Chapter 34 Vertebrates.

Chapter 34 Vertebrates

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

By the end of the Cambrian period, some 540 million years ago
Vertebrates 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 There are approximately 52,000 species of vertebrates Which include the largest organisms ever to live on the Earth

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

Chordates Chordates have a notochord and a dorsal, hollow nerve cord, post-anal tail, and pharyngeal slits during some part of their development Vertebrates are a subphylum of the phylum Chordata Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia Two groups of invertebrate deuterostomes, the urochordates and cephalochordates, are more closely related to vertebrates than to invertebrates

Derived Characters of Chordates
All chordates share a set of derived characters Although some species possess some of these traits only during embryonic development Muscle segments Brain Mouth Anus Dorsal, hollow nerve cord Notochord Muscular, post-anal tail Pharyngeal slits or clefts Figure 34.3

In most vertebrates, a more complex, jointed skeleton develops
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

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

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

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

Tunicates – Invertebrate Chrodates
Tunicates, subphylum Urochordata belong to the deepest-branching lineage of chordates 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 Pharynx with slits Notochord Tail Dorsal, hollow nerve cord Atrium Stomach Intestine Excurrent siphon Incurrent siphon Muscle segments (c) A tunicate larva is a free-swimming but nonfeeding “tadpole” in which all four chief characters of chordates are evident. Figure 34.4c

Tunicates – Invertebrate Chrodates
As an adult a tunicate draws in water through an incurrent siphon, filtering food particles (a) An adult tunicate, or sea squirt, is a sessile animal (photo is approximately life-sized). (b) In the adult, prominent pharyngeal slits function in suspension feeding, but other chordate characters are not obvious. Tunic Pharynx with numerous slits Atrium Excurrent siphon Incurrent siphon to mouth Stomach Esophagus Intestine Anus Excurrent siphon Figure 34.4a, b

Lancelets – Invertebrate Chrodates
Lancelets, subphylum Cephalochordata are named for their bladelike shape. Lancelets are marine suspension feeders that retain the characteristics of the chordate body plan as adults. Tentacle Mouth Pharyngeal slits Atrium Digestive tract Atriopore Segmental muscles Anus Notochord Dorsal, hollow nerve cord Tail 2 cm Figure 34.5

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

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 Notochord (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 to distant sites in the embryo. Migrating neural crest cells Ectoderm Dorsal edges of neural plate Neural crest Neural tube Figure 34.7a, b

Neural Crest Cells Neural crest cells give rise to a variety of structures, including some of the bones and cartilage of the skull (c) The cells give rise to some of the anatomical structures unique to vertebrates, including some of the bones and cartilage of the skull. Figure 34.7c

Hagfishes The least derived craniate lineage that still survives is class Myxini, the hagfishes Hagfishes are jawless marine craniates that have a cartilaginous skull and axial rod of cartilage derived from the notochord but lack vertebrae Figure 34.9 Slime glands

Derived Characteristics of Vertebrates
Vertebrates are craniates that have a backbone During the Cambrian period A lineage of craniates evolved into vertebrates Vertebrates have Vertebrae enclosing a spinal cord An elaborate skull Fin rays, in aquatic forms

Lampreys Lampreys Represent the oldest living lineage of vertebrates
Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord

Lampreys Lampreys are jawless vertebrates inhabiting various marine and freshwater habitats Figure 34.10

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

Gnathostomes are vertebrates that have jaws Today, jawless vertebrates
Are far outnumbered by those with jaws Gnathostomes have jaws That evolved from skeletal supports of the pharyngeal slits Mouth Gill slits Cranium Skeletal rods Figure 34.13

Other characters common to gnathostomes include
Enhanced sensory systems, including the lateral line system An extensively mineralized endoskeleton Paired appendages

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

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

Ray-Finned Fishes and Lobe-Fins
The vast majority of vertebrates Belong to a clade of gnathostomes called Osteichthyes (BONY FISHES) 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

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

Ray-Finned Fishes Class Actinopterygii, the ray-finned fishes includes nearly all the familiar aquatic osteichthyans (a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide (b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones (c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development (d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitat Figure 34.17a–d

The lobe-fins, class Sarcopterygii
Have muscular and pectoral fins Include coelacanths, lungfishes, and tetrapods Figure 34.18

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 Tetrapods have some specific adaptations Four limbs and feet with digits Ears for detecting airborne sounds

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 Tetrapod limb skeleton Bones supporting gills Figure 34.19

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

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

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

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

Amphibian means “two lives”
Amphibians Amphibian means “two lives” A reference to the metamorphosis of an aquatic larva into a terrestrial adult Figure 34.22a–c (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. (b) The tadpole is an aquatic herbivore with a fishlike tail and internal gills. (c) During metamorphosis, the gills and tail are resorbed, and walking legs develop.

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

A Phylogeny of Amniotes
Figure 34.23 Synapsids Ancestral amniote Reptiles Diapsids Archosaurs Saurischians Lepidosaurs Dinosaurs Parareptiles Turtles Crocodilians Pterosaurs Ornithischian dinosaurs Saurischian dinosaurs other than birds Birds Plesiosaurs Ichthyosaurs Tuatara Squamates Mammals

Derived Characters of Amniotes
Amniotes are named for the major derived character of the clade, the amniotic egg Amniotic eggs contain specialized membranes that protect the embryo (leathery shell) – the shell prevents desiccation of the embryo The amniotic egg removes the need to return to water for reproduction – the embryonic membrane allows for gas and waste exchange; food supplies are stored in yolk; and the amnion protects the embryo in a fluid filled cavity from mechanical shock In amniotes, there is more efficient reproduction with internal fertilization – fewer gametes required New hatchlings are more fully developed in amniotes

Extraembryonic membranes
Amniotes The extraembryonic membranes have various functions Figure 34.24 Shell Albumen Yolk (nutrients) Amniotic cavity with amniotic fluid Embryo 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”). 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. Amnion. The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock. 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. Extraembryonic membranes

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

Reptiles The reptile clade includes the tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs. Reptiles have scales that create a waterproof barrier and lay shelled eggs on land Figure 34.25

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

The other major living lineage of lepidosaurs
Evolution of Reptiles 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)

(c) Wagler’s pit viper (Tropidolaemus wagleri), a snake
Snakes Snakes are legless lepidosaurs That evolved from lizards Figure 34.27c (c) Wagler’s pit viper (Tropidolaemus wagleri), a snake

Some turtles have adapted to deserts
Are the most distinctive group of reptiles alive today Some turtles have adapted to deserts And others live entirely in ponds and rivers

(d) Eastern box turtle (Terrapene carolina carolina)
Turtles All turtles have a boxlike shell Made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs Figure 34.27d (d) Eastern box turtle (Terrapene carolina carolina)

Alligators and Crocodiles
Crocodilians Belong to an archosaur lineage that dates back to the late Triassic Figure 34.27e (e) American alligator (Alligator mississipiensis)

Reptiles Have Waterproofed Skin
Reptiles have several adaptations for terrestrial living not generally found in amphibians: Scales containing keratin waterproof the skin – helping prevent dehydration in dry air. This adaptation permits life on terrestrial habitats and provides mechanical and chemical protection of the body They have well-developed lungs so they are better able to exchange gases with their atmosphere (air instead of water)

Many of the characters of birds
Birds are archosaurs But almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight Many of the characters of birds Are adaptations that facilitate flight

Flight in Birds A bird’s most obvious adaptations for flight are its wings and feathers Figure 34.28a–c (a) wing (b) Bone structure Finger 1 (c) Feather structure Shaft Barb Barbule Hook Vane Forearm Wrist Palm Finger 3 Finger 2

The Origin of Birds Birds probably descended from theropods
A group of small, carnivorous dinosaurs By 150 million years ago feathered theropods had evolved into birds Archaeopteryx remains the oldest bird known Figure 34.29 Toothed beak Airfoil wing with contour feathers Long tail with many vertebrae Wing claw

Flight in Birds The demands of flight have rendered the general body form of many flying birds similar to one another Figure 34.30b–d (b) Mallards. Like many bird species, the mallard exhibits pronounced color differences between the sexes. (c) Laysan albatrosses. Like most birds, Laysan albatrosses have specific mating behaviors, such as this courtship ritual. (d) Barn swallows. The barn swallow is a member of the order Passeriformes. Species in this order are called perching birds because the toes of their feet can lock around a branch or wire, enabling the bird to rest in place for long periods.

Foot Structure in Birds
Foot structure in bird feet shows considerable variation 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)

Mammals are amniotes that have hair and produce milk
Mammals, class Mammalia are represented by more than 5,000 species Mammary glands, which produce milk are a distinctively mammalian character Hair is another mammalian characteristic Mammals generally have a larger brain than other vertebrates of equivalent size

Early Evolution in Mammals
The jaw was remodeled during the evolution of mammals from nonmammalian synapsids And two of the bones that formerly made of the jaw joint were incorporated into the mammalian middle ear Sound Jaw joint Key Dentary Angular Squamosal Articular Quadrate Dimetrodon Morganucodon Eardrum Middle ear Stapes Inner ear Incus (evolved from quadrate) Malleus (evolved from articular) (b) During the evolutionary remodeling of the mammalian skull, the quadrate and articular bones became incorporated into the middle ear as two of the three bones that transmit sound from the eardrum to the inner ear. The steps in this evolutionary remodeling are evident in a succession of fossils. (a) The lower jaw of Dimetrodon is composed of several fused bones; two small bones, the quadrate and articular, form part of the jaw joint. In Morganucodon, the lower jaw is reduced to a single bone, the dentary, and the location of the jaw joint has shifted. Figure 34.32a, b

Monotremes Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus Figure 34.33

Marsupials Marsupials include opossums, kangaroos, and koalas
A marsupial is born very early in its development and completes its embryonic development while nursing within a maternal pouch called a marsupium Figure 34.34a (a) A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).

Convergent Evolution in Marsupials
In Australia, convergent evolution has resulted in a diversity of marsupials that resemble eutherians in other parts of the world Figure 34.35 Marsupial mammals Eutherian mammals Plantigale Marsupial mole Sugar glider Wombat Tasmanian devil Kangaroo Deer mouse Mole Woodchuck Flying squirrel Wolverine Patagonian cavy

Eutherians (Placental Mammals)
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

Major Eutherian Orders
Figure 34.36 ORDERS AND EXAMPLES MAIN CHARACTERISTICS Monotremata Platypuses, echidnas Proboscidea Elephants Sirenia Manatees, dugongs Cetartiodactyla Artiodactyls Sheep, pigs cattle, deer, giraffes Lagomorpha Rabbits, hares, picas Carnivora Dogs, wolves, bears, cats, weasels, otters, seals, walruses Xenarthra Sloths, anteaters, armadillos Cetaceans Whales, dolphins, porpoises Echidna African elephant Manatee Tamandua Jackrabbit Coyote Bighorn sheep Pacific white- sided porpoise Lay eggs; no nipples; young suck milk from fur of mother Long, muscular trunk; thick, loose skin; upper incisors elongated as tusks Aquatic; finlike forelimbs and no hind limbs; herbivorous Reduced teeth or no teeth; herbivorous (sloths) or carnivorous (anteaters, armadillos) Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping Sharp, pointed canine teeth and molars for shearing; carnivorous Hooves with an even number of toes on each foot; herbivorous Aquatic; streamlined body; paddle-like forelimbs and no hind limbs; thick layer of insulating blubber; carnivorous Diet consists mainly of insects and other small invertebrates Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous Hooves with an odd number of toes on each foot; herbivorous Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous Chisel-like, continuously growing incisors worn down by gnawing; herbivorous Short legs; stumpy tail; herbivorous; complex, multichambered stomach Teeth consisting of many thin tubes cemented together; eats ants and termites Embryo completes development in pouch on mother Marsupialia Kangaroos, opossums, koalas Tubulidentata Aardvark Hyracoidea Hyraxes Chiroptera Bats Primates Lemurs, monkeys, apes, humans Perissodactyla Horses, zebras, tapirs, rhinoceroses Rodentia Squirrels, beavers, rats, porcupines, mice Eulipotyphla “Core insecti- vores”: some moles, some shrews Star-nosed mole Frog-eating bat Indian rhinoceros Golden lion tamarin Red squirrel Rock hyrax Koala

Primates The mammalian order Primates include lemurs, tarsiers, monkeys, and apes Humans are members of the ape group Most primates have hands and feet adapted for grasping Primates also have A large brain and short jaws Forward-looking eyes close together on the face, providing depth perception Well-developed parental care and complex social behavior A fully opposable thumb

The hominoids consists of primates informally called apes
Figure 34.40a–e (a) Gibbons, such as this Muller's gibbon, are found only in southeastern Asia. Their very long arms and fingers are adaptations for brachiation. (b) Orangutans are shy, solitary apes that live in the rain forests of Sumatra and Borneo. They spend most of their time in trees; note the foot adapted for grasping and the opposable thumb. (c) Gorillas are the largest apes: some males are almost 2 m tall and weigh about 200 kg. Found only in Africa, these herbivores usually live in groups of up to about 20 individuals. (d) Chimpanzees live in tropical Africa. They feed and sleep in trees but also spend a great deal of time on the ground. Chimpanzees are intelligent, communicative, and social. (e) Bonobos are closely related to chimpanzees but are smaller. They survive today only in the African nation of Congo.

Humans are bipedal hominoids with a large brain
Diverged from Old World monkeys about 20–25 million years ago Humans are bipedal hominoids with a large brain Homo sapiens is about 160,000 years old Which is very young considering that life has existed on Earth for at least 3.5 billion years

Derived Characters of Hominids
A number of characters distinguish humans from other hominoids Upright posture and bipedal locomotion Larger brains Language capabilities Symbolic thought The manufacture and use of complex tools Shortened jaw

Chapter 34 Vertebrates.

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