Reptiles

1. Reptiles

2. Reptiles • First truly terrestrial vertebrates • ~7000 species worldwide • ~300 species in U.S. and Canada

3. Reptiles • Probably best remembered for what they once were, rather than what they are now • Mesozoic era - age of reptiles • Dominant group for >150 millions years

4. Reptiles • 12 or so principal groups of reptiles evolved • Only 4 groups remain today

5. Order Squamata • Snakes and lizards • >5800 species • Most successful group

6. Order Crocodilia • Crocodiles, alligators, caiman • ~25 species • Have survived for 200 million years • Today: concerns that humans may drive them to extinction

7. Order Chelonia (Testudines) • Turtles • ~330 species • Ancient group that survived, remained mostly unchanged from early ancestors

8. Order Rhynchocephalia • Snout head or tuatara • Only 1 species • From New Zealand - sole surviving species of ancestral stock

9. Reptilian Characteristics • Tough, dry scaly skin • Protection against desiccation, physical injury • Thin epidermis shed periodically • Much thicker dermis with chromatophores

10. Reptilian Characteristics • Dermis converted into snakeskin, alligator leather for shoes, purses, and so on • Scales of keratin (epidermal) • Not homologous to bony, dermal fish scales

11. Reptilian Characteristics • Crocodilian scales remain throughout life • Grow gradually to replace wear

12. Reptilian Characteristics • In snakes and lizards, new scales grow beneath old • Old scales shed with old skin

13. Reptilian Characteristics • Turtles add new layers of keratin under old layers of the plate-like scutes (modified scales)

14. Shedding • Snakes turn old skin (scales, epidermis) inside out when shedding

15. Shedding • Lizards split skin and leave it right side out, or slough it off in pieces

16. Amniotic Egg Chorioallantoic membrane

17. Amniotic Egg • Reptiles are able to lay their eggs in sheltered locations on land • Young hatch as lung-breathing juveniles, not aquatic larvae

18. Amniotic Egg • Amniotic egg widened division between amphibians and reptiles • Probably greatly contributed to decline of amphibians and rise of reptiles

19. Reptile Jaws • Reptile jaws designed for crushing prey • Fish, amphibian jaws designed for quick closure, but little force after • Reptile jaw muscles larger, longer, arranged for better mechanical advantage

20. Reptile Copulatory Organ • Copulatory organ permitting internal fertilization • Internal fertilization required for a shelled egg • Copulatory organ formed from an evagination of cloaca

21. Reptile Circulation • More efficient circulatory system, higher blood pressure • All reptiles have at least an incomplete separation of the ventricles • Flow patterns prevent mixing

22. Reptile Circulation • Crocodilians have two completely separated ventricles • All reptiles have two functionally separate circulations

23. Reptile Lungs • Improved lungs • Depend almost exclusively on lungs for gas exchange • Supplemented by pharyngeal membrane respiration in some aquatic turtles

24. Reptile Lungs • Lungs have larger respiratory surface than in amphibians • Air sucked into lungs rather then forced in by mouth muscles • Negative pressure • Skin breathing completely abandoned

25. Reptile Kidney • Kidneys more advanced (metanephric) • Very efficient at conserving water • Excretes uric acid (rather than urea, ammonia) • A semisolid paste

26. Better Body Support • Limbs better design for walking on land • More ventral, less lateral • Many dinosaurs walked on only hindlimbs

27. Nervous System • Much more advanced - relatively larger cerebrum • CNS connections more advanced - permit complex behaviors not found in amphibians

28. Nervous System • Sense organs generally well-developed • Hearing generally poorly developed in most

29. Order Chelonia • Turtles • Very ancient group • Little change in morphology since Triassic period

30. Order Chelonia • Body enclosed in shell • Dorsal carapace • Ventral plastron

31. Order Chelonia • Thoracic vertebrae and ribs built into shell • Shell of two layers • Inner of bone • Outer of keratin • New keratin deposited under old as turtle grows, ages

32. Order Chelonia • Jaws lack teeth • Equipped with tough, horny plates for gripping, chewing food

33. Order Chelonia • Respiration poses a problem • Shell prevents expansion of chest for breathing • Adapted to use certain abdominal, pectoral muscles as a “diaphragm”

34. Order Chelonia • Air drawn in by contracting limb flank muscles to make body cavity larger • Exhalation also active - shoulder muscles contracted, viscera compressed, air forced out of lungs

35. Order Chelonia • Deformable plastron in snappers allows some elastic recovery during exhalation • Compressive force of water against body also can force air out

36. Order Chelonia • Many water turtles acquire enough O2 when inactive by pumping water in and out of mouth • Pharyngeal breathing • Can stay submerged for extended periods • Must lung breathe more frequently when active

37. Order Chelonia • Nervous system - tiny brain • Typical of most reptiles • Never exceeding 1% of body weight, but cerebrum larger than in amphibians • Turtle can learn, as quickly as a rat, to run a maze

38. Order Chelonia • Have both middle & inner ear, but sound perception is poor • Turtles are virtually mute • Tortoises may grunt or roar

39. Order Chelonia • Poor hearing compensated for by: • Good sense of smell • Acute vision • Color perception as good as that of humans

40. Order Chelonia • Mating & reproduction • Many varieties of courtship • Males of aquatic species may swim around looking for proper leg stripe pattern • Pheromones also • Males use claws

41. Order Chelonia • Terrestrial species may vocalize • Males may track females (pheromones) for days

42. Order Chelonia • Males may mark territory with fecal pellets • Courtship involves rubbing limbs against scent glands (underside of jaw) and sniffing

43. Order Chelonia • Biting, ramming, hooking are directed at other males • Biting - head & limbs • Ramming - rearing up, smacking shells • Hooking - bulldozing under plastron to flip or hurry

44. Order Chelonia • Turtles are oviparous • Fertilization is internal, and all species bury eggs in ground in nests • 4 to >100 eggs

45. Order Chelonia • Exercise care in constructing nest • Deposit eggs and abandon them • Incubation 1-14 months • 40-60 days most typical

46. Order Chelonia • Movements to nesting areas very faithful • Terrestrial species use familiarity with area, sun • Marine species use variety of mechanisms to traverse large distances

47. Order Chelonia • Earth’s magnetic field • Polarized light • Sun & stars • Low frequency sounds • Green sea turtles find Ascension Island (20 km) in mid-Atlantic from coastal Brazil - 2200 km

48. Order Chelonia • Size - marine turtles largest • Buoyed by aquatic environment • May reach 2 m in length, 725 kg in weight • Biggest species is leatherback

49. Order Chelonia • Green sea turtle may exceed 360 kg • Economically valuable - heavily exploited - rarely gets to large size

50. Order Chelonia • Land tortoises generally not as large as aquatic forms • Some may weigh several hundred kg • Giant tortoises of Galapagos Islands among world’s largest terrestrial turtles