chapter 24 animals ii: the chordates (sections 24.1 - 24.3)

Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 24 Animals II: The Chordates

(Sections 24.1 - 24.3)

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

Fig 24.1a, p. 378

Lancelets

Fig 24.1a, p. 378

anus

tail extends past anus

eyespot

notochord

dorsal nerve cord

pharynx with gill slits

Lancelets

Fig 24.1b, p. 378

Lancelets

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.

Fig 24.2, p. 378

pharynx with gill slits

A

C

1 cm

Larval and Adult Tunicates

Fig 24.2a, p. 378

Larval and Adult Tunicates

Fig 24.2c, p. 378

Larval and Adult Tunicates

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

Fig 24.3, p. 379

Vertebrates Craniates Chordates Tetrapods Amniotes

ancestral chordate

Bony appendages

Amniote eggs

Swim bladder or lung(s)

Backbone

Tunicates Reptiles (with birds)Lancelets

Jaws

Four limbs

Cartilaginous fishesHagfishes Lampreys

Ray-finned fishes

Lobe-finned fishes

MammalsAmphibians

Braincase1

2

3

4

5

6

7

Evolutionary Tree of Vertebrates

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

Fig 24.5, p. 380

supporting structure for gill slits

jaw, derived from support structure

jaw

location of spiracle (modified gill slit)

jaw supportgill slits

Proposed Evolution of Jaws

jaw

location of spiracle (modified gill slit)

jaw supportjaw, derived from support structure

Fig 24.5, p. 380

supporting structure for gill slitsgill slits

Stepped Art

Proposed Evolution of Jaws

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

Fig 24.7a, p. 381

liverintestine

ovary nerve cord

stomachanus gills

brain

heart

swim bladder kidney

Body Plan of a Perch

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

Fig 24.8, p. 381

pectoral finpelvic fin

Lungfish: A Lobe-Finned Fish

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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