vertebrates 9

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Vertebrates

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Page 1: Vertebrates 9

Vertebrates

Page 2: Vertebrates 9

Chordates have a notochord and a dorsal, hollow nerve cord

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Notochord• The notochord is a longitudinal, flexible rod

between the digestive tube and nerve cord• It provides skeletal support throughout most of the

length of the chordate• In most vertebrates, a more complex, jointed

skeleton develops and the adult retains only remnants of the embryonic notochord

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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

• The nerve cord develops into the central nervous system; the brain and the spinal chord

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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

• Functions of pharyngeal slits Suspension- feeding structures in many invertebrate

chordates Gas exchange in vertebrates (except vertebrates with

limbs, the tetrapods) Develop into parts of the ear, head and neck in tetrapods

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Muscular, Post-Anal Tail• Chordates have a tail posterior to the anus• In many species, the tail is greatly reduced during

embryonic development

• The tail contains skeletal elements and muscles• It provides propelling force in many aquatic species

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Craniates are chordates that have a head

• Derived Characters of Craniates– Craniates have two clusters of Hox genes; lancelets and

tunicates have only one cluster– One feature unique to craniates is the neural crest, a

collection of cells near the dorsal margins of the closing neural tube in an embryo

– Neural crests cells give rise to a variety of structures, including some of the bones and cartilage of the skull

– In aquatic craniates the pharyngeal clefts evolved into gill slits

– Craniates have a heart with at least two chambers, red blood cells with hemoglobin, and kidneys

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Vertebrates are craniates that have a backbone

• Derived Characters of Vertebrates– Vertebrates have the following derived characters• Vertebrae enclosing of a spinal chord• An elaborate skull• Fin rays, in the aquatic form

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Gnathostomes are vertebrates that have jaws

• 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

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Derived Characters of Gnathostomes

• Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits

• Other characters common to gnathostomes Genome duplication; including duplication of Hox

genes An enlarged forebrain associated with enhanced

smell and vision In aquatic gnathosotmes, the lateral line system,

which is sensitive to vibrations

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Chondrichthyans (Sharks, Rays, and Their Relatives)

• Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage

• The largest and most diverse group of chondrichthyans includes the sharks, rays and skates

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• Sharks have a streamlined body and are swift swimmers

• The largest sharks are suspension feeders, but most are carnivores

• Sharks have a short digestive tract, a ridge called the spiral valve to increase the digestive surface area

• Sharks have acute senses, including sight, smell and the ability to detect electrical fields from nearby animals

• The reproductive tract, excretory system and digestive tract empty in a common cloaca

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• Shark eggs are fertilized internally but embryos can develop in different ways

– Oviparous: eggs hatch outside the mother’s body – Ovoviviparous: the embryo develops within the egg

retained in the mother’s body– Viviparous: the embryo develops within the uterus

and is nourished through a yolk sac placenta from the mother’s blood

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• Most fishes breathe by drawing water over gills protected by an operculum

• Fishes control their buoyancy with an air sac known as a swim bladder

• Fishes have a lateral line systen• Most species are oviparous, but some have internal

fertilization and birthing

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Tetrapods are gnathostomes that have limbs

• 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

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Amniotes are tetrapods that have a terrestrially adapted egg

• Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals

• Derived Characters of Amniotes Amniotes are named for the major derived character of the

clade, the amniotic egg, which contains membranes that protect the embryo

The extra embryonic membranes are the amnion, chorion, yolk sac and allantois

The amniotic eggs of most reptiles and some mammals have a shell

• Amniotes have other terrestrial adaptations, such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs

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Figure 34.26

Extraembryonic membranes

Shell

Amniotic cavitywith amnioticfluid

Embryo

AmnionAllantois Chorion

Yolk sac

Yolk(nutrients)

Albumen

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Mammals are amniotes that have hair and produce milk

• Derived Characters of Mammals Mammary glands, which produce milk Hair A high metabolic rate, due to endothermy A larger brain than other vertebrates of equivalent size Differentiated teeth

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Marsupials• Marsupials include opossums, kangaroos, and koalas• The embryo develops within a placenta in the

mother’s uterus• A marsupial is born very early in its development• It completes its embryonic development while

nursing in a maternal pouch called a marsupium

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Eutherians (Placental Mammals)• Compared with marsupials, eutherians have a more

complex placenta• Young eutherians complete their embryonic

development within a uterus, joined to the mother by the placenta

• Molecular and morphological data give conflicting dates on the diversification of eutherians

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Monotremata

Orders and Examples Main Characteristics Orders and Examples Main Characteristics

Platypuses,echidnas

Echidna

ProboscideaElephants

African elephant

SireniaManatees,dugongs

Manatee

Lay eggs; no nipples;young suck milk fromfur of mother

Long, muscular trunk;thick, loose skin; upperincisors elongatedas tusks

Aquatic; finlike fore-limbs and no hindlimbs; herbivorous

XenarthraSloths,anteaters,armadillos

Tamandua

LagomorphaRabbits, hares,picas

Jackrabbit

Reduced teeth or noteeth; herbivorous(sloths) or carnivorous(anteaters, armadillos)

Chisel-like incisors;hind legs longer thanforelegs and adaptedfor running and jumping;herbivorous

Sharp, pointed canineteeth and molars forshearing; carnivorous

Hooves with an evennumber of toes on eachfoot; herbivorous

Aquatic; streamlined body; paddle-like fore-limbs and no hind limbs; thick layer of insulating blubber;carnivorous

CarnivoraDogs, wolves,bears, cats,weasels, otters,seals, walruses Coyote

CetartiodactylaArtiodactylsSheep, pigs,cattle, deer,giraffes

CetaceansWhales,dolphins,porpoises

MarsupialiaKangaroos,opossums,koalas

Koala

Completes embryonicdevelopment in pouchon mother’s body

TubulidentataAardvarks

Aardvark

Teeth consisting ofmany thin tubescemented together;eats ants and termites

HyracoideaHyraxes

Rock hyrax

Short legs; stumpytail; herbivorous;complex, multi-chambered stomach

RodentiaSquirrels,beavers, rats,porcupines,mice Red squirrel

Chisel-like, continuouslygrowing incisors worndown by gnawing;herbivorous

PrimatesLemurs, monkeys,chimpanzees,gorillas, humans Golden lion

tamarin

Opposable thumbs;forward-facing eyes;well-developed cerebralcortex; omnivorous

PerissodactylaHorses, zebras,tapirs,rhinoceroses

Indian rhinoceros

Hooves with an oddnumber of toes oneach foot; herbivorous

ChiropteraBats

Frog-eating bat

Eulipotyphla“Coreinsectivores”:some moles,some shrews

Star-nosedmole

Eat mainly insectsand other smallinvertebrates

Adapted for flight;broad skinfold thatextends from elongatedfingers to body andlegs; carnivorous orherbivorousBighorn sheep

Pacific white-sided porpoise

Figure 34.41b

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Primates

• Derived Characters of Primates– Most primates have hands and feet adapted for

grasping, and flat nails– a large 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)