lesson overview lesson overview what is an animal? lesson overview what is an animal?

Lesson OverviewLesson Overview What is an Animal?What is an Animal?

Lesson Lesson OverviewOverview

What is an Animal?What is an Animal?


THINK ABOUT IT – An osprey circles a salt marsh searching

for prey. It dives, catches a fish, and carries it back to its young.

– On the bottom of the bay, worms burrow beneath rocks carpeted with orange sponges.

– In the air above, mosquitos swarm, searching for a blood meal. All these different inhabitants of the Atlantic coast are animals.


Characteristics of AnimalsWhat characteristics do all animals

share?


Characteristics of Animals What characteristics do all animals

share?

Animals, which are members of the kingdom Animalia, are multicellular, heterotrophic, eukaryotic organisms whose cells lack cell walls.


Characteristics of Animals– Animals are all heterotrophs; they obtain

nutrients and energy by eating other organisms. – Animals are also multicellular; their bodies

are composed of many cells. – The cells that make up animal bodies are

eukaryotic, containing a nucleus and membrane-bound organelles.

– Unlike the cells of algae, fungi, and plants, animal cells lack cell walls.


Types of AnimalsWhat characteristics distinguish

invertebrates and chordates?


Types of AnimalsWhat characteristics distinguish invertebrates and chordates?

Invertebrates include all animals that lack a backbone, or vertebral column.

All chordates exhibit four characteristics during at least one stage of life: a dorsal, hollow nerve cord; a notochord; a tail that extends beyond the anus; and pharyngeal pouches.


Invertebrates – Invertebrates include all animals that

lack a backbone, or vertebral column.

– More than 95 percent of animal species are informally called invertebrates. Invertebrates include at least 33 phyla.

– Invertebrates include sea stars, worms, jellyfishes, and insects, like butterflies.

– They range in size from dust mites to giant squid more than 20 meters long.


Chordates – Fewer than 5 percent of animal

species are chordates, members of the clade commonly known as Phylum Chordata.

– All chordates exhibit four characteristics during at least one stage of life: a dorsal, hollow nerve cord; a notochord; a tail that extends beyond the anus; and pharyngeal pouches.


Chordates – The hollow nerve cord runs along

the dorsal (back) part of the body. Nerves branch from this cord at intervals.

– The notochord is a long supporting rod that runs through the body just below the nerve cord. Most chordates have a notochord only when they are embryos.


Chordates – At some point in their lives, all

chordates have a tail that extends beyond the anus.


Chordates – Pharyngeal pouches are paired

structures in the throat region, which is also called the pharynx.

– In some chordates, such as fishes, slits develop that connect pharyngeal pouches to the outside of the body. The pharyngeal pouches may develop into gills used for gas exchange.


Chordates – Most chordates develop a

backbone, or vertebral column, constructed of bones called vertebrae.

– Chordates with backbones are called vertebrates and include fishes, amphibians, reptiles, birds, and mammals.


What Animals Do to SurviveWhat essential functions must animals

perform to survive?


What Animals Do to Survive What essential functions must animals

perform to survive?

Like all organisms, animals must maintain homeostasis by gathering and responding to information, obtaining and distributing oxygen and nutrients, and collecting and eliminating carbon dioxide and other wastes. They also reproduce.


Maintaining Homeostasis – All organisms must keep their internal environment

relatively stable, a process known as maintaining homeostasis. In animals, maintaining homeostasis is the most important function of all body systems.

– For example, reptiles, birds, and mammals cannot excrete salt. Those that spend time hunting or feeding in salt water, such as the marine iguana, have adaptations that allow them to remove salt from their bodies.

– Marine iguanas maintain homeostasis by sneezing a combination of salt and nasal mucus that sometimes coats their bumpy heads and spiny necks.


Maintaining Homeostasis – Often, homeostasis is maintained by

feedback inhibition, or negative feedback, a system in which the product or result of a process limits the process itself.

– For example, if you get too cold, you shiver, using muscle activity to generate heat.

– If you get too hot, you sweat, which helps you lose heat.


Gathering and Responding to Information

– The nervous system gathers information using cells called receptors that respond to sound, light, chemicals, and other stimuli.

– Other nerve cells collect and process that information and determine how to respond.



– Some invertebrates have only a loose network of nerve cells, with no real center.

– Other invertebrates and most chordates have large numbers of nerve cells concentrated into a brain.



– Animals often respond to the information processed in their nervous system by moving.

– Muscle tissue generates force by becoming shorter when stimulated by the nervous system.

– Muscles work together with some kind of supporting structure called a skeleton to make up the musculoskeletal system.


Gathering and Responding to Information – Skeletons vary widely from phylum to phylum.

– Some invertebrates, such as earthworms, have skeletons that are flexible and function through the use of fluid pressure.

– Insects and some other invertebrates have external skeletons. The hard shell of a lobster is an external skeleton.

– The bones of vertebrates form an internal skeleton. Your bones are part of your internal skeleton.


Obtaining and Distributing Oxygen and Nutrients

– All animals must breathe to obtain oxygen. Small animals that live in water or in wet places can “breathe” by allowing oxygen to diffuse across their skin.

– Larger animals use a respiratory system based on one of many different kinds of gills, lungs, or air passages.



– All animals must eat to obtain nutrients.

– Most animals have a digestive system that acquires food and breaks it down into forms cells can use.



– After acquiring oxygen and nutrients, animals must transport them to cells throughout their bodies by using some kind of circulatory system.

– The structures and functions of respiratory and digestive systems must work together with circulatory systems.


Collecting and Eliminating CO2 and Other Wastes

– Animals’ metabolic processes generate carbon dioxide and other waste products, some of which contain nitrogen in the form of ammonia.

– Both carbon dioxide and ammonia are toxic in high concentrations and must be excreted, or eliminated from the body.



Many animals eliminate carbon dioxide by using their respiratory systems.



– Most complex animals have a specialized organ system—the excretory system—for eliminating other wastes, such as ammonia.

– The excretory system concentrates or processes these wastes and either expels them immediately or stores them before eliminating them.



Before wastes can be discharged, the circulatory system must collect them from cells throughout the body and then deliver them to the respiratory or excretory system. The collection and elimination of wastes requires close interactions between these systems.


Reproducing

– Most animals reproduce sexually by producing haploid gametes.

– Sexual reproduction helps create and maintain genetic diversity, which increases a species’ ability to evolve and adapt as its environment changes.

– Like many vertebrates, a pygmy marsupial frog cares for her young while they develop. Unlike most animals, she carries her eggs on her back.


Reproducing – Many invertebrates and a few

vertebrates can also reproduce asexually.

– Asexual reproduction produces offspring that are genetically identical to the parent.

– It allows animals to increase their numbers rapidly but does not generate genetic diversity.


Lesson OverviewLesson Overview

Animal Body Plans Animal Body Plans and Evolutionand Evolution


THINK ABOUT IT – Animals alive today have typically

been produced by two processes: the development of a multicellular individual from a single fertilized egg cell, and the evolution of a modern species from its ancestors over many millions of years.

– The history of the evolutionary changes to animal body structures has been known for years.


THINK ABOUT IT Today, exciting research is revealing how changes in the genes that control embryological development are connected to the evolution of body structures. This research field, often referred to as “evo-devo,” is one of the hottest areas in biology today.


Features of Body PlansWhat are some features of animal body

plans?


Features of Body PlansWhat are some features of animal body

plans?

Features of animal body plans include levels of organization, body symmetry, differentiation of germ layers, formation of body cavities, patterns of embryological development, segmentation, cephalization, and limb formation.


Levels of Organization – As the first cells of most animals develop, they

differentiate into specialized cells that are organized into tissues. A tissue is a group of cells that perform a similar function.

– Animals typically have several types of tissues, including epithelial, muscle, connective, and nervous tissues.

– Epithelial tissues cover body surfaces, inside and out. The epithelial cells that line lung surfaces, for example, have thin, flat structures through which gases can diffuse easily.


Levels of Organization – Tissues combine during growth

and development to form organs and organ systems that carry out complex functions.

– Your digestive system, for example, includes all the tissues and organs of your lips and mouth, as well as your stomach, intestines, and anus.


Body Symmetry – The bodies of most

animals exhibit some type of symmetry.

– Some animals, such as the sea anemone, exhibit radial symmetry, in which body parts extend from a central point. Any number of imaginary planes drawn through the center of the body could divide it into equal halves.


Body Symmetry – The most successful animal

groups exhibit bilateral symmetry, in which a single imaginary plane divides the body into left and right sides that are mirror images of one another.

– Animals with bilateral symmetry have a definite front (anterior), end and a back (posterior), end.

– Bilaterally symmetrical animals also have an upper (dorsal), side and a lower (ventral), side.


Differentiation of Germ Layers – During embryological development, the cells of most

animal embryos differentiate into three layers called germ layers.

– Cells of the endoderm, or innermost germ layer, develop into the linings of the digestive tract and much of the respiratory system.

– Cells of the mesoderm, or middle layer, give rise to muscles and much of the circulatory, reproductive, and excretory organ systems.

– The ectoderm, or outermost layer, produces sense organs, nerves, and the outer layer of the skin.


Formation of a Body Cavity – Most animals have some kind of

body cavity—a fluid-filled space between the digestive tract and body wall.

– A body cavity provides a space in which internal organs can be suspended and room for those organs to grow.


Formation of a Body Cavity Most complex animal phyla have a true coelom, a body cavity that develops within the mesoderm and is completely lined with tissue derived from mesoderm.


Formation of a Body Cavity – Some invertebrates

have only a primitive jellylike layer between the ectoderm and endoderm.

– Other invertebrates lack a body cavity altogether, and are called acoelomates.


Formation of a Body Cavity – Still other

invertebrate groups have a pseudocoelom, which is only partially lined with mesoderm.


Patterns of Embryological Development – Every animal

that reproduces sexually begins life as a zygote, or fertilized egg.

– As the zygote begins to develop, it forms a blastula, a hollow ball of cells.


Patterns of Embryological Development

– As the blastula develops, it folds in on itself, forming an elongated structure with a tube that runs from one end to the other. This tube becomes the digestive tract.


Patterns of Embryological Development – At first this digestive tract has only a single

opening. However, an efficient digestive tract needs two openings.

– In phyla that are protostomes, the blastopore becomes the mouth. In protostomes, including most invertebrates, the anus forms from a second opening, which develops at the opposite end of the tube.


Patterns of Embryological Development

– In deuterostomes, the blastopore becomes the anus, and the mouth is formed from a second opening that develops. Chordates and echinoderms are deuterostomes.


Segmentation: Repeating Parts – As many bilaterally symmetrical animals

develop, their bodies become divided into numerous repeated parts, or segments, and are said to exhibit segmentation. A centipede exhibits segmentation.

– Segmented animals, such as worms, insects, and vertebrates, typically have at least some internal and external body parts that repeat on each side of the body.


Segmentation: Repeating Parts Bilateral symmetry and segmentation are found together in many of the most successful animal groups, including humans.


Cephalization: Getting a Head – Animals with bilateral symmetry

typically exhibit cephalization, the concentration of sense organs and nerve cells at their anterior end.

– The most successful animal groups, including arthropods and vertebrates, exhibit cephalization.


Cephalization: Getting a Head – Insect and vertebrate embryo heads are

formed by the fusion and specialization of several body segments during development.

– As those segments fuse, their internal and external parts combine in ways that concentrate sense organs and nerve cells in the head.

– Animals with heads usually move in a “head-first” direction so that the concentration of sense organs and nerve cells comes in contact with new parts of the environment first.


Limb Formation: Legs, Flippers, and Wings

– Segmented, bilaterally symmetrical animals typically have external appendages on both sides of the body.

– These appendages vary from simple groups of bristles in some worms, to jointed legs in spiders, wings in dragonflies, and a wide range of limbs, including bird wings, dolphin flippers, and frog legs.


Body PlansThe body plans of modern invertebrates and chordates suggest evolution from a common ancestor.


Body Plans

The body plans of modern invertebrates and chordates suggest evolution from a common ancestor.


The Cladogram of AnimalsHow are animal phyla defined?


The Cladogram of AnimalsHow are animal phyla defined?

Animal phyla are typically defined according to adult body plans and patterns of embryological development.


The Cladogram of Animals– The features of animal body plans

provide information for building the cladogram, or phylogenetic tree, of animals.

– The evolutionary history presented in a cladogram represents a set of evolutionary hypotheses based on characteristics of living species, evidence from the fossil record, and comparative genomic studies.


The Cladogram of Animals– This cladogram presents our current

understanding of relationships among animal phyla.

– During the course of evolution, important traits evolved, as shown by the red circles.


Differences Between Phyla – The cladogram of animals indicates

the sequence in which important body plan features evolved.

– Every phylum has a unique combination of ancient traits inherited from its ancestors and new traits found only in that particular phylum.


Differences Between Phyla – The complicated body systems of vertebrates

aren’t necessarily better than the “simpler” systems of invertebrates.

– Any system found in living animals functions well enough to enable those animals to survive and reproduce.

– For example, monkey brains are more complex than fish brains. But fish brains obviously work well enough to enable fish, as a group, to survive.


Changes Within Phyla: Themes and Variations

– Within each phylum, different groups represent different variations on the basic body plan theme that have evolved over time.

– Land vertebrates, for example, typically have four limbs. Many, such as frogs, walk (or hop) on four limbs that we call “legs.”


Changes Within Phyla: Themes and Variations

– Among birds, the front limbs have evolved into wings.

– In many primates, the front limbs have evolved into what we call “arms.”

– Both wings and arms evolved through changes in the standard vertebrate forelimb.


Evolutionary Experiments – In a sense, you can think of each phylum’s body plan as an

evolutionary “experiment,” in which a particular set of body structures performs essential functions.

– The very first versions of most major animal body plans were established hundreds of millions of years ago. Ever since that time, each phylum’s evolutionary history has shown variations in body plan as species have adapted to changing conditions.

– If the changes have enabled members of a phylum to survive and reproduce, the phylum still exists.

– If the body plan hasn’t functioned well enough over time, members of the phylum, or particular groups within the phylum, have become extinct.



Invertebrate Evolution Invertebrate Evolution and Diversityand Diversity


THINK ABOUT IT – Many modern multicellular phyla

first appeared during a period called the “Cambrian Explosion,” between 530 and 515 million years ago.

– How did so many kinds of animals evolve so quickly? What simpler forms could they have evolved from?


Origins of the InvertebratesWhen did the first animals evolve?


Origins of the Invertebrates When did the first animals evolve?

Fossil evidence indicates that the first animals began evolving long before the Cambrian Explosion.


Origins of the Invertebrates– For roughly 3 billion years after the first

prokaryotic cells evolved, all prokaryotes and eukaryotes were single-celled.

– Animals evolved from ancestors they shared with organisms called choanoflagellates, single-celled eukaryotes that sometimes grow in colonies.

– Choanoflagellates share several characteristics with sponges, the simplest multicellular animals.


Traces of Early Animals – Our oldest evidence of multicellular

life comes from microscopic fossils that are roughly 600 million years old.

– The first animals were tiny and soft-bodied, so few fossilized bodies exist.

– Recent studies have uncovered incredibly well preserved fossils of eggs and embryos that are 565-million-years-old.


Traces of Early Animals – Other fossils from this time period

have been tentatively identified as parts of sponges and animals similar to jellyfish.

– Paleontologists have also identified what are called “trace fossils,” tracks and burrows made by animals whose body parts weren’t fossilized.


The Ediacaran Fauna – Some important discoveries about invertebrate life

before the Cambrian Period come from fossils in the Ediacara Hills of Australia.

– Strange fossils, which date from roughly 565 to about 544 million years ago, show body plans that are different from those of anything alive today.

– Many of the organisms were flat and lived on the bottom of shallow seas.

– They show little evidence of cell, tissue, or organ specialization, and no organization into a front and back end.


The Cambrian Explosion – The Cambrian Period began about 542

million years ago.

– Two major Cambrian fossil sites are in Chengjiang, China, and in the Burgess Shale of Canada.

– Cambrian fossils show that over a period of 10–15 million years, animals evolved complex body plans, including specialized cells, tissues, and organs.


The Cambrian Explosion A number of Cambrian fossils have been identified as ancient members of modern invertebrate phyla, such as the fossil of arthropod Marrella shown.


The Cambrian Explosion Some early Cambrian fossils represent extinct groups so peculiar that no one knows what to make of them.


The Cambrian Explosion – By the end of the Cambrian Period,

all the basic body plans of modern phyla had been established.

– Later evolutionary changes, which produced the more familiar body structures of modern animals, involved variations on these basic body plans.


Modern Invertebrate Diversity – Today, invertebrates are the most

abundant animals on Earth.

– Invertebrates live in nearly every ecosystem, participate in nearly every food web, and vastly outnumber so-called “higher animals,” such as reptiles and mammals.


Cladogram of InvertebratesWhat does the cladogram of invertebrates

illustrate?


Cladogram of Invertebrates What does the cladogram of invertebrates

illustrate?

The cladogram of invertebrates presents current hypotheses about evolutionary relationships among major groups of modern invertebrates. It also indicates the sequence in which some important features evolved.


Cladogram of Invertebrates– This cladogram of invertebrates

shows current hypotheses of evolutionary relationships among modern invertebrates. Groups shown close together are more closely related than are groups shown farther apart. The sequence in which some important features evolved is also shown.


Sponges– Phylum: Porifera (“pore bearers”)

– Sponges are the most ancient members of the kingdom Animalia.

– They are multicellular, heterotrophic, lack cell walls, and contain a few specialized cells.


Cnidarians– Phylum: Cnidaria—includes

jellyfishes, sea fans, sea anemones, hydras, and corals

– Cnidarians are aquatic, soft-bodied, carnivorous, radially symmetrical animals with stinging tentacles arranged in circles around their mouths.

– They are the simplest animals to have body symmetry.


Arthropods– Phylum: Arthropoda (arthron = “joint,” podos =

“foot”)—includes spiders, centipedes, insects, and crustaceans

– Arthropods have bodies divided into segments, a tough external skeleton called an exoskeleton, cephalization, and jointed appendages, which are structures such as legs and antennae that extend from the body wall.

– Arthropods appeared in the sea about 600 million years ago and have since colonized freshwater habitats, land, and air.


Nematodes (Roundworms)– Phylum: Nematoda

– Nematodes are unsegmented worms with pseudocoeloms, specialized tissues and organ systems, and digestive tracts with two openings—a mouth and an anus.

– Nematodes were once thought to be closely related to flatworms, annelids, and mollusks but have been found to be more closely related to the arthropods.


Flatworms– Phylum: Platyhelminthes

– Flatworms are soft, unsegmented, flattened worms that have tissues and internal organ systems.

– They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.

– Flatworms do not have coeloms.


Annelids– Phylum: Annelida (annellus =

“little ring”)—includes earthworms, some marine worms, and leeches

– Annelids are worms with segmented bodies and a true coelom lined with tissue derived from mesoderm.


Mollusks– Phylum: Mollusca—includes snails,

slugs, clams, squids, and octopi– Mollusks are soft-bodied animals that

have an internal or external shell.– They have true coeloms surrounded by

mesoderm and complex organ systems.– Many mollusks have a free-swimming

larva, or immature stage, called a trochophore.


Echinoderms– Phylum: Echinodermata (echino = “spiny,”

dermis = “skin”)—includes sea stars, sea urchins, and sand dollars

– Echinoderms have spiny skin and an internal skeleton.

– They also have a water vascular system—a network of water-filled tubes that include suction-cuplike tube feet, which are used for walking and gripping prey.

– Most exhibit five-part radial symmetry and are deuterostomes.



Chordate Evolution Chordate Evolution and Diversityand Diversity


THINK ABOUT IT At first glance, fishes, amphibians, reptiles, birds, and mammals appear to be very different. Yet, all are members of the phylum in which we ourselves are classified—phylum Chordata.


Origins of the ChordatesWhat are the most ancient chordates?


Origins of the Chordates What are the most ancient chordates?

Embryological studies suggest that the most ancient chordates were related to the ancestors of echinoderms.


The Earliest Chordates – The Cambrian fossil deposits include

some early chordate fossils, such as Pikaia, which is shown in the figure.

– Scientists first thought it was a worm but then determined that it had a notochord and paired muscles arranged in a series, like those of simple modern chordates.


The Earliest Chordates – In 1999, fossil beds from later in the

Cambrian Period yielded specimens of Myllokunmingia, the earliest known vertebrate.

– These fossils show muscles arranged in a series, traces of fins, sets of feathery gills, a head with paired sense organs, and a skull and skeletal structures likely made of cartilage.

– Cartilage is a strong connective tissue that is softer and more flexible than bone. It supports all or part of a vertebrate’s body.


Modern Chordate Diversity – Modern chordates consist of six

groups: the nonvertebrate chordates and the five groups of vertebrates—fishes, amphibians, reptiles, birds, and mammals.


Modern Chordate Diversity – About 96 percent of all modern

chordate species are vertebrates, with fishes making up the largest group.

– Today’s chordate species are only a small fraction of the total number of chordates that have existed over time.


Cladogram of Chordates What can we learn by studying the

cladogram of chordates?


Cladogram of Chordates What can we learn by studying the

cladogram of chordates?

The cladogram of chordates presents current hypotheses about relationships among chordate groups. It also shows at which points important vertebrate features, such as jaws and limbs, evolved.


Cladogram of ChordatesThe cladogram of chordates presents current hypotheses about the evolutionary relationships among chordate groups.


Cladogram of ChordatesThe circles represent the appearance of certain adaptive features, such as jaws and limbs, during chordate evolution. Each time a new body plan adaptation evolved, a major adaptive radiation occurred.


Nonvertebrate Chordates – Fossil evidence suggests that the

ancestors of living nonvertebrate chordates diverged from the ancestors of vertebrates more than 550 million years ago.

– Two chordate groups lack backbones: tunicates and lancelets.


Nonvertebrate Chordates – Adult turnicates (subphylum

Urochordata) look more like sponges than us. They have neither a notochord nor a tail. But their larval forms have all the key chordate characteristics.

– For example, the small, fishlike lancelets (subphylum Cephalochordata) live on the sandy ocean bottom.


Jawless Fishes The earliest fishes appeared in the fossil record about 510 million years ago. They had no true jaws or teeth, and their skeletons were made of cartilage.

Some armored jawless fishes, such as those shown in the figure, became extinct about 360 million years ago.


Jawless Fishes Two other ancient clades of jawless fishes gave rise to the two clades of modern jawless fishes: lampreys and hagfishes.


Jawless Fishes – Lampreys and hagfishes both lack

vertebrae and have notochords as adults.

– Lampreys are filter feeders as larvae and parasites as adults.

– Hagfishes have pinkish gray, wormlike bodies, secrete incredible amounts of slime, and tie themselves into knots!


Sharks and Their Relatives – Other ancient fishes evolved a

revolutionary feeding adaptation: jaws.

– Jaws make it possible to bite and chew plants and other animals.

– Dunkleosteus, an ancient fish, could eat just about anything.


Sharks and Their Relatives – Early fishes also evolved paired

pectoral (anterior) and pelvic (posterior) fins.

– Paired fins offered more control of body movement, while tail fins and powerful muscles gave greater thrust.


Sharks and Their Relatives – The evolution of paired fins and tail

fins launched the adaptive radiation of the class Chondrichthyes: the sharks, rays, and skates.

– The Greek word chondros means “cartilage,” the tissue that makes up the skeletons of these “cartilaginous” fishes.


Bony Fishes Another group of ancient fishes evolved skeletons made of true bone, launching the radiation of the class Osteichthyes, the bony fishes.


Ray-Finned Fishes – Most living bony fishes belong to a

huge group called ray-finned fishes.

– Ray-finned fishes are aquatic vertebrates with skeletons of true bone; most have paired fins, scales, and gills.

– Most fishes you are familiar with, such as eels, goldfish, and catfish, are ray-finned fishes.


Lobe-Finned Fishes – Lobe-finned fishes are bony fishes

that evolved fleshy fins supported by larger, more substantial bones.

– The modern fishes that are descendants of ancient lobe-finned fishes include lungfishes and coelacanths.


Lobe-Finned Fishes Another group of ancient lobe-finned fishes evolved into the ancestors of four-limbed vertebrates, or tetrapods.


Amphibians Amphibians are vertebrates that also, with some exceptions, require water for reproduction, breathe with lungs as adults, have moist skin with mucous glands, and lack scales and claws.


The Unique “Fishapod” – Fossils indicate that various lines

of lobe-finned fishes evolved sturdier appendages, which resembled the limbs of tetrapods.

– A series of transitional fossils have been discovered that document the skeletal transformation from lobe-fins to limbs, as shown on the following slides.


The Unique “Fishapod”


The Unique “Fishapod”– Eusthenopteron was an early bony fish that

used its muscular front fins for steering more than for swimming.

– Panderichthys was a fish with sturdier, more mobile, and proportionately larger front fins than earlier fishes had.

– Tiktaalik was not quite a fish and not quite a tetrapod. It had stout, stubby front fins with flexible wrists that likely enabled it to prop itself up on land, but it had no digits. It had gills and lungs.


The Unique “Fishapod”– Acanthostega had digits on its front feet but

spent most of its time in the water. Though it had gills, it may have used its limbs to prop itself out of oxygen-poor water so it could breathe air with its lungs.

– Ichthyostega had sturdy hind feet with several digits. It probably used them more to paddle through the water than to walk on land.

– Proterogyrinus was a true tetrapod and agile both in water and on land, similar to today’s alligators.


The Unique “Fishapod” The Tiktaalik fossilshows both fish and tetrapod features, so its discoverers informally refer to it as a “fishapod”—part fish, part tetrapod.


Terrestrial Adaptations – Early amphibians evolved ways to breathe

air and protect themselves from drying out, which fueled another adaptive radiation.

– Amphibians became the dominant vertebrates of the Carboniferous Period, but climate changes caused most amphibian groups to become extinct by the end of the Permian Period.


Terrestrial Adaptations Only three orders of amphibians survive today—frogs and toads, salamanders, and caecilians.


Reptiles – Reptiles were the first vertebrates to

evolve adaptations to drier conditions.

– A reptile is a vertebrate with dry, scaly skin, well-developed lungs, strong limbs, and shelled eggs that do not develop in water.


Reptiles Living reptiles are represented by four groups: lizards and snakes, crocodilians, turtles and tortoises, and the tuatara.


Reptiles – As the Carboniferous Period ended

and the Permian Period began, Earth’s climate became cooler and less humid, and adaptive radiation of reptiles began.

– This cladogram shows current hypotheses about the relationships between living and extinct reptiles.


Enter the Dinosaurs – The Triassic and Jurassic periods

saw a great adaptive radiation of reptiles. Dinosaurs lived all over the world, and they were diverse in appearance and in habit.

– The evolutionary lineage that led to modern birds came from one group of feathered dinosaurs.


Exit the Dinosaurs – At the end of the Cretaceous Period, a

worldwide mass extinction occurred. According to current hypotheses, it was caused by a series of natural disasters: a string of volcanic eruptions, a fall in sea level, and a huge asteroid smashing into what is now the Yucatán Peninsula in Mexico.

– After these events, dinosaurs, along with many other animal and plant groups, became extinct both on land and in the sea.


Birds – Birds are reptiles that regulate their

internal body temperature (endothermy.)

– They have an outer covering of feathers; strong yet lightweight bones; two legs covered with scales that are used for walking or perching; and front limbs modified into wings.


Bird Roots – Recent fossil discoveries support

the hypothesis that birds evolved from a group of dinosaurs.

– The first birdlike fossil discovered was Archaeopteryx, which shows both bird characteristics (flight feathers) and dinosaur characteristics (teeth and bony tail).

– A fossil and an artist’s conception of Archaeopteryx are shown.


Bird Classification – Birds, the traditional class Aves,

make up a clade that is part of the clade containing dinosaurs.

– Because the clade containing dinosaurs is part of a larger clade of reptiles, modern birds are also reptiles.


Bird Classification – The traditional class Reptilia, which

includes living reptiles and dinosaurs but not birds, however, is not a clade.


Mammals – Characteristics unique to

mammals include mammary glands in females that produce milk to nourish young, and hair.

– Mammals also breathe air, have four-chambered hearts, and regulate their internal body temperature.


The First Mammals – True mammals first appeared

during the late Triassic Period.

– They were very small and resembled modern tree shrews.


The First Mammals – While dinosaurs ruled, mammals remained generally

small and were probably active mostly at night. – New fossils and DNA analyses suggest that the first

members of modern mammalian groups, including primates, rodents, and hoofed mammals, evolved during this period.

– After the great dinosaur extinction, mammals diversified, increased in size, and occupied many niches.

– The Cenozoic Era is usually called the Age of Mammals.


Modern Mammals – By the beginning of the Cenozoic Era, three major groups of

mammals had evolved—monotremes, marsupials, and placentals. – These three groups differ in their means of reproduction and

development.– Only five species of the egg-laying monotremes, including

the duckbill platypus, exist today, all in Australia and New Guinea. – Marsupials, which include kangaroos, koalas, and wombats,

bear live young that usually complete their development in an external pouch.

– Placental mammals have embryos that develop further while still inside the mother. After birth, most placental mammals care for their young and nurse them to provide nourishment.


Lesson OverviewLesson OverviewPrimate EvolutionPrimate Evolution


THINK ABOUT IT – Primates means “first” in Latin.

But what are primates “first” in?

– When primates appeared, there was little to distinguish them from other mammals. As primates evolved, however, several characteristics became distinctive.


What Is a Primate?What characteristics do all primates

share?


What Is a Primate?What characteristics do all primates share?

In general, a primate is a mammal that has relatively long fingers and toes with nails instead of claws, arms that can rotate around shoulder joints, a strong clavicle, binocular vision, and a well-developed cerebrum.


What Is a Primate?– Primates share several adaptations for

a life spent in trees. – In general, a primate is a mammal that

has relatively long fingers and toes with nails instead of claws, arms that can rotate around shoulder joints, a strong clavicle, binocular vision, and a well-developed cerebrum.

– You can see most of these characteristics in a lemur.


Fingers, Toes, and Shoulders Primates typically have five flexible fingers and toes on each hand or foot that can grip objects firmly and precisely, enabling many primates to run along tree limbs and swing from branches with ease.


Fingers, Toes, and Shoulders Most primates have thumbs and big toes that can move against the other digits, allowing them to hold objects firmly in their hands or feet.


Fingers, Toes, and Shoulders Primates’ arms can rotate in broad circles around a strong shoulder joint attached to a strong clavicle, or collar bone, making them well suited for climbing.


Binocular Vision – Many primates have forward-facing

eyes, giving them excellent binocular vision. – Binocular vision is the ability to

combine visual images from both eyes, providing depth perception and a three-dimensional view of the world.

– This comes in handy for judging the locations of tree branches, from which many primates, like this lemur, swing.


Well-Developed Cerebrum – In primates, the “thinking” part of the

brain—the cerebrum—is large and intricate, which enables more-complex behaviors than are found in many other mammals.

– For example, many primate species create elaborate social systems that include extended families, adoption of orphans, and even warfare between rival troops.


Evolution of PrimatesWhat are the major evolutionary groups of

primates?


Evolution of Primates What are the major evolutionary groups of

primates?

Primates in one of these groups look very little like typical monkeys. This group contains the lemurs and lorises. The other group includes tarsiers and the anthropoids, the group that includes monkeys, great apes, and humans.


Evolution of PrimatesHumans and other primates evolved from a common ancestor that lived more than 65 million years ago.


Evolution of Primates: Early in their history, primates split into two groups.


Evolution of PrimatesPrimates in one of these groups look very little like typical monkeys. This group contains the lemurs and lorises.


Evolution of Primates: The other group includes tarsiers and the anthropoids


Lemurs and Lorises – Lemurs and lorises are small,

nocturnal primates with large eyes adapted to seeing in the dark. Many have long snouts.

– Living members include the bush babies of Africa, the lemurs of Madagascar, and the lorises of Asia.


Tarsiers and AnthropoidsAnthropoids, or humanlike primates, include monkeys, great apes, and humans.


Tarsiers and Anthropoids Anthropoids split into two groups around 45 million years ago, as the continents on which they lived moved apart.


New World Monkeys – The New World monkeys are

found in Central and South America.– Members of this group live

almost entirely in trees. They have long, flexible arms that enable them to swing from branches.

– New World monkeys also have a long, prehensile tail that can coil tightly enough around a branch to serve as a “fifth hand.”


Old World Monkeys and Great Apes

– The other anthropoid branch, which evolved in Africa and Asia, includes the Old World monkeys and great apes.

– Old World monkeys spend time in trees but lack prehensile tails.


Old World Monkeys and Great Apes

– Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans.

– Recent DNA analyses confirm that, among the great apes, chimpanzees are humans’ closest relatives.


Hominine EvolutionWhat adaptations enabled later hominine

species to walk upright?


Hominine Evolution What adaptations enabled later hominine

species to walk upright?

The skull, neck, spinal column, hip bones, and leg bones of early hominine species changed shape in ways that enabled later species to walk upright.


Hominine Evolution– Between 6 and 7 million years

ago, the lineage that led to humans split from the lineage that led to chimpanzees.

– The hominoids in the lineage that led to humans are called hominines and include modern humans and all other species more closely related to us than to chimpanzees.


Hominine Evolution– Hominines evolved the

ability to walk upright, grasping thumbs, and large brains.

– The skull, neck, spinal column, hip bones, and leg bones of early hominine species changed shape in ways that enabled later species to walk upright.


Hominine EvolutionThis figure shows some ways in which the skeletons of modern humans differ from those of hominoids such as gorillas.


Hominine Evolution– The evolution of bipedal, or two-

footed, locomotion was very important, because it freed both hands to use tools.

– The hominine hand evolved an opposable thumb that could touch the tips of the fingers, enabling the grasping of objects and the use of tools.


Hominine Evolution– Hominines evolved much larger

brains.

– Most of the difference in brain size results from an expanded cerebrum, which is, as you recall, the “thinking” part of the brain.


New Findings and New Questions

– The study of human ancestors is exciting and constantly changing.

– Recent discoveries in Africa have doubled the number of known hominine species and the length of the known hominine fossil record.

– These data have enhanced the picture of our species’ past, but questions still remain as to how fossil hominines are related to one another—and to humans.


Relatives Versus Ancestors – The hominine fossil record includes

seven genera—Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo—and at least 20 species.

– All these species are relatives of modern humans, but not all of them are human ancestors.


Relatives Versus Ancestors


The Oldest Hominine? In 2002, paleontologists in Africa discovered a fossil skull roughly 7 million years old. This fossil, called Sahelanthropus, is a million years older than any known hominine.


The Oldest Hominine? – Sahelanthropus had a brain about

the size of a modern chimp, but its short, broad face was more like that of a human.

– Scientists are still debating whether this fossil represents a hominine.


Australopithecus – Hominines of the genus

Australopithecus lived from about 4 million to about 1.5 million years ago. Australopithecus afarensis fossils are shown.

– These hominines were bipedal apes, but their skeletons suggest that they probably spent some time in trees.

– The structure of their teeth suggests a diet rich in fruit.


Australopithecus Australopithecus afarensis fossils indicate the species had small brains. Excavations have found fossilized humanlike footprints that were probably made by members of A. afarensis about 3.6 million years ago. Such finds show that homines walked bipedally before large brains evolved.


Australopithecus Other A. afarensis fossils indicate that males were much larger than females.


Lucy – The best-known

A. afarensis specimen is a partial skeleton of an adult female discovered in 1974, nicknamed “Lucy.”

– Lucy stood about 1 meter tall and lived about 3.2 million years ago.


The Dikika Baby – In 2006, an Ethiopian researcher

announced the discovery of some 3.3 million-year-old fossils of a very young A. afarensis female, nicknamed “the Dikika Baby.”

– The skeleton included a nearly full skull and jaws, torso, spinal column, limbs, and left foot.

– Leg bones confirmed that the Dikika Baby walked bipedally, while her arm and shoulder bones suggest that she would have been a better climber than modern humans.


Paranthropus The more-recent Paranthropus species had huge, grinding back teeth, and their diets probably included coarse and fibrous plant foods like those eaten by modern gorillas.


Paleontologists place Paranthropus on a separate, dead-end branch of our family tree.


Hominine Relationships – A series of hominine adaptive

radiations produced a number of species whose relationships are difficult to determine.

– As a result, what once looked like a simple hominine “family tree” with a single main trunk now looks more like a shrub with multiple trunks.


The Road to Modern Humans What is the current scientific thinking

about the genus Homo?


The Road to Modern HumansWhat is the current scientific thinking about the genus Homo?

If you look at the Hominine Time Line, you can see that many species in our genus existed before our species, Homo sapiens, appeared. Furthermore, at least three other Homo species existed at the same time as early humans.


Many species in our genus existed before our species, Homo sapiens, appeared.


At least three other Homo species existed at the same time as early humans.


The Genus Homo: About 2 million years ago, a new group of hominine species appeared.


The Genus Homo – The fossils of this new group of

hominine species resemble modern human bones, and so they are classified in the genus Homo.

– One set of fossils was found with tools made of stone and bone, so it was named Homo habilis, which means “handy man” in Latin.


The Genus Homo The earliest fossils that researchers assign to the genus Homo belong to Homo ergaster.


The Genus Homo H. ergaster was larger than H. habilis and had a bigger brain and downward-facing nostrils that resemble those of modern humans.


Out of Africa—But When and Who?

– Researchers agree that our genus originated in Africa and migrated from there to populate the world.

– Some current hypotheses about when hominines first left Africa and which species made the trip are shown in the figure.


The First to Leave – Fossil and molecular evidence suggest

that some hominines left Africa long before Homo sapiens evolved and that more than one Homo species made the trip in waves.

– Hominines began migrating out of Africa at least 1.8 million years ago. Hominine remains from that period were found in the Republic of Georgia, which is north of Turkey and far from Africa.


Homo erectus in Asia – According to some researchers,

groups of Homo erectus traveled across India and through China to Southeast Asia.

– Some of the oldest fossils of H. erectus were uncovered on the Indonesian island of Java, suggesting that these hominines spread very rapidly once they left Africa.


The First Homo sapiens – There are two main hypotheses of how Homo

sapiens arose.– The multiregional model suggests that, in

several parts of the world, modern humans evolved independently from widely separated populations of H. erectus.

– The “out-of-Africa” model proposes that modern humans evolved in Africa about 200,000 years ago, migrated through the Middle East, and replaced the descendants of earlier hominine species.


The First Homo sapiens – Recently, molecular biologists analyzed

mitochondrial DNA from living humans around the world and determined they last shared a common African ancestor between 200,000 and 150,000 years ago.

– More recent DNA data suggest that a small subset of those African ancestors left northeastern Africa between 65,000 and 50,000 years ago to colonize the world, supporting the out-of-Africa hypothesis.


Modern Humans The story of modern humans over the past 200,000 years involves two main species: Homo neanderthalensis and Homo sapiens.


Homo neanderthalensis – Neanderthals flourished in Europe and

western Asia beginning about 200,000 years ago.

– Evidence suggests that they made stone tools, lived in complex social groups, had controlled use of fire, were excellent hunters, and performed simple burial rituals.

– Neanderthals survived in parts of Europe until about 28,000–24,000 years ago.


Modern Homo sapiens Anatomically modern Homo sapiens arrived in the Middle East from Africa about 100,000 years ago.


Modern Homo sapiens

– By about 50,000 years ago, H. sapiens populations, including some now known as Cro-Magnons, were using new technology to make more sophisticated stone blades and were making tools from bones and antlers.

– They produced spectacular cave paintings and buried their dead with elaborate rituals.


Modern Homo sapiens – Neanderthals and H. sapiens lived side by

side in the Middle East for about 50,000 years. – Later, both groups moved into Europe,

where they coexisted for several thousand years. – For the last 24,000 years, however, Homo

sapiens has have been Earth’s only hominine. – Why did Neanderthals disappear? Did they

interbreed with H. sapiens? No one knows for sure.

lesson overview lesson overview what is an animal? lesson overview what is an animal?

Documents

animal bodies

invertebrates invertebrates

types of animals

percent of animal species

animal cells lack cell

chordates fewer

chordates pharyngeal

hollow nerve cord