The Vertebrates

• The vertebrates are a sub-group of the phylum chordata, creatures with a notochord

• In vertebrates the notochord disappears as the organism develops and is replaced by a backbone or spine.

Phylum ChordataSubphylum Vertebrata

Features of Vertebrates

• Internal skeleton, composed of cartilage and/or bone.

• A vertebral column (or spine) of vertebrae made of bone and/or cartilage.

• A cranium or skull that protects the brain– In addition most vertebrates have

• Pharyngeal pouches at some stage of life• A post-anal tail (a posterior tail above or behind anus)

• A notochord that disappears as the spine grows

The main Classes of Vertebrates

• Agnatha: the jawless fish (lampreys, hagfish)

• Chondrichthyes: cartilage fish (sharks, rays)

• Osteichthyes: the boney fish (most fish)

• Amphibia: amphibians (frogs, salamanders)

• Reptilia: the reptiles (lizards, snakes, crocodiles)

• Aves: the birds (penguins, robins, ostriches)

• Mammalia: the mammals (cats, mice, humans)

Early Evolution of Vertebrates• Some biologists think vertebrates first evolved

about 550 million years ago, however the oldest fossils date to the Ordovician period (440-510 MYA)

• The earliest fossils are of jawless fish, similar to class Agnatha. (probably evolved from ancestors of lancelets)

• About 440 million years ago (Silurian or late Ordovician period), jaws evolved from gill arches.

• About 370 million years ago (Devonian period) some lobe-finned fish moved inland and evolved into amphibians

• By 300 million years ago reptiles had appeared• The earliest mammals appeared about 200 million

years ago• Birds are the most recent vertebrates, with fossils

dating back about 150 million years.

Geological Timescale

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Jawless FishCartilage Fish

Boney FishAmphibians

ReptilesMammals

Birds

Synapsids

Dinosaurs

Systems• All vertebrates have well developed organ

systems, including:– Internal skeletal system (endoskeleton)– Integument, or body covering that may include

skin, scales, feathers or hair.– Muscles capable of rapid movement– Respiratory system with gills or lungs– A closed circulatory system with multi-

chambered heart.– A two-ended digestive system– A brain and well developed nervous system

The fish used to be placed in the now-defunct Class Pisces, but this class was later split into the three more modern classes. Now the term fish is an informal term for any members of these three classes

The Fishes

• “Fish” is a non-scientific name that is used to refer to three different classes of vertebrate.– Class Agnatha (jawless fish)– Class Chondrichthyes (cartilage fish)– Class Osteichthyes (bony fish)

Geological Timescale

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Jawless Fish

Cartilage fish: “sharks”

Osteichthyes

Lancelets

Agnatha: the Jawless Fish

• These fish have eel-like bodies, with no jaws and no paired fins. Their skeletons are cartilage. There are two main types:– Lampreys: parasites on other fish– Hagfish: bottom-feeders

Mouth of a lampreyadult lamprey

Hagfish

Chondrichthyes: Cartilage fish

• These fish have jaws, but their skeletons are made of cartilage. They do have paired fins, but arranged differently than the more common bony fish. There are three main types:– Sharks– Rays– Skates

Sharks

Gill slits Pectoral fins(paired)

Pelvic fins(paired)

Anal fin

Jaws

Anterior dorsal fin

Caudal(tail) fin

Also see the diagram on page 805 of your text book

Skates and Rays• Skates and rays have flattened bodies, with

extended, wing-like fins. In manta rays, the pectoral fins have become “horns” below the mouth.

Skate Ray

Pectoral fins

Pelvic fins

Osteichthyes: The boney fish• These fish have skeletons that contain at

least some true bone.• Parts of the skeleton may still be made of

cartilage or softer, less calcified bones than found in other vertebrates.

Most familiar fish are osteichthyes (and so are a few strange ones)

Features of Osteichthyes

• Gills covered by an operculum• Bones• Paired fins• Lateral line sense organs

Parts of a fish

Lateral Line

Operculum

Pectoral fin

Pelvic fin

Anterior dorsal fin

Posterior dorsal fin

Anal fin

Caudal fin

Eye

Enrichment: Some Strange FishThe Sea horse doesn’t even look like a fish. It’s orientation is all wrong and it’s fins and tail are highly modified. The males carry the young. But it is a true fish anyways.

The coelacanth was thought to have been extinct for 60 million years, until a fisherman caught one off the coast of South Africa. It is a lobe-finned fish.

The lungfish is able to crawl short distances across land on its lobed fins, and can breath air. They are found in Africa, South America and Australia

The Angler fish dangles a bit of glowing bait in front of its face to attract prey, which it then grabs and swallows with its large mouth.

Enrichment: Not a fish!

Whales and dolphins look like fish, but they are actually mammals.

Jellyfish, starfish, silverfish, crayfish may have the word fish in their name, but they are not true fish.

Jellyfish = CnidariaStarfish = EchinodermSilverfish = InsectCrayfish = Crustacean

the prehistoric Ichthyosaur (below) was actually a reptile.

Clown Fish

Class Amphibia“The Amphibians”

Amphibians

• Features of modern amphibians– Moist, thin skin with no scales– Feet (if present) have no claws, often webbed– Respiration is through a combination of gills,

skin and lungs– Eggs lack shell or membranes. Fertilized

externally. Dry out unless protected.– Most have larval and adult stage, and must

undergo metamorphosis

Orders of Amphibians

• Kingdom Animalia, Phylum Chordata, Class Amphibia,– Order Anura: Frogs and Toads– Order Urodela: Salamanders, Newts– Order Apoda: Caecilians, legless amphibians

• Amphibians first appeared about 370 million years ago. They probably evolved from lobe-finned fish that came on to land to crawl from pond to pond.

Ichthyostega (prehistoric amphibian)

Frogs andsalamanders

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First Am

phibians

Apoda (Caecilians)Fish

Lobe-finned fish

Urodela (salamanders)

Anura (Frogs)

Ichthyostega Salamander Frog

Amphibians

Am

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Caecilian

Frog (a sample amphibian)Like most amphibians the frog has a moist skin. The skeleton and internal organs are similar to those in most “higher” vertebrates. The frog must return to water in order to reproduce (its eggs would dry out on land). Frogs undergo a metamorphosis from a fish-like tadpole into the adult frog.

Metamorphosis• Most amphibians have a larval

form and an adult form.– The larva’s respiration is

generally through external gills– The adult’s respiration is through

a combination of lungs and skin breathing.

Axolotl, a salamander larva

Tadpole, a frog larva

Amphibian Facts• The largest amphibian

is the Chinese giant salamander

• The smallest amphibian is the Brazilian gold frog

• The most poisonous amphibians (some would say the most toxic animals in the world) are the three varieties of dart-poison frogs (AKA poison arrow frogs)

Assignment• Skim through chapter 42

– Note the diagrams of internal frog systems• Read page 833• Answer the following questions

– 1. When, and from what ancestor, did the earliest amphibians evolve?

– 2. describe the main differences between the orders of amphibians.

– 3. Why do most amphibians require a body of water in order to reproduce?

– 4. Describe the life cycle of a frog.

Amphibians evolved about 370 million years ago. They probably evolved from a lobe-finned fish similar to modern lungfish.

The Anura have large legs, especially hind legs for jumping. Urodela (salamanders) have smaller legs, Apoda (ceacilians) have no legs.

They require a wet area for mating, also their eggs would dry out on land unless protected.

Frogs hatch from small gelatinous eggs (AKA. Spawn) in the form of tadpoles. As the tadpole grows it develops legs and its tail resorbs (gradually disappears) until the adult has the familiar frog shape

Class Reptilia“The Reptiles”

Evolution of the Reptiles

• Reptiles appeared more than 300 million years ago.

• They flourished during the Mesozoic era (245 million to 65 million years ago), so this time period is called “the age of reptiles”

• 65 million years ago, many species became extinct. Only four orders of reptiles survived to modern times.

Geological Timescale

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First Reptiles

Age of Reptiles

Birds

Mammals

Snakes & Lizards

Crocodilians

Turtles

Synapsids / Therapsids

Dinosaurs (& related orders)

Reptiles diversify

ReptilesAmphibians

Tuataras

Extinction

Reptile Evolution

mammals

Turtles LizardsSnakes

Tuataras Crocodiles

Birds

DinosaursPrimitive Reptiles

Ichthyostega

frogs

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Reptiles 1 2

3

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Features of Modern Reptiles

• Modern reptiles have:– Waterproof skin, usually covered in scales– Feet (if present) have claws– A three or four chambered heart*– Ectothermic body temperature regulation. (ie.

“cold-blooded”) – Well developed lungs, eliminating the need for

gills or skin breathing**– Amniotic eggs (have a shell or protective

membrane, and are fertilized internally.)*four chambered in crocodilians, three chambered in all other reptiles.

**some snakes have limited skin-breathing ability.

Surviving Orders of Reptiles• Kingdom Animalia, Phylum Chordata,

Class Reptilia*– Order Chelonia: Turtles and Tortoises– Order Crocodilia: Crocodiles, alligator, caiman– Order Squamata:

• Suborder Lacertilia: Lizards• Suborder Serpentes: Snakes

– Order Rhynchocephalia: Tuataras

*recently some taxonomists have suggested replacing “Reptilia” with “Sauropsida” but we will continue to use the more traditional name.

Turtle crocodile

Lizard and snakeTuatara

The Amniotic EggSecret to the Reptile’s Success

Unlike the eggs of amphibians and fish, the amniotic egg of reptiles, birds and monotremes is internally fertilized (through sexual contact) and has a protective outer membrane or shell that prevents it drying out.It contains enough nutrients in the yolk to nourish the embryo.The allantois is a sac that holds wastes until the embryo hatches, and also provides some oxygen.

The amniotic egg freed the reptiles of the need to return to the water to reproduce.

Evolution of the heartAs reptiles evolved, so did their hearts. Early reptiles had a 3 chambered heart, just like the amphibians.

As they became more active, a “septum” began to appear in their hearts.

At first the septum served little purpose, but slowly it became an advantage..

The septum prevented oxygen-rich blood from mixing as much with the oxygen poor blood. This allowed a higher activity level for the reptiles

The septum evolved to divide more and more of the heart. Most reptiles today have a fairly significant septum.

In a few reptiles, like crocodiles, the septum completely divided the heart

This four chambered heart was passed on to the most successful descendants of the reptiles, the birds and mammals.

Reptile Facts

• Smallest reptile is the Jaragua Sphaero a dwarf gecko

• The largest (living) reptile is the salt water crocodile.

• Tuataras have a tiny “third eye” on the top of their heads, related to a human’s pineal gland.

Assignments

• Skim pages 839-854, Read page 855• Copy the phylogenic tree from p. 841• Draw & label a diagram of the Amniotic

egg, from page 843. List the features of the amniotic egg.

• Draw a diagram of the heart of a typical reptile (p.846)

• List the distinguishing features of each of the four surviving orders of reptiles.

Class Aves

The Birds

• The earliest accepted fossils of birds date back to 150 million years ago.– Recent finds of dinosaur fossils with feather-like

scales suggest an earlier evolution of birds, but this is still debated.

• Archaeopteryx lithographica is the oldest confirmed bird species.– It had several reptilian features, including claws on its

wings, teeth and a long bony tail.– See page 863 for a drawing of Archaeopteryx

Evolution of the Birds

Geological Timescale (Birds)

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Feathereddinosaurs

Dinosaurs

Birds

Archeopteryx

Features of Modern BirdsFeatures of Modern Birds

Skin covered in feathersSkin covered in feathers Wings in place of the forelimbsWings in place of the forelimbs Light-weight rigid skeletonLight-weight rigid skeleton

– Many of the bones are hollow to reduce weightMany of the bones are hollow to reduce weight

Endothermic metabolism (“warm blood”)Endothermic metabolism (“warm blood”)– Birds maintain a high body temperature (40Birds maintain a high body temperature (40°°-41-41°°C)C)

Unique respiratory systemUnique respiratory system A beak in place of teethA beak in place of teeth Amniotic eggs with hard shellsAmniotic eggs with hard shells

Bird’s Respiratory System

Birds have many sacs attached to their lungs. As they inhale, air passes through the lungs and fills the sacs. As they exhale, the air passes through the lungs again. Essentially they pass twice as much air through the lungs with each breath.

Lungs

Air Sacs

Flight• Over 90% of all birds are able

to fly.• Flight has been made

possible by many adaptations:– Wings with an “airfoil” shape.– “Keel” shaped breast bone with

attachment points for large muscles that operate the wings.

– Hollow bones to reduce weight– Feathers insulate and propel.

• Down feathers for insulation• Contour feathers give birds shape• Flight feathers give propulsion

Diversity in Birds• There are 29 different orders of birds

– Only the twelve most common are described in the textbook

– The smallest bird is a Cuban hummingbird not much larger than a bumblebee (5 cm long including tail, about 1/20 ounce or just over 1 gram)

– The largest bird is an African ostrich (9 ft tall, 350 lb, or 2.7m, 160 kg) It is flightless, but a good runner.

– Penguins are the fastest swimming birds (Penguins are also flightless, the BBC video that showed flying penguins was an expensive Computer Generated April fool’s joke)

A Few Orders of Birds

• Falconiformes: Birds of prey, or “raptors”

• Anserformes: Ducks and Geese

• Strigiformes: Owls• Passeriformes: Songbirds

• And there are 25 more orders…

Assignments

• Skim through pages 861-874 of the text.• Carefully read page 875• Create a brief set of notes (about one

page) that summarizes the main things you have learned about birds – be prepared to show your summary to me in the next class

• Answer questions 16 to 22 on page 876

The Mammals

Origin of Mammals

• Mammals probably evolved from the synapsids, an early reptile family that included Dimetrodon,

• The Therapsids, like this Lycaenops were a later type of synapsid that looked more mammal-like

• The first true mammals that appeared about 150 million years ago were small, shrew-like organisms

Geological Timescale (Mammals)

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Synapsids Therapsids

150

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Age of Mammals

Mammals

Ext

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ion

Characteristics of Mammals• Endothermy (warm-blooded)• Skin covered in hair or fur

• In whales and humans the hair is reduced to small patches

• Four chamber heart, • with fully divided ventricle and separate circulation

• Mammary glands• Mammals secrete milk to help nourish their young

• Single jawbone• Reptiles have a split lower jaw, mammals have a fused one.

• Specialized teeth• Whereas reptile teeth are all similarly pointed, mammals can have

different shapes (molars, canines, bicuspids etc.) • Diaphragm: a specialized muscle that makes breathing more efficient

Three Subclasses of Mammals

• the Monotremes (Prototheria) 0.2%– The monotremes are egg-laying mammals

(1 order with 3 species)• The Marsupials (Metatheria) 5.8%

– Marsupials give birth to immature offspring, and then carry them in pouches. (1 order, 334 species)

• The Placental Mammals (Eutheria) 94%– Placental mammals give birth to well developed

offspring after a longer gestation period. (18 orders,

over 5400 species)

The MonotremesKingdom Animalia, Phylum Chordata, Class Mamalia, (Subclass Prototheria)

• Order Monotremata: (only 3 species exist)• “Duck-billed” Platypus• “Short-beaked” Echidna• “Long-beaked” Echidna (aka. “Spiny Anteater”)

• Monotremes lay eggs, but they nurture their young with secretions from nippleless mammary glands.

The Marsupials

• Subclass Marsupialia: (about 280 species in 8 orders)– Including:

• Kangaroo• Wallaby• Tasmanian Devil • Tasmanian wolf (believed extinct)• Marsupial mole• Koala• Wombat• Opossum (only native marsupial in North America)

Interesting facts about marsupials

• Most female marsupials have 2 vaginas within a single cloaca

• Most male marsupials have a forked penis

• Marsupials have a gestation period of less than 5 weeks (some of them much less).

• Kangaroos don’t fart, (or more accurately, they produce no methane gas from their digestion)

• A baby kangaroo is about an inch long when born. It crawls to its mother’s pouch and stays there for about 9 months.

Placental Mammals

• Can produce a placenta.• Give birth to well-developed

offspring.– In fact, some species offspring can

be standing and running minutes after being born.

• Have longer gestation periods than marsupials.

For your information only. Don’t try to memorize!

Main Orders of Placental Mammals(about 5500 species in )

• Order Rodentia: mice, rats, squirrels, porcupines, beaver• Order Edentata: ant-eaters, sloths, armadillos• Order Lagomorpha: rabbits, hares, pikas• Order Insectivora: shrews, moles, hedgehogs• Order Primates: monkeys, lemurs, apes, humans• Order Chiroptera: bats• Order Carnivora: dogs, cats, bears, seals, sealions• Order Artiodactyla: ungulates, deer, cows, pigs, camels• Order Perissodactyla: horses, zebra, rhinoceros, tapirs• Order Cetacea: whales, dolphins, porpoises, orcas• Order Sirenia: manatees and dugongs• Order Proboscidea: elephants, mammoths (extinct)

While I don’t expect you to memorize all these orders of mammals, I do give them as examples of the diversity of the class.

The five in bold print are of particular interest, because they clearly illustrate how

different mammals can be.You should be aware of them, as well as

any other orders that interest you.

Mammals: Assignments

• Read:– Pages 881 to 896

• In your notebook:– List the organs and systems found in most mammals.

The drawing on page 885 may help you list some of the organs

– Copy the phylogenetic tree from page 891 (just the names, not the pictures)

• In your assignments book:– Do questions 6 to 20

Comparison of VertebratesClass Heart

chambersblood limbs covering

Agnatha (jawless fish) 2 Ectotherm

(cold)None Skin/

scalesChondrichthyes (shark) 2 Ectotherm

(cold)Fins Plaquoid

scales Osteichthyes (fish) 2 Ectotherm

(cold)Fins Wet skin

and/or scalesAmphibia 2, 3 Ectotherm

(cold)No claws

Moist skin

Reptilia 3, 4 Ectotherm(cold)

Claws (except snakes)

Dry skin and/or scales

Aves 4 Endotherm

(warm)WingsClaws

Skin and Feathers

Mammalia 4 Endotherm

(warm)varies Skin and

hair / fur

Mammal Organ Systems• All vertebrates have well developed organ

systems, but those of mammals are among the best developed.

• Organ systems include:– Integumentary system (skin, with hair or fur)– Muscular system (muscles– skeletal, cardiac, smooth)– Skeletal system (bones, cartilage, connective tissues)– Digestive system (esophagus, stomach, intestines etc.)– Cardiovascular or circulatory system (heart, blood

vessels)– Lymphatic and Immune systems (nodes, vessels)– Respiratory system (fully developed lungs, trachea)– Excretory or Urinary system (kidneys, bladder)– Reproductive system (most species have a uterus)– Endocrine system (glands)– Nervous system (brain, dorsal spinal cord)

How a Mammal is Organized

• Levels of organization:

Cells tissues organs organ-systems

Many similar cells working together form a tissueSeveral tissues working together form an organSeveral organs working together form a system

Major Tissue Types

• The four major tissue types are:– Muscle tissues: movement– Nervous tissue: communication– Epithelial tissue: covering organs and surfaces– Connective tissue: connecting and supporting.

• Each tissue type has several sub-types: – for example, muscle tissue could be skeletal

muscle, cardiac muscle or smooth muscle tissue.

Body Cavities• Body cavities are compartments within the body

that house organs.• Humans, like most mammals have four main

body cavities:– Cranial Cavity: Holds the brain– Spinal Cavity: Surrounds the spinal cord– Thoracic Cavity: Contains the heart, esophagus,

lungs, and other respiratory organs– Abdominal Cavity: Contains the organs of the

digestive, reproductive and excretory systems

• The cranial and spinal cavities are often referred to as dorsal cavities because they are mainly at the back of the body.

• The thoracic and abdominal cavities are the ventral cavities because they are on the front or stomach side of the body.

• Sometimes the lower portion of the abdominal cavity is called the pelvic cavity.

diaphragm

Systems

• You have learned about the organ systems in past courses, so we will do just a quick review of a few of the systems here.