animal evolution – the chordates chapter 26 part 1
TRANSCRIPT
Animal Evolution – The Chordates
Chapter 26 Part 1
Impacts, IssuesTransitions 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
Fig. 26-2b, p. 434
a Dorsal, hollow nerve cord
b Notochord c Pharynx with gill slits
d Tail extends beyond anus
eyespot
tentacle-like structures around mouth
segmented muscles
(myomeres)midgut hindgut
aorta gonad pore of atrial cavity anusepidermis
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
Fig. 26-3a, p. 435
nerve cord notochord
gut
pharynx with gill slits
Fig. 26-3b, p. 435
Fig. 26-3c, p. 435
Fig. 26-3c, p. 435
pharynx with gill slits
Fig. 26-3d, p. 435
1 cm
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
Fig. 26-4a, p. 435
tentacles gill slits (twelve pairs) mucous glands
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
Fig. 26-6a, p. 437
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. 26-6b, 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. 26-6c, p. 437
location of spiracle (modified gill slit)
jaw support
jaw
C Sharks and other modern jawed fishes have strong jaw supports.
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
Fig. 26-5, p. 436
lancelets
tunicates
hagfishes
lampreyscartilaginous
fishes
ray-finned fishes
lobe-finned fishes
lungfishes
amphibians
“reptiles”
birds mammals
amniotes
tetrapods
swim bladder or lungs
jawed vertebrates
vertebrates
craniates
ancestral chordates
Origin of the first jawless fishes.
Jawed fishes, including the placo-derms and sharks, evolve.
Adaptive radiation of fishes, and the first amphibians move onto land.
Diversification of fishes and amphibians. Armored fishes go extinct.
Reptiles arise and start to diversify. Early amphibians in decline.
Dinosaurs and marine reptiles evolve.
Birds, mammals, and modern amphibians arise. Dinosaurs dominate.
Dinosaur diversity peaks, then extinction by period’s end.
Adaptive radiation of mammals.
Ordovician Carboniferous Jurassic Tertiary
488 443 416 359 299 251 200 146 66
Silurian Devonian Permian Triassic Cretaceous
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
Fig. 26-9a, p. 439
swim bladder kidney
ovary nerve cord
brain
cloaca intestine stomach liver heart gills
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 (four-legged 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
Fig. 26-16c, p. 442
snakes
lizards
“stem” reptiles tuataras
ichthyosaurs
plesiosaurs
birds
therapod dinosaurs
other dinosaurs
pterosaursarchosaurs
crocodilians
turtles
therapsidsanapsids
synapsids mammals
PALEOZOIC ERA MESOZOIC ERA
TERTIARY TO PRESENT
CARBONIFEROUS PERMIAN TRIASSIC JURASSIC CRETACEOUS
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• Scale-covered body• Cloaca for waste disposal• Four approximately equal limbs (except snakes)• Internal fertilization• Body temperature determined by surroundings
(ectotherms)
Crocodile Body Plan
Fig. 26-18, p. 444
kidney (control of water, solute levels in internal environment)
olfactory lobe (sense of smell)
hindbrain, midbrain, forebrain
spinal cord
vertebral column
gonad
snout
unmatched rows of teeth on upper and lower jaws
esophagus
lung
heart
liver
stomach
intestine cloaca
Animation: Crocodile body plan
Turtles and Tortoises
Turtles and tortoises have a bony, scale-covered shell attached to the backbone
Fig. 26-19b, p. 445
hard shell vertebral column
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
Fig. 26-19f (1), p. 445
venom gland
hollow fang
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