1. Chapter 34 Vertebrates

2. The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone Mammals, birds, lizards, snakes, turtles, amphibians, and the various classes of fishes. There are approximately 52,000 species of vertebrates The vertebrates belong to one of the two major phyla in the Deuterostomia, the chordates. Echinodermata is the other phyla

4. Concept 34.1 Shared Features of all Chordates Although chordates vary widely in appearance, all share the presence of four anatomical structures at some point in their lifetime. –Notochord –Dorsal, hollow nerve cord –Pharyngeal slits –Muscular, postanal tail

5. The notochord –Is a longitudinal, flexible rod located between the digestive tube and the nerve cord and provides skeletal support The Dorsal, hollow nerve cord of a chordate embryo –Develops into the central nervous system: the brain and the spinal cord

6. 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

7. 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 Muscular, postanal tail

9. Cephalochordata Lancelets, Cephalochordates All are marine suspension feeders –That retain the characteristics of the chordate body plan as adults

10. Urochordata Tunicates, Urochordates –Are marine suspension feeders commonly called sea squirts Tunicates most resemble chordates during their larval stage –Which may be as brief as a few minutes

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

13. The least derived craniate lineage that still survives –Is Myxini, the hagfishes Hagfishes are jawless marine craniates –That have a cartilaginous skull and axial rod of cartilage derived from the notochord

14. Concept 34.3 Craniates with a Backbone = Vertebrates Vertebrates represent only 5% of animals Vertebrates are craniates that have a backbone Vertebrates have –Vertebrae enclosing a spinal cord –An elaborate skull –Fin rays, in aquatic forms

15. Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord They are jawless vertebrates that feed by clamping their mouth onto a live fish They inhabit various marine and freshwater habitats

17. Lampreys are jawless vertebrates –Inhabiting various marine and freshwater habitats Figure 34.10

18. Concept 34.4 Vertebrates with a Jaw = Gnathostomes 4 groups of fishes –1 Cartilaginous fish and 3 Bony fish 3 groups of tetrapods –Salamanders to primates Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates Gnathostomes include sharks and their relatives, ray-finned fishes, lobe-finned fishes, amphibians, reptiles (including birds), and mammals

19. Derived Characters of Gnathostomes Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits

21. Chondrichthyes Sharks and Rays, have relatively flexible endoskeletons of cartilage rather than bone. There are about 750 species All have well-developed jaws and paired fins. The cartilaginous skeleton of these fishes is a derived characteristic, not a primitive one.

22. Sharks Carnivores that swallow their prey whole or use their powerful jaws to tear flesh. Eggs are fertilized internally. –Males transfer sperm via claspers on their pelvic fins Oviparous sharks encase their eggs in protective cases and lay them outside the mother’s body. Ovoviviparous sharks retain fertilized eggs in the oviduct. –The embryo completes development in the uterus, nourished by the egg yolk. A few sharks are viviparous, providing nutrients through a placenta to the developing offspring.

23. Rays Rays are closely related to sharks, but feed along the bottom and have dorsal compressed bodies –The tail of many rays is whiplike and may bear venomous barbs for defense against threats.

24. Osteichthyes The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes Osteichthyes includes the bony fish (informally call fihes) and tetrapods

26. Bony Fish Ray-finned fishes Lobe-finned fishes Lungfishes Bony fishes are the most numerous group of vertebrates, both in individuals and in species (about 30,000 species).

27. The reproductive modes of fishes vary extensively. –Most species are oviparous however, internal fertilization occurs in many fish groups and some are even viviparous. Most fishes have a swim bladder. –The positive buoyancy provided by air counters the negative buoyancy of the tissues. Bony fishes are generally maneuverable swimmers. –Their flexible fins are better for steering and propulsion than the stiffer fins of sharks. Fishes have a lateral line system (used to sense vibrations)

28. Class Actinopterygii Ray-finned fishes –Bass, trout, perch, tuna and herring –In this group, the fins are supported by long flexible rays, –The fins may be modified for maneuvering, defense, and other functions.

29. Class Actinistia Lobe-finned fishes –Many lobe-fins were large, bottom dwellers that may have used their paired, muscular fins to “walk” along the bottom. –Coelacanths were thought to have become extinct 75 million years ago, but a living coelacanth was caught off the coast of South Africa in 1938

30. Class Dipnoi Lungfishes All three genera occur in the Southern Hemisphere –Inhabit stagnant ponds and swamps where they gulp air into lungs for metabolism. –Lungfishes also have gills, which are the main organs for gas exchange. –When ponds shrink during the dry season, some lungfishes can burrow into the mud and aestivate. The ancestor of amphibians was probably a lungfish.

31. Concept 34.5: Tetrapods are gnathostomes that have limbs 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

32. Derived Characters of Tetrapods Tetrapods have some specific adaptations –Four limbs, and feet with digits –A neck, which allows separate movement of the head –Fusion of the pelvic girdle to the backbone –The absence of gills (except some aquatic species) –Ears for detecting airborne sounds

34. Concept 34.5 Tetrapods Amphibians were the first tetrapods to spend a substantial portion of their time on land. This led to the evolution of the leg. As the earths flora diversified, so did the fauna. Dense aquatic vegetation made movement difficult. –This may have caused a modified fin to evolve into a simple leg-like limb.

36. Extraordinary fossil discoveries over the past 20 years –Have allowed paleontologists to reconstruct the origin of tetrapods

37. Class Amphibia 6,150 species of: –Salamanders (Order Urodela) –Frogs (Order Anura) –Caecilians (Order Apoda) Amphibian means “two lives,” a reference to the metamorphosis of many frogs from an aquatic stage, the tadpole, to the terrestrial adult.

39. Tadpoles are usually aquatic herbivores with gills and swim by undulating the tail. During metamorphosis, the tadpole develops legs, and gills are replaced by lungs. Adult frogs are carnivorous hunters.

40. Most amphibians retain close ties with water and are most abundant in damp habitats. –Those adapted to drier habitats spend much of their time in burrows or under moist leaves where the humidity is higher. –Most amphibians rely heavily on their moist skin to carry out gas exchange with the environment. Some terrestrial species lack lungs entirely and breathe exclusively through their skin and oral cavity.

41. Most species have external fertilization, with eggs shed in ponds or moist habitats. –Some species lay vast numbers of eggs in temporary pools where mortality is high. –In contrast, others display parental care and lay relatively few eggs. In some species, males or females may house eggs on their back, in the mouth, or even in the stomach. Some species are ovoviviparous or viviparous.

42. Many amphibians display complex and diverse social behavior, especially during the breeding season. –Then, many male frogs fill the air with their mating calls as they defend breeding territories or attract females. For the past 25 years, zoologists have been documenting the decline in amphibian populations throughout the world. –Habitat loss –Possibly global warming

43. Concept 34.6 Amniotes The amniote clade includes mammals and reptiles: turtles, lizards, snakes, crocodiles and birds. The evolution of amniotes from an amphibian ancestor involved many adaptations for terrestrial living including –the amniotic egg –waterproof skin –increasing use of the rib cage to ventilate the lungs.

44. The amniotic eggs enabled terrestrial vertebrates to complete their life cycles entirely on land. –In contrast to the shell-less eggs of amphibians, the amniotic eggs of most amniotes have a shell that retains water and can be laid in a dry place. –The calcareous shells of bird eggs are inflexible, while the leathery eggs of many reptiles are flexible. –Most mammals have dispensed with the shell. The embryo implants in the wall of the uterus and obtains its nutrition from the mother.

45. Amniote Clades An evolutionary radiation of amniotes gave rise to two main groups, called Diapsids and Synapsids.

46. The synapsids included mammal-like reptiles, the therapsids, from which mammals evolved. The anaspid (not mentioned) lineage is probably extinct. –Turtles had been considered the only surviving anaspid lineage, but molecular comparisons place the turtles somewhere within the diapsids. The diapsids include most or all (depending on placement of turtles) groups of modern reptiles and birds.

47. The classical classification of amniotes is at odds with several alternatives that are based on strict application of cladistic conventions, in which each taxa must represent a monophyletic group.

48. Reptiles The reptile clade includes –The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs Reptiles –Have scales that create a waterproof barrier –Lay shelled eggs on land

51. 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

52. The diapsids are composed of two main lineages –The lepidosaurs (lizards and snakes) and the archosaurs (turtles, crocs, dinosaurs and birds) One surviving lineage of lepidosaurs –Is represented by two species of lizard-like reptiles called tuatara

53. 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 Figure 34.27b (b) Australian thorny devil lizard (Moloch horridus)

54. Snakes are probably descendents of lizards that adapted to a burrowing lifestyle through the loss of limbs. –This limbless condition remains today, even though most snakes live above ground. –Vestigial pelvic and limb bones in primitive snakes such as boas, are evidence that snakes evolved from reptiles with legs.

55. All snakes are carnivorous. –Snakes have acute chemical sensors and are sensitive to ground vibrations. The flicking tongue fans odors toward olfactory organs on the roof of the mouth. –Heat-detecting organs of pit vipers, including rattlesnakes, enable these night hunters to locate warm animals. –Some poisonous snakes inject their venom through a pair of sharp hollow or grooved teeth. –Loosely articulated jaws enable most snakes to swallow prey larger than the diameter of the snake itself.

56. Archosaurs Crocodilians –Belong to an archosaur lineage that dates back to the late Triassic Figure 34.27e (e) American alligator (Alligator mississipiensis)

57. Crocodiles and alligators (crocodilians) are among the largest living reptiles. –They spend most of their time in water, breathing air through upturned nostrils. –Crocodilians are confined to the tropics and subtropics.

58. Birds are archosaurs –Almost every part of a typical bird’s anatomy is modified in some way to enhance flight. One adaptation to reduce weight is the absence of some organs. –For instance, females have only one ovary. –Lack of a urinary bladder. Modern birds are toothless and grind their food in a muscular gizzard near the stomach.

59. The skeletons of birds have several adaptations that make them light, flexible, but strong. –The bones are honeycombed to reduce weight without sacrificing much strength.

60. Flying requires a great expenditure of energy from an active metabolism. –Birds are endothermic, using their own metabolic heat to maintain a constant body temperature. Feathers and, in some species, a layer of fat provides insulation. –Efficient respiratory and circulatory systems with a four-chambered heart keep tissues well supplied with oxygen and nutrients.

61. Birds have excellent vision and excellent coordination. The large brains of birds (proportionately larger than those of reptiles or amphibians) support very complex behavior. –During the breeding season, birds engage in elaborate courtship rituals. This culminates in copulation, contact between the mates’ vents, the openings to their cloacas. –After eggs are laid, the avian embryo is kept warm through brooding by the mother, father, or both, depending on the species.

62. The most obvious adaptations for flight are wings.

63. Feathers are among the most remarkable of vertebrate adaptations. –They are both extremely light and strong. –Feathers are made of the protein keratin, the same material in reptile scales and mammalian hair and nails. Feathers may have functioned first as insulation during the evolution of endothermy and were later co-opted as flight equipment.

64. The evolution of flight required radical alteration in body form but provided many benefits. –Flight enhanced hunting and scavenging. It enabled many birds to exploit flying insects. –Flight provides an easy escape from predators. –It enables many birds to migrate great distances to exploit different food resources and seasonal breeding areas. The arctic tern migrates round-trip between the Arctic to Antarctic each year.

65. Other adaptations include structure in bird feet Figure 34.31 Grasping bird (such as a woodpecker) Perching bird (such as a cardinal) Raptor (such as a bald eagle) Swimming bird (such as a duck)

66. Cladistic analyses of fossilized skeletons support the hypothesis that the closest reptilian ancestors of birds were theropods. –These were relatively small, bipedal, carnivorous dinosaurs (such as the velociraptors of Jurassic Park). –While most researchers agree that the ancestor of birds was a feathered theropod, others place the origin of birds much earlier, from an ancestor common to both birds and dinosaurs.

67. The most famous Mesozoic bird is Archeopteryx, known from fossils from Bavaria. –This ancient bird lived about 150 million years ago, during the late Jurassic period. –Archeopteryx had clawed forelimbs, teeth, and a long tail containing vertebrae.

68. Without its feathers, Archeopteryx would probably be classified as a theropod dinosaur. Its skeletal anatomy indicates that it was a weak flyer, perhaps a tree-dwelling glider.

69. There about 10,000 extant species of birds classified in about 28 orders. –These include a few flightless birds, the ratites, which lack a keeled breastbone and large pectoral muscles. –The ratites include the ostrich, kiwi, and emu.

70. Most birds are carinates because they have a sternal keel, which anchor the large pectoral muscles. –Carinate birds exhibit a great variety of feather colors, beak and foot shapes, behaviors, and flying styles. –Nearly 60% of living bird species are in the order passeriformes, or perching birds.

71. Concept 34.7 Class Mammalia With the extinction of the dinosaurs and the fragmentation of continents that occurred at the close of the Mesozoic era, mammals underwent an extensive adaptive radiation. There are about 5,300 extant species of mammals. Mammals have –Mammary glands, which produce milk –Hair –A high metabolic rate, due to endothermy –A larger brain than other vertebrates of equivalent size –Differentiated teeth

72. Vertebrates of the class Mammalia were first defined by Linnaeus by the presence of mammary glands. –All mammalian mothers nourish their babies with milk, a balanced diet rich in fats, sugars, proteins, minerals, and vitamins, produced in the mammary glands. –All mammals also have hair, made of the keratin. Hair and a layer of fat under the skin retain metabolic heat, contributing to endothermy in mammals. –Endothermy adaptations include a muscular diaphragm and a four-chambered heart.

74. Most mammals are born rather than hatched. –Fertilization is internal, and the embryo develops in the mother’s uterus. –In eutherian (placental) mammals and marsupials the lining of the uterus and extraembryonic membranes collectively form a placenta, where nutrients diffuse into the embryo’s blood.

75. Mammals evolved from reptiles. –Therapsids –Fossils show small stages in the evolution of the mammalian legs, skull, jaws, and teeth. While therapsids disappeared during the Mesozoic, mammals coexisted with dinosaurs and underwent a great adaptive radiation in the Cenozoic in the wake of the Cretaceous extinctions. –Modern mammals are split into three groups: monotremes (egg-laying mammals), marsupials (mammals with pouches) and eutherian (placental) mammals.

76. Monotremes - playtpuses and echidnas - are the only living mammals that lay eggs. –The reptile-like egg contains enough yolk to nourish the developing embryo. Monotremes have hair and females produce milk in specialized glands. –After hatching, the baby sucks milk from the mother’s fur because they lack nipples.

77. Marsupials include opossums, kangaroos, bandicoots, and koalas. A marsupial is born very early in development and completes its embryonic development while nursing within a maternal pouch, the marsupium. –In most species, the tiny offspring climbs from the exit of the female’s reproductive tract to the mother’s pouch.

78. In Australia, marsupials have radiated and filled niches occupied by eutherian mammals in other parts of the world. Through convergent evolution, these diverse marsupials resemble eutherian mammals that occupy similar ecological roles. Fig. 34.32

79. Compared to marsupials –Eutherians have a longer period of pregnancy Young eutherians –Complete their embryonic development within a uterus, joined to the mother by the placenta Eutherians include all other mammals (rodents, bats, primates, cetaceans, etc.)

81. The current hypothesis, based on molecular systematics, for the evolutionary relationships among eutherian orders clusters them into four main clades.

82. Primates The mammalian order Primates includes lemurs, tarsiers, monkeys, and apes Humans are members of the ape group Most primates have hands and feet adapted for grasping, and flat nails

83. Other derived characters of primates –A large brain and short jaws –Forward-looking eyes close together on the face, providing depth perception –Complex social behavior and parental care –A fully opposable thumb (in monkeys and apes)

86. Concept 34.8: Humans are mammals that have a large brain and bipedal locomotion The species Homo sapiens is about 200,000 years old, which is very young, considering that life has existed on Earth for at least 3.5 billion years

87. Derived Characters of Humans A number of characters distinguish humans from other apes –Upright posture and bipedal locomotion –Larger brains capable of language, symbolic thought, artistic expression, the manufacture and use of complex tools –Reduced jawbones and jaw muscles –Shorter digestive tract

88. The human and chimpanzee genomes are 99% identical Changes in regulatory genes can have large effects

89. Homo Sapiens Homo sapiens appeared in Africa by 195,000 years ago All living humans are descended from these African ancestors