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Chapter 34. Vertebrates. Overview: Half a Billion Years of Backbones By the end of the Cambrian period, some 540 million years ago An astonishing variety of animals inhabited Earth’s oceans One of these types of animals Gave rise to vertebrates, one of the most successful groups of animals.

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Chapter 34

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Chapter 34

Chapter 34

Vertebrates


Chapter 34

  • Overview: Half a Billion Years of Backbones

  • By the end of the Cambrian period, some 540 million years ago

    • An astonishing variety of animals inhabited Earth’s oceans

  • One of these types of animals

    • Gave rise to vertebrates, one of the most successful groups of animals


Chapter 34

Figure 34.1

  • The animals called vertebrates

    • Get their name from vertebrae, the series of bones that make up the backbone


Chapter 34

  • There are approximately 52,000 species of vertebrates

    • Which include the largest organisms ever to live on the Earth


Chapter 34

  • Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord

  • Vertebrates are a subphylum of the phylum Chordata

  • Chordates are bilaterian animals

    • That belong to the clade of animals known as Deuterostomia

  • Two groups of invertebrate deuterostomes, the urochordates and cephalochordates

    • Are more closely related to vertebrates than to invertebrates


Chapter 34

Chordates

Craniates

Vertebrates

Gnathostomes

Osteichthyans

Lobe-fins

Tetrapods

Amniotes

Echinodermata(sister group to chordates)

Chondrichthyes(sharks, rays, chimaeras)

Cephalaspidomorphi(lampreys)

Amphibia(frogs, salamanders)

Cephalochordata(lancelets)

Reptilia(turtles, snakes,crocodiles, birds)

Actinopterygii(ray-finned fishes)

Urochordata(tunicates)

Actinistia(coelacanths)

Dipnoi(lungfishes)

Myxini(hagfishes)

Mammalia(mammals)

Milk

Amniotic egg

Legs

Lobed fins

Lungs or lung derivatives

Jaws, mineralized skeleton

Vertebral column

Head

Brain

Notochord

Ancestral deuterostome

Figure 34.2

  • A hypothetical phylogeny of chordates


Derived characters of chordates

Dorsal,hollownerve cord

Brain

Notochord

Musclesegments

Mouth

Anus

Pharyngealslits or clefts

Muscular,post-anal tail

Figure 34.3

Derived Characters of Chordates

  • All chordates share a set of derived characters

    • Although some species possess some of these traits only during embryonic development


Notochord

Notochord

  • The notochord

    • Is a longitudinal, flexible rod located between the digestive tube and the nerve cord

    • Provides skeletal support throughout most of the length of a chordate

  • In most vertebrates, a more complex, jointed skeleton develops

    • And the adult retains only remnants of the embryonic notochord


Dorsal hollow nerve cord

Dorsal, Hollow Nerve Cord

  • The nerve cord of a chordate embryo

    • Develops from a plate of ectoderm that rolls into a tube dorsal to the notochord

    • Develops into the central nervous system: the brain and the spinal cord


Pharyngeal slits or clefts

Pharyngeal Slits or Clefts

  • In most chordates, grooves in the pharynx called pharyngeal clefts

    • Develop into slits that open to the outside of the body

  • These pharyngeal slits

    • Function as suspension-feeding structures in many invertebrate chordates

    • Are modified for gas exchange in aquatic vertebrates

    • Develop into parts of the ear, head, and neck in terrestrial vertebrates


Muscular post anal tail

Muscular, Post-Anal Tail

  • Chordates have a tail extending posterior to the anus

    • Although in many species it is lost during embryonic development

  • The chordate tail contains skeletal elements and muscles

    • And it provides much of the propelling force in many aquatic species


Tunicates

Tunicates

  • Tunicates, subphylum Urochordata

    • Belong to the deepest-branching lineage of chordates

    • Are marine suspension feeders commonly called sea squirts


Chapter 34

Notochord

Dorsal, hollownerve cord

Tail

Excurrent siphon

Musclesegments

Incurrentsiphon

Intestine

Stomach

Atrium

Pharynx with slits

(c) A tunicate larva is a free-swimming butnonfeeding “tadpole” in which all fourchief characters of chordates are evident.

  • Tunicates most resemble chordates during their larval stage

    • Which may be as brief as a few minutes

Figure 34.4c


Chapter 34

Incurrentsiphonto mouth

Excurrentsiphon

Excurrent siphon

Atrium

Pharynxwith numerousslits

Anus

Intestine

Tunic

Esophagus

Stomach

(b) In the adult, prominent pharyngeal slits function in suspension feeding, but other chordate characters are not obvious.

(a) An adult tunicate, or sea squirt, is a sessile animal (photo is approximately life-sized).

Figure 34.4a, b

  • As an adult

    • A tunicate draws in water through an incurrent siphon, filtering food particles


Lancelets

Tentacle

2 cm

Mouth

Pharyngeal slits

Atrium

Notochord

Digestive tract

Atriopore

Dorsal, hollownerve cord

Segmentalmuscles

Anus

Tail

Figure 34.5

Lancelets

  • Lancelets, subphylum Cephalochordata

    • Are named for their bladelike shape


Chapter 34

  • Lancelets are marine suspension feeders

    • That retain the characteristics of the chordate body plan as adults


Early chordate evolution

Early Chordate Evolution

  • The current life history of tunicates

    • Probably does not reflect that of the ancestral chordate


Chapter 34

BF1

Otx

Hox3

Nerve cord of lancelet embryo

BF1

Hox3

Otx

Brain of vertebrate embryo(shown straightened)

Midbrain

Forebrain

Hindbrain

Figure 34.6

  • Gene expression in lancelets

    • Holds clues to the evolution of the vertebrate form


Chapter 34

  • Concept 34.2: Craniates are chordates that have a head

  • The origin of a head

    • Opened up a completely new way of feeding for chordates: active predation

  • Craniates share some common characteristics

    • A skull, brain, eyes, and other sensory organs


Derived characters of craniates

Neuraltube

Neuralcrest

Dorsal edgesof neural plate

Ectoderm

Ectoderm

(a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube.

(b) Neural crest cells migrate todistant sites in the embryo.

Migrating neuralcrest cells

Notochord

Figure 34.7a, b

Derived Characters of Craniates

  • One feature unique to craniates

    • Is the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryo


Chapter 34

(c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull.

Figure 34.7c

  • Neural crest cells

    • Give rise to a variety of structures, including some of the bones and cartilage of the skull


The origin of craniates

The Origin of Craniates

  • Craniates evolved at least 530 million years ago

    • During the Cambrian explosion


Chapter 34

(a)Haikouella. Discovered in 1999 in southern China, Haikouella had eyes and a brain but lacked a skull, a derived trait of craniates.

Figure 34.8a

  • The most primitive of the fossils

    • Are those of the 3-cm-long Haikouella


Chapter 34

5 mm

(b) Haikouichthys.Haikouichthys had a skull and thus is considered a true craniate.

Figure 34.8b

  • In other Cambrian rocks

    • Paleontologists have found fossils of even more advanced chordates, such as Haikouichthys


Hagfishes

Slime glands

Figure 34.9

Hagfishes

  • The least derived craniate lineage that still survives

    • Is class Myxini, the hagfishes


Chapter 34

  • Hagfishes are jawless marine craniates

    • That have a cartilaginous skull and axial rod of cartilage derived from the notochord

    • That lack vertebrae


Chapter 34

  • Concept 34.3: Vertebrates are craniates that have a backbone

  • During the Cambrian period

    • A lineage of craniates evolved into vertebrates


Derived characters of vertebrates

Derived Characters of Vertebrates

  • Vertebrates have

    • Vertebrae enclosing a spinal cord

    • An elaborate skull

    • Fin rays, in aquatic forms


Lampreys

Lampreys

  • Lampreys, class Cephalaspidomorphi

    • Represent the oldest living lineage of vertebrates

    • Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord


Chapter 34

Figure 34.10

  • Lampreys are jawless vertebrates

    • Inhabiting various marine and freshwater habitats


Fossils of early vertebrates

Dorsal viewof head

Dentalelements

Figure 34.11

Fossils of Early Vertebrates

  • Conodonts were the first vertebrates

    • With mineralized skeletal elements in their mouth and pharynx


Chapter 34

Pteraspis

Pharyngolepis

Figure 34.12

  • Armored, jawless vertebrates called ostracoderms

    • Had defensive plates of bone on their skin


Origins of bone and teeth

Origins of Bone and Teeth

  • Mineralization

    • Appears to have originated with vertebrate mouthparts

  • The vertebrate endoskeleton

    • Became fully mineralized much later


Chapter 34

  • Concept 34.4: Gnathostomes are vertebrates that have jaws

  • Today, jawless vertebrates

    • Are far outnumbered by those with jaws


Derived characters of gnathostomes

Gill slits

Cranium

Mouth

Skeletal rods

Figure 34.13

Derived Characters of Gnathostomes

  • Gnathostomes have jaws

    • That evolved from skeletal supports of the pharyngeal slits


Chapter 34

  • Other characters common to gnathostomes include

    • Enhanced sensory systems, including the lateral line system

    • An extensively mineralized endoskeleton

    • Paired appendages


Fossil gnathostomes

(a) Coccosteus, a placoderm

Figure 34.14a

Fossil Gnathostomes

  • The earliest gnathostomes in the fossil record

    • Are an extinct lineage of armored vertebrates called placoderms


Chapter 34

(b) Climatius, an acanthodian

Figure 34.14b

  • Another group of jawed vertebrates called acanthodians

    • Radiated during the Devonian period

    • Were closely related to the ancestors of osteichthyans


Chondrichthyans sharks rays and their relatives

Chondrichthyans (Sharks, Rays, and Their Relatives)

  • Members of class Chondrichthyes

    • Have a skeleton that is composed primarily of cartilage

  • The cartilaginous skeleton

    • Evolved secondarily from an ancestral mineralized skeleton


Chapter 34

(a) Blacktip reef shark (Carcharhinus melanopterus).Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins.

Pelvic fins

Pectoral fins

(b) Southern stingray (Dasyatis americana).Most rays are flattened bottom-dwellers thatcrush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into their gaping mouth.

Figure 34.15a, b

  • The largest and most diverse subclass of Chondrichthyes

    • Includes the sharks and rays


Chapter 34

(c) Spotted ratfish(Hydrolagus colliei). Ratfishes, or chimaeras, typically live at depths greaterthan 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin.

Figure 34.15c

  • A second subclass

    • Is composed of a few dozen species of ratfishes


Chapter 34

  • Most sharks

    • Have a streamlined body and are swift swimmers

    • Have acute senses


Ray finned fishes and lobe fins

Ray-Finned Fishes and Lobe-Fins

  • The vast majority of vertebrates

    • Belong to a clade of gnathostomes called Osteichthyes


Chapter 34

  • Nearly all living osteichthyans

    • Have a bony endoskeleton

  • Aquatic osteichthyans

    • Are the vertebrates we informally call fishes

    • Control their buoyancy with an air sac known as a swim bladder


Chapter 34

Adipose fin(characteristic oftrout)

Dorsal fin

Caudal fin

Swim bladder

Spinal cord

Brain

Nostril

Cut edge of operculum

Anal fin

Gills

Anus

Gonad

Liver

Heart

Lateral line

Stomach

Urinary bladder

Kidney

Intestine

Pelvic fin

Figure 34.16

  • Fishes breathe by drawing water over four or five pairs of gills

    • Located in chambers covered by a protective bony flap called the operculum


Ray finned fishes

(a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide

(b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones

(c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development

(d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitat

Figure 34.17a–d

Ray-Finned Fishes

  • Class Actinopterygii, the ray-finned fishes

    • Includes nearly all the familiar aquatic osteichthyans


Chapter 34

  • The fins, supported mainly by long, flexible rays

    • Are modified for maneuvering, defense, and other functions


Lobe fins

Figure 34.18

Lobe-Fins

  • The lobe-fins, class Sarcopterygii

    • Have muscular and pectoral fins

    • Include coelacanths, lungfishes, and tetrapods


Chapter 34

  • Concept 34.5: Tetrapods are gnathostomes that have limbs and feet

  • One of the most significant events in vertebrate history

    • Was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods


Derived characters of tetrapods

Derived Characters of Tetrapods

  • Tetrapods have some specific adaptations

    • Four limbs and feet with digits

    • Ears for detecting airborne sounds


The origin of tetrapods

Bonessupportinggills

Tetrapodlimbskeleton

Figure 34.19

The Origin of Tetrapods

  • In one lineage of lobe-fins

    • The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life


Chapter 34

Millions of years ago

420

370

340

310

295

280

265

415

400

385

355

325

Silurian

Devonian

Carboniferous

Permian

To present

Paleozoic

Ray-finned fishes

Coelacanths

Lungfishes

Eusthenopteron

Panderichthys

Elginerpeton

Metaxygnathus

Acanthostega

lchthyostega

Hynerpeton

Greerpeton

Amphibians

Amniotes

Figure 34.20

  • Extraordinary fossil discoveries over the past 20 years

    • Have allowed paleontologists to reconstruct the origin of tetrapods


Amphibians

Amphibians

  • Class Amphibia

    • Is represented by about 4,800 species of organisms

  • Most amphibians

    • Have moist skin that complements the lungs in gas exchange


Chapter 34

(a) Order Urodela. Urodeles (salamanders) retain their tail as adults.

Figure 34.21a

  • Order Urodela

    • Includes salamanders, which have tails


Chapter 34

(b) Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults.

Figure 34.21b

  • Order Anura

    • Includes frogs and toads, which lack tails


Chapter 34

(c) Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians.

Figure 34.21c

  • Order Apoda

    • Includes caecilians, which are legless and resemble worms


Chapter 34

(b) The tadpole is an aquatic herbivore witha fishlike tail and internal gills.

(c) During metamorphosis, the gills and tail are resorbed, andwalking legs develop.

(a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air.

Figure 34.22a–c

  • Amphibian means “two lives”

    • A reference to the metamorphosis of an aquatic larva into a terrestrial adult


Chapter 34

  • Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg

  • Amniotes are a group of tetrapods

    • Whose living members are the reptiles, including birds, and the mammals


Chapter 34

dinosaurs other

Saurischian

than birds

Ornithischiandinosaurs

Crocodilians

Ichthyosaurs

Plesiosaurs

Squamates

Mammals

Pterosaurs

Parareptiles

Tuatara

Turtles

Birds

Saurischians

Dinosaurs

Lepidosaurs

Archosaurs

Synapsids

Diapsids

Reptiles

Ancestralamniote

Figure 34.23

  • A phylogeny of amniotes


Derived characters of amniotes

Derived Characters of Amniotes

  • Amniotes are named for the major derived character of the clade, the amniotic egg

    • Which contains specialized membranes that protect the embryo


Chapter 34

Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.

Allantois. The allantois is a disposal

sac for certain metabolic wastes pro-

duced by the embryo. The membrane

of the allantois also functions with

the chorion as a respiratory organ.

Extraembryonic membranes

Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).

Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock.

Embryo

Amniotic cavitywith amniotic fluid

Yolk (nutrients)

Albumen

Shell

Figure 34.24

  • The extraembryonic membranes

    • Have various functions


Chapter 34

  • Amniotes also have other terrestrial adaptations

    • Such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs


Early amniotes

Early Amniotes

  • Early amniotes

    • Appeared in the Carboniferous period

    • Included large herbivores and predators


Reptiles

Reptiles

  • The reptile clade includes

    • The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs


Chapter 34

Figure 34.25

  • Reptiles

    • Have scales that create a waterproof barrier

    • Lay shelled eggs on land


Chapter 34

  • Most reptiles are ectothermic

    • Absorbing external heat as the main source of body heat

  • Birds are endothermic

    • Capable of keeping the body warm through metabolism


The origin and evolutionary radiation of reptiles

The Origin and Evolutionary Radiation of Reptiles

  • The oldest reptilian fossils

    • Date to about 300 million years ago

  • The first major group of reptiles to emerge

    • Were the parareptiles, which were mostly large, stocky herbivores


Chapter 34

  • As parareptiles were dwindling

    • The diapsids were diversifying

  • The diapsids are composed of two main lineages

    • The lepidosaurs and the archosaurs


Chapter 34

  • The dinosaurs

    • Diversified into a vast range of shapes and sizes

    • Included the long-necked giants called the theropods


Chapter 34

Figure 34.26

  • Traditionally, dinosaurs were considered slow, sluggish creatures

    • But fossil discoveries and research have led to the conclusion that dinosaurs were agile and fast moving

  • Paleontologists have also discovered signs of parental care among dinosaurs


Lepidosaurs

(a) Tuatara (Sphenodon punctatus)

Figure 34.27a

Lepidosaurs

  • One surviving lineage of lepidosaurs

    • Is represented by two species of lizard-like reptiles called tuatara


Chapter 34

Figure 34.27b

(b) Australian thorny devil lizard (Moloch horridus)

  • The other major living lineage of lepidosaurs

    • Are the squamates, the lizards and snakes

  • Lizards

    • Are the most numerous and diverse reptiles, apart from birds


Chapter 34

(c) Wagler’s pit viper (Tropidolaemus wagleri), a snake

Figure 34.27c

  • Snakes are legless lepidosaurs

    • That evolved from lizards


Turtles

Turtles

  • Turtles

    • Are the most distinctive group of reptiles alive today

  • Some turtles have adapted to deserts

    • And others live entirely in ponds and rivers


Chapter 34

Figure 34.27d

(d) Eastern box turtle (Terrapene carolina carolina)

  • All turtles have a boxlike shell

    • Made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs


Alligators and crocodiles

Figure 34.27e

(e) American alligator (Alligator mississipiensis)

Alligators and Crocodiles

  • Crocodilians

    • Belong to an archosaur lineage that dates back to the late Triassic


Birds

Birds

  • Birds are archosaurs

    • But almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight


Derived characters of birds

Derived Characters of Birds

  • Many of the characters of birds

    • Are adaptations that facilitate flight


Chapter 34

Finger 1

(b) Bone structure

Palm

(a) wing

Finger 2

Forearm

Wrist

Finger 3

Shaft

Vane

Barb

Shaft

Barbule

Hook

Figure 34.28a–c

(c) Feather structure

  • A bird’s most obvious adaptations for flight

    • Are its wings and feathers


The origin of birds

The Origin of Birds

  • Birds probably descended from theropods

    • A group of small, carnivorous dinosaurs


Chapter 34

Wing claw

Toothed beak

Airfoil wing with contour feathers

Long tail with many vertebrae

Figure 34.29

  • By 150 million years ago

    • Feathered theropods had evolved into birds

  • Archaeopteryx

    • Remains the oldest bird known


Living birds

(a) Emu. This ratite lives in Australia.

Figure 34.30a

Living Birds

  • The ratites, order Struthioniformes

    • Are all flightless


Chapter 34

(b) Mallards. Like many bird species, the mallard exhibits pronounced color differences between the sexes.

(c) Laysan albatrosses. Like most birds, Laysan albatrosses have specific mating behaviors, such as this courtship ritual.

(d) Barn swallows. The barn swallow is a member of the order Passeriformes. Species in this order are called perching birds because the toes of their feet can lock around a branch or wire, enabling the bird to rest in place for long periods.

Figure 34.30b–d

  • The demands of flight

    • Have rendered the general body form of many flying birds similar to one another


Chapter 34

Raptor(such as a bald eagle)

Grasping bird (such as a woodpecker)

Swimming bird(such as a duck)

Perching bird (such as a cardinal)

Figure 34.31

  • Foot structure in bird feet

    • Shows considerable variation


Chapter 34

  • Concept 34.7: Mammals are amniotes that have hair and produce milk

  • Mammals, class Mammalia

    • Are represented by more than 5,000 species


Derived characters of mammals

Derived Characters of Mammals

  • Mammary glands, which produce milk

    • Are a distinctively mammalian character

  • Hair is another mammalian characteristic

  • Mammals generally have a larger brain

    • Than other vertebrates of equivalent size


Early evolution of mammals

Early Evolution of Mammals

  • Mammals evolved from synapsids

    • In the late Triassic period


Chapter 34

Jaw joint

Jaw joint

Dimetrodon

Morganucodon

Key

Dentary

Angular

Squamosal

Eardrum

Middle ear

Inner ear

Articular

Quadrate

Inner ear

Eardrum

Stapes

(a) The lower jaw of Dimetrodon is composed of several fused bones; two small bones, the quadrate and articular, form part of the jaw joint. In Morganucodon, the lower jaw is reduced to a single bone, the dentary, and the location of the jaw joint has shifted.

Middle ear

Stapes

Incus (evolvedfrom quadrate)

Sound

Sound

Malleus (evolvedfrom articular)

Morganucodon

Dimetrodon

(b) During the evolutionary remodeling of the mammalian skull, the quadrate and articular bones became incorporated into the middle ear as two of the three bones that transmit sound from the eardrum to the inner ear. The steps in this evolutionary remodeling are evident in a succession of fossils.

Figure 34.32a, b

  • The jaw was remodeled during the evolution of mammals from nonmammalian synapsids

    • And two of the bones that formerly made of the jaw joint were incorporated into the mammalian middle ear


Chapter 34

  • Living lineages of mammals originated in the Jurassic

    • But did not undergo a significant adaptive radiation until after the Cretaceous


Monotremes

Figure 34.33

Monotremes

  • Monotremes

    • Are a small group of egg-laying mammals consisting of echidnas and the platypus


Marsupials

Marsupials

  • Marsupials

    • Include opossums, kangaroos, and koalas


Chapter 34

(a) A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).

Figure 34.34a

  • A marsupial is born very early in its development

    • And completes its embryonic development while nursing within a maternal pouch called a marsupium


Chapter 34

(b) Long-nosed bandicoot. Most bandicoots are diggers and burrowers that eat mainly insects but also some small vertebrates andplant material. Their rear-opening pouch helps protect the young from dirt as the mother digs. Other marsupials, such as kangaroos, have a pouch that opens to the front.

Figure 34.34b

  • In some species of marsupials, such as the bandicoot

    • The marsupium opens to the rear of the mother’s body as opposed to the front, as in other marsupials


Chapter 34

Marsupial mammals

Eutherian mammals

Plantigale

Deer mouse

Mole

Marsupial mole

Sugar glider

Flying squirrel

Wombat

Woodchuck

Wolverine

Tasmanian devil

Patagonian cavy

Kangaroo

Figure 34.35

  • In Australia, convergent evolution

    • Has resulted in a diversity of marsupials that resemble eutherians in other parts of the world


Eutherians placental mammals

Eutherians (Placental Mammals)

  • Compared to marsupials

    • Eutherians have a longer period of pregnancy

  • Young eutherians

    • Complete their embryonic development within a uterus, joined to the mother by the placenta


Chapter 34

This clade of eutherians evolved in Africa when the continent was isolated from other landmasses. It includesEarth’s largest living land animal (the African elephant), as well as species that weighless than 10 g.

This diverse clade includes terrestrial and marine mammals as well as bats,the only flying mammals. A growingbody of evidence, including Eocene fossils of whales with feet,supports putting whales inthe same order (Cetartiodactyla)

as pigs, cows, and hippos.

This is the largest eutherian clade. It includes the rodents, which make up the largest mammalian order by far, with about 1,770 species. Humansbelong to the order Primates.

All members of this clade, which underwent an adaptive radiation in South America, belong to the order Xenarthra. One species, the nine-banded armadillo, is found in the southern United States.

Proboscidea Sirenia

Tubulidentata Hyracoidea

Afrosoricida (golden moles and tenrecs)

Macroscelidea (elephant shrews)

Rodentia

Lagomorpha

Primates

Dermoptera (flying lemurs)

Scandentia (tree shrews)

Carnivora

Cetartiodactyla

Perissodactyla

Chiroptera

Eulipotyphla

Pholidota (pangolins)

Monotremata

Marsupialia

Xenarthra

Monotremes

Marsupials

Eutherians

Possible phylogenetic tree of mammals.All 20 extant orders of mammals are listed at the top of the tree. Boldfaced orders are explored on the facing page.

Ancestral mammal

Figure 34.36

  • Phylogenetic relationships of mammals


Chapter 34

MAIN CHARACTERISTICS

ORDERS

AND EXAMPLES

ORDERS

AND EXAMPLES

MAIN CHARACTERISTICS

Embryo completes development in pouch on mother

Marsupialia

Kangaroos,

opossums,

koalas

Lay eggs; nonipples; young suck milk fromfur of mother

MonotremataPlatypuses, echidnas

Echidna

Koala

Tubulidentata

Aardvark

Teeth consisting of many thin tubes cemented together; eats ants and termites

ProboscideaElephants

Long, musculartrunk; thick, loose skin; upper incisors elongated as tusks

African elephant

Aardvark

Hyracoidea

Hyraxes

Short legs; stumpy tail; herbivorous; complex, multichambered

stomach

Aquatic; finlikeforelimbs and no hind limbs; herbivorous

SireniaManatees,dugongs

Rock hyrax

Manatee

Chisel-like, continuously growing incisors worn down by gnawing;herbivorous

Rodentia

Squirrels,

beavers, rats,

porcupines,

mice  

XenarthraSloths, anteaters,armadillos

Reduced teeth orno teeth; herbivorous(sloths) or carnivorous (anteaters, armadillos)

Red squirrel

Tamandua

Primates

Lemurs,

monkeys,

apes,

humans

Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous

Lagomorpha Rabbits, hares, picas

Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping

Golden lion tamarin

Jackrabbit

Perissodactyla

Horses,

zebras, tapirs,

rhinoceroses

Hooves with an odd number of toeson each foot; herbivorous

Sharp, pointed canineteeth and molars for shearing; carnivorous

CarnivoraDogs, wolves,bears, cats, weasels, otters,

seals, walruses

Indian rhinoceros

Coyote

Chiroptera

Bats

Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous

Hooves with an even number of toes on each foot; herbivorous

CetartiodactylaArtiodactylsSheep, pigs cattle, deer,giraffes

Frog-eating bat

Bighorn sheep

Aquatic; streamlinedbody; paddle-like forelimbs and no hind limbs; thicklayer of insulating blubber; carnivorous

Eulipotyphla

“Core insecti-

vores”: some

moles, some

shrews

Diet consists mainly of insects and other small invertebrates

CetaceansWhales,dolphins,porpoises

Star-nosed mole

Pacific white-sided porpoise

Figure 34.36

  • The major eutherian orders


Primates

Primates

  • The mammalian order Primates include

    • Lemurs, tarsiers, monkeys, and apes

  • Humans are members of the ape group


Derived characters of primates

Derived Characters of Primates

  • Most primates

    • Have hands and feet adapted for grasping

  • Primates also have

    • A large brain and short jaws

    • Forward-looking eyes close together on the face, providing depth perception

    • Well-developed parental care and complex social behavior

    • A fully opposable thumb


Living primates

Figure 34.37

Living Primates

  • There are three main groups of living primates

    • The lemurs of Madagascar and the lorises and pottos of tropical Africa and southern Asia


Chapter 34

  • The tarsiers of Southeast Asia

  • The anthropoids, which include monkeys and hominids worldwide


Chapter 34

Anthropoids

0

Chim-panzees

Gorillas

Tarsiers

Gibbons

Humans

Orangutans

Old World monkeys

New World monkeys

Lemurs, lorises, and pottos

10

20

Millions of years ago

30

40

50

Ancestral primate

60

Figure 34.38

  • The oldest known anthropoid fossils, about 45 million years old

    • Indicate that tarsiers are more closely related to anthropoids


Chapter 34

  • The fossil record indicates that monkeys

    • First appeared in the New World (South America) during the Oligocene

  • The first monkeys

    • Evolved in the Old World (Africa and Asia)


Chapter 34

(a) New World monkeys, such as spider monkeys (shown here), squirrel monkeys, and capuchins, have a prehensile tail and nostrils that open to the sides.

(b) Old World monkeys lack a prehensile tail, and their nostrils open downward. This group includes macaques (shown here), mandrills, baboons, and rhesus monkeys.

Figure 34.39a, b

  • New World and Old World monkeys

    • Underwent separate adaptive radiations during their many millions of years of separation


Chapter 34

(a) Gibbons, such as this Muller's gibbon, are found only in southeastern Asia. Their very long arms and fingers are adaptations for brachiation.

(b) Orangutans are shy, solitary apes that live in the rain forests of Sumatra and Borneo. They spend most of their time in trees; note the foot adapted for grasping and the opposable thumb.

(c) Gorillas are the largest apes: some males are almost 2 m tall and weigh about 200 kg. Found only in Africa, these herbivores usually live in groups of up to about 20 individuals.

(e) Bonobos are closely related to chimpanzees but are smaller. They survive today only in the African nation of Congo.

(d) Chimpanzees live in tropical Africa. They feed and sleep in trees but also spend a great deal of time on the ground. Chimpanzees are intelligent, communicative, and social.

Figure 34.40a–e

  • The other group of anthropoids, the hominoids

    • Consists of primates informally called apes


Chapter 34

  • Hominoids

    • Diverged from Old World monkeys about 20–25 million years ago


Chapter 34

  • Concept 34.8: Humans are bipedal hominoids with a large brain

  • Homo sapiens is about 160,000 years old

    • Which is very young considering that life has existed on Earth for at least 3.5 billion years


Derived characters of hominids

Derived Characters of Hominids

  • A number of characters distinguish humans from other hominoids

    • Upright posture and bipedal locomotion

    • Larger brains

    • Language capabilities

    • Symbolic thought

    • The manufacture and use of complex tools

    • Shortened jaw


The earliest humans

The Earliest Humans

  • The study of human origins

    • Is known as paleoanthropology


Chapter 34

  • Paleoanthropologists have discovered fossils of approximately 20 species of extinct hominoids

    • That are more closely related to humans than to chimpanzees


Chapter 34

Paranthropusrobustus

Homoneanderthalensis

Homosapiens

0

Paranthropusboisei

Homoergaster

?

0.5

1.0

Australopithecusafricanus

1.5

2.0

Kenyanthropusplatyops

2.5

Australopithecusgarhi

Homoerectus

3.0

Millions of years ago

Australopithecusanamensis

3.5

Homohabilis

Homorudolfensis

4.0

4.5

Ardipithecusramidus

Australopithecusafarensis

5.0

5.5

Orrorin tugenensis

6.0

6.5

Sahelanthropustchadensis

Figure 34.41

7.0

  • These species are known as hominids


Chapter 34

  • Hominids originated in Africa

    • Approximately 6–7 million years ago

  • Early hominids

    • Had a small brain, but probably walked upright, exhibiting mosaic evolution


Chapter 34

  • Two common misconceptions of early hominids include

    • Thinking of them as chimpanzees

    • Imagining human evolution as a ladder leading directly to Homo sapiens


Australopiths

Australopiths

  • Australopiths are a paraphyletic assemblage of hominids

    • That lived between 4 and 2 million years ago


Chapter 34

(b) The Laetoli footprints, more than 3.5 million years old, confirm that upright posture evolved quite early in hominid history.

(a) Lucy, a 3.24-million-year-old skeleton, represents the hominid species Australopithecus afarensis.

(c) An artist’s reconstruction of what A. afarensis may have looked like.

Figure 34.42a–c

  • Some species walked fully erect

    • And had human-like hands and teeth


Bipedalism

Bipedalism

  • Hominids began to walk long distances on two legs

    • About 1.9 million years ago


Tool use

Tool Use

  • The oldest evidence of tool use—cut marks on animal bones

    • Is 2.5 million years old


Early homo

Early Homo

  • The earliest fossils that paleoanthropologists place in our genus Homo

    • Are those of the species Homo habilis, ranging in age from about 2.4 to 1.6 million years

  • Stone tools have been found with H. habilis

    • Giving this species its name, which means “handy man”


Chapter 34

Figure 34.43

  • Homo ergaster

    • Was the first fully bipedal, large-brained hominid

    • Existed between 1.9 and 1.6 million years


Chapter 34

  • Homo erectus

    • Originated in Africa approximately 1.8 million years ago

    • Was the first hominid to leave Africa


Neanderthals

Neanderthals

  • Neanderthals, Homo neanderthalensis

    • Lived in Europe and the Near East from 200,000 to 30,000 years ago

    • Were large, thick-browed hominids

    • Became extinct a few thousand years after the arrival of Homo sapiens in Europe


Homo sapiens

Figure 34.44

Homo sapiens

  • Homo sapiens

    • Appeared in Africa at least 160,000 years ago


Chapter 34

  • The oldest fossils of Homo sapiens outside Africa

    • Date back about 50,000 years ago


Chapter 34

Figure 34.45

  • The rapid expansion of our species

    • May have been preceded by changes to the brain that made symbolic thought and other cognitive innovations possible


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