Amniote origins and nonavian reptiles

Presentation

1. Amniote Origins and Nonavian Reptiles 1

2. Origin and Early Evolution of Amniotes Amphibians were first tetrapods to invade land The need to return to water for reproduction limited their distribution Amniotes evolved an egg that broke the tie to freshwater Amniotic egg contains a series of extraembryonic membranes that, among other features, takes the aquatic environment with the egg 2

3. Origin and Early Evolution of Amniotes Amniotic egg Amnion - provides an aquatic environment for development Allantois - respiratory surface and waste collection Chorion - encloses the other two membranes Yolk sac - nourishes the embryo 3

4. Origin and Early Evolution of Amniotes Amniotes arose in the late Paleozoic (300 mya) Early diversification produced three patterns of temporal fenestra in the temporal region of the skull Anapsid - no fenestra. Present early in evolution of amniotes. Only turtles today, but this is a derived condition Diapsid - two fenestra. Present in birds and all “reptiles” except turtles Five clades Lepidosaurs - lizards, snakes, tuataras Archosaurs - dinosaurs, pterosaurs, crocodilians, birds Sauropterygians - plesiosaurs now extinct Ichthyosaurs - aquatic reptiles now extinct Turtles - controversial placement 4

5. Origin and Early Evolution of Amniotes Amniotes arose in the late Paleozoic (300 mya) Early diversification produced three patterns of temporal fenestra in the temporal region of the skull Anapsid - no fenestra. Present early in evolution of amniotes. Only turtles today, but this is a derived condition Diapsid - two fenestra. Present in birds and all “reptiles” except turtles Synapsid - one fenestra. Present in mammals and their extinct relatives (therapsids and pelycosaurs) 5

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7. Adaptations of Amniotes Amniotic egg - egg with four extraembryonic membranes Amnion, allantois, chorion, yolk sac Required internal fertilizations Evolution of copulatory organs in many amniotes 7

8. Adaptations of Amniotes Thicker and more waterproof skin Use as a respiratory surface diminished Evolution of keratinaceous structures Scales, hair, feathers, and claws 8

9. Adaptations of Amniotes Rib ventilation of the lungs Amniote lungs better developed than anamniotes More surface area, but better ventilation too Air drawn in through creation of negative pressure 9

10. Adaptations of Amniotes Stronger jaws Fish jaws evolved for suction and quick closure Cannot apply pressure to captured items Amniotes expanded jaw musculature to seize and hold on to prey 10

11. Adaptations of Amniotes High-pressure cardiovascular system Functional separation of oxygenated and deoxygenated blood By separating the systemic and pulmonary loops, amniotes can maintain higher blood pressure Amphibians 15-40 mmHg Reptiles 88 mm Hg 11

12. Adaptations of Amniotes Water-conserving nitrogen excretion Amphibians excrete nitrogenous wastes as ammonia (some as urea) Because ammonia is toxic at low concentrations, it must be removed in a dilute solution This requires lots of water Amniotes living away from water evolved the means to concentration nitrogenous wastes as urea or uric acid Less toxic at higher concentrations Requires less water to rid the body of 12

13. Adaptations of Amniotes Expanded brain and sensory organs Cerebrum and cerebellum are relatively large in amniotes Especially so in birds and mammals Enlargement of the cerebrum is associated with integration of sensory info and control of muscles during locomotion Olfaction Sight Specialized chemoreception 13

14. Changes to “Reptile” Classification Traditionally defined as Snakes, lizards, tuataras, crocodilians, and turtles Plus extinct groups such as dinosaurs, plesiosaurs, and pterosaurs 14

15. Changes to “Reptile” Classification Morphological evidence suggest birds and “reptiles” have more in common Diapsid skull Ankle characteristics Presence of beta keratin 15

16. Changes to “Reptile” Classification As such, “reptiles” is paraphyletic Its continues use, though incorrect, is largely for convenience 16

17. Changes to “Reptile” Classification Birds and crocodilians belong in the clade Archosauria Includes the extinct dinosaurs and pterosaurs Lepidosaurs are the tuataras, lizards, and snakes Turtles were the outgroup 17

18. Changes to “Reptile” Classification The paraphyletic group traditionally known as “reptile” are informally known as nonavian reptiles Comprised of four clades Testudines Squamata Sphenodonta Crocodilia 18

19. Testudines - turtles Appear in the fossil record 240 mya Morphologically similar to modern turtles Except: shell reduced and teeth present 19

20. Testudines - turtles Modern turtles lack teeth Have tough keratinized plates instead Shell composed of bone, with large scales and in two parts Carapace - upper Plastron - lower 20

21. Testudines - turtles Shell Bony parts from expansion and fusion of ribs, vertebrae, and dermally ossifying elements Evolution of shell: Broadening of ribs Evolution of plastron Evolution of carapace 21

22. Testudines - turtles Unique respiratory processes Because ribs are fused to shell, turtles cannot expand the chest to breathe Abdominal and pectoral muscles used as a diaphragm Movement of the limbs also ventilates the lungs Mouth and cloaca may also assist in gas exchange 22

23. Testudines - turtles Reproduction Internal fertilization Oviparous Eggs buried and abandoned Sex determination by ambient temperature Cooler = more males 23

24. Squamata: lizards and snakes Most diverse of the living nonavian reptiles 95% of all reptile species Lizards appeared in the Jurassic period Did not diversify until the Cretaceous Snakes appeared in the late Jurassic Likely evolved from lizards 24

25. Squamata: lizards and snakes In both lizards and snakes the skull is kinetic Has moveable joints Allows for seizure and manipulation of prey Increased bite force In snakes, kineticism is greater and allows for swallowing of very large prey 25

26. Lacertilia: lizards Very diverse group Terrestrial, burrowings, aquatic, arboreal, and aerial members Familiar lizards include: Geckos - small, nocturnal forms with adhesive pads on feet 26

27. Lacertilia: lizards Very diverse group Terrestrial, burrowings, aquatic, arboreal, and aerial members Familiar lizards include: Iguanids - brightly colored New World lizards with frills and crests 27

28. Lacertilia: lizards Very diverse group Terrestrial, burrowings, aquatic, arboreal, and aerial members Familiar lizards include: Skinks - elongate bodies, tight fitting scales and reduced limbs 28

29. Lacertilia: lizards Very diverse group Terrestrial, burrowings, aquatic, arboreal, and aerial members Familiar lizards include: Monitors/varanids - large active predators 29

30. Lacertilia: lizards Very diverse group Terrestrial, burrowings, aquatic, arboreal, and aerial members Familiar lizards include: Chameleons - arboreal lizards of Africa and Madagascar 30

31. Lacertilia: lizards Body form Most have four limbs Limbs may be reduced or absent Short bodies Eyelids are movable External ear openings Ectothermic Adapted for hot, dry conditions Lipids in skin minimize water loss Little water loss during excretion - uric acid 31

32. Serpentes: snakes Limbless today Early fossils had external limbs Pelvic girdle persists in a few snakes Vertebrae are shorter and wider than those in other vertebrates Permits lateral undulations for movement 32

33. Serpentes: snakes Body form Spectacle covers and protects eye No movable eyelid Don’t blink Generally poor vision No external ears or tympanic membrane Capable of hearing and detecting vibrations Chemical sense are more useful Jacobson’s organs (vomeronasal) on roof of mouth Tongue flicked out to gather chemicals and draw them pst the vomeronasal organ 33

34. Serpentes: snakes Body form Boids and pit vipers have pit organs for sensing radiant energy Can detect difference of 0.003℃ 34

35. Serpentes: snakes Movement - much variation Lateral undulation - S-shaped pattern. Results in fast movement, loops appear to stay stationary Concertina movement - useful when moving in tight channels like tree hollows Rectilinear movement - used when stalking prey. Slow and deliberate. earthworm-like 35

36. Serpentes: snakes Movement - much variation Lateral undulation - S-shaped pattern. Results in fast movement, loops appear to stay stationary Concertina movement - useful when moving in tight channels like bark Rectilinear movement - used when stalking prey. Slow and deliberate. earthworm-like 36

37. Serpentes: snakes Movement - much variation Lateral undulation - S-shaped pattern. Results in fast movement, loops appear to stay stationary Concertina movement - useful when moving in tight channels like bark Rectilinear movement - used when stalking prey. Slow and deliberate. earthworm-like 37

38. Serpentes: snakes Movement - much variation Sidewinder motion - used in loose, sandy soils of deserts Flying???? 38

39. Serpentes: snakes Feeding Most grasp prey with mouth and swallow it whole while it is still living Some snakes kill by constriction Generally ambush predators Some snakes kill by venom 20% of all snakes Venom is modified saliva All snakes mildly venomous Neurotoxin Hemorrhagin 39

40. Serpentes: snakes R eproduction Most are oviparous Some viviparity and ovoviviparity Viviparous snakes nourish young with placentae 40

41. Sphenodonta: tuataras Two living species Found in New Zealand Once more widespread, declined at end of Mesozoic Recent localized declines due to invasive species 41

42. Sphenodonta: tuataras Two living species Low reproductive and growth rate Slow rate of morphological evolution Share many features with ancient diapsids 42 Iguana

43. Crocodilia: crocodilians With birds are the only survivors of the archosaurian lineage that gave rise to dinosaurs Modern crocodilians are similar to crocodilians from the mesozoic Unchanged for 200 million years 25 spp. Divided into three groups Crocodiles - Worldwide Alligators and caimans - New World Gharials - India and Nepal 43

44. Crocodilia: crocodilians With birds are the only survivors of the archosaurian lineage that gave rise to dinosaurs Modern crocodilians are similar to crocodilians from the mesozoic Unchanged for 200 million years Divided into three groups Crocodiles - Worldwide Alligators and caimans - New World Gharials - India and Nepal 44

45. Crocodilia: crocodilians With birds are the only survivors of the archosaurian lineage that gave rise to dinosaurs Modern crocodilians are similar to crocodilians from the mesozoic Unchanged for 200 million years Divided into three groups Crocodiles - Worldwide Alligators and caimans - New World Gharials - India and Nepal 45

46. Crocodilia: crocodilians Body form Elongate snout with well-developed jaw musculature Thecodont teeth set into sockets Secondary palate Four-chambered heart 46

47. Crocodilia: crocodilians Reproduction Oviparous Eggs have temperature-dependant sex determination High parental care 47