Vertebrates

1. Vertebrates Chapter 34

2. The Chordates • Distinguished by four principle features some time in their lives: • nerve cord • notochord • pharyngeal slits • postnatal tail • Muscles arranged in segmented blocks • Most have internal skeleton

3. Principle Chordate Features

4. The Nonvertebrate Chordates • Tunicates • exhibit neither a major body cavity nor visible segmentation • tadpole larva clearly exhibit all basic characteristics of a chordate • adults exist as sessile filter-feeders

5. Tunicates

6. The Nonvertebrate Chordates • Lancelets • scaleless, fishlike marine chordates • notochord runs entire length of dorsal nerve cord • feed on microscopic plankton using cilia-generated current

7. Characteristics of Vertebrates • Vertebral column • Distinct, well-differentiated head • Neural crest • Internal organs • Endoskeleton

8. Overview of the Evolution of Vertebrates • First vertebrates evolved in the oceans about 470 mya. • hinged-jaw • amphibians on land • reptiles take over • split into birds and mammals

9. Overview of the Evolution of Vertebrates • Four classes are land-dwelling tetrapods • Amphibia - amphibians • Reptilia - reptiles • Aves - birds • Mammalia - mammals

10. Fishes • Over half of all vertebrates are fishes. • Characteristics • vertebral column • jaws and paired appendages • gills • single-loop blood circulation • nutritional deficiencies

11. Evolution of the Fishes

12. History of the Fishes • First fishes • members of five Ostracoderm orders • jawless bottom-dwellers • Evolution of the jaw • jaws developed about 410 mya

13. History of the Fishes • Rise of active swimmers • Sharks and bony fishes replaced primitive fishes due to a superior swimming design. • caudal (tail) fin • dorsal (stabilizing) fins • pectoral (shoulder - elevator) fins • pelvic (hip- elevator) fins

14. History of the Fishes • Sharks become top predators • sharks among first vertebrates to develop teeth • sit on top of jaws • programmed tooth loss • teeth are always new and sharp • extremely advanced reproduction • shark eggs fertilized internally

15. History of the Fishes • Bony fishes dominate the water • bony fish evolved at same time as sharks, but adopted a heavy internal skeleton made of bone • strong base for muscles • evolved in fresh water • highly mobile fins, thin scales, and completely symmetrical tails

16. History of the Fishes • Important adaptations of bony fishes • swim bladder - regulates buoyancy • lateral line system - assesses rate of movement through water as pressure waves against the lateral line • gill cover (operculum) - flexing the operculum permits bony fish to pump water over their gills

17. History of the Fishes • Path to land • Lobe-finned fishes evolved 390 mya. • have paired fins that consist of a long fleshy muscular lobe supported by a central core of bones that form fully articulated joints • amphibians almost certainly evolved from lobe-finned fishes

18. Lobe-Finned Fish and Primitive Amphibians

19. Amphibians • First vertebrates to walk on land • Characteristics • legs • cutaneous respiration • lungs • pulmonary veins • partially divided heart

20. History of the Amphibians • Adaptations for the invasion of land • legs to support body’s weight • lung to extract oxygen from the air • redesigned heart to drive new respiratory system • reproduction in water to prevent egg desiccation • system to prevent body desiccation

21. History of the Amphibians • Rise and fall of amphibians • became common during Carboniferous period 360-280 mya • began to leave marshes for dry uplands during early Permian period • large size and complete body covering indicate skin was not used as respiratory system

22. History of the Amphibians • By the end of Permian, therapsid (reptile) ousted amphibians from their niche on land • by the end of the Triassic, there were only 15 families of amphibians left • almost all were aquatic • only two groups are known from Jurassic period (213-144 mya) • Anura - frogs and toads • Urodela - salamanders and newts

23. History of the Amphibians • Amphibians today • Anura - amphibians without tails • most live in or near water, and return to water to reproduce • eggs fertilized externally and hatch into tadpoles • metamorphosis

24. History of the Amphibians • Urodela (Caudata) - salamanders • have elongated bodies, long tails, and sooth, moist skin • fertilization is usually external

25. History of the Amphibians • Apoda (Gymnophiona) • caecilians - highly specialized group of tropical burrowing amphibians • legless, but have jaws and teeth • internal fertilization

26. Reptiles • Characteristics • amniotic egg • chorion - outermost membrane • amnion - encases embryo • yolk sac - surrounds yolk (food) • allantois - surrounds waste cavity • dry skin • thoracic breathing

27. Rise and Fall of Dominant Reptiles • Pelycosaurs: a better predator • first land vertebrates to kill organisms their own size

28. Rise and Fall of Dominant Reptiles • Therapsids: speeding up metabolism • extremely high food consumption • endotherms?

29. Rise and Fall of Dominant Reptiles • Thecodonts: wasting less energy • warmer climates - ectothermic • first bipedal land vertebrates

30. Rise and Fall of Dominant Reptiles • Dinosaurs: learning to run • body located directly over legs • increased speed and agility

31. Today’s Reptiles • Of the 16 orders of reptiles that have existed, only 4 survive • turtles • lizards and snakes • tuataras • crocodiles

32. Evolutionary Relationships

33. Rise and Fall of Dominant Reptiles • Other important characteristics • internal fertilization • improved circulatory system • ectothermic - heat obtained from external sources • endothermic - generate own heat • homeothermic - constant body temperature • poikilothermic - body temperature fluctuates with ambient temperature

34. Living Reptiles • Order Chelonia: turtles and tortoises • differ from other reptiles because their bodies are encased within a protective shell • anapsid - lack temporal opening in the skull, characteristic of other living reptiles

35. Rise and Fall of Dominant Reptiles • Order Rhynchocephalia: tuatara • lizardlike animals about half a meter long • contain parietal eye • only found on island off New Zealand coast

36. Rise and Fall of Dominant Reptiles • Order Squamata: lizards and snakes • three suborders • Sauria - lizards • Amphisbaenia - worm lizards • Serpentes - snakes • paired copulatory organ in males • lower jaw not joined directly to skull

37. Rise and Fall of Dominant Reptiles • Order Crocodilia: crocodiles and alligators • remained relatively unchanged • only two species of alligators • southern US and China • resemble birds more than other living reptiles (care for young and four-chambered heart)

38. Birds • Class Aves contains 28 orders containing 166 families and about 8,600 species. • key characteristics • feathers • modified reptilian scales • flight skeleton • thin, hollow bones

39. History of the Birds • Descended from dinosaurs • Archaeopteryx • Aves listed as separate class because of key evolutionary novelties of feathers, light bones, and super-efficient lungs

40. History of the Birds • Birds today • adaptations for flight energy demands • efficient respiration • efficient circulation • endothermy

41. Mammals • Key mammalian characteristics • hair • heat loss • camouflage • sensory structures • defense weapon • mammary glands • about 50% of energy in milk comes from fat

42. Key Mammalian Characteristics • endothermy • crucial adaptation that allowed activity at any time of the day to colonize severe environments • placenta • specialized organ allowing food, water, and oxygen to pass from mother to child • teeth • heterodont dentition

43. Key Mammalian Characteristics • digestion of plants • cellulose major source of food for herbivores • mammals do not have necessary digestive enzymes to break apart cellulose • some have evolved four-chambered stomachs • some contain mutualistic bacteria in a cecum

44. Key Mammalian Characteristics • hooves and horns • hooves specialized pads of keratin • horns composed of core of bone surrounded by keratin sheath • flight • bats have wing of leathery membrane of skin stretched over the bones of four fingers • second largest order of mammals • echolocation

45. Orders of Mammals • Origin of mammals • first mammals arose about 220 mya • tiny shrewlike creatures with large eye sockets - nocturnal? • Early divergence • Subclass Prototheria • duckbill platypus • Subclass Theria • marsupials and placental mammals

46. History of the Mammals • Orders of mammals • monotremes: egg-laying mammals • lay shelled eggs • marsupials: pouched mammals • finish development in external pouch • placental mammals • placenta nourishes embryo throughout entire development

47. Evolution Among Primates • Primates • two distinct features allowed them to succeed in arboreal environment: • grasping fingers and toes • binocular vision • Evolution of prosimians • earliest primates split into prosimians and anthropoids about 40 mya • “before monkeys”

48. Anthropoids • Higher primates - includes apes, monkeys, and humans • one of most contentious issues in primate biology is identity of first anthropoid • Direct descendents: • New World monkeys • Old World monkeys

49. Primate Evolutionary Tree