Vertebrates

Vertebrates

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The animals called vertebrates 

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Get their name from vertebrae, the series of bones that make up the backbone

There are approximately 52,000 species of vertebrates 

They include the largest organisms ever to live on the Earth

Ancestral deuterostome Brain

Notochord Head

Jaws, mineralized skeleton

Vertebral column

Lobed fins

Lungs or lung derivatives

Mammalia (mammals)

Reptilia (turtles, birds)

Actinistia (coelacanths) Dipnoi (lungfish es) Amphibia (frogs

Actinopterygii (ray-finned fishes)

Chondrichthyes (sharks, rays, chimaeras)

Cephalaspidomorphi (lampreys)

Myxini (hagfishes)

Urochordata (tunicates) Cephalochordata (lancelets)

Echinodermata (sister group to chordates)

Phylogen y of Chordate s Chordates Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Tetrapods Amniotes

Milk

Amniotic egg

Legs

Derived Characters of Chordates 

All chordates share a set of derived characters 

Although some species possess some of these traits only during embryonic Dorsal, hollow development nerve cord Muscle segments

Brain

Notochord

Mouth Anus

32.1

Muscular, post-anal tail

Pharyngeal slits or clefts

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 

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In most vertebrates, a more complex, jointed skeleton develops 

32.1

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 

32.1

Pharyngeal Slits or Clefts 

In most chordates, grooves in the pharynx called pharyngeal clefts 

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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 

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Muscular, Post-Anal Tail 

Chordates have a tail extending posterior to the anus 

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Although in many species it is lost during embryonic development

The chordate tail contains skeletal elements and muscles 

32.1

And it provides much of the propelling force in many aquatic species

Craniates are chordates that have a head 

The origin of a head 

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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 closingDorsal neural tube in an Neural embryo edges Neural of neural plate

crest

Ectoderm

tube

Ectoderm

Notochord

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(a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube.

Migrating neural crest cells (b) Neural crest cells migrate to distant sites in the embryo.

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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.

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Hagfishes 

The least derived craniate lineage that still survives 

Is class Myxini, the hagfishes Slime glands

Vertebrates are craniates that have a backbone 

During the Cambrian period 

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A lineage of craniates evolved into vertebrates

Vertebrates have Vertebrae enclosing a spinal cord  An elaborate skull  Fin rays, in aquatic forms 

Lampreys 

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

32.3

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Lampreys are jawless vertebrates 

32.3

Inhabiting various marine and freshwater habitats

Gnathostomes are vertebrates that have jaws 

Today, jawless vertebrates 

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Are far outnumbered by those with jaws

Gnathostomes have jaws 

That evolved from skeletal supports of the pharyngeal slits

Gill slits

Cranium

Mouth Skeletal rods

Chondrichthyans (Sharks, Rays, and Their Relatives) 

Members of class Chondrichthyes 

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Have a skeleton that is composed primarily of cartilage

The cartilaginous skeleton 

32.4

Evolved secondarily from an ancestral mineralized skeleton

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The largest and most diverse subclass of Chondrichthyes 

Includes the sharks and rays

(a) Blacktip reef shark (Carcharhinus melanopterus). Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins. Pectoral 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.

32.4

Pelvic fins

Ray-Finned Fishes and Lobe-Fins 

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The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes Nearly all living osteichthyans have a bony endoskeleton Aquatic osteichthyans

Are the vertebrates we informally call fishes  Control their buoyancy with an air sac 32.4 known as a swim bladder 

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Fishes breathe by drawing water over four or five pairs of gills 

Located in chambers covered by a protective bony flap called the operculum Dorsal fin Spinal cord Swim bladder Nostril

Caudal fin

Brain

Cut edge of operculum Gills

Gonad

Urinary Anus bladder

Heart Liver Kidney

32.4

Adipose fin (characteristic of trout)

Intestine

Stomach Pelvic fin

Anal fin Lateral line

Ray-Finned Fishes 

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Class Actinopterygii, the ray-finned fishes includes nearly all the familiar aquatic osteichthyans The fins, supported mainly by long, flexible rays are modified for maneuvering, defense, Yellowfin tuna (Thunnus and other (a)functions albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide

(b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones

32.4

(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

Lobe-Fins 

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

Coelacanth –

In the fossil record for over 400 million years, this fish was thought extinct until somebody caught one in 1938.

Lungfish –

Molecular evidence supports the theory that ancestors of this fish gave rise to terrestrial

Tetrapods are gnathostomes that have limbs and feet 

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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 

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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

Bones supporting gills

Tetrapod limb skeleton

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Extraordinary fossil discoveries over the past 20 years have allowed paleontologists to reconstruct the origin of tetrapods

Millions of years ago 420

415

Silurian

400

385

Devonian

370

355

340

325

310

295

Carboniferous

280 265 Permian

Paleozoic

Ray-finned fishes Coelacanths Lungfishes Eusthenopteron Panderichthys Elginerpeton Metaxygnathus Acanthostega lchthyostega Hynerpeton Greerpeton

Amphibians Amniotes

To present

Amphibians 

Class Amphibia 

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Is represented by about 4,800 species of organisms

Most amphibians 

Have moist skin that complements the lungs in gas exchange

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Amphibian means “two lives” 

A reference to the metamorphosis of an aquatic larva into a terrestrial adult (b) The tadpole is an aquatic herbivore with a fishlike tail and internal gills.

(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.

(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 

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Amniotes are named for the major derived character of the clade, the amniotic egg 

32.5

Whose living members are the reptiles, birds, and the mammals

Which contains specialized membranes that protect the embryo

Diapsids

Reptiles

Ancestral amniote

au rs

Sq ua ma tes Ma mm als

Ich thy os au rs Tu ata ra

Ple sio s

Bir ds

Cr oc od ilia ns Pte ros au Or rs nit h d i n is c os hia au rs n Sa u din risc o h tha sau ian n b rs o ird th s e

Pa rar ep tile s Tu rtle s

r

A Phylogeny of Amniotes

Saurischians

Dinosaurs

Lepidosaurs

Archosaurs

Synapsids

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The extraembryonic membranes 

Have various functions Extraembryonic membranes Allantois. The allantois is a disposal sac for certain metabolic wastes produced 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. 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”).

Embryo

Amniotic cavity with amniotic fluid Yolk (nutrients)

Albumen Shell

32.6

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Amniotes also have other terrestrial adaptations 

32.7

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

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Reptiles Have scales that create a waterproof barrier  Lay shelled eggs on land 

32.7

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Most reptiles are ectothermic 

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Absorbing external heat as the main source of body heat

Birds are endothermic 

Capable of keeping the body warm through metabolism

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Derived Characters of Birds Many of the characters of birds are adaptations that facilitate flight 

For example, wings and feathers

Finger 1 (b) Bone structure Palm

(a) wing

Finger 2 Forearm Wrist Shaft

Vane Shaft

32.8

Finger 3

Barb Barbule Hook (c) Feather structure

The Origin of Birds 

Birds probably descended from theropods 

A group of small, carnivorous dinosaurs

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Mammals are amniotes that have hair and produce milk

Mammals, class Mammalia 

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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 32.9brain 

Monotremes A small group of egg-laying mammals consisting of echidnas and the platypus

32.10

Marsupials 

Marsupials 

Include opossums, kangaroos, and koalas

32.10

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A marsupial is born very early in its development 

And completes its embryonic development while nursing within a maternal pouch called a marsupium

(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).

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Phylogenetic relationships of mammals

This clade of eutherians evolved in Africa when the continent was isolated from other landmasses. It includes Earth’s largest living land animal (the African elephant), as well as species that weigh less than 10 g.

32.10

All members of this clade, which underwent an adaptive radiation in South America, belong to the order Xenarthra. One species, the nine-banded armadillo, is found in the southern United States.

This is the largest eutherian clade. It includes the rodents, which make up the largest mammalian order by far, with about 1,770 species. Humans belong to the order Primates.

Monotremata

Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida (golden moles and tenrecs) Macroscelidea Marsupialia (elephant shrews)

Monotremes

Marsupials

Xenarthra

Rodentia Lagomorpha Primates Dermoptera (flying lemurs) Scandentia (tree shrews)

This diverse clade includes terrestrial and marine mammals as well as bats, the only flying mammals. A growing body of evidence, including Eocene fossils of whales with feet, supports putting whales in the same order (Cetartiodactyla) as pigs, cows, and hippos.

Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphla Pholidota (pangolins)

Eutherians

Possible phylogenetic tree of mammals. All 20 extant orders of mammals are listed at the top of the tree. Boldfaced orders are explored on the facing page. Ancestral mammal

ORDERS AND EXAMPLES

Lay eggs; no nipples; young suck milk from fur of mother

Monotremata Platypuses, echidnas

The major eutherian orders

MAIN CHARACTERISTICS

ORDERS AND EXAMPLES Marsupialia Kangaroos, opossums, koalas

Embryo completes development in pouch on mother

Echidna

Proboscidea Elephants

African elephant

Sirenia Manatees, dugongs Manatee

Xenarthra Sloths, anteaters, armadillos Tamandua

Lagomorpha Rabbits, hares, picas

Koala Long, muscular trunk; thick, loose skin; upper incisors elongated as tusks

Tubulidentata Aardvark

Aquatic; finlike forelimbs and no hind limbs; herbivorous

Hyracoidea Hyraxes

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

Rock hyrax Rodentia Squirrels, beavers, rats, porcupines, mice Primates Lemurs, monkeys, apes, humans

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Cetaceans Whales, dolphins, porpoises

Pacific whitesided porpoise

Short legs; stumpy tail; herbivorous; complex, multichambered stomach Chisel-like, continuously growing incisors worn down by gnawing; herbivorous

Red squirrel

Golden lion tamarin

Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous

Sharp, pointed canine teeth and molars for shearing; carnivorous

Perissodactyla Horses, zebras, tapirs, rhinoceroses Indian rhinoceros

Hooves with an odd number of toes on each foot; herbivorous

Hooves with an even number of toes on each foot; herbivorous

Chiroptera Bats

Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous

Coyote

Cetartiodactyla Artiodactyls Sheep, pigs cattle, deer, giraffes Bighorn sheep

Teeth consisting of many thin tubes cemented together; eats ants and termites Aardvark

Jackrabbit Carnivora Dogs, wolves, bears, cats, weasels, otters, seals, walruses

MAIN CHARACTERISTICS

Frog-eating bat Aquatic; streamlined body; paddle-like forelimbs and no hind limbs; thick layer of insulating blubber; carnivorous

Eulipotyphla “Core insectivores”: some moles, some shrews

Diet consists mainly of insects and other small invertebrates Star-nosed mole

The oldest known anthropoid fossils, about 45 million years old Indicate that tarsiers are more closely related to anthropoids

20

30

40

50

60

Ancestral primate

Humans

Chimpanzees

Gorillas

Orangutans

Gibbons

Old World monkeys

10

New World monkeys

0

Tarsiers

Anthropoids

Lemurs, lorises, and pottos

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Millions of years ago

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Derived Characters of Primates  Most primates 

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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 

32.11

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New World and Old World monkeys 

Underwent separate adaptive radiations during their many millions of years of separation

(a) New World monkeys, such as spider (b) Old World monkeys lack a prehensile tail, and their nostrils monkeys (shown here), squirrel monkeys, and open downward. This group includes macaques (shown here), capuchins, have a prehensile tail and nostrils mandrills, baboons, and rhesus monkeys. that open to the sides.

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The other group of anthropoids, the hominoids 

(a) Gibbons, such as this Muller's gibbon, are found only in southeastern Asia. Their very long arms and fingers are adaptations for brachiation.

Consists of primates informally called apes

(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 (c) Gorillas are the largest apes: some foot adapted for grasping and the opposable males are almost 2 m tall and weigh thumb. about 200 kg. Found only in Africa, these herbivores usually live in groups of up to about 20 individuals. (e) Bonobos are closely related to chimpanzees but are smaller. They survive today only in the African nation of Congo. (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.

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Humans are bipedal hominoids with a large brain

Homo sapiens is about 160,000 years old 

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Which is very young considering that life has existed on Earth for at least 3.5 billion years

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 32.11

The Earliest Humans 

The study of human origins 

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Is known as paleoanthropology

Paleoanthropologists have discovered fossils of approximately 20 species of extinct hominoids 

32.12

That are more closely related to humans than to chimpanzees

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32.12 These species are known as hominids Paranthropus robustus

0

Paranthropus boisei

0.5 1.0

Millions of years ago

2.5 3.0 3.5

Kenyanthropus platyops Australopithecus garhi

5.0

Homo Homo rudolfensis habilis Ardipithecus ramidus

Australopithecus afarensis

5.5 6.0 6.5 7.0

Homo erectus

Australopithecus anamensis

4.0 4.5

Homo ? ergaster

Australopithecus africanus

1.5 2.0

Homo Homo neanderthalensis sapiens

Orrorin tugenensis Sahelanthropus tchadensis

32.12

Early Hominids 

Hominids originated in Africa 

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Approximately 6–7 million years ago

Early hominids 

32.12

Had a small brain, but probably walked upright, exhibiting mosaic evolution

Australopiths 

Australopiths are a paraphyletic assemblage of hominids 

32.12

That lived between 4 and 2 million years ago

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Some species walked fully erect 

And had humanlike hands and teeth

(a) Lucy, a 3.24-million-year-old skeleton, represents the hominid species Australopithecus afarensis. (b) The Laetoli footprints, more than 3.5 million years old, confirm that upright posture evolved quite early in hominid history.

32.12

(c) An artist’s reconstruction of what A. afarensis may have looked like.

Bipedalism and Tool Use 

Hominids began to walk long distances on two legs 

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About 1.9 million years ago

The oldest evidence of tool use—cut marks on animal bones 

32.12

Is 2.5 million years old

Early Homo 

The earliest fossils that paleoanthropologists place in our genus Homo 

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Are those of the species Homo habilis, ranging in age from about 2.4 to 1.6 million years

Stone tools have been found with H. habilis

Giving this species its name, which means 32.12 “handy man” 

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Homo ergaster Was the first fully bipedal, large-brained hominid  Existed between 1.9 and 1.6 million years 

32.12

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Homo erectus Originated in Africa approximately 1.8 million years ago  Was the first hominid to leave Africa 

32.12

Neanderthals 

Neanderthals, Homo neanderthalensis Lived in Europe and the Near East from 200,000 to 30,000 years ago  Were large, thick-browed hominids  Became extinct a few thousand years after the arrival of Homo sapiens in Europe 

32.12

Homo sapiens 

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Appeared in Africa at least 160,000 years ago The oldest fossils of Homo sapiens outside Africa 

32.12

Date back about 50,000 years ago

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The rapid expansion of our species 

32.12

May have been preceded by changes to the brain that made symbolic thought and other cognitive innovations possible