Download Animal Evolution – The Chordates

Animal Evolution – The Chordates
Chapter 26 Part 1
Impacts, Issues
Transitions Written in Stone
 Fossils such as Archaeopteryx, an ancient
winged dinosaur with feathers, are evolutionary
evidence of transitions between species
26.1 The Chordate Heritage
 Chordates
•
•
•
•
•
•
•
Most diverse lineage of deuterostomes
Some are invertebrates; most are vertebrates
Bilateral and coelomate
Cephalized and segmented
Complete digestive system
Closed circulatory system
Classified by embryonic characteristics
Modern Chordate Groups
Embryonic Chordate Characteristics
 Four characteristics of chordate embryos may
not persist in adults
• Notochord of stiff connective tissue that extends
the length of the body and supports it
• Dorsal, hollow nerve cord parallels the notochord
• Gill slits across the wall of the pharynx
• Tail that extends beyond the anus
Invertebrate Chordates
 Lancelets are the only group of chordates that
retains all chordate characteristics as adults
Fig. 26-2b, p. 434
a Dorsal, hollow b Notochord
nerve cord
c Pharynx
with gill slits
d Tail extends
beyond anus
eyespot
aorta gonad pore of atrial
segmented
tentacle-like epidermis muscles midgut
hindgut cavity
anus
structures
(myomeres)
around mouth
Fig. 26-2b, p. 434
Animation: Lancelet body plan
Invertebrate Chordates
 Tunicates have typical chordate larvae, but
adults retain only the pharynx with gill slits
Fig. 26-3a, p. 435
nerve
cord
notochord
gut
pharynx with gill slits
Fig. 26-3a, p. 435
Fig. 26-3b, p. 435
Fig. 26-3c, p. 435
pharynx
with gill
slits
Fig. 26-3c, p. 435
1 cm
Fig. 26-3d, p. 435
Craniates
 Craniates have a braincase of cartilage or bone
(cranium) that encases the brain, paired eyes,
and other sensory structures on the head
 Craniates includes fishes, amphibians, reptiles,
birds, and mammals
 Hagfishes are the only modern craniates that
are not vertebrates
Hagfishes
 Soft bodied, boneless fishes
Fig. 26-4a, p. 435
tentacles
gill slits (twelve pairs)
mucous glands
Fig. 26-4a, p. 435
Fig. 26-4b, p. 435
Fig. 26-4c, p. 435
26.1 Key Concepts
Characteristics of Chordates
 Four traits characterizes the chordates:
•
•
•
•
A supporting rod (notochord)
A hollow, dorsal nerve cord
A pharynx with gill slits in the wall
A tail extending past an anus
 Certain invertebrates and all vertebrates belong
to this group
26.2 Vertebrate Traits and Trends
 Vertebrates are chordates with an internal
skeleton (endoskeleton) of cartilage or bone
with a supportive backbone (vertebral column)
made up of individual vertebrae
 Modern vertebrates (except lampreys) have
jaws derived from gill-supporting structures
Gill-Supporting Structures
supporting
structure
for gill slits
gill slits
A In early jawless fishes, supporting
elements reinforced a series of gill slits
on both sides of the body.
Fig. 26-6a, p. 437
jaw, derived
from support
structure
B In early jawed fishes (e.g., placoderms), the
first elements were modified and served as
jaws. Cartilage reinforced the mouth’s rim.
Fig. 26-6b, p. 437
location of spiracle
(modified gill slit)
jaw support
jaw
C Sharks and other modern jawed
fishes have strong jaw supports.
Fig. 26-6c, p. 437
Animation: Evolution of jaws
Evolution of Internal Skeleton
 Fishes evolved appendages (fins) for swimming
 Pelvic and pectoral fins gave rise to paired limbs
in amphibians, which began the move to land
Evolution of Other Systems
 Living in water (fish)
• Blood moves in a single circuit from heart to gills
(respiratory organs that function in water)
 Moving to land
• Modification of the respiratory system (lungs)
and circulatory system (two circuits)
• Efficient kidneys to conserve water, and a
system of internal fertilization
Chordate Family Tree
ray-finned
―reptiles‖
fishes
lungfishes
tunicates
lampreys
lobe-finned
cartilaginous
amphibians
birds mammals
lancelets
hagfishes
fishes
fishes
amniotes
tetrapods
swim bladder
or lungs
jawed
vertebrates
vertebrates
craniates
ancestral chordates
Origin
of the
first
jawless
fishes.
Jawed
fishes,
including
the placoderms
and
sharks,
evolve.
Adaptive
radiation
of fishes,
and the
first
amphibians
move
onto land.
Diversification
of fishes and
amphibians.
Armored
fishes go
extinct.
Reptiles Dinosaurs
arise and and marine
start to
reptiles
diversify. evolve.
Early
amphibians
in decline.
Ordovician Silurian Devonian Carboniferous
488
443
416
359
Permian
299
Birds,
mammals,
and modern
amphibians
arise.
Dinosaurs
dominate.
Triassic
251
Dinosaur
diversity
peaks, then
extinction
by period’s
end.
Jurassic
Cretaceous
200
146
Adaptive
radiation
of
mammals.
Tertiary
66
Fig. 26-5, p. 436
Animation: Vertebrate evolution
26.2 Key Concepts
Trends Among Vertebrates
 In vertebrate lineages, a backbone replaced the
notochord
 Jaws and fins evolved in water
 Fleshy fins with skeletal supports evolved into
limbs that allowed vertebrates to walk onto land
 On land, lungs replaced gills and circulation
changed in concert
26.3 The Jawless Lampreys
 Lampreys have no jaws or paired fins; they
undergo metamorphosis, and many are
parasites of other fishes
26.4 The Jawed Fishes
 Jawed fishes typically have paired fins and a
body covered with scales
 Cartilaginous fishes (Chondrichthyes) have a
cartilage skeleton, gill slits, and teeth that shed
• Sharks and rays
 Bony fishes (Osteichthyes) have a bony
skeleton, gill covers, and a swim bladder
• Ray-finned fishes, lungfishes, coelacanth
Ray-Finned Bony Fishes
Fig. 26-9a, p. 439
swim bladder
kidney
ovary
nerve cord
brain
cloaca
intestine
stomach liver
heart
gills
Fig. 26-9a, p. 439
Fig. 26-9b, p. 439
Fig. 26-9c, p. 439
Fig. 26-9d, p. 439
Lungfish
 Lungfishes have gills and lunglike sacs for
breathing air
Coelacanth
 The only modern lobe-finned fish; closely related
to amphibians
26.5 Amphibians—
First Tetrapods on Land
 Tetrapods (four-legged walkers)
• Branched from lobe-finned fishes in Devonian
 Amphibians
• Land-dwelling vertebrates that return to water to
breed, undergo metamorphosis, and have a
three-chambered heart
Adapting to Life on Land
Fig. 26-12a, p. 440
Fig. 26-12b, p. 440
Fig. 26-12c, p. 440
Fig. 26-12d, p. 440
Modern Amphibians
 Salamanders and newts
• Body form most like early tetrapods, side-to-side
walking motion
 Caecilians
• Includes many limbless, blind burrowers
 Frogs and toads
• Tailless adults with long, muscular hind legs
Salamander and Caecilian
Frog
26.6 Vanishing Acts
 Amphibians depend on standing water to breed
and have a thin skin unprotected by scales
 These features make them vulnerable to habitat
loss, disease, and pollution – causing
deformities and threatening species
Frog Deformity
26.3-26.6 Key Concepts
Transition from Water to Land
 Vertebrates evolved in the seas, where
cartilaginous and bony fishes still live
 Of all vertebrates, modern bony fishes are most
diverse
 One group gave rise to aquatic tetrapods (fourlegged walkers), the descendants of which
moved onto dry land
26.7 The Rise of Amniotes
 Amniotes are animals with embryos that
develop inside a waterproof egg; their
waterproof skin and highly efficient kidneys
make them well adapted to dry habitats
Amniotes
 Four branches of amniotes lead to synapsids
(mammals), anapsids (turtles), lizards and
snakes, and crocodiles and birds
 Reptiles are an artificial group referring to
amniotes other than bird or mammals
 Dinosaurs are extinct amniotes; birds are their
descendents
The Ruling Reptiles
 For 125 million years, dinosaurs dominated the
land and sea (Example: Ichthyosaurs)
Amniote Phylogeny
snakes
lizards
―stem‖
reptiles
tuataras
ichthyosaurs
plesiosaurs
birds
therapod
dinosaurs
other
dinosaurs
pterosaurs
archosaurs
crocodilians
turtles
anapsids
therapsids
mammals
synapsids
CARBONIFEROUS
PERMIAN
PALEOZOIC ERA
TRIASSIC
JURASSIC
CRETACEOUS
MESOZOIC ERA
TERTIARY
TO
PRESENT
Fig. 26-16c, p. 442
26.8 So Long, Dinosaurs
 K-T asteroid impact hypothesis
• Asteroid impacts changed life on Earth, defining
the Cretaceous-Tertiary (K-T) boundary
• Most dinosaurs became extinct
26.9 Diversity of Modern Reptiles
 Reptile characteristics
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Scale-covered body
Cloaca for waste disposal
Four approximately equal limbs (except snakes)
Internal fertilization
Body temperature determined by surroundings
(ectotherms)
Crocodile Body Plan
olfactory
hindbrain,
vertebral column
lobe (sense midbrain, spinal
gonad
of smell)
forebrain cord
kidney (control
of water, solute
levels in internal
environment)
snout
unmatched
rows of teeth
lung
liver
intestine cloaca
on upper and
heart stomach
lower jaws
esophagus
Fig. 26-18, p. 444
Animation: Crocodile body plan
Turtles and Tortoises
 Turtles and tortoises have a bony, scalecovered shell attached to the backbone
hard shell
vertebral column
Fig. 26-19b, p. 445
Lizards
 Lizards, the most diverse reptiles, have many
interesting defenses
Tuataras
 The two remaining species of tuataras have a
third eye under the skin of the forehead
Snakes
 Snakes are legless, but some have bony
remnants of hindlimbs
venom
gland
hollow
fang
Fig. 26-19f (1), p. 445
Crocodilians
 Crocodilians, close relatives of birds, are the
only reptiles with a four-chambered heart
Animation: Bony fish body plan
Animation: Cartilaginous fishes
Animation: Evolution of limb bones
Animation: Jawless fishes
Animation: Salamander locomotion
Animation: Tortoise shell and skeleton
Animation: Tunicate body plan