THE ORIGIN AND EVOLUTION
OF VERTEBRATES
KINDOM ANIMALIA
PHYLUM CHORDATA
Porifera
Cnidaria
Platyhelminthes
sponges jellyfish flatworms roundworms
Nematoda
Mollusca Arthropoda Chordata
Annelida Echinodermata
mollusks
multicellularity
Ancestral Protist
tissues
bilateral symmetry
body cavity
segmentation
Animal Evolution
coelom
starfish vertebrates
endoskeleton
segmentedworms
insectsspiders
backbone
specialization & ↑ body complexity
specialized structure & function,muscle & nerve tissue
distinct body plan; cephalization
↑ body complexity↑ digestive & repro sys
↑ digestive sys
↑ body size
redundancy,specialization, ↑ mobility
↑ body & brain size, ↑ mobility
radial
bilateral
ANCESTRALDEUTEROSTOME
Notochord
Commonancestor ofchordates
Head
Vertebral column
Jaws, mineralized skeleton
Lungs or lung derivatives
Lobed fins
Limbs with digits
Amniotic egg
Milk
Echinodermata
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
Ch
ord
ate s
Cran
iates
Verteb
rat esG
nath
ost o
mes
Osteich
thyan
s
Lo
be-fin
sT
etrapo
ds
Am
nio
tes
We will explore 11 clades of the phylum Chordata
Introduction to the vertebrates
A. Neural crest, enhanced cephalization, vertebral column, and a closed circulatory system characterize the subphylum Vertebrata 1. Neural crest a. Embryonic feature that allows for many unique vertebrate characteristics, e.g. bones and cartilage are formed from the neural crest cells throughout the body.b. Forms along the dorsal side of the embryo. The neural crest, embryonic source of many unique vertebrate characters.
Chordates have a notochord and a dorsal, hollow nerve cord
• Chordates (phylum Chordata) are bilaterian animals that belong to the clade of animals known as Deuterostomia
• Chordates comprise all vertebrates and two groups of invertebrates, the urochordates and cephalochordates
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1. Embryos all have a common skeletal structure called a notochord. The notochord is a flexible rod located between the digestive tube and nerve chord. a. Provides skeletal support.b. In most vertebrates, it’s replaced by a jointed skeleton.c. Remains of the notochord exist as disks between the vertebrae. 2. Dorsal, hollow nerve cord a. Develops into the brain and spinal cord of the adult.
3. Pharyngeal slits Water enters through the mouth and passes out through the slits in the pharynx, without going through the digestive system.
i. Slits function as suspension-feeding devices in many invertebrate chordates ii. Slits have been modified in more evolved vertebrates for: - Gas exchange - Hearing - Jaw support 4. Postanal tail Provides propulsion for swimming
Musclesegments
Notochord
Dorsal,hollow
nerve cord
Muscular,post-anal tail
Pharyngealslits or clefts
Anus
Mouth
4 Derived Characteristics of Chordates
Vertebrates– fish, amphibians, reptiles, birds, mammals
– internal bony skeleton• backbone encasing
spinal column
• skull-encased brain
– deuterostome
postanaltail notochord
hollow dorsalnerve cord
pharyngealpouches
Chordata
becomes brain & spinal cord
becomes vertebrae
becomes gills or Eustachian tube
becomes tail or tailbone
Mouth
Cirri
Pharyngeal slits
Atrium
Digestive tract
Atriopore
Segmentalmuscles
Anus
Notochord
Tail
Dorsal,hollow
nerve cord
1 cm
• Lancelets (Cephalochordata) are named for their bladelike shape
• They are marine suspension feeders that retain characteristics of the chordate body plan as adults
Cephalochordata
Notochord
Dorsal, hollownerve cord
Tail
Musclesegments
Intestine
Stomach
Atrium
Pharynx with slits
(a) Tunicate larva (b) Adult tunicate (c) Adult tunicate
Excurrentsiphon
Incurrentsiphon
Water flow
Excurrent siphon
Anus
Intestine
EsophagusStomach
Incurrentsiphonto mouth
Excurrentsiphon
Atrium
Tunic
Pharynxwith
numerousslits
• Tunicates (Urochordata) are more closely related to other chordates than are lancelets
• When attacked, tunicates, or “sea squirts,” shoot water through their excurrent siphon
Urochordata
Early Chordate Evolution
• Ancestral chordates may have resembled lancelets
• The same Hox genes that organize the vertebrate brain are expressed in the lancelet’s simple nerve cord tip
• Genome sequencing suggests that– Genes associated with the heart and thyroid are
common to all chordates– Genes associated with transmission of nerve
impulses are unique to vertebrates
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Pharyngeal slits
Segmented muscles
5 mm
Hagfishes
• The most basal group of craniates is Myxini, the hagfishes
• Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae
• They have a small brain, eyes, ears, and tooth-like formations
• Hagfishes are marine; most are bottom-dwelling scavengers
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Lampreys
Lampreys
• Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates
• They are jawless vertebrates that feed by clamping their mouth onto a live fish, suck blood
• They inhabit various marine and freshwater habitats
• They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord
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Dental elements(within head)
Conodonts were the first vertebrates with mineralized skeletal elements
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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Fishes and amphibians A. Vertebrate jaws evolved from skeletal supports of pharyngeal slits
1. Animals that replaced jawless vertebrates, and are Gnathostomes. 2. Members of group have two pairs of fins. 3. Jaws and fins allowed fish to become active in pursuit of food and in biting off chunks of flesh.
4. Jaws evolved from modifications of skeletal elements of anterior pharyngeal gill slits.
Hypothesis for the evolution of vertebrate jaws
5. Fishes were prevalent about 360 to 400 million years ago- the “Age of Fishes” 6. Two groups are alive today: a. Class Chondricthyes: Sharks and rays have cartilaginous skeletons
Fossil of an early Gnathostome.
0.5 m
(a) Blacktip reef shark (Carcharhinus melanopterus)
(b) Southern stingray (Dasyatis americana)
(c) Spotted ratfish (Hydrolagus colliei)
Dorsal fins
Pectoralfins Pelvic fins
Chondrichthyans (Sharks, Rays, and Their Relatives)
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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• The reproductive tract, excretory system, and digestive tract empty into a common cloaca
• 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 uterus and is nourished by the egg yolk
– Viviparous: The embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood
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Ray-Finned Fishes and Lobe-Fins
• The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes
• Osteichthyans include the bony fish and tetrapods– Aquatic osteichthyans are the vertebrates we informally
call fishes
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Nostril
BrainSpinal cord
Swimbladder
Dorsal fin
Adipose finCaudalfin
Cutedge ofoperculum
Gills
Kidney
Heart
Liver
Stomach
Intestine
Gonad
Pelvicfin
Anus
Anal fin
Lateralline
Urinarybladder
Ray-Finned Fishes
• Actinopterygii, the ray-finned fishes, include nearly all the familiar aquatic osteichthyans
• Ray-finned fishes originated during the Silurian period (444 to 416 million years ago)
• The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions
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Yellowfin tuna (Thunnus albacares)
Redlionfish(Pteroisvolitans)
Commonsea horse(Hippocampusramulosus)
Fine-spotted moray eel(Gymnothorax dovii)
Lowerjaw
Scalycovering
Dorsal spine
5 cm
Lobe-Fins
• The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral fins
• Lobe-fins also originated in the Silurian period
Tetrapods are gnathostomes that have limbs
• 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
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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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Flat skull
Eyes on top of skull
Head
Neck
Shoulder bonesRibs
Scales
Fin Fin skeleton
Elbow
Radius
Humerus
Ulna
“Wrist”
ScalesFinsGills andlungs
NeckRibsFin skeletonFlat skullEyes on topof skull
TetrapodCharacters
FishCharacters
Tetrapods evolved from specialized fishes that inhabited shallow water The origin of tetrapods.
1. The first tetrapods to spend much time on land were amphibians. Amphibian orders.
Order Urodela – Salamanders, retain tails as adults
Order Anura – Frogs, lack tails as adults
Order Apoda – Caecilians, lack legs
2. There were earlier tetrapods. These were specialized fish that
occupied shallow ponds, breathed air by gulping, and developed lobed walking fins for moving from one pond
to another. 3. Why go on dry land? There were no other competitors for plants and insects that serve as food.
4. Amphibians need to return to water to lay eggs and for development of larvae.
Lungfishes
Limbswith digits
Amphibians
Amniotes
Silurian PALEOZOICDevonian Carboniferous Permian
415 400 385 370 355 340 325 310 295 280 265 0Time (millions of years ago)
Key tolimb bones
UlnaRadiusHumerus
Eusthenopteron
Panderichthys
Tiktaalik
Acanthostega
Tulerpeton
(a) Order Urodela (salamanders)
(b) OrderAnura(frogs)
Order Apoda(caecilians)
(c)
• Amphibians (class Amphibia) are represented by about 6,150 species
• Order Urodela includes salamanders, which have tails
Amphibians
(a) Tadpole
(b) During metamorphosis
(c) Mating adults
• Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult
• Most amphibians have moist skin that complements the lungs in gas exchange
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• Fertilization is external in most species, and the eggs require a moist environment
• In some species, males or females care for the eggs on their back, in their mouth, or in their stomach
ANCESTRALAMNIOTE
Parareptiles
Turtles
Crocodilians
Pterosaurs
Ornithischiandinosaurs
Saurischian dinosaursother than birds
Birds
Plesiosaurs
Ichthyosaurs
Tuataras
Squamates
Mammals
Rep
tilesS
ynap
sids
Diap
sids
Arch
osau
rs
Lep
ido
saurs
Din
osau
rs
Sau
rischi an
s
Amniotes (includes reptiles, mammals, and birds)
Amniotes are tetrapods that have a terrestrially adapted egg
A. Evolution of the amniotic egg expanded the success of vertebrates on land
1. Amniotic eggs allowed vertebrates to sever the link with water and live their whole lives on land.
2. Specialized membranes, called extra-embryonic membranes that function in gas exchange, waste storage, and transfer of nutrients.
a. Membranes develop from tissues derived from the embryo.
b. One membrane, the amnion, gives the name for the amniotic egg.
Reptiles• The reptile clade
includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and some extinct groups
• Reptiles have scales that create a waterproof barrier
• Most reptiles lay shelled eggs on land
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• 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
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Reptilian heritage is evident in all amniotes 1. Scales of keratin, waterproof skin - prevent dehydration.- Reptiles cannot breathe through skin, so all gas exchange occurs via lungs. 2. Shelled amniotic eggs require internal fertilization. Shell forms around fertilized egg in the reproductive tract. 3. Reptiles don’t use metabolism to regulate body temperature; they are ectotherms. Ectotherms absorb external heat (i.e. sunlight) Reptiles are able to survive on about 10% of calories required by mammals. 4. Oldest reptiles are from the late Carboniferous (about 300 million years ago) dinosaurs and pterosaurs.
5. Modern reptiles include 6,500 species that are in four groups: a. Testudines – Turtles - Some species returned to water; all lay eggs on land. b. Sphenodontia – Tuataras c. Squamata – Lizards, snakes - Lizards are the most numerous group. - Snakes are descendants of lizards and have vestigial pelvic and limb bones. d. Crocodilia – Crocodiles, alligators - This is the group most closely related to dinosaurs .
(a) Tuatara(Sphenodonpunctatus)
Australianthorny devillizard (Molochhorridus)
(b)
(d) Eastern box turtle(Terrapene carolinacarolina)
(c) Wagler’s pit viper(Tropidolaemus wagleri)
(e) American alligator (Alligator mississippiensis)
Birds
• Birds are archosaurs, but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight
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• Many characters of birds are adaptations that facilitate flight
• The major adaptation is wings with keratin feathers
• Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth
Derived Characters of Birds
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(a) Wing
Vane
Shaft
ForearmWrist
ShaftBarbBarbuleHook(c) Feather structure
(b) Bone structure
Finger 1
Finger 2
Finger 3
Palm
Birds began as feathered reptiles, evolved to fly: 1. Honeycombed skeletons are light and strong good for flight. Figure 34.25 (p. 698) – Form fits function: the avian wing and feather.
2. Toothless for weight reduction. 3. Endothermic = use metabolic energy to generate heat. - Feathers provide insulation. - Efficient circulatory system supports high rate of metabolism necessary for flying. 4. Acute vision Large brains that allow complex behavior. 5. Wings - Flight enhanced the ability to hunt and scavenge, escape predators, and move with changing seasons.
6. Theropods were the closest dinosaur relative of birds. Example: Velociraptor Archeopteryx is an example of a Mesozoic bird that shows reptilian features.
Archaeopteryx, a Jurassic bird-reptile.
7. Modern birds include about 8,600 species.
Some are flightless = ratites.
Behavior and morphology has adapted to fulfill distinct niches
Mammals are amniotes that have hair and produce milk
• Mammals, class Mammalia, are represented by more than 5,300 species
• 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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Mammals diversified extensively in the wake of the Cretaceous extinctions 1. Radiation of mammals occurred during two events: a. Extinction of dinosaurs b. Fragmentation of continents 2. There are about 4,500 species of extant mammals
4. The earliest mammals evolved from reptiles about 220 million years ago. Therapsids gave rise to mammals. Early example is the Morganucodon in previous figure. 5. Major groups of mammals: a. Monotremes – lay eggs and produce milk, but have no nipples.- Platypus, echidna
b. Marsupials – born early in embryonic development; climb to mother’s pouch and attach to a nipple.- Opossum, kangaroo
• Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus
Monotremes
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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(a) A young brushtail possum
(b) Long-nosed bandicoot
Convergent evolution of marsupials and eutherians (placental mammals).
Plantigale
Marsupialmammals
Eutherianmammals
Marsupial mole
Sugar glider
Wombat
Tasmanian devil
Kangaroo
Deer mouse
Mole
Flyingsquirrel
Woodchuck
Wolverine
Patagonian cavy
ANCESTRALMAMMAL
Mo
no
tremes
(5 specie s)
Marsu
pia ls
(324 spec ies)
Eu
therian
s(5,010 sp
ecies)
Monotremata
Marsupialia
ProboscideaSireniaTubulidentataHyracoideaAfrosoricidaMacroscelidea
Xenarthra
RodentiaLagomorphaPrimatesDermopteraScandentia
CarnivoraCetartiodactylaPerissodactylaChiropteraEulipotyphiaPholidota
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
Primates and the evolution of Homo sapiens A. Primate evolution provides context for understanding human origins 1. Hands and feet adapted for grasping. Possess opposable thumb. 2. Large brains allow complex social behavior.
– Hands, feet for grasping– Flat nails
– A large brain 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)
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Derived Characters of Primates
• There are three main groups of living primates– Lemurs, lorises, and pottos
– Tarsiers
– Anthropoids (monkeys and apes)
Living Primates
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B. Hominid lineage diverged from other primates about 7 million years ago. Humans compared to other hominids: a. Brain size – large size allows development of language and social behavior. b. Jaw shape – shortened to give a flatter face.
c. Bipedalism = walking on two legs.
- Frees hands to do other things.
- Eyes set higher; can see farther.
d. Females smaller than males
e. Extended parental care changes family structure and enhances learning and social behavior.
d. Females smaller than males
e. Extended parental care changes family structure and enhances learning and social behavior.
ANCESTRALPRIMATE
Time (millions of years ago)
60 50 40 30 20 10 0
Lemurs, lorises,and bush babies
Tarsiers
New World monkeys
Old World monkeys
Gibbons
Orangutans
Gorillas
Chimpanzeesand bonobos
Humans
An
thro
po
ids
(b) Old World monkey: macaque(a)New World monkey:spider monkey with prehensile tail
(a) Gibbon(b) Orangutan
(c) Gorilla
(d) Chimpanzees
(e) Bonobos
Humans are mammals that have a large brain and bipedal locomotion
• The species Homo sapiens is about 200,000 years old, which is very young, considering that life has existed on Earth for at least 3.5 billion years
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Derived Characters of Humans
• A number of characters distinguish humans from other apes– Upright posture and bipedal locomotion
– Larger brains capable of language, symbolic thought, artistic expression, the manufacture and use of complex tools
– Reduced jawbones and jaw muscles
– Shorter digestive tract
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• The human and chimpanzee genomes are 99% identical
• How can we be this close, yet so different?
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7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Mil
lio
ns
of
yea
rs a
go
Australo-pithecusanamensis
Kenyanthropusplatyops
Australopithecusafricanus
Paranthropusboisei
Paranthropusrobustus
Homoergaster
Homoneanderthalensis
Homosapiens
Homo erectus
Homo rudolfensisHomo
habilis
Australopithecusgarhi
?
Australopithecusafarensis
Ardipithecus ramidus
Orrorin tugensis
Sahelanthropustchadensis
• Hominins originated in Africa about 6–7 million years ago
• Early hominins show evidence of small brains and increasing bipedalism
Ardi, 4.4 million years old
• Misconception: Early hominins were chimpanzees– Correction: Hominins and chimpanzees shared a common ancestor
• Misconception: Human evolution is like a ladder leading directly to Homo sapiens– Correction: Hominin evolution included many branches or coexisting species, though only humans survive today
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Australopiths
• Australopiths are a paraphyletic assemblage of hominins living between 4 and 2 million years ago
• Some species, such as Australopithecus afarensis walked fully erect
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Evidence that Hominins walked upright 3.5 million years ago.
(a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis
• Homo erectus originated in Africa by 1.8 million years ago
• It was the first hominin to leave Africa
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Neanderthals
• Neanderthals, Homo neanderthalensis, lived in Europe and the Near East from 350,000 to 28,000 years ago
• They were thick-boned with a larger brain, they buried their dead, and they made hunting tools
• Debate is ongoing about the extent to which genetic material was exchanged between neanderthals and Homo sapiens
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Hypothesis: Neanderthals gave rise to European humans.
Expectedphylogeny:
Chimpanzees
Neanderthals
Living Europeans
Other living humans
Chimpanzees
Neanderthal 1
Neanderthal 2
European and otherliving humans
EXPERIMENT
RESULTS
Figure 34.50
Homo Sapiens
• Homo sapiens appeared in Africa by 195,000 years ago
• All living humans are descended from these African ancestors
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• The oldest fossils of Homo sapiens outside Africa date back about 115,000 years and are from the Middle East
• Humans first arrived in the New World sometime before 15,000 years ago
• In 2004, 18,000-year-old fossils were found in Indonesia, and a new small hominin was named: Homo floresiensis
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• Homo sapiens were the first group to show evidence of symbolic and sophisticated thought
• In 2002, a 77,000-year-old artistic carving was found in South Africa
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Clade DescriptionC
ho
rdat
es:
no
toch
ord
; d
ors
al,
ho
llo
wn
erv
e co
rd;
ph
aryn
ge
al s
lits
; p
ost
-an
al t
ail
Cra
nia
tes:
tw
o s
ets
of
Ho
xg
enes
, n
eura
l cr
est
Ver
teb
rate
s:
Dix
gen
es
du
pli
cati
on
,b
ackb
on
e o
f ve
rteb
rae
Gn
ath
ost
om
es:
hin
ged
jaw
s,
fou
r se
ts o
f H
ox
gen
es
Os
teic
hth
yan
s: b
on
y s
kele
ton
Lo
be-
fin
s: m
usc
ula
r fi
ns
or
lim
bs
Tet
rap
od
s: f
ou
r li
mb
s, n
eck
, fu
sed
pe
lvic
gir
dle
Am
nio
tes:
am
nio
tic
eg
g,
rib
cag
e ve
nti
lati
on
Cephalochordata(lancelets)
Urochordata(tunicates)
Myxini(hagfishes andrelatives)
Petromyzontida(lampreys)
Chondrichthyes(sharks, rays,skates, ratfishes)
Actinopterygii(ray-finned fishes)
Actinistia(coelacanths)Dipnoi(lungfishes)
Amphibia(salamanders,frogs, caecilians)
Reptilia(tuataras, lizardsand snakes, turtles,crocodilians, birds)
Mammalia(monotremes,marsupials,eutherians)
Basal chordates; marine suspension feeders thatexhibit four key derived characters of chordates
Marine suspension feeders; larvae display thederived traits of chordates
Jawless marine organisms; have head that includesa skull and brain, eyes, and other sensory organs
Jawless vertebrates; typically feed by attaching to alive fish and ingesting its blood
Aquatic gnathostomes; have cartilaginous skeleton,a derived trait formed by the reduction of anancestral mineralized skeletonAquatic gnathostomes; have bony skeleton andmaneuverable fins supported by rays
Ancient lineage of aquatic lobe-fins still survivingin Indian OceanFreshwater lobe-fins with both lungs and gills; sistergroup of tetrapods
Have four limbs descended from modified fins; mosthave moist skin that functions in gas exchange; manylive both in water (as larvae) and on land (as adults)
One of two groups of living amniotes; have amnioticeggs and rib cage ventilation, key adaptations for lifeon land
Evolved from synapsid ancestors; include egg-layingmonotremes (echidnas, platypus); pouched marsupials(such as kangaroos, opossums); and eutherians(placental mammals, such as rodents, primates)
Figure 34.UN10
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