Biology Unit 3

cientists classify animals into the nine phyla based on their adult body plan and embryological development. Features of an animal body plan include:

- levels of organization (specialized cells, tissues, organs, organ systems) - body symmetry (bilateral or radial) differentiation of germ layers - formation of body cavities (coelom, pseudocoelom, acoelom) - patterns of embryological development (protostome or deuterostome) segmentation - cephalization (does it have a head?) limb formation

When do scientists believe the first primates appeared?

About 60 to 70 million years ago.

About how many of Earth's animal species are invertebrates?

About 95% of the animal species on earth are invertebrates.

According to the fossil record, how long has life existed on Earth?

According tot the fossil record, life has existed on Earth for 3.5 billion years.

Currently, most scientists believe that the Homo genus originated in

Africa and spread out from there. There also seems to be a consensus that the first Homo species left Africa about 1.8 million years ago. Which species that was, however, remains uncertain.

What characteristics do all animals share?

All animals are multi-cellular. The cells of all animals have a nucleus and they do not have a cell wall. All animals eat food.

Which of the following is not a primate?

All are primates. (human, gorilla, and baboon.)

What characteristics do all chordates share?

All chordates have a notochord, paired pharyngeal pouches (or gill slits), or post-anal tail, and a dorsal nerve cord at some time during their life cycles.

Which of the following describes the major types of animals?

All chordates share a common ancestor; but there is no common ancestor of all invertebrates.

Which of the following is true about primates?

All primates except for humans have prehensile feet.

What phylum do all vertebrates belong to?

All vertebrates belong to the phylum Chordata.

What is an invertebrate?

An invertebrate is an animal that does not have a backbone.

Which fishes are considered the most advanced?

Bony fish are (Osteichthyes) are considered the most advanced fish.

Fossil evidence has shown that animals appeared on Earth well before the

Cambrian Explosion, which occurred around 530 million years ago. Based on fossil and molecular evidence, scientists have constructed cladograms for invertebrates and chordates that represent the current thought about the evolutionary relationships among the invertebrate and chordate groups. These cladograms also show at which point important features evolved.

What type of body cavity do chordates have?

Chordates have a coelom.

What type of body symmetry do chordates have?

Chordates have bilateral body symmetry.

What advantages did multicellularity have for the first animals?

Collections of cells could access more oxygen and collect more food. They could also control their internal environment and be more efficient by working as a team.

Why do some dolphins wear sponges as "gloves" to cover their rostra?

Dolphins that live in areas of the ocean that have a harder substrate use the sponges to protect their rostra from being injured when digging up fish.

What happens to the notochord in vertebrates?

During the embryonic stage, the notochord in a vertebrate is replaced by a column of bone or cartilage. This becomes the animals' backbone.

What five classes of animals belong to phylum Chordata?

Fish, amphibians, reptiles, birds, mammals all belong to the phylum Chordata.

What are the five classes of vertebrates?

Fish, amphibians, reptiles, birds, mammals are the five classes of vertebrates.

How long have sponges had the same basic body structure?

For around 600 million years

What type of fish are hagfish and lampreys?

Hagfish and lampreys are jawless fish.

The oldest known member of the Homo genus found so far is

Homo habilis, which means "handy man." This species was given this name because one specimen was found with tools made of stone and bone. Homo habilis lived about 2.5 to 1.6 million years ago. The earliest fossil evidence of Homo sapiens places the emergence of modern humans at about 200,000 years ago.

What function does the shape of the star-nosed moles's nose serve?

It helps the mole find food.

What common chordate characteristics do lancelets have? What features do they lack?

Lancelets have a notochord. They are bilaterally symmetrical and segmented. They lack common chordate characteristics like jaws, an anterior brain with associated sensory organs, and paired fins.

What are three of the characteristics primates share?

Primates have opposable thumbs, forward-facing eyes, and high-intelligence.

When do scientists believe the first modern humans appeared? What other Homo species was alive at that time?

Scientists believe modern humans first appeared about 150,000 years ago. Homo neanderthalensis also lived at that time.

What groups do scientists think share a common evolutionary origin with chordates?

Scientists believe that echinoderms, hemichordates, and chordates share a common evolutionary origin.

What environmental conditions do scientists believe may have contributed to the development of bipedalism, or walking on two feet?

Scientists believe that the climate may have cooled about 10 million years ago, leading to the development of open grassy savannahs where there was once tropical jungle. As hominids adapted to this more open environment, scientists believe they began walking on two feet.

When do scientists believe that the lineage that led to humans split from the linage that led to great apes?

Scientists believe that the lineage that led to humans split from the lineage that led to great apes about 6 million years ago.

Which of the following occurred before the Cambrian Explosion?

Some animals demonstrated signs of segmentation and bilateral symmetry.

Explain how an animal's body is organized and how this contributes to an animal's complexity.

Specialized cells are grouped together into tissues. Tissues make up complex organs. Organs work together in organ systems to carry out complex tasks.

What is a blastopore? What does the blastopore become?

The blastophore is an opening in the blastula. The blastospore will develop into the animal's digestive tract.

Describe the adaptation of the platypus that helps it forage successfully for food.

The duck-billed platypus has a bill that can sense electrical currents emitted by living organisms, which give away its prey's location.

Describe the first living organisms that appeared on Earth.

The first living organisms that appeared on Earth were single-celled organisms without a nucleus, much like bacteria. They're single-celled eukaryotes that sometimes grew in colonies.

What does fossil evidence indicate about about the order in which these three vertebrates evolved: a bony fish with a jaw, a jawless fish, and a fish with leg-like fins.

The fish with leg-like fins was the last to evolve.

What vertebrate class is the most successful?

The fishes are the most successful vertebrate class.

List the 8 invertebrate phyla.

The main invertebrate phyla are Porifera (sponges), Cnidaria, Echinodermata, Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms), Mollusca (mollusks), and Arthropoda.

Predict which types of tissues arise from each germ layer.

The mesoderm forms muscle tissue. The ectoderm forms skin and nervous tissue, and the endoderm forms the digestive and respiratory tissue.

Describe the sequence in which scientists believe life evolved.

The most primitive living things grew in the water millions of years ago. Gradually, organisms developed the ability to make food using photosynthesis. Over millions of years, more complicated organisms developed, including protists, fungi, plants, and animals.

How does the manner in which the platypus swim help it find food?

The platypus swings its bill from side to side to pick up electrical currents from prey organisms that may be under the substrate. It stores the food in its cheek pouches until it surfaces.

What are the vertebrate classes? Give an example of an animal that belongs to each class.

The seven vertebrate classes are: Agnatha (hagfish), Chondrichthyes (sharks), Osteichthyes (bony fish), Amphibia (frogs), Reptilia (turtles), Aves (birds, and Mammalia (humans).

What adaptation helps this snake avoid being eaten by birds of prey?

The sidewinder has evolved a coloration that helps it blend in with the sand, making it more difficult for birds of prey to spot it.

What adaptation allows the sidewinder snake move through the hot sand without burning its scales?

The sidewinder moves sideways through the sand while maintaining two points of contact between its body and the sand. This holds the sand in place and helps the snake propel itself forward very quickly and avoid being burned.

To remember the difference between radial symmetry and bilateral symmetry, remember these things:

The term radial = radiate - body parts of animals with radial symmetry radiate out from a central point, like spokes on a wheel. The prefix bi- means "two" (bicycle = two wheels) - the two sides of an animal with bilateral symmetry are mirror images for each other.

What are the three germ layers called?

The three germ layers are called ectoderm, mesoderm, endoderm.

How many phyla include invertebrate chordates?

There are two phyla that include invertebrate chordates.

White acorn barnacles (top) and California mussels (bottom) have some things in common, too.

They are both stationary as adults. They feed, get oxygen, remove waste, and reproduce by opening their shells and letting water in and out. But, surprisingly, they don't belong to the same phylum.

All animals have certain characteristics:

They are multicellular and their cells have a nucleus. So animals are eukaryotes. Unlike plants, animals cannot make their own food. They must get the nutrients they need by eating other organisms. Therefore, all animals are heterotrophic.

Which statement is true of homo sapiens?

They have been Earth's only hominine for the last 24,000 years.

The article also mentions two groups of invertebrates that are part of the phylum Chordata. What are the names of these groups?

Tunicates and lancelets are two groups of invertebrates that are members of the phylum Chordata.

What other features do vertebrates share?

Vertebrates also have a brain that is encased in a skull and two pairs of appendages (arms, legs, fins, or wings, for example.)

What are the general characteristics of vertebrates?

Vertebrates are relatively large. They have specialized body parts and bilateral symmetry. And they are widely distributed over the Earth.

How are the bodies of vertebrates similar to one another?

Vertebrates have an internal skeleton made up of bone and cartilage. They have a spinal column and a brain enclosed in a skull. They have a closed circulatory system and a heart with two, three, four chambers. Most vertebrates also have two pairs of appendages that may be fins, limbs, or wings depending on what type of animal it is.

Do most chordates exhibit cephalization? How do you know?

Yes, most chordates exhibit cephalization because they have an anterior enlargement of the nerve chord, or brain, that's associated with specialized sensory organs.

Acoelomate animals do not have

a cavity between their digestive tract and the body wall.

prehensile tail

a long tail that can grip and hang onto a branch as hard as a hand

nare

a nostril

chromatophore

a pigment-containing cell that allows some animals to change color in order to regulate body temperature or to camouflage themselves from predators

adaptive radiation

a process by which members of a species evolve in different ways to take advantage of different environments. In the history of chordate evolution, the appearance of new adaptations, such as jaws and paired appendages, often led to adaptive radiation.

feedback inhibition

a process in which the response to a stimulus counters the action of the stimulus

mucus

a slippery fluid

nictitating membrane

a third eyelid that can be drawn across the eye for protection or moisture, but that can still be seen through

Animals that don't have a body cavity are called

acoelomates

The lizard's detachable tail and the slime produced by the hagfish are

adaptations in body structure that allow those animals to survive in their environment. These two animals are, by no means, the only animals where structure allows for specialized function.

In 2009, scientists announced the discovery of a skeleton that they do believe is

an ancestor of modern humans. The skeleton, nicknamed "Ardi," belonged to a bipedal female with a brain about the size of a chimpanzee's and long arms that likely helped her climb trees. This Ardipithecus ramidus skeleton has been determined to be about 4.4 million years old.

chordate

animal that has a dorsal, hollow nerve cord, a notochord, a tail that extends beyond the anus, and pharyngeal pouches at some time during its life cycle

Which of the following is a segmented worm with a true coelom?

annelid

Most primates live in trees, which means they are mostly

arboreal

Chordates

are characterized by deuterostome development and a body plan that includes bilateral symmetry, cephalization, three germ layers, a true coelom, and segmentation.

Which of the following is a segmented animal with an exoskeleton and jointed appendages?

arthropod

Most chordates develop a backbone made of bone or cartilage. These chordates belong to the vertebrate group. The invertebrate chordates, the tunicates and lancelets, exhibit all of the characteristics of chordates, but they do not have a backbone. Invertebrates that do not belong to phylum Chordata lack both a

backbone and a notochord.

Animals cannot survive if they do not maintain homeostasis. And, if an animal species is to survive, members of that species must also reproduce. Some animals reproduce asexually. Reproducing asexually allows an animal to reproduce quickly. However,

because only one parent is involved in asexual reproduction and all of the offspring are essentially genetically identical to that parent, genetic diversity is lost. This loss of genetic diversity can have disastrous results if the population encounters disease or adverse conditions. Sexual reproduction, on the other hand, requires two parents and results in greater genetic diversity. Greater genetic diversity in a population can help organisms adapt to environmental changes through the process of natural selection.

But trilobites were not the first animals. Scientists believe that the first animals evolved long before the Cambrian period. However,

because their tiny bodies are believed to have been soft, they didn't leave behind much fossil evidence. In 2006, however, scientists found the oldest evidence of multicellular life so far when they found a microscopic multicellular embryo from about 565 million years ago.

All primates have

binocular vision

Which of the following pairs of modern chordate groups are most closely related?

birds and crocodilians

Protostomes are animals in which the mouth forms from the

blastopore

Remember that a true coelom is a

body cavity that is completely lined with mesoderm.

coelom

body cavity that is lined entirely with mesoderm

A pseudocoelom is a

body cavity that is only partially lined with mesoderm

Which of the following do all animals not need to do in order to survive

capture prey

Which of the following is an animal waste product?

carbon dioxide

The first of these derived characters is the development of vertebrae between hagfish and lampreys. Hagfish are eel-shaped, slime-producing marine animals. They have four hearts, but no jaws or stomach. They are unique in the animal world because they have a partial skull, but no vertebrae. Lampreys are also eel-like and they don't have jaws either. Instead, they have a tooth-filled sucker. Unlike hagfish, lampreys do have vertebrae. However, their vertebrae are not made of bone like those of most other vertebrates. Instead, their skeleton is composed of

cartilage, which is a strong connective tissue that is softer and more flexible than bone.

Bony fish have skeletons of true bone. Sharks and their relatives, which evolved before true bone appeared, have skeletons made of

cartilage. The oldest known bony fish fossils are about 420 million years old. Less than 100 million years after bony fish are thought to have evolved, the development of lungs allowed some chordates to breathe air.

Which of the following is not a characteristic of primates?

cartilaginous skeleton

More complex animals also tend to have their sense organs and nerve cells grouped at the anterior, or front end, of their bodies. This end is often different enough that it's called a head. This evolutionary tendency is called

cephalization

Instead of bone, however, an arthropod's skeleton is made up of

chitin. You may recall that chitin is also the main component in the cell walls of fungi.

Tunicates are invertebrates, but they are also

chordates

Primates also have

clavicles, which give them a wide range of arm movement; without it, monkeys would be unable to swing through trees. Unlike other mammals, primates have nails instead of claws. This allows for greater dexterity and manipulation of tools.

Echinoderms are the only deuterostome invertebrates and are, therefore, considered to be

closer relatives to chordates than the other invertebrates.

Which of the following is a radially symmetrical animal with stinging tentacles?

cnidarian

The simplest animals that have body symmetry are the

cnidarians

The simplest animals with body symmetry and specialized cells and tissues are

cnidarians

Most complex animals have a fluid-filled space between their digestive tract and the body wall. This space is called a

coelom

cloaca

common opening in which reproductive cells and solid and liquid waste are expelled from the body

The classifications vertebrate and invertebrate are informal groupings. They make it easier to talk about such a large group of organisms. However, because the invertebrate grouping depends on a feature that these organisms lack (a backbone) rather than something they share, scientists do not

consider it a true clade. Remember that a clade is one common ancestor and all of its descendants, living and extinct, that share a set of derived characters.

Endothermy, an adaptation that arose in both birds and mammals, is the ability to

control body heat. All of these adaptions allowed different chordates to colonize all of the different environments that they live in today.

In chordates and echinoderms, the blastopore becomes the anus and the mouth develops from a second opening that appears after the blastopore. Animals in which the blastopore becomes the anus are called

deuterostomes

The acquisition of nutrients and their distribution to body systems is a function of the

digestive and circulatory systems.

Fossil evidence strongly supports the hypothesis that birds evolved from a group of-

dinosaurs

Which of the following is a radially symmetrical deuterostome invertebrate most closely related to chordates?

echinoderm

Amniotic eggs, which are eggs protected by a membrane, allowed for

embryonic development on land without the danger of drying out. Amniotic eggs are thought to have evolved in early reptiles about 360 to 268 million years ago.

Body plants evolve as adaptations that

enable members of a phylum to survive and reproduce

Germ layers include

endoderm (innermost), mesoderm (middle), and ectoderm (outermost). Sponges do not show germ layer differentiation. Cnidarians have two germ layers. All other animals have all three germ layers.

In most animals, there are four main types of tissues—

epithelial, muscle, connective, and nervous tissue.

Which body system do animals use to eliminate waste, such as ammonia?

excretory system

Arthropods also have a hard outer covering called an

exoskeleton

Primates are an order of mammals that includes monkeys, apes, and humans. Primates are characterized by various traits, including

eyes that are positioned facing forward. This arrangement provides primates with stereoscopic vision, giving them better depth perception. This is especially helpful for monkeys since they maneuver through trees.

One of the ways an animal's body maintains homeostasis is though a process called

feedback inhibition. Feedback inhibition is also called negative feedback. For feedback inhibition to occur, the body's response to a stimulus must cause a reaction that counters that stimulus.

zygote

fertilized egg

Which of the following is an unsegmented acoelomate worm?

flatworm

All animals need certain things to survive. They need

food and water. They need oxygen and a suitable place to live, too. Oh, and one more thing—they need to keep from being eaten!

Whether they live in the desert, in the forest, or underground, all animals need

food, water, and oxygen. And they need to be able to get the nutrients and oxygen to all the cells in their bodies. They also need to be able to eliminate wastes, maintain homeostasis, and reproduce. An animal's body is a living system. It requires inputs—food, water, and oxygen. It also has outputs—waste. As with all systems, an organism's inputs and outputs must be balanced in order for the organism to continue to survive.

Because they are hard, exoskeletons are easily

fossilized. Remember that the hard parts of animals, such as their teeth and bones, are much more likely to be fossilized than soft body parts. Numerous fossils of one ancient arthropod, called a trilobite, have been found. In fact, people have found trilobite fossils on every continent on Earth. Trilobites lived from the lower Cambrian period, which was about 520 million years ago, to the end of the Permian, about 240 million years ago. They went extinct about five million years before dinosaurs came about.

Scientists believe that anthropoids split into two groups when the continents split apart 45 million years ago. One of these groups can be

found in Central and South America and is called the New World monkeys. The other group of anthropoids evolved in Africa and Asia. This group includes the Old World monkeys and the great apes, or hominoids.

Which of the following animals are considered hominoids?

gibbons and orangutans

hominoid

great apes; includes gibbons, orangutans, gorillzas, chimpanzees, and humans does not include tarsiers.

Lobsters and insects do have some things in common. Both have bodies that are divided into segments and they both have jointed legs. They both

have a head and an exoskeleton. And they belong to the same phylum—Arthropoda.

thympanum

hearing structure

Nerves branch in intervals from which of the following structures in a chordate embryo?

hollow nerve chord

Remember that homeostasis is a relatively stable internal environment. An animal's body systems—its circulatory system, respiratory system, digestive system, musculoskeletal system, nervous system, and excretory system—work together to maintain

homeostasis

To survive, all animals must maintain

homeostasis. Remember that homeostasis is a relatively constant internal environment. To do this, all animals need to gather and respond to information in their environment, obtain and distribute nutrients and oxygen throughout their bodies, and collect and eliminate waste. An animal's body systems—its circulatory system, respiratory system, digestive system, excretory system, musculoskeletal system, and nervous system—all work together to maintain homeostasis.

The hominids in the linage that led to modern humans are called

hominines. At some point in hominine evolution, the shape of the skull, spinal cord, pelvis, and thighbones changed to allow early hominines to walk upright on two feet.

Today, scientists call the primate lineage that led to modern humans,

hominines. Humans are the only surviving members of the hominine lineage. The development of bipedality was a very important development in the evolution of hominines. Scientists are not exactly sure when or why hominines developed the ability to walk on two feet, but they hypothesize that it may have been to free both hands to carry food or to use tools.

hominine

hominoid lineage that led to humans

Overview: Primates

https://www.connexus.com/content/render.aspx?idDocument=2821259

larvae

immature life stage of some animals

Primates are very

intelligent and are known to be able to solve complex problems, form relationships, and learn new skills for finding food and functioning in social groups.

Many animals with bilateral symmetry develop repeated parts, or segments, during development. Segmented animals have some

internal or external body part that repeats on each side of its body. Chordates, for example, are segmented, bilaterally symmetrical animals. They have appendages on either side of their bodies. Some have arms and legs while others have wings or flippers.

Scientists divide animals into two general categories—

invertebrates and vertebrates

At some point, between lampreys and sharks, chordates developed

jaws and paired appendages. Fish with jaws first appear in the fossil record about 425 million years ago.

Sensing and responding to the environment in order to maintain homeostasis does not just mean getting away from predators. It can also mean

keeping the body at the correct temperature. Reptiles, for example, cannot regulate their own body temperature. They must rely on sources of heat in their environment instead. This is why you might find a lizard stretched out on a rock in the sun. It helps them warm up.

Which of the following primates have the best sense of smell?

lemurs

Small, nocturnal primates with large eyes adapted to seeing in the dark include-

lemurs and lorises

Generally, primates have

longer gestation periods and longer lifespans than other mammals their size.

Primates that have a long, prehensile tail are called

lorises

Which of the following must an animal do to survive?

maintain homeostasis

A true coelom develops within the mesoderm and the space is completely lined with

mesoderm

Pseudocoelomates have a body cavity, but the space is only partially lined with

mesoderm

Which of the following is a unsegmented animal with a free swimming larval stage?

mollusk

The order Primate includes

monkeys, lemurs, orangutans, gorillas, chimpanzees, and humans. Today, there are around 250 living primate species. The smallest primate, the pygmy mouse lemur, weighs about an ounce (30 g) and could sit in the palm of your hand. The largest primate, the gorilla, weighs around 400 pounds (181 kg)

The embryonic development of complex animals also differs from those that are

more primitive.

Along with bipedality, hominines also developed

much larger brains than their closest living relatives, the chimpanzees. On average, a human's brain is a little over 25 percent larger than a chimp's. Most of the difference comes from a markedly larger cerebrum. The cerebrum is the part of the brain that is responsible for learning, memory, and conscious thought.

Sponges might not look much like animals. They don't have brains, or hearts, or stomachs. They don't have muscles, a mouth, or lungs, either. But they are

multicellular, eukaryotic heterotrophs. And, most importantly, their cells do not have a cell wall.

Before the discovery of Ardi, "Lucy" was the oldest known

oldest known hominine fossil. This Australopithecus afarensis skeleton was found in 1974. The skeleton belonged to an adult female and is about 3.2 million years old. In 2006, scientists found an even more complete A. afarensis skeleton. This one belonged to a young female and has been nicknamed the "Dikika Baby."

Through evolutionary processes, many of the primates' _____________ receptors have been deactivated.

olfactory

Most primates are

omnivores

pharyngeal pouch

one of a pair of structures found in the throat region of chordates

All primates also have

opposable thumbs and fingers, which enable them to grasp things. Primates' limbs are different from other animals' limbs in that they contain two bones in the forearm and lower leg, allowing for greater precision in movement.

Groups of tissues make up

organs, and organs work together in organ systems to meet the animal's basic needs. Sponges have some specialized cells, but they lack tissues and organs. Sponges also lack symmetry. They are asymmetrical. But the bodies of other animals exhibit some sort of symmetry.

All primates have five fingers, a characteristic called

pentadactylism

The invertebrate group also includes several different

phyla of worms. Like flatworms, nematodes, or roundworms, are unsegmented worms. However, roundworms possess a pseudocoelom while flatworms do not. The phylum Annelida, which includes earthworms, contains segmented worms with a true coelom.

In which grip is the thumb used as a counter force?

power grip

When you are doing holding a fork, you are using a

precision grip.

An exoskeleton

protects and supports an arthropod's body like your internal skeleton protects and supports your body.

In most invertebrates, the blastopore becomes the mouth. At the other end of the tube, the anus is formed. Animals in which the blastopore becomes the mouth are called

protostomes

From teeth to thighs to tiny toe bones, scientists have found the fossil remains of more than 6,000 individuals. Since scientists discovered the fossil skeleton nicknamed "Lucy" in 1974, additional fossil finds and improved technologies have nearly doubled the branches on the hominine family tree. And, with new bones being found every year, scientists continue to

put together a better, more complete picture of the earliest human ancestors.

The nervous systems of complex animals gather information using cells called

receptors

The Cambrian Explosion resulted in the evolution of the

representatives of the most animal phyla

Which of the following is an unsegmented worm with a pseudocoelom?

roundworm

Ancient chordates are thought to be most closely related to which of the following species?

sea stars

Fossil evidence has shown that

several Homo species existed before Homo sapiens appeared. It also appears that at least three other Homo species—Homo neanderthalensis, Homo erectus, and Homo floresiensis—existed at the same time as early Homo sapiens.

You may recall that an exoskeleton is a hard outer coating. This hard outer coating is actually the animal's

skeleton

Adaptive radiation is thought to have driven the evolution of

some of the more important chordate adaptions. Remember that adaptive radiation is the process by which a single species or a small group of species evolves into several forms in order to thrive in different environments.

The most ancient members of the kingdom Animalia are

sponges

Suppose scientists could compare the DNA of modern humans from around the world with the DNA of Homo erectus populations from the humans' native homelands. If DNA samples from modern humans were found to be most similar to the Homo erectus DNA from their homeland, that finding would

support the multi-regional model

The development of four limbs allowed animals to crawl out of the water. Vertebrates with four limbs are called

tetrapods. In 2010, Polish scientists found the oldest known fossil footprints made by a tetrapod. These footprints are about 395 million years old. This is about 20 million years earlier than scientists had previously thought tetrapods had moved onto land.

While many of the animal fossils that scientists have found have come from the Cambrian Period, recent discoveries in microfossils have led scientists to believe that

that the first animals actually evolved long before this period.

You may recall that cephalization means that the animal's body has a distinct head region where sense organs and nerve cells are concentrated. Segmentation means that

the animal's body is divided into several repeated parts. Insects, for example, have three body parts and three pairs of jointed legs. In fact, all arthropods have joined appendages.

pseudocoelom

the body cavity of invertebrate metazoan animals where the body wall meets the intestine not lined with a mesodermal epithelium.

What binds the cells in a sponge together?

the cells in a sponge are bound together with collagen fibers

Remember that the blastopore is

the first opening that forms in the blastula, or hollow ball of cells that develops when a zygote starts to grow.

A primate's forward-facing eyes allow

the images from both eyes to be combined, giving primates binocular vision and a 3D image of the world. They also tend to have arms that can rotate around the shoulder joint, allowing for easier climbing.

With well over a million identified species, arthropods are far more numerous than the next most plentiful animal phylum—

the mollusks. Scientists estimate that there are between 50,000 to 130,000 mollusk species. Snails, slugs, clams, mussels, squids, and octopi are all mollusks. Mollusks have internal shells

Deuterostomes are animals in which

the mouth forms from the second opening in the blastopore. Chordates, including humans, are deuterostomes.

According to evolutionary theory, all animals living today evolved from a common ancestor. The various animal phyla represent branch points from this ancestor. Some animals are more primitive than others. The complexity of animals is shown in

the number and type of germ layers present, the type of body cavity, whether the animal is a protostome or deuterostome, the presence or absence of segmentation, and the presence or absence of cephalization.

Animal body plans differ in

the number and type of germ layers present. They also differ in the formation of a body cavity.

thorax

the part of the body between the head and the abdomen; the middle section of an insect's body

abdomen

the part of the body between the thorax and the pelvis

Modern humans belong to

the phylum Chordata, the class Mammalia, and the order Primate.

The sponges are considered

the simplest animals. They possess some specialized cells, but no body symmetry.

One example of feedback inhibition that you may be familiar with is

the way an air conditioner works in a house. The air conditioner is set to a particular temperature. If the house gets too hot, the air conditioner turns on. This causes the temperature inside the house to drop. This response causes the air conditioner to turn off. Over time, the temperature goes up again and the air conditioner turns back on. By cycling on and off this way, the air conditioner keeps the environment inside the home relatively constant. An animal's body systems work in a similar way—they turn on in response to a stimulus and turn off when conditions return closer to a particular set point.

Today, scientists classify the major animal phyla by

their adult body plan and the pattern of their embryonic development (whether they are protostomes or deuterostomes). Each phylum has a combination of ancient characteristics and those that define the phyla. Roundworms, for example, are characterized by a body plan that includes bilateral symmetry, cephalization, and protostome development.

The one characteristic that sets all animals apart from the multicellular, eukaryotic, heterotopic members of the kingdoms "Protista, Fungi, and Plantae" is that-

their cells lack a cell wall.

The phylum Echinodermata includes sea stars, sea urchins, and sand dollars. Echinoderms are more closely related to chordates than they are to other invertebrates because of

their deuterostome development.

The phylum Mollusca includes snail, slugs, octopi, and clams. Mollusks may look very different from one another, but one thing they all have in common is that

their larvae are free-swimming. Larvae are immature forms that are a part of an animal's life cycle.

Gill slits are paired structures in a region of the throat called the pharynx. Because of their location,

they are also called pharyngeal pouches. In some animals, like mammals, the pharyngeal pouches disappear as the animal matures. In fish, however, the pharyngeal pouches develop into gills.

From sponge to bird to human, there is a huge diversity of form in the animal world. And, yet, many animals share an underlying body plan. Over millions of years, natural selection has acted on this basic plan and produced the enormous variation seen in animals today. Birds, whales, and octopi certainly have different features, but these features all have one thing in common—

they have all evolved to help the animals carry out their essential functions in their environments.

The cladogram suggests that the Cambrian Explosion most likely took place after the development of which characteristics?

three germ layers

Each animal phylum has a unique body plan. As an animal develops, its cells differentiate and become specialized. These specialized cells form groups called

tissues

The first mammals resembled

tree shews

Even though they look quite different when they mature, most mollusks have a free-swimming larval stage called a

trochophore. Annelids, which include earthworms and leeches, also have a trochophore stage in their life cycles, providing evidence that mollusks and annelids probably shared a common ancestor.

During this free-swimming stage, the larvae are called

trochophores

In which type of climate do primates live?

tropical and subtropical

Cold-blooded reptiles are prone to losing heat when they aren't absorbing it from the sun. As they lose heat, they also lose energy, which causes them to move more slowly. This energy loss increases their vulnerability to predators. In order to regain energy, reptiles have to absorb it from the environment. For lizards, this usually means sitting out in the open on a rock that has been warmed by the sun. This

"basking" behavior also increases their chances of becoming prey.

The prefix proto- means

"first." A protosome's mouth forms from the first opening, the blastospore.

The prefix deutero- means

"second." A deuterostome's mouth forms from a second opening.

What is the definition of a vertebrate?

A vertebrate is any animal that has a backbone, or a spinal column.

To remember the difference between the three germ layers and the tissues they develop into, remember these things:

- Endo- means "inside" or "within." Cells of the endoderm develop into the inner linings of the digestive tract and respiratory system. - Ecto- means "outside" or "outer." Cells of the ectoderm form the skin, nerves, and sense organs (like ears and eyes). - Meso- means "middle." Cells of the mesoderm form the muscles.

Primates are mammalian chordates with the following characteristics:

- They have relatively long fingers and toes with nails instead of claws. - They have arms that can rotate about the shoulder joints and a strong clavicle, or collar bone. - They have forward-facing eyes and, therefore, binocular vision. - They have a well-developed cerebrum.

Kingdom animalia contains a great diversity of organisms. However, all animals share some basic characteristics that distinguish them from organisms in other kingdoms:

-Animals are multicellular and all of their cells have a nucleus. -Animal cells are surrounded by a cell membrane and do not have cell walls. -Animals are composed of specialized cells that form tissues, organs, and organ systems. -Typically, animals reproduce sexually. -Animals are heterotrophs, meaning they must obtain energy by ingesting food. -All animals, in one or all stages of their lifetime, are capable of motion. -Because of their nervous system and muscle tissue, animals are able to react to stimuli encountered in their environment.

What is a third characteristic of chordates? When in their development do humans possess this characteristic?

A third characteristic of chordates is that they all have paired gill slits. Humans have gill slits in the embryonic stage.

Scientists classify animals into nine phyla:

-Porifera: This phylum contains the simplest animals, the sponges. Sponges contain some specialized cells, but no other features of a more complex body plan. - Cnidaria: This phylum includes the simplest animals with symmetry. Cnidarians are radially symmetric and have two germ layers. Jellyfishes, sea fans, and sea anemones are members of phylum Cnidaria. -Arthropoda: This phylum includes bilaterally symmetric, segmented animals with exoskeletons and jointed appendages, such as insects, spiders, and scorpions. -Nematoda: This phylum contains nonsegmented worms with pseudocoeloms. -Platyhelminthes: This phylum contains the simplest animals with three germ layers. These flattened worms are bilaterally symmetrical, nonsegmented, and they have no coelom. -Annelida: This phylum includes segmented worms with a true coelom, such as earthworms, leeches, and some marine worms. -Mollusca: This phylum includes soft-bodied animals that have an internal or external shell, such as snails, slugs, and clams. -Echinodermata: This phylum contains radially symmetrical, deuterostomes with spiny skin and an internal skeleton, such as sea stars, sea urchins, and sand dollars. Because they are deuterostomes, echinoderms are considered to be closer relatives to chordates than the other invertebrates. -Chordata: This phylum includes animals with a dorsal nerve cord, a notochord, pharyngeal pouches, and a post-anal tail at some point in their development. Lancelets and tunicates are invertebrate chordates, but most other chordates are vertebrates. Examples of vertebrate chordates include fishes, amphibians, reptiles, birds, and mammals.

An animal body plan refers to the organization of particular body structures in an animal. There are eight features of animal body plans:

-level of organization -body symmetry -differentiation of germ layers -formation of a body cavity -patterns of embryonic development -segmentation -cephalization -limb formation

All chordates exhibit these four characteristics at some point during their life cycle:

1. They have a dorsal, hollow nerve cord. 2. They have a notochord. 3. They have a tail that extends past the anus. 4. They have gill slits.

To survive as an individual, all animals must maintain homeostasis by doing the following:

1. gathering and responding to information in their environment 2. obtaining and distributing oxygen and nutrients throughout their body 3. collecting and eliminating wastes from their body

Approximately when did the first true mammals appear?

220 million years ago

About how many species of primates are there?

230

The anthropoids spilt into two groups about

45 million years ago when the continents moved apart. The New World monkeys live in Central and South America and have prehensile tails that can help them grip tree branches. The other group of anthropoids includes the Old World monkeys and the great apes. Like the New World monkeys, the Old World monkeys also live in trees, but they do not have a prehensile tail. The great apes, or hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans.

Based on molecular clock data, scientists currently believe that humans and chimpanzees last shared a common ancestor about

5 to 10 million years ago. In 2002, a team of scientists uncovered a skull that is perhaps the oldest hominine found so far. The skull belongs to the genus Sahelanthropus and has been determined to be about 7 million years old. Scientists are relatively sure that Sahelanthropus is a hominine and a relative of modern humans. Whether Sahelanthropus turns out to be an ancestor of modern humans or not, however, is still in question.

What is a blastula?

A blastula is hollow ball of cells that results from mitosis within the embryo.

How did the development of a larger cerebrum help primates survive in their environment?

A larger cerebrum allowed primates to process what they saw, heard, and touched. This would allow hem to escape predators and discover new ways to get food.

What is a notochord?

A notochord is a flexible rod-like support that lies just below the nerve chord.

What is a notochord? In most chordates, when is the notochord present?

A notochord is an internal supporting rod of connective tissue. Most chordates have a notochord only when they are embryos.

Along with a notochord, what is a second major characteristic of chordates?

A second characteristic of chordates is that they all have a tubular nerve chord that runs along the dorsal side of their bodies.

Worms with segmented bodies and a true coelom that is lined with tissue derived from mesoderm belong in phylum

Annelida

Insects are members of the phylum

Arthropoda. Spiders, centipedes, and crustaceans are members of this phylum, too. Arthropods are bilaterally symmetrical, segmented animals that show cephalization.

Nonhuman primates have never been native to

Australia

How did the development of binocular, or stereoscopic, vision help primates survive in their environment?

Binocular vision gave early primates depth perception, which made it easier to move through trees to find food and avoid predators.

Sponges have kept the same body structure for millions of years. So why haven't they evolved?

Mainly because they don't need to. Remember that evolution is driven by the need to adapt to an environment. Sponges are very well adapted to their aquatic life and, therefore, they have had no need to significantly change for millions of years.

The other two phyla that include non-chordate invertebrates are

Mollusca and Echinodermata.

What group makes up most of the invertebrate species?

Most invertebrate species are insects or other arthropods.

Scientists split primates into two large groups:

One group includes lemurs and lorises while the other group includes tarsiers and anthropoids. Anthropoids are humanlike primates. This group includes monkeys, great apes, and humans.

Scientists split primates into two groups:

One group, which includes the lemurs and lorises, are small, nocturnal primates with large eyes. The other group contains tarsiers and anthropoids. Anthropoids are humanlike primates.

How do these adaptations help primates survive in their environments?

Opposable thumbs allow primates to grasp objects, such as tree limbs or tools. Forward-facing eyes allow for depth perception. High Intelligence allows for more complex problem solving.

Bilateral Symmetry

Organisms with bilateral symmetry have two sides that are mirror images of each other. Animals with definite anterior and posterior ends exhibit bilateral symmetry. Ex: a butterfly.

Radial Symmetry

Organisms with radial symmetry have body parts that extend out from a central point. The starfish has a body with radial symmetry.

How was the production of oxygen on the primitive Earth important to the formation of animals?

Oxygen is necessary for the formation of collagen, a protein found only in animals.

One of the earliest chordates scientists have found in the fossil record so far is called

Pikaia. Like tunicates, scientists believe Pikaia was an invertebrate. They also believe it had a notochord and muscle pairs lining its sides, characteristics it shares with today's chordates. Pikaia lived during the mid-Cambrian period—about 510 to 500 million years ago.

Which of the following variations would you expect to see in land vertebrates?

varying shapes of forelimbs

Bipedalism is the ability to

walk on two legs