Vertebrates

1. Vertebrates History , structural and functional features

2. The Chordates Chordates (phylum Chordata) are deuterostome coelomates -Nearest relatives are echinoderms (the only other deuterostomes)

3. The Chordates Four features characterize chordates 1. Nerve cord 2. Notochord 3. Pharyngeal slits 4. Postanal tail

4. The Chordates All chordates have all four of these characteristics at some time in their lives Other characteristics also distinguish chordates 1. Chordate muscles are arranged in segmented blocks called somites 2. Most chordates have an internal skeleton against which the muscles work

5. The Chordates

6. Nonvertebrates The Nonvertebrate Chordates Phylum chordata can be divided into three subphyla 1. Urochordata 2. Cephalochordata 3. Vertebrata

7. Subphylum Urochordata Tunicates are marine animals -Larvae are tadpolelike and have notochord and nerve cord -Are free-swimming but do not feed -Adults typically lose the tail and notochord -Are immobile filter-feeders -Many secrete a tunic (cellulose sac) that surrounds the animal

8. Subphylum Urochordata

9. Subphylum Urochordata (Cont.)

10. Subphylum Cephalochordata Lancelets are scaleless chordates -Notochord persists throughout animal’s life -Have no distinguishable head -Feed on plankton using cilia-generated currents -Closest relatives to vertebrates

11. Subphylum Vertebrata Vertebrates: chordates with a spinal column -Distinguished from nonvertebrates by 1. Vertebral column – Encloses and protects the dorsal nerve cord 2. Head – Distinct and well-differentiated possessing sensory organs

12. Subphylum Vertebrata Vertebratesalso have -Neural crest – A unique group of embryonic cells that forms many vertebrate structures -Internal organs – Liver, kidneys, endocrine glands, heart and closed circulatory system -Endoskeleton – Made of cartilage or bone -Makes possible great size and extraordinary movement

13. Subphylum Vertebrata

14. Subphylum Vertebrata The first vertebratesappeared in the oceans about half a billion years ago -Jawed fishes soon became dominant -Their descendants, the amphibians, invaded the land -Reptiles replaced them as the dominant land vertebrates -Gave rise to birds and mammals

15. Fishes Fishes are the most diverse vertebrate group -Over half of all vertebrates -Vary greatly in size, shape, color and appearance

16. Fishes Fishes have the following characteristics 1. Vertebral column 2. Jaws and paired appendages 3. Internal gills 4. Single-loop blood circulation 5. Nutritional deficiencies

17. History of the Fishes The first fishes had mouths with no jaws -Agnathaextant as hagfish (class Myxini) and lampreys (class Cephalaspidomorphi) -Ostracoderms are now extinct The development of jaws occurred in the late Silurian period (438-408 MYA) -Jaws evolved from the anterior gill arches that were made of cartilage

18. History of the Fishes

19. History of the Fishes The Devonian period (408-360 MYA) saw two types of jawed fishes -Spiny fishes (Acanthodii) -Smaller fishes that dominated early on -Armored fishes (Placodermi) -Larger fishes that dominated late At the end of the period, these early fishes were replaced by sharks and bony fishes -These had more improved jaws

20. History of the Fishes In the Carboniferous period (360-280 MYA), sharks (Class Chondrichthyes) became the dominant sea predators -A light, flexible skeleton, and paired fins made them superior swimmers

21. History of the Fishes Sharks were among the first vertebrates to develop teeth -Evolved from rough scales on mouth’s skin -Easily lost but continuously replaced Sharks (and bony fishes) have a fully developed lateral line system -Series of sensory organs under the skin that detects changes in pressure waves

22. History of the Fishes Reproduction in sharks differs from that of other fishes -Shark eggs are fertilized internally, and pups are born alive -A few species do lay fertilized eggs Sharks have long gestation periods and relatively few offspring -Therefore, are not able to recover quickly from population declines

23. History of the Fishes Bony fishes evolved at the same time as sharks about 400 MYA -However, they adopted a heavy internal skeleton made completely of bone Bony fishes are the most species rich group of all vertebrates (> 30,000 living species) They developed significant adaptations that enabled them to dominate life in the water -Swim bladder and gill cover

24. History of the Fishes Swim bladder -A gas-filled sac that allows bony fishes to regulate their buoyant density -Gas addition = Gas gland -Gas release = Oval body Gill cover -A hard plate, the operculum, covers gills -Its flexing permits water pumping over gills

25. History of the Fishes

26. Two Major Groups of Bony Fishes Ray-finned fishes (class Actinopterygii) -Parallel bony rays support & stiffen each fin -There are no muscles within the fins Lobe-finned fishes (class Sarcopterygii) -Have paired fins that consist of a long felshy muscular lobe -Supported by central co-jointed bones -Almost certainly the amphibian ancestors

27. Two Major Groups of Bony Fishes

28. Amphibians Amphibians (class Amphibia) are damp-skinned vertebrates -First vertebrates to walk on land

29. Amphibians Amphibianshave several key characteristics 1. Legs 2. Lungs 3. Cutaneous respiration 4. Pulmonary veins 5. Partially divided heart

30. History of Amphibians Successful invasion of lands by vertebrates required several adaptations 1. Legs to support body’s weight 2. Lungs to extract oxygen from air 3. Redesigned heart to drive larger muscles 4. Reproduction in H2O to prevent egg drying 5. System to prevent whole body desiccation

31. History of Amphibians Amphibians evolved from lobe-finned fish Ichthyostega was one of the first amphibians -Efficient limbs for land crawling -Improved olfactory and auditory structures -However, still fishlike -Spent much of life in water

32. History of Amphibians In 2006, a transitional fossil was found between fish and Ichthyostega -Tiktaalik lived about 375 MYA -Shoulder and limb bones like those of an amphibian -Fins like those of a lobe-finned fish -Spent most of its life in water -Capable of moving onto land to capture food or escape predators

34. History of Amphibians Amphibians first became common in the Carboniferous period (360-280 MYA) -Began to leave marshlands for dry upland in the early Permian period (280-248 MYA) -Large size & complete body covering point to reliance on lung, not skin, for respiration The Triassic period (248-213 MYA) saw the virtual extinction of amphibians from land

35. Modern Amphibians Modern amphibians are descended from three families of the Tertiary period (65-2 MYA) -These accomplished a highly successful invasion of wet habitats all over the world Today there are about 5,670 species in 37 different families, comprising three orders: -Anura (“without tail”) -Caudata (“visible tail”) -Apoda (“without legs”)

36. Modern Amphibians Order Anura (frogs and toads) -Frogs have smooth, moist skin and long legs -Most live in or near water -Toads have bumpy, dry skin and short legs -Most live in dry environments -Eggs are fertilized externally -Hatched into swimming tadpole larvae -Undergo metamorphosis into adults

37. Modern Amphibians Order Caudata (salamanders) -Have long bodies, tails & smooth, moist skin -Live in moist places -Eggs are fertilized internally -Larvae similar to adults Order Apoda (caecilians) -Tropical, burrowing amphibians -Legless with small eyes and jaws with teeth -Fertilization is internal

38. Modern Amphibians

39. Reptiles Over 7000 species of reptiles (class Reptilia) now live on Earth All living reptiles exhibit three key features 1. Amniotic eggs, which are watertight 2. Dry skin, which covers body and prevents water loss 3. Thoracic breathing, which increases lung capacity

40. Reptiles Reptiles, birds and mammals are amniotes The amniotic egg has four membranes -Chorion – Allows O2 entry -Amnion – Fluid-filled cavity -Yolk sac – Provides food -Allantois – Excretes wastes

41. Reptiles

42. History of Reptiles Reptiles dominated earth for 250 million years Reptiles are distinguished by the number of holes on side of the skull behind eye orbit: -0 (anapsids), 1 (synapsids), 2 (diapsids)

43. History of Reptiles The synapsids rose to dominance first -Pelycosaurs were first land vertebrates to kill beasts their own size -Therapsids replaced them about 250 MYA -May have been endotherms

44. History of Reptiles Therapsids were replaced by diapsids about 230 MYA -Most became extinct 170 MYA -One group survived and has living descendants today – the mammals A number of different diapsids occurred in the Triassic period (248-213 MYA)

45. History of Reptiles Archosaurs were the first land vertebrates to be bipedal -Gave rise to dinosaurs about 220 MYA Dinosaurs dominated for over 150 million years -Became extinct 65 MYA -Asteroid’s impact

46. Modern Reptiles Modern reptiles developed two important characteristics: 1. Internal fertilization: Sperm fertilizes egg before protective membranes are formed 2. Improved circulation: Oxygen is provided to the body more efficiently

47. Modern Reptiles

48. Modern Reptiles All living reptiles are ectothermic -Obtain heat from external sources There are four surviving orders of reptiles -Chelonia (turtles and tortoises) -Rhynchocephalia (tuataras) -Squamata (lizards and snakes) -Crocodylia (crocodiles and alligators)

49. Order Chelonia Tortoises are terrestrial -Have dome-shaped shell Turtles are mostly aquatic -Have disc-shaped shells Both lack teeth but have sharp beaks Marine turtles must return to land to lay eggs

50. Order Rhynchocephalia Contains only two species of tuataras -Large, lizardlike animals about half a meter long -Only found on islands near New Zealand -Feature a parietal eye -Inconspicuous “third eye” on top of head