• Vertebrates are chordates with a backbone. • Even though many vertebrates appear different, Introduction to Vertebrates they are very much alike internally, indicating that in the distant past they had a common ancestor. • Present-day differences in vertebrates reflect their different evolutionary paths.
© Lisa Michalek
Adaptations of Vertebrates Adaptations of Vertebrates • The backbone provides support for and protects a dorsal nerve cord. • Vertebrates are chordates with a backbone. • It also provides • The individual segments that make up the backbone are called vertebrae. a site for muscle attachment. • In most vertebrates, the backbone • These functions completely replaces allowed vertebrates the notochord found to grow larger than in invertebrate chordates. their invertebrate ancestors. • In addition to a backbone, vertebrates have a bony skull that encases and protects their brain.
Adaptations of Vertebrates Adaptations of Vertebrates • The tissues of vertebrates compose organs. • Vertebrates share a number of other characteristics, including segmentation, bilateral symmetry, and two pairs of jointed appendages, such as limbs or • The organs compose organ systems. fins. • Vertebrate organ systems tend to be more complex than the organ systems • They exhibit cephalization and have complex brains and sense organs. found in invertebrates. • All vertebrates have a true coelom and a closed circulatory system with a chambered heart. The First Vertebrates The First Vertebrates
Unlike most of the fishes that we are now familiar with, the earliest fishes, The first chordates evolved about 550 million years ago. • • called agnathans, had neither jaws nor paired fins. • At that time, many different groups of organisms appeared in the shallow Agnathans did have seas that covered a large portion of Earth s continents. • ’ a backbone, which • According to the fossil record, the first vertebrates were fishes. provided a central axis for muscle attachment. • As their muscles pulled against the backbone, the agnathans propelled themselves along the ocean bottom.
The First Vertebrates Evolution of Fishes
• Within another 50 million years, jawless fishes had diversified into a great • About 430 million years variety of species. ago, the acanthodians (spiny fishes) appeared. • The major group was the ostracoderms which had • Acanthodians had strong jaws with jagged, bony edges that served as teeth, primitive fins and massive enabling them to hold onto prey. plates of bony tissue on their body. • The development of jaws in fishes was a key evolutionary innovation. • Jawless fishes dominated the oceans for about 100 million years, until they • Jaws are thought to have evolved from gill arch supports made of cartilage were replaced by new kinds of fishes that were hunters. (a lightweight, strong, flexible tissue).
Evolution of Fishes Evolution of Fishes About 20 million years after the acanthodians appeared, the placoderms The spiny fishes had internal skeletons of cartilage, although some fossils • • evolved. indicate that their skeletons also contained some bone. • Placoderms were jawed fishes with massive heads armored with bony plates. • Their scales also contained small plates of bone. • By the end of the Devonian period, almost all of the early fishes, including the placoderms, had disappeared. • After dominating the seas for almost 50 million years, they were replaced by swifter swimmers, the sharks and bony fishes. Sharks and Bony Fishes Sharks and Bony Fishes
•By the end of the Devonian period, almost all of the • Sharks have a skeleton composed of cartilage. early fishes had disappeared. • Calcium carbonate is deposited in the outer layer of the cartilage. •At about the same time • A thin layer of bone covers this reinforced cartilage. (400 million years ago), • The result is a very light but strong skeleton. sharks and bony fishes appeared. •Sharks and bony fishes, which are superior swimmers, thrived in the Devonian seas. •Most have streamlined bodies that are well adapted for rapid movement through the water.
Sharks and Bony Fishes Modern Fishes
• Bony fishes have a skeleton made of bone, which is heavier and less flexible • Today there are more fishes than any other group of vertebrates. than cartilage. • Today’s fishes belong to one of three major groups: the agnathans, the • Bony fishes have a swim bladder, which compensates for this increased cartilaginous fishes and the bony fishes. weight. • The agnathans • This gas-filled sac (hagfishes and buoys them in the the lampreys) water, just as an resemble the air-filled balloon early jawless fishes. buoys a swimmer.
Modern Fishes Evolution of Amphibians • The first cartilaginous fishes (sharks) and the bony fishes evolved at about the • The first group of vertebrates to live on land was the same time, 400 million years ago. amphibians, which appeared about 370 million years ago. • These two groups of fishes likely evolved from the same early, jawless fishes that gave rise to the acanthodians and the placoderms. • Amphibians probably shared • The shark’s a common ancestor with relatives, the modern lungfishes and skates and rays other lobe-finned fishes. evolved later. • The pattern of bones in an amphibian’s limbs bears a strong resemblance to that of a lobe-finned fish. • While several species of lobe-finned fishes exist today, those species thought to be ancestral to amphibians are extinct. The ‘Age of Amphibians’ Evolution of Amphibians • Although amphibians first appeared in the Devonian period, they increased greatly in numbers during the Carboniferous period. • During this time (The age of Amphibians) the number of amphibian families increased from 14 to about 34. • By the late Carboniferous period, much of what was to become North America was covered by low-lying tropical swamplands. • Amphibians thrived in this moist environment, sharing it with early reptiles.
The ‘Age of Amphibians’ Adaptations for Life on Land
• In the Permian period that followed, amphibians reached their greatest • Life on land is quite different from life in the water. Therefore, a number of diversity, increasing to 40 families. major adaptations allowed some species to successfully invade the land. • In the early Permian period, a remarkable change occurred among – Legs. Legs support the body’s weight as well as allow movement from place to place. amphibians, many of them began to leave the marshes for dry uplands. – Lungs. The delicate structure of a fish’s gills depends on water for support. On land, lungs carry out gas exchange. • By the middle Permian, – Heart. Walking on land requires a greater expenditure of energy than swimming. Land 60 percent of all animals tend to have higher metabolic rates than aquatic animals. This requires greater amphibian species amounts of oxygen. The structure of the vertebrate heart allows oxygen to be were living in dry delivered to the body efficiently. environments.
Modern Amphibians Modern Amphibians • All of today’s amphibians are descendants of the amphibians that survived into the Jurassic period. • The middle Permian period marked the peak of amphibian success. • They are found in aquatic and moist habitats throughout the temperate and • By the end of this period a tropical regions of the world. new kind of vertebrate, a reptile called a therapsid, • Frogs and toads make up had become common and the largest and most familiar began to replace the amphibians. group of modern amphibians. • By the end of the Triassic period that followed, there were only 15 families • Salamanders and newts are of amphibians. far less numerous. • Caecilians account for less than 1 percent of today’s amphibian species. Evolution of Amphibians Early Reptiles • Fluid loss is a problem for all terrestrial animals that live on land. • The adaptations that permitted amphibians to live on land further developed in reptiles. • Two very important adaptations for terrestrial life evolved in reptiles. • Reptiles were the first animals to have skin and eggs that are both almost watertight.
Early Reptiles Evolution of Terrestrial Vertebrates
• When reptiles first evolved, about 320 million years ago, Earth was entering a long, dry period. • Early reptiles were better suited to these conditions than amphibians were, and the reptiles quickly diversified. • Within 50 million years, reptiles had replaced amphibians as the dominant terrestrial vertebrates.
Evolution of Dinosaurs Evolution of Dinosaurs • One factor that affected dinosaur evolution was the movement of • Beginning about 235 million years ago, dinosaurs dominated life on land for the continents, which altered Earth’s climate. roughly 150 million years. • When the dinosaurs first appeared, all of Earth’s landmasses were • They evolved from the thecodonts, an extinct joined in a single supercontinent called Pangaea. group of crocodile-like reptiles. • There were few mountain ranges over this enormous stretch of • During their long history, dinosaurs changed a great deal because the world land, and the interior was dry. they inhabited changed. • Coastal climates were much the same all over the world, quite • Dinosaurs represent a long parade of change and adaptation. warm, with a dry season followed by a very wet rainy season. • As Pangaea broke apart, the climates of the various landmasses varied. • Some species of dinosaurs could not adapt and became extinct, while new kinds flourished. Breakup of Pangaea Triassic Dinosaurs • The oldest known dinosaur fossils are in rocks from the early Triassic period (about 235 million years ago). • One of the first known dinosaurs, Eoraptor, was a 30 cm (1 ft) long bipedal carnivore. • By the end of the Triassic period some 22 million years later, small, carnivorous dinosaurs were very common and had largely replaced the thecodonts.
Triassic Dinosaurs Triassic Dinosaurs 2. Drought Resistance. Dinosaurs were well adapted to the dry conditions found in Pangaea during the late Triassic period. • There are at least three reasons why dinosaurs were so successful. 3. Extinction of other animal species. At the end of the Triassic period a large 1. Leg Structure. Legs positioned directly under the body provided good support for meteorite struck Northeastern Canada the dinosaur’s body weight, enabling dinosaurs to be faster and more agile (Manicouagan Crater). This event runners than the thecodonts. Dinosaurs were better able to catch prey and might have been responsible escape from predators. for the great loss of animal diversity that occurred at the end of the Triassic period. Thecodonts and many other species became extinct, but the dinosaurs survived.
The Jurassic Period The Jurassic Period The Golden Age of Dinosaurs • By the late Jurassic • The Jurassic period is considered the golden age of dinosaurs because of the period, the carnivorous variety and abundance of dinosaurs that lived during this time. theropods were common. • They included the largest land animals of all time, the sauropods. • Theropods stood on two – Sauropods had enormous, barrel-shaped bodies, powerful legs and had short arms. heavy column-like legs, and very long necks Their large heads were equipped with sharp teeth, and each foot had sickle- and tails. • shaped claws used for ripping open prey. – Sauropods were the dominant herbivore • This anatomy was well suited for rapid running and quick, slashing attacks. of the Jurassic period. • Theropods preyed on the large herbivorous dinosaurs and were the dominant terrestrial predators until the end of the Cretaceous period. Were Dinosaurs Warmblooded? Were Dinosaurs Warmblooded?
• Ectothermic animals (such as today’s reptiles) are animals whose metabolism • Were dinosaurs ectotherms or endotherms? is too slow to produce enough heat to warm their bodies. For a long time it was assumed that dinosaurs were • Such animals must absorb heat from their environment. • – Their body temperature changes as the temperature of their environment changes. ectotherms, as modern reptiles are. • Ectotherms are sometimes referred to as “coldblooded.” • However, new evidence indicates that at least some • Mammals and birds are endothermic animals. dinosaurs were endotherms. – They maintain a high, constant body temperature by producing heat internally. Endotherms are sometimes referred to as warmblooded. • The microscopic structure of the bones of some dinosaurs • “ ” resembles that of modern endotherms, both in growth rate and growth pattern. • In addition, chemical analysis indicates that the bones of some Cretaceous dinosaurs probably formed under endothermic conditions.
The Cretaceous Extinction The Cretaceous Extinction • Toward the end of the Cretaceous period, sea levels began to fall and the •A crater 200 mi wide off the coast of Mexico’s climate began to cool. Yucatan peninsula is very likely the site where this • Many kinds of dinosaurs began to decrease in number. meteorite or asteroid collided with Earth • 65 million years ago, all dinosaurs abruptly disappeared from the fossil record. approximately 65 million years ago, at the end of • Most scientists now agree that the major contributing cause was the Cretaceous period. the impact on Earth of A thin line of sediment one or more meteorites • or asteroids, the largest marks the end of the of which may have been Cretaceous period in 5 to 10 mi in diameter. rocks throughout the world. •This sediment is rich in iridium, a mineral rare in Earth’s crust but common in meteorites.
The Cretaceous Extinction Global Temperatures Through Time • Scientists think that such an impact would have thrown large amounts of material from Earth’s surface into the atmosphere. • This material would have blocked out sunlight for a considerable period of time and created a prolonged, worldwide cold period. • The endothermic birds and mammals, which were relatively small and insulated with feathers and fur, survived. • The smaller ectothermic reptiles and amphibians also survived. • The dinosaurs did not survive. The Cretaceous Extinction Atmospheric Oxygen Through Time • Scientists are not sure why the dinosaurs did not survive this period of intense cold. • Disease or competition from mammals might have led to their extinction. • However, if most Cretaceous dinosaurs were endotherms, as some scientists now think they were, they would not have been able to survive the cold. • They lacked the insulation of birds and mammals and could not lower their activity level as smaller reptiles and amphibians could.
Evolution of Birds Evolution of Birds
• The earliest know bird is Archaeopteryx (‘ancient wing’). • The impressions of feathers on some Archaeopteryx fossils raised questions about their classification as dinosaurs. • Archaeopteryx was about the size of a crow and shared many features with small theropods. • Archaeopteryx fossils appear avian (birdlike) –It had a long reptilian tail. due to the feathers on –It had no breastbone to their wings and tails. anchor its flight muscles, • They also had other avian features, like a as do modern birds. fused collar bone –Unlike the hollow bones (wishbone) which of modern birds, its dinosaurs did not have. bones were solid. –It also had forelimbs similar to those of a dinosaur.
Evolution of Birds Evolution of Birds • Today, most biologists agree that Archaeopteryx • The fossil record now reveals a diverse collection of toothed birds with hollow is very closely related bones and breastbones adapted for flight. to the small dinosaur • By the early Cretaceous period, only 15 million years after Archaeopteryx lived, Compsognathus. a variety of birds • Some biologists have classified Archaeopteryx as a “feathered dinosaur.” with many of • Recent fossil discoveries in China support this opinion. the features of modern birds • However, many biologists continue to classify birds in a separate class, Aves, had evolved. because of their distinct features. Evolution of Birds Modern Birds • There are more species of birds than of any other terrestrial vertebrate. • All but a few of the modern orders of birds are thought to have arisen after the Cretaceous extinction. • Since the impressions of feathers are rarely fossilized and since modern birds have hollow delicate bones, the fossil record of birds is incomplete. • Relationships among the families of modern birds are mostly inferred from studies of the degree of DNA similarity among living birds.
Modern Birds Modern Birds
• These studies suggest that the ostrich and its relatives belong to the oldest • Birds live in a wide variety of environments and differ group of living birds. greatly in appearance. • Ducks, geese, and waterfowl • While most birds have wings and can fly, the ostrich has likely arose next and were wings and does not fly. followed by a diverse group of woodpeckers, parrots, • The penguin’s wings have swifts, and owls. been modified to be used as flippers that propel • Next came the songbirds, it swiftly through ocean waters. which include 60 percent Striking colors often found in male birds help them of today’s bird species. • attract a mate. • The most recent birds to appear were the more specialized orders, including many birds of prey, flamingos, and penguins.
Modern Birds Modern Reptiles • All birds eat frequently because they have a high metabolic • Of the 16 orders of reptiles known to have rate and typically store little body fat. existed, only four remain today. • The first group, turtles have changed • The beaks of birds are adapted to the type of food the bird very little in structure since the time of the eats. dinosaurs. • The vast majority of living reptiles • Most birds consume small, belong to the second group to evolve, snakes energy-rich meals of fruits, and lizards. seeds, worms, or insects. • Tuataras belong to the third group of surviving reptiles to evolve. • Hawks and owls are • The fourth line of living reptiles, the predators; they eat rabbits, crocodilians, crocodiles and their relatives, rodents, and other small including the familiar mammals, and sometimes snakes and lizards. alligators, appeared on Earth much later than the first three groups. • Gulls and pelicans eat fish. –Crocodilians have changed very little Vultures feed on dead animals. in more than 200 million years. • –Like dinosaurs, crocodilians are descendents of the thecodonts. Modern Reptile Heart Modern Reptiles
• In some ways, such as the structure of their heart, crocodilians resemble birds far more than they resemble other living reptiles. – And crocodilians are the only living reptiles that care for their young. • Today, many biologists think that birds are direct descendants of the dinosaurs. – If this is true, then crocodilians and birds are more closely related to dinosaurs, and to each other, than they are to other living reptiles. – This close evolutionary relationship may account for some of their similarities.
Evolutionary Relationships Evolution of Mammals
• The first mammals appeared about 220 million years ago, just as the dinosaurs were evolving from thecodonts. • It is most likely that mammals were descendants of the therapsids, an extinct order of animals that were probably endotherms. • Mammals are the only vertebrates that have fur and mammary glands. • Early mammals, such as Eozostrodon, were small, about the size of mice. – They were insect eating, tree dwellers that were active at night.
Evolution of Mammals Diversification of Mammals • For 155 million years, while the dinosaurs flourished, mammals were a minor group that changed little. • After the Cretaceous extinction, the world’s climate was no longer dry. • The adaptations that served reptiles in dry climates were no longer so important. • Only 5 orders of mammals arose in that time, and their fossils are scarce. • Mammals and birds became the dominant vertebrate on land. • In the Cretaceous extinction, most animal species larger than a small dog disappeared. • In the Tertiary period, mammals rapidly diversified, taking over many of the ecological roles once dominated by dinosaurs. • The smaller reptiles, including lizards, turtles, crocodilians, and snakes survived. • Mammals and birds also survived. Diversification of Mammals Ice Age Mammals • Today, all very large land animals are mammals. • Mammals reached their greatest diversity in the late Tertiary period, about 15 million years ago. • However, many large land mammals existed during the last ice age (about 2 million to 10,000 years ago). • At that time, tropical conditions existed over much of Earth. • At that time, many species of enormous mammals roamed earth. • During the last 15 million years, world climates have changed, and the area covered by tropical habitats has decreased. • As a result, the number of mammalian species has declined.
Ice Age Mammals Ice Age Mammals • Giant ground sloths lived then and weighed three tons, as large as a modern elephant. • The shoulders of Irish elk were over 7 ft high, and the span of the antlers could be up to 12 ft. • Enormous vegetarian cave bears populated Europe • All of these giant mammals are now extinct. during the ice ages. • Today, only elephants approach the size of the enormous mammoths and giant camels that roamed Earth then.
• Large lion like saber-toothed cats hunted with jaws that opened an incredible 120 degrees to allow the cat to drive its huge upper pair of saber teeth into prey.
Later Mammals Modern Mammals
• Today, there are more than 4,500 species of mammals, and they inhabit • The first group of mammals to evolve laid eggs, as did their early ancestors. virtually every habitat on Earth. The only surviving direct descendants of these early mammals are They are found in jungles, deserts, and on polar ice. • – two species of echidna – They live in fresh-water streams, and deep in the ocean. and the duckbill platypus. – They even populate the air (bats are among the most successful of all mammal groups). • These egg-laying mammals are in a • Mammals range in size from the blue whale, which may weigh as much as 150 tons, to the tiny Kitti’s hognose bat, weighing less than 0.1 oz. group of their own called the monotremes. • Most mammals are covered with a dense coat of fur, but some have little fur. – Whales have only a few hairs. Modern Mammals Modern Mammals • Mammals other than monotremes show one of two patterns of development. 2. Placentals. Placental mammals include dogs, cats, horses, sheep, • Both of these groups give birth to live young, but their embryos develop in gorillas, humans, and most of the different ways. other mammals you are familiar 1. Marsupials. Marsupial mammals include kangaroos, opossums, with. Placental mammals develop koalas, and wombats. within their mother’s body and are Their young are born nourished by an organ called the at a very immature placenta. stage and complete their development in their mother’s pouch (called a marsupium).
Evolution of Primates Characteristics of Primates • Fossil evidence indicates that small, insect-eating mammals with large eyes • Primates had two and small, sharp teeth lived about 80 million years ago during the age of features that enabled dinosaurs. them to stalk and • These ancient mammals capture prey in the were the ancestors of the first primates. branches of trees. • A primate is a member 1. Grasping hands and of the mammalian order. feet. The grasping • The first primates hands and feet of evolved about 50 million years ago. primates enable them to cling to their mothers when they are young, grip limbs, hang from branches, and seize food.
Characteristics of Primates Prosimians 2. Forward orientation of the eyes. Unlike the eyes of their ancestors, which •According to the fossil record, the modern primates were located on the sides of the head, the eyes of primates are positioned that most closely resemble early primates are the at the front of the face. prosimians. This forward placement of the eyes produces overlapping binocular vision •A prosimian is a member that enables the primate brain to judge distance more precisely (depth perception). of a group of mostly night-active primates The ability to judge depth is very important for an animal that leaps from that live in trees. branch to branch high above the ground. •Modern prosimians • Some other mammals have binocular vision, but include lorises, lemurs, and tarsiers. only primates have both binocular vision and •Fossil evidence indicates that prosimians were grasping hands. common about 38 million years ago in North America, Europe, Asia, and Africa. Nonhuman Primates Monkeys
• Feeding mainly on fruits and leaves, monkeys were among the first primates •About 36 million years ago, a change to have opposable thumbs. occurred in how primates live. • An opposable thumb, such as your own, stands out at an angle from the other fingers and can be bent •Many primate species became diurnal. inward toward them to –Diurnal animals are active during the day, and hold an object. they sleep at night. • This gives the hand a greatly increased level of ability to •The evolution of a diurnal pattern gave manipulate objects. primates more opportunities to feed and enabled them to better detect predators. •Modern day-active primates include monkeys and apes.
Apes • Apes, which share a common ancestor with monkeys, first appeared about 30 million years ago. • Modern apes include gibbons, orangutans, gorillas, and chimpanzees. • Apes have larger brains with respect to their body size than monkeys, and none of the apes have tails.