. Evolution of the Amniotic Egg
Allows animals to complete their entire life cycle on land
Has shell that retains water (or is lost when kept inside mammals)
Specialized extraembryonic membranes (not part of the animal)

22. Evolution of the Amniotic Egg
Amnion - Protects from dehydration and mechanical shock
Yolk Sac - Nutrient storage
Albumin - Nutrient storage
Allantois - stores waste, gas exchange
Chorion - gas exchange

23. Amniotes

24. Amniotes

25. How Reptiles differ from Amphibians
Tough, dry skin
Amniotic egg
Crushing or gripping jaws
Copulatory organs
More efficient circulatory system with a higher blood pressure
More developed lungs (thoracic breathing)
Better water conservation
Better body support and limbs
Better nervous system

26. Classification Phylum: Chordata Subphylum: Vertebrata
Superclass: Gnathostomata
Class: Reptilia (not real)
Class: Testudines (Turtles and Tortoises)
Class: Spenodontia (Tuataras)
Class: Squamata (Lizards and Snakes)
Class: Crocodilia (Crocodiles and Alligators)

27. Reptile Radiation Synapsids (therapsids) - led to mammals Sauropsids
Anapsids??? (turtles)
Diapsids (all others)

29. Class: Testudines (Chelonia)
Evolved on land and returned to water (lay eggs on land)
Protective Shell
Carapace
Plastron

30. Class: Sphenodontia Tuataras Two living species (New Zealand)
Not a True Lizard (no external ears)
Very Primitive (similar to mesozoic reptiles
Well developed eye below skin?

31. Class: Squamata Lizards terrestrial, burrowing, aquatic, arboreal
geckos, iguanas, skinks, chameleons
terrestrial, burrowing, aquatic, arboreal
moveable eyelids
Paired copulatory organs
Lower jaw not attached to skull

32. Class: Squamata

33. Class: Squamata

34. Class: Squamata

35. Class: Squamata

36. Class: Squamata Snakes Lack limbs Lack moveable eyelids
Jacobson’s organ
Pit Vipers (heat)
Venom
neurotoxins
hemolytic enzymes

37. Class: Squamata

38. Class: Squamata

39. Class: Squamata

40. Class: Squamata

41. Feeding Adaptations Teeth curved and pointed inward
Hinged Quadrate bone
Bones of jaw are attached by muscles and ligaments
Moveable palate
Elastic skin
No sternum

42. Class: Crocodilia Largest living reptiles
Most closely related to dinosaurs
Complete secondary palate
Four chambered heart
Nest temperature

43. Dinosaurs and Pterosaurs
Ornithischian
Saurischian (closely related to birds)
Pterosaurs
flying reptiles