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VertebratesChapter 35
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The Chordates (phylum Chordata)
deuterostome coelomates
nearest relatives are echinoderms
(the only other deuterostomes)
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Four features characterize chordates
1. nerve cord
2. notochord3. pharyngeal slits
4. postanal tail
All chordates have all fourof these characteristics at
some time in their lives
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Other characteristics
1. muscles arranged in segmented blocks called somites
2. internal skeleton against which the muscles work (most)
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The Nonvertebrate Chordates
Phylum chordata three subphyla
1. Urochordata2. Cephalochordata
3. Vertebrata
nonvertebrates
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Subphylum Urochordata
tunicates are marine animals larvae are tadpolelike
have notochord and nerve cord free-swimming but do not feed
adults typically lose the tailand notochord
immobile filter-feeders endostyle traps microscopic food
particles in a mucus sheet
many secrete a tunic (cellulosesac) that surrounds the animal
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Subphylum Cephalochordata
Lancelets scaleless chordates notochord persists throughout animals life no distinguishable head
use cilia-generated currents to feed on plankton
closest relatives tovertebrates
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Subphylum Vertebrata
chordates with a spinal columndistinguished from nonvertebrates by
vertebral column: encloses and protects the dorsal nerve cord
head: distinct and well-differentiated; sensory organs
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neural crest: a unique group of embryonic cells thatforms many vertebrate structures
internal organs: liver, kidneys, endocrine glands, heartand closed circulatory system
endoskeleton: made of cartilage or bone
makes possible great size and extraordinary movement
Fig. 35.6 Embryonic development of a vertebra
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Phylogeny of the extant vertebrates
first vertebrates appeared in the oceans about half abillion years ago
jawed fishes soon became dominant their descendants, the amphibians, invaded the land reptiles replaced them as the dominant land
vertebrates gave rise to birds and mammals
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Fishes
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Fishes
most diverse vertebrate group over half of all vertebrates variety - size, shape, color and appearance
have the following characteristics1. vertebral column2. jaws and paired appendages
3. internal gills4. single-loop blood circulation5. nutritional deficiencies
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History
first fishes had mouths with no jawsAgnatha extant as hagfish (class Myxini)and lampreys (class Cephalaspidomorphi)Ostracoderms are now extinct
development of jawsoccurred in the lateSilurian period
(438 - 408 MYA)
jaws evolved from the anterior gillarches that were made of cartilage
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Hagfish
(class Myxini)
Placoderm fossil
Lampreys (class
Cephalaspidomorphi)
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Devonian period (408-360 MYA): two types of jawed fishes
spiny fishes (Acanthodii) smaller fishes that dominated early on armored fishes (Placodermi) larger fishes that dominated late
at the end of the period, these early fishes were replaced bysharks and bony fishes (more improved jaws!)
Carboniferous period (360-280 MYA)Class Chondrichthyes (sharks) became the dominant sea predators
light, flexible skeletonand paired fins madethem superior
swimmers
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Sharks
among the first vertebrates to develop teeth evolved from rough scales on mouths skin easily lost but continuously replaced
lateral line system (in both sharks and bony fishes)
fully developed series of sensory organs under the skin thatdetects changes in pressure waves (more in CH45)
Reproduction in most sharks: differs from that of other fishes eggs are fertilized internally, and pups are born live
a few species do lay fertilized eggs
long gestation periods and relatively few offspring not able to recover quickly from population declines
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Bony fishes the most species rich group of all extant vertebrates
(> 30,000 extant species)
evolved at ~ same time as sharks
heavy internal skeleton
made completely of bone
developed significantadaptations that enabledthem to dominate life in
the water swim bladder gill cover (operculum) gas gland oval body
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Two Major Groups
Ray-finned fishes(class Actinopterygii) parallel bony rays support
and stiffen each fin no muscles within the fins
Lobe-finned fishes(class Sarcopterygii) paired long fleshy muscular
lobes supported by central
co-jointed bones almost certainly theamphibian ancestors
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Amphibians (class Amphibia)
damp-skinned vertebrates
first vertebrates to walkon land
several key characteristics1. legs2. lungs3. cutaneous respiration
4. pulmonary veins5. partially divided heart
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Amphibians (class Amphibia)
successful invasion of lands by vertebrates requiredseveral adaptations
1. legs to support bodys weight2. lungs to extract oxygen from air
3. redesigned heart to drive larger muscles4. reproduction in H2O to prevent egg drying5. system to prevent whole body desiccation
Ichthyostega one of the first amphibians efficient limbs for land crawling
improved olfactory and auditory structures however, still fishlike (spent much of life in
water)
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Tiktaalik
2006 discovery of transitionalfossil between fish andIchthyostega
lived about 375 MYA
shoulder and limb bones like those of
an amphibian fins like those of a lobe-finned fish spent most of its life in water capable of moving onto land to
capture food or escape predators
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Amphibiansfirst became common in the Carboniferous period (360-280 MYA)
14 known families aquatic or semi-aquatic
began to leave marshlands for dry upland in the early Permianperiod (280-248 MYA)
large size and complete body covering point to reliance onlung, not skin, for respiration
40 families (Age of Amphibians)
Triassic period (248-213 MYA) virtual extinction of amphibians from land
modern amphibians are descended from three families of theTertiary period (65-2 MYA)
accomplished a highly successful invasion of wet habitats allover the world
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Modern Amphibians
today there are about 5,670 species in 37 differentfamilies, comprising three orders:
Anura (without tail)
Caudata (visible tail)Apoda (without legs)
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Order Anura (frogs and toads) frogs have smooth, moist skin and long legs toads have bumpy, dry skin and short legs eggs are fertilized externally hatch into swimming tadpole larvae undergo metamorphosis into adults
Order Caudata (salamanders) long bodies, tails & smooth, moist skin live in moist places eggs are fertilized internally
larvae similar to adults
Order Apoda (caecilians) tropical, burrowing amphibians legless with small eyes and jaws with teeth
fertilization is internal
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Reptiles (class Reptilia)
dominated earth for250 million years
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Reptiles (class Reptilia)
7000 extant species of reptiles all living reptiles exhibit three key features1. amniotic eggs, which are watertight2. dry skin, which covers body and prevents water loss3. thoracic breathing, which increases lung capacity
Amniotes reptiles, birds and mammals
four membraneschorion: allows O2 entryamnion: fluid-filled cavityyolk sac: provides foodallantois: excretes wastes
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Reptiles distinguished by the number of holes on side of the
skull behind eye orbit
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Synapsids
rose to dominance firstPelycosaurs first land vertebrates to kill
beasts their own size
Therapsids replaced them about 250 MYA may have been endotherms
replaced by diapsids about 230 MYA most became extinct 170 MYA one group survived and has living
descendants today
(the mammals)
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Archosaurs
first land vertebrates to be bipedal gave rise to dinosaurs about 220 MYA
Dinosaurs dominated for over 150 million years extinction 65 MYA
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Modern Reptiles
developed two important characteristics:1. internal fertilization: sperm fertilizes egg beforeprotective membranes are formed
2. improved circulation:
oxygen is provided to thebody more efficiently
all extant reptilesare ectothermic(obtain heat from
external sources)
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Order Chelonia
Tortoises terrestrial dome-shaped shell
Turtles mostly aquatic disc-shaped shells
both lack teeth but havesharp beaks
marine turtles must return to
land to lay eggs
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Dorsal portion: carapace
Ventral portion: plastron inner layer: ~ 60 bones that includeportions of backbone and ribs
outer layer: covered by horny scales
called scutes (part of the epidermis) scutes: made up of a fibrous
protein called keratin (also makes
up the scales of other reptiles)
leatherback sea turtle and the soft-shelled turtles have shells coveredwith leathery skin instead of scutes
Testudo: mascot of the U of Maryland
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Order Rhynchocephalia
only two species of tuataras large, lizardlike animals only found on islands near New Zealand
parietal eyeinconspicuous third
eye on top of head
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I have never been called to attend a case of Gila monster bite,and I dont want to be. I think a man who is fool enough to getbitten by a Gila monster ought to die. The creature is sosluggish and slow of movement that the victim of its bite iscompelled to help largely in order to get bitten.
Dr. Ward, Arizona Graphic, September 23, 1899
Beaded lizardwestern Mexico
Gila monstersouthwestern U.S.
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Order Crocodylia
25 species, large, primarily aquatic, carnivorous crocodiles
live near or in water in tropical and subtropical regions typically nocturnal
alligators exist in only two species one in southern US; other in China
caimans are native to Central America gharials live only in India and Burma
crocodiles resemble birds more thanthey do other living reptiles in that
build nests and care for their young
have a four-chambered heart
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Chinese
alligator
Gharial (family Gavialidae)
Endangered species
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Most paleontologists agree that birds are the directdescendants of theropod dinosaurs
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diff f h b i f d l i
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differ from other vertebrates in two fundamental traits:1. hair/fur
long, keratin-rich filaments that extend from hair follicles(insulation, camouflage, sensory structure)
2. mammary glandsfemales possess mammary glands that secrete milk
other notable features include: endothermy
depends on more efficient:
circulation: four-chambered heart respiration: diaphragm
placenta specialized organ that brings fetal
and maternal blood into close contact
several adaptations in some groups:
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p g p
1. specialized teeth
different types of teeth are highlyspecialized to match particulareating habits
2. digestion of plants
herbivorous mammals rely onmutualistic partnerships withbacteria for cellulose breakdown
3. development of hooves
and hornshooves are specialized keratin padshorns are bone surrounded by keratinantlers are made of bone, not keratin
4. flying mammals: bats bat wing is a leathery membrane of skin
and muscle stretched over 4 finger bones
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Evolution of Primates
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evolved two features that allowed them to succeed in an
arboreal environment1. grasping fingers and toes (first digit is opposable)2. binocular vision (eyes are shifted toward the front of the face)
about 40 MYA, the earliest primates split into twogroups: prosimians and anthropoids
Prosimians most are nocturnal
only a few survive (lemurs, lorises and tarsiers)Anthropoids diurnal include monkeys, apes and humans
some anthropoids migrated to S. America > 30 MYA
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p g descendants called New World monkeys
all are arboreal grasp objects with long, prehensile tails
anthropoids that remained inAfrica gave rise to two lineagesOld World monkeys ground-dwelling or arboreal none have prehensile tails
Hominoids apes and humans larger brains than monkeys and
lack tails
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Ardi
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Ardi
Ardipithecus ramidus4.4 mya Ardipithecus kadabba5.6 mya
taller than Australicopithecus
brain smaller than Australicopithecus about 20% size of modern humans
reduced canines (hominid dentition) bipedal grasping hallux
Genus Homo
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first humans evolved from australopithecine ancestorsabout 2 MYA(thought to be Australopithecus afarensis)
1960s, hominid bones were found near stone tools inAfrica early human was called Homo habilis(handy man) closely resembled Australopithecusin body shape and size,
but had larger brain volume
The Genus Homo
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active debate whether Homo
should be lumped into habilisorsplit into three species
increasing number ofresearchers favor the splittingH. rudolfensis(most ancient)
H. habilis
H. ergaster(most likely ancestor
to later species)
Out of Africa: Homo erectusH.erectuswas a lot larger than H. habilis(1.5 m tall vs 1 m)
had larger brain, more rounded jaw, able to talk
H. erectusbecame widespread in Africa
then migrated to Asia and Europe
H. erectussurvived for over a million yearslonger than any other human species
A New Addition: Homo floresiensis
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2004, a new human species was discovered in the tinyIndonesian Island of Flores
youngest fossils only 15,000 years old!
H. floresiensis diminutive stature
coexisted with and preyed
on a miniature species of
elephant (now extinct also)
believed to be more
closely-related to H. erectus
than to H. sapiens
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Neanderthals
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Neanderthals
made diverse tools took care of sick and buried dead first evidence of belief in life after death abruptly disappeared about 34,000 years ago
replaced by fossils of H. sapienscalled the Cro-Magnons
DNA analysis indicates that Cro-Magnons andNeanderthals did not interbreed
Neanderthals are our cousins, not our ancestors
Cro-Magnons had a complex social organization thought to have full language capabilities
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Human Races
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visual cues (primarily skin color) to define
races groupings based on overall genetic
similarity are different from those based onskin color or other visual features
different groups of people have interbredduring the entire course of history
constant gene flow prevented theformation of different humansubspecies
only 8% of genetic differences can beaccounted for by racial differences
human races do not reflect significantpatterns of underlying biological
differentiation
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Larvacea
Table 35.5
why are Apes aparaphyletic group?
evolutionary originsof bipedalism?
Bonus topics:
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