Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 24
Animals II: The Chordates
(Sections 24.1 - 24.3)
Albia Dugger • Miami Dade College
24.1 Windows on the Past
• Fossils are physical evidence of changes that led to modern
animal diversity
• Radiometric dating assigns fossils to places in time
• Structure, biochemistry, and genetic makeup of living
organisms provide information about branchings
Transition Fossils
• Fossils reveal that birds
evolved from feathered
dinosaurs, and that
some early birds had a
bony tail and teeth
24.2 The Chordate Heritage
• Chordates are distinguished by their embryonic traits
• Chordates include vertebrates and two lineages of marine
invertebrates
• chordate
• Animal with an embryo that has a notochord, dorsal nerve
cord, pharyngeal gill slits, and a tail that extends beyond
the anus
Chordate Characteristics
• Four features define chordate embryos:
• a notochord
• a dorsal hollow nerve cord
• a pharynx with gill slits
• a muscular tail extending past the anus
• These features may or may not persist in adults
Key Terms
• notochord
• A rod of stiff but flexible connective tissue that runs the
length of the body in chordate larvae or embryos and
supports it
Invertebrate Chordates
• Invertebrate chordates include lancelets and tunicates
• lancelet
• Invertebrate chordate that has a fishlike shape and retains
the defining chordate traits into adulthood
• tunicate
• Invertebrate chordate that loses its defining chordate traits
during the transition to adulthood
Lancelets
• Gill slits filter food particles
out of the water and also
function in gas exchange
Lancelets
Fig 24.1a, p. 378
Lancelets
eyespot
notochord
dorsal nerve cord
pharynx with gill slits
tail extends
past anus
anus
Fig 24.1a, p. 378
Lancelets
Fig 24.1b, p. 378
ANIMATION: Lancelet body plan
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Tunicates
• Larvae swim about briefly, then undergo metamorphosis
• Adults retain only the pharynx with gill slits
• Adults feed by drawing water in through an oral opening, past
gill slits, then expels it through a second opening
Larval and Adult Tunicates.
Larval and Adult Tunicates
A
pharynx
with gill
slits
C
1 cm
Fig 24.2, p. 378
Larval and Adult Tunicates
Fig 24.2a, p. 378
Larval and Adult Tunicates
Fig 24.2c, p. 378
ANIMATION: Tunicate body plan
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Overview of Chordate Evolution
• Craniates are chordates with a braincase of cartilage or bone
• Most craniates are vertebrates
• craniate
• Chordate with a braincase
• vertebrate
• Animal with a backbone
Chordate Evolution (cont.)
• Vertebrae and other skeletal elements are components of the
vertebrate endoskeleton
• Jaws evolved from bony parts that supported gill slits of early
jawless fishes
• endoskeleton
• Internal skeleton made up of hardened components such
as bones
Chordate Evolution (cont.)
• Evolutionary modifications allowed animals to move from
water onto land:
• Fins would evolved into limbs of tetrapods
• A subset of tetrapods, amniotes produce eggs that allow
embryos to develop away from water
Key Terms
• tetrapod
• Vertebrate with four legs, or a descendant thereof
• amniote
• Vertebrate in which the embryo develops surrounded by
fluid enclosed by membranes inside the egg
Evolutionary Tree of Vertebrates
Evolutionary Tree of Vertebrates
Vertebrates
Craniates
Chordates
Tetrapods
Amniotes
Lobefinned
fishes
CartilaginousRay-finned
Lancelets Tunicates HagfishesLampreys fishes
fishes
Reptiles
(with birds) Mammals
Amphibians
7 Amniote eggs
6 Four limbs
5 Bony appendages
4 Swim bladder or lung(s)
3 Jaws
2 Backbone
1 Braincase
ancestral chordate
Fig 24.3, p. 379
Key Concepts
• Characteristics of Chordates
• Four traits characterize chordate embryos: a supporting
rod (notochord), a dorsal nerve cord, a pharynx with gill
slits in the wall, and a tail that extends past the anus
• Certain invertebrates and all vertebrates belong to this
group
ANIMATION: Vertebrate Evolution
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24.3 The Fishes
• The number and diversity of fishes exceed those of all other
vertebrate groups combined
• Fishes are divided into jawless and fishes with jaws
• Fishes with jaws are divided into cartilaginous fishes and
bony fishes
Jawless Fishes
• The first fishes were jawless – two lineages survive – both
have a cylindrical body, no fins or scales, and move with a
wiggling motion
• hagfish
• Jawless fish with a cranium (skull case) but no backbone
• lamprey
• Jawless vertebrates with a backbone of cartilage
• Some are parasites of other fish
Two Modern Jawless Fishes
• Hagfish
• Parasitic lamprey
Fishes With Jaws
• Jawed fishes likely evolved from jawless ancestors when
some gill supports became modified
• Jawed fishes typically have scales and paired fins
• Jawed fished are divided into the cartilaginous fishes and the
bony fishes
Proposed Evolution of Jaws
Proposed Evolution of Jaws
supporting
structure for
gill slits
gill slits
jaw, derived
from support
structure
location of spiracle
(modified gill slit)
jaw support
jaw
Fig 24.5, p. 380
Proposed Evolution of Jaws
supporting
structure for
gill slits
gill slits
jaw, derived
from support
structure
location of spiracle
(modified gill slit)
jaw support
jaw
Stepped Art
Fig 24.5, p. 380
Cartilaginous Fishes (Chondrichthyes)
• Cartilaginous fishes include sharks and rays
• Some sharks have rows of teeth, some are filter feeders
• Rays include filter feeders (mantas) and bottom feeders
(stingrays)
• cartilaginous fish
• Fish with a skeleton of cartilage
• Gills are visible at the surface
Two Cartilaginous Fishes
Bony Fishes
• There are two lineages of bony fishes:
• Ray-finned fishes are the most diverse, including salmon,
sardines, bass, swordfish, trout, tuna, halibut, carp, and cod
• Lobe-finned fishes include coelacanths and lungfishes
Key Terms
• bony fish
• Fish with a lung or swim bladder and a skeleton consisting
largely of bone
• lobe-finned fish
• Fish with fleshy fins that contain bones
• ray-finned fish
• Fish with fins supported by thin rays derived from skin;
member of most diverse lineage of fishes
Bony-Fish Body Plan
• Aspects of the fish body plan adapt fish to life in water:
• A swim bladder allows ray-finned fish to adjust its
buoyancy
• Kidneys filter blood and adjust volume and solute
composition
• Lungfishes have gills and one or two air-filled lungs
Body Plan of a Perch
Body Plan of a Perch
swim bladder
kidney
ovary
nerve cord
brain
anus
intestine
stomach
liver
heart
gills
Fig 24.7a, p. 381
Ray-Finned Fish Diversity
ANIMATION: Bony fish body plan
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Lungfish: A Lobe-Finned Fish
• Pelvic and pectoral fins are supported by bones
Lungfish: A Lobe-Finned Fish
pelvic fin
pectoral fin
Fig 24.8, p. 381
Key Concepts
• The Fishes
• The first vertebrates were jawless fish
• Most modern fishes have jaws
• Sharks and their relatives are jawed fishes with a cartilage
skeleton
• Ray-finned fishes and lobe-finned fishes are jawed bony
fishes
• Ray-finned fishes are the most diverse vertebrate group
ANIMATION: Jawless Fishes
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ANIMATION: Evolution of Jaws
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ANIMATION: Cartilaginous Fishes
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