Chapter 34

1. Chapter 34 Vertebrates

2. Overview: Half a Billion Years of Backbones • By the end of the Cambrian period, some 540 million years ago • An astonishing variety of animals inhabited Earth’s oceans • One of these types of animals • Gave rise to vertebrates, one of the most successful groups of animals

3. Figure 34.1 • The animals called vertebrates • Get their name from vertebrae, the series of bones that make up the backbone

4. There are approximately 52,000 species of vertebrates • Which include the largest organisms ever to live on the Earth

5. Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord • Vertebrates are a subphylum of the phylum Chordata • Chordates are bilaterian animals • That belong to the clade of animals known as Deuterostomia

6. Chordates Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Tetrapods Amniotes Echinodermata(sister group to chordates) Chondrichthyes(sharks, rays, chimaeras) Cephalaspidomorphi(lampreys) Amphibia(frogs, salamanders) Cephalochordata(lancelets) Reptilia(turtles, snakes,crocodiles, birds) Actinopterygii(ray-finned fishes) Urochordata(tunicates) Actinistia(coelacanths) Dipnoi(lungfishes) Myxini(hagfishes) Mammalia(mammals) Milk Amniotic egg Legs Lobed fins Lungs or lung derivatives Jaws, mineralized skeleton Vertebral column Head Brain Notochord Ancestral deuterostome Figure 34.2 • A hypothetical phylogeny of chordates

7. Dorsal,hollownerve cord Brain Notochord Musclesegments Mouth Anus Pharyngealslits or clefts Muscular,post-anal tail Figure 34.3 Derived Characters of Chordates • All chordates share a set of derived characters • Although some species possess some of these traits only during embryonic development

8. Notochord • The notochord • Is a longitudinal, flexible rod located between the digestive tube and the nerve cord • Provides skeletal support throughout most of the length of a chordate • In most vertebrates, a more complex, jointed skeleton develops • And the adult retains only remnants of the embryonic notochord

9. Dorsal, Hollow Nerve Cord • The nerve cord of a chordate embryo • Develops from a plate of ectoderm that rolls into a tube dorsal to the notochord • Develops into the central nervous system: the brain and the spinal cord

10. Pharyngeal Slits or Clefts • In most chordates, grooves in the pharynx called pharyngeal clefts • Develop into slits that open to the outside of the body • These pharyngeal slits • Function as suspension-feeding structures in many invertebrate chordates • Are modified for gas exchange in aquatic vertebrates • Develop into parts of the ear, head, and neck in terrestrial vertebrates

11. Muscular, Post-Anal Tail • Chordates have a tail extending posterior to the anus • Although in many species it is lost during embryonic development • The chordate tail contains skeletal elements and muscles • And it provides much of the propelling force in many aquatic species

12. Concept 34.2: Craniates are chordates that have a head • The origin of a head • Opened up a completely new way of feeding for chordates: active predation • Craniates share some common characteristics • A skull, brain, eyes, and other sensory organs

13. Neuraltube Neuralcrest Dorsal edgesof neural plate Ectoderm Ectoderm (a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube. (b) Neural crest cells migrate todistant sites in the embryo. Migrating neuralcrest cells Notochord Figure 34.7a, b Derived Characters of Craniates • One feature unique to craniates • Is the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryo

14. (c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull. Figure 34.7c • Neural crest cells • Give rise to a variety of structures, including some of the bones and cartilage of the skull

15. Slime glands Figure 34.9 Hagfishes • The least derived craniate lineage that still survives • Is class Myxini, the hagfishes

16. Concept 34.3: Vertebrates are craniates that have a backbone • During the Cambrian period • A lineage of craniates evolved into vertebrates

17. Derived Characters of Vertebrates • Vertebrates have • Vertebrae enclosing a spinal cord • An elaborate skull • Fin rays, in aquatic forms

18. Origins of Bone and Teeth • Mineralization • Appears to have originated with vertebrate mouthparts • The vertebrate endoskeleton • Became fully mineralized much later

19. Concept 34.4: Gnathostomes are vertebrates that have jaws • Today, jawless vertebrates • Are far outnumbered by those with jaws

20. Gill slits Cranium Mouth Skeletal rods Figure 34.13 Derived Characters of Gnathostomes • Gnathostomes have jaws • That evolved from skeletal supports of the pharyngeal slits

21. Other characters common to gnathostomes include • Enhanced sensory systems, including the lateral line system • An extensively mineralized endoskeleton • Paired appendages (fins for swimming)

22. Chondrichthyans (Sharks, Rays, and Their Relatives) • Members of class Chondrichthyes • Have a skeleton that is composed primarily of cartilage • The cartilaginous skeleton • Evolved secondarily from an ancestral mineralized skeleton

23. (a) Blacktip reef shark (Carcharhinus melanopterus).Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins. Pelvic fins Pectoral fins (b) Southern stingray (Dasyatis americana).Most rays are flattened bottom-dwellers thatcrush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into their gaping mouth. Figure 34.15a, b • The largest and most diverse subclass of Chondrichthyes • Includes the sharks and rays

24. (c) Spotted ratfish(Hydrolagus colliei). Ratfishes, or chimaeras, typically live at depths greaterthan 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin. Figure 34.15c • A second subclass • Is composed of a few dozen species of ratfishes

25. Most sharks • Have a streamlined body and are swift swimmers • Have acute senses

26. Ray-Finned Fishes and Lobe-Fins • The vast majority of vertebrates • Belong to a clade of gnathostomes called Osteichthyes

27. Nearly all living osteichthyans • Have a bony endoskeleton • Aquatic osteichthyans • Are the vertebrates we informally call fishes • Control their buoyancy with an air sac known as a swim bladder

28. Adipose fin(characteristic oftrout) Dorsal fin Caudal fin Swim bladder Spinal cord Brain Nostril Cut edge of operculum Anal fin Gills Anus Gonad Liver Heart Lateral line Stomach Urinary bladder Kidney Intestine Pelvic fin Figure 34.16 • Fishes breathe by drawing water over four or five pairs of gills • Located in chambers covered by a protective bony flap called the operculum

29. Concept 34.5: Tetrapods are gnathostomes that have limbs and feet • One of the most significant events in vertebrate history • Was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

30. Derived Characters of Tetrapods • Tetrapods have some specific adaptations • Four limbs and feet with digits • Ears for detecting airborne sounds

31. Bonessupportinggills Tetrapodlimbskeleton Figure 34.19 The Origin of Tetrapods • In one lineage of lobe-fins • The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

32. Millions of years ago 420 370 340 310 295 280 265 415 400 385 355 325 Silurian Devonian Carboniferous Permian To present Paleozoic Ray-finned fishes Coelacanths Lungfishes Eusthenopteron Panderichthys Elginerpeton Metaxygnathus Acanthostega lchthyostega Hynerpeton Greerpeton Amphibians Amniotes Figure 34.20 • Extraordinary fossil discoveries over the past 20 years • Have allowed paleontologists to reconstruct the origin of tetrapods

33. Amphibians • Class Amphibia • Is represented by about 4,800 species of organisms • Most amphibians • Have moist skin that complements the lungs in gas exchange

34. (a) Order Urodela. Urodeles (salamanders) retain their tail as adults. Figure 34.21a • Order Urodela • Includes salamanders, which have tails

35. (b) Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults. Figure 34.21b • Order Anura • Includes frogs and toads, which lack tails

36. (c) Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians. Figure 34.21c • Order Apoda • Includes caecilians, which are legless and resemble worms

37. (b) The tadpole is an aquatic herbivore witha fishlike tail and internal gills. (c) During metamorphosis, the gills and tail are resorbed, andwalking legs develop. (a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air. Figure 34.22a–c • Amphibian means “two lives” • A reference to the metamorphosis of an aquatic larva into a terrestrial adult

38. Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg • Amniotes are a group of tetrapods • Whose living members are the reptiles, including birds, and the mammals

39. Derived Characters of Amniotes • Amniotes are named for the major derived character of the clade, the amniotic egg • Which contains specialized membranes that protect the embryo

40. Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. Allantois. The allantois is a disposal sac for certain metabolic wastes pro- duced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ. Extraembryonic membranes Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”). Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock. Embryo Amniotic cavitywith amniotic fluid Yolk (nutrients) Albumen Shell Figure 34.24 • The extraembryonic membranes • Have various functions

41. Amniotes also have other terrestrial adaptations • Such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs

42. Early Amniotes • Early amniotes • Appeared in the Carboniferous period • Included large herbivores and predators

43. Reptiles • The reptile clade includes • The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs

44. Figure 34.25 • Reptiles • Have scales that create a waterproof barrier • Lay shelled eggs on land

45. Most reptiles are ectothermic • Absorbing external heat as the main source of body heat • Birds are endothermic • Capable of keeping the body warm through metabolism

46. The Origin and Evolutionary Radiation of Reptiles • The oldest reptilian fossils • Date to about 300 million years ago • The first major group of reptiles to emerge • Were the parareptiles, which were mostly large, stocky herbivores

47. The dinosaurs • Diversified into a vast range of shapes and sizes • Included the long-necked giants called the theropods

48. Figure 34.26 • Traditionally, dinosaurs were considered slow, sluggish creatures • But fossil discoveries and research have led to the conclusion that dinosaurs were agile and fast moving • Paleontologists have also discovered signs of parental care among dinosaurs

49. (a) Tuatara (Sphenodon punctatus) Figure 34.27a Lepidosaurs • One surviving lineage of lepidosaurs • Is represented by two species of lizard-like reptiles called tuatara

50. Figure 34.27b (b) Australian thorny devil lizard (Moloch horridus) • The other major living lineage of lepidosaurs • Are the squamates, the lizards and snakes • Lizards • Are the most numerous and diverse reptiles, apart from birds