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The First True Terrestrial Tetrapods

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1 The First True Terrestrial Tetrapods
Reptiles The First True Terrestrial Tetrapods


3 # of Species of Reptiles
Species Numbers by Higher Taxa: Amphisbaenia (amphisbaenians) 165 Sauria (lizards) 4765 Serpentes (snakes) 2978 Testudines (turtles) 307 Crocodylia (crocodiles) 23 Rhynchocephalia (tuataras) 2 Reptiles total 8240

4 Reptile Characteristics
Ectothermic Dry skin covered in scales Most have 2 pairs of short legs & clawed feet Oviparous reproduction (Internal fertilization – to avoid desiccation of gametes) Eggs have a leathery shell and yolk (amniotic) Lungs to breathe 3 or 4 chambered heart No metamorphosis (young look like miniature parent) Hibernate & aestivate

5 Ectothermy Body temperature regulated by ambient air temperature

6 Dry Scaly Skin The body of reptiles is covered with horny epidermal scales to reduce water loss and provide protection.

7 Reptile Legs Short tetrapods for walking
Positioning of the legs more directly under the animal. This position provided more support than the splayed arrangement of the Amphibian legs.

8 Paired Limbs The paired limbs usually have five toes and are variously adapted for: Swimming Running Climbing (Absent altogether in the snakes)


10 Oviparous Amniotic eggs have a leathery shell to prevent desiccation

11 Amniotic Egg

12 Amniotic Egg Structures & Functions
Chorion provides a special hard covering that is permeable to respiratory gases (O2 and CO2) while being impermeable to water vapor. Allantois is a storage reservoir for metabolic waste products such as nitrogenous compounds. Amnion is a fluid filled sac that acts as a cushion for the embryo and also prevents desiccation. Yolk sac contains food for the embryo, thus eliminating the need for a larval stage.



15 Reptile Lungs Respiration is no longer through the skin, but only through internally protected and moistened lungs. They have a much greater surface area for the exchange of gases. They are inflated and deflated by the expansion & contraction of the rib cage.

16 Reptile Hearts Reptiles have a 3-chambered heart
Crocodiles have a 4-chambered heart




20 Excretory Waste The excretory waste of the reptiles is uric acid unlike the dilute, water wasting ammonia in the urine of Amphibians.

21 Family Amphisbaenidae (Worm Lizards)
Size: The total body length ranges from 10 cm to about 70 cm. Distribution: Mostly Africa & South America with a few species in Europe and North America. Habitat: Soil. Reproduction: usually oviparous, but some are live-bearing

22 Lizard Anatomy

23 Lizard Reproduction


25 Hatchling Komodo Dragon

26 Snake Anatomy

27 Jacobson’s Organ

28 Snake Reproduction


30 Turtle Anatomy

31 Turtle Shell Anatomy

32 Turtle Shell Anatomy


34 Fusion of ribs, vertebrae, & carapace


36 Turtle Life Cycle

37 Turtle Reproduction                                                                

38 Crocodilians Crocodiles, Alligators, Caimans, & Gavials


40 Gavial

41 Alligator

42 Crocodile


44 Caiman

45 The temperature inside the nest of several crocodilian species decides the sex of the young. ~50-80 eggs If the nest temperature is 30ºC, females will hatch from all the eggs If the temperature is above 34ºC, all will be males. If the temperature is in between, there will be young of both sexes.

46 Crocodilian Reproduction


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