VERTEBRATE EVOLUTION AND DIVERSITY

– Vertebrates have unique endoskeletons composed of: • A cranium (skull) • A backbone made of a series of bones called vertebrae

Vertebra

Cranium(protects brain)

Figure 17.26

Characteristics of Chordates– Chordates (phylum Chordata) all share four key

features that appear in the embryo and sometimes the adult:• A dorsal, hollow nerve cord• A notochord• Pharyngeal slits• A post-anal tail

Muscle segments

Notochord

Dorsal,

hollow

nerve cord

Pharyngeal

slits

Brain

Mouth

Anus

Post-anal

tail

Figure 17.27

– Another chordate characteristic is body segmentation, apparent in the:• Backbone of vertebrates • Segmental muscles of all chordates

– Chordates consists of three groups of invertebrates:• Lancelets are bladelike animals without a cranium.• Tunicates, or sea squirts, also lack a cranium.• Hagfishes are eel-like forms that have a cranium.

– All other chordates are vertebrates.

Mouth

Tail

Lancelet Tunicates

Figure 17.28

Ancestralchordate

Tunicates

Lancelets

Hagfishes

Lampreys

Cartilaginousfishes

Bony fishes

Amphibians

Reptiles

Mammals

Chordates

Vertebrates

TetrapodsAmniotes

Figure 17.29

(a) Hagfish (inset: slime)

Figure 17.30a

– Lampreys:• Are vertebrates• Have a cranium• But lack jaws

(b) Lamprey (inset: mouth)Figure 17.30b

– The two major groups of living fishes are the:• Cartilaginous fishes (sharks and rays) with a flexible

skeleton made of cartilage

(c) Shark, a cartilaginous fish

Lateral line

Figure 17.30c

• And bony fishes with a skeleton reinforced by hard calcium salts

– Bony fishes include:• Ray-finned fishes• Lungfishes• Lobe-finned fishes

(d) Bony fish

Lateral line

Operculum

Figure 17.30d

– Cartilaginous and bony fishes have a lateral line system that detects minor vibrations in the water.

– To provide lift off the bottom:• Cartilaginous fish must swim but• Bony fish have swim bladders, gas-filled sacs that make

them buoyant

Amphibians– Amphibians:• Exhibit a mixture of aquatic and terrestrial adaptations• Usually need water to reproduce• Typically undergo metamorphosis from an aquatic larva to

a terrestrial adult• Were the first vertebrates to colonize land • Descended from fishes that had lungs and fins with

muscles

(a) Tadpole and adult golden palm tree frog

(b) Frogs and salamanders: the two major groups of amphibians

Red-eyed tree frog Texas barred tiger salamander

Figure 17.31

– Terrestrial vertebrates are collectively called tetrapods, which means “four feet.”

– Tetrapods include:• Amphibians• Reptiles• Mammals

Reptiles– Reptiles (including birds) and mammals are

amniotes, which produce amniotic eggs that consist of a fluid-filled shell inside of which the embryo develops.

– Reptile adaptations to living on land include:• Amniotic eggs • Scaled, waterproof skin

– Reptiles include:• Snakes• Lizards• Turtles• Crocodiles• Alligators• Birds

Figure 17.33

Snake

Lizard

Turtle

Birds

– Recent genetic evidence shows that birds evolved from a lineage of small, two-legged dinosaurs.

– Birds have many adaptations that make them lighter in flight:• Honeycombed bones• One instead of two ovaries• A beak instead of teeth

– Unlike other reptiles, birds are endotherms, maintaining a warmer and steady body temperature.

Mammals– The first true mammals:• Arose about 200 million years ago • Were probably small, nocturnal insect-eaters

– Most mammals are terrestrial although dolphins, porpoises, and whales are totally aquatic.

– Mammalian hallmarks are:• Hair • Mammary glands that produce milk, which nourishes the

young

– There are three major groups of mammals:• Monotremes, egg-laying mammals

Monotremes(hatched from eggs)

Echidna adult and egg

Figure 17.35a

• Marsupials, pouched mammals with a placenta

Marsupials(embryonic at birth)

Kangaroo newborn and motherFigure 17.35b

• And eutherians, placental mammals

Eutherians(fully developed at birth)

Wildebeest newborn and motherFigure 17.35c

– Primates are distinguished by characteristics that were shaped by the demands of living in trees. These characteristics include:• Limber shoulder joints• Eyes in front of the face• Excellent eye-hand coordination• Extensive parental care

– Hominoids, the ape relatives of humans

Ring-tailedlemur

Tarsier

Black spider monkey(New World monkey)

Patas monkey (Old World monkey)

Gorilla (ape)

Gibbon (ape)

Chimpanzee (ape)

Orangutan (ape)

HumanFigure 17.37

– Upright posture and an enlarged brain appeared at separate times during human evolution.

– Different human features evolved at different rates.

Australopithecus and the Antiquity of Bipedalism

– Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna.

– Fossil evidence pushes bipedalism in A. afarensis back to at least 4 million years ago.

(a) Australopithecusafarensis skeleton

(b) Ancient footprints (c) Model of anAustralopithecusafarensis male

Figure 17.39

Homo Habilis and the Evolution of Inventive Minds

– Homo habilis, “handy-man”:• Had a larger brain, intermediate in size between

Australopithecus and modern humans• Walked upright• Made stone tools that enhanced hunting, gathering, and

scavenging on the African savanna

Homo Erectus and the Global Dispersal of Humanity

– Homo erectus was the first species to extend humanity’s range from Africa to other continents.

– The global dispersal began about 1.8 million years ago.

– Homo erectus:• Was taller than H. habilis• Had a larger brain• Gave rise to Neanderthals

© 2010 Pearson Education, Inc.

The Origin and Dispersal of Homo Sapiens

– The oldest known fossils of our own species, Homo sapiens:• Were discovered in Ethiopia • Date from 160,000 to 195,000 years ago

• DNA studies strongly suggest that all living humans can trace their ancestry back to a single African Homo sapiens woman who lived 160,000 to 200,000 years ago.