Today is Monday,March 16th, 2015

Pre-Class:So we’re in the chordates group, right? (say yes)

Who’s our closest relative outside the chordates?

In This Lesson:Vertebrates and

Invertebrates(Lesson 2 of 3)

Today’s Agenda

• A tour of the invertebrates.– Squishy! Crunchy!

• A tour of the vertebrates.– Careful, these buggers (mostly) have jaws!• Technically they’re not “buggers.”

• Meeting Your Inner Fish.

• Where is this in my book?– Chapters 33-34.

By the end of this lesson…

• You should be able to describe defining characteristics and phylogenies of major animal phyla.

• You should be able to distinguish chordates from other invertebrates using four criteria.

Accompanying this lesson…

• To go along with this lesson and to help you better organize what will be a wide-ranging set of notes, use this “worksheet” I called, creatively:– Animals

• You’ll be responsible for those defining characteristics, so know ‘em well.

Animal Evolution Overview

Multicellularity

ANCESTRAL PROTIST

Porif

era

(Spo

nges

)

Specialized Tissues

Cnid

aria

(Sea

Jelli

es)

Body Cavity

Plat

yhel

min

thes

(Fla

twor

ms)

True Coelom

Nem

atod

a(R

ound

wor

ms)

Endoskeleton

Anne

lida

(Seg

men

ted

Wor

ms)

Segmentation

Arth

ropo

da(In

sect

s/Sp

ider

s/Cr

usta

cean

s)

BackboneEchn

inod

erm

ata

(Sea

Sta

rs)

Chor

data

(Bac

kbon

es)

Mol

lusc

a(M

ollu

sks)

Bilateral Symmetry

“You spineless little…”

• Since 95% of all known animal species are invertebrates, we better start with them.

• Invertebrates are, by definition, animals that lack a backbone (we’ll talk about that word later).– They include everything from sea sponges on up to sea stars,

but they’re a very diverse group in between.• On the following slides, we’ll talk a look at some of the

most important details of each major group in both the vertebrates and invertebrates.

• You should take note of the “category” of animals, example animals, and a defining characteristic.

Who lives in a pineapple under the sea?• Sponges (Phylum Porifera) are known as sessile

animals in that they cannot move.• They don’t really have tissues, meaning that

none of their cells really…work together.– They do have different cell types, but they’re still

considered metazoans.• More advanced than protozoa, but only a little.

• They’re also sequential hermaphrodites, alternating between male and female.

• DEFINING CHARACTERISTIC: They’re sessile filter feeders with a single cavity known as a spongocoel, which opens at the top as an osculum.– Sponges bring water in through porocytes, then

into the spongocoel, then out through the osculum. http://www.mbgnet.net/salt/animals/1sponge.jpg

Tube Sponge(Cribrochalina olemda)

Video Break!

• Porifera– Sponge Dye

Peanut Butter and Jellyfish

http://www.terraspirit.com/memories/110810_moonjellyfish.jpg

Moon Jellyfish(Aurelia aurita)

• Phylum Cnidaria (jellies, anemones, and coral) are the most ancient animals to actually have tissues, thus, they’re the first eumetazoans.

• DEFINING CHARACTERISTIC: They have two body forms.– Some are polyps (sessile, like sponges) and some

are medusa (motile, like the photo), and some experience both.

– Like Porifera, cnidarians also have a central one-holed cavity, this time called a gastrovascular cavity.

– They also tend to have stinging cells called nematocysts for feeding. Eww.

• Lastly, they have a hydrostatic skeleton for support.– Such skeletons are not bony but instead use fluid in

the coelom or gastrovascular cavity.

Bilateria• Bilateria are a clade within the animal kingdom.– DEFINING CHARACTERISTIC: These animals are

bilaterally symmetrical.• Within bilateria:– Protostomia (mouth first)• Lophotrochozoa are named for features that some have, like

the lophophore (feeding tentacles) or the trochophore larva (stage of development).– Annelids and molluscs are lophotrochozoans.

• Ecdysozoa are characterized by shedding an exoskeleton.– Arthropods and nematodes.

– Deuterostomia (butt first)

http://icb.oxfordjournals.org/content/41/3/608/F1.large.jpg

Lophotrochozoa: Phylum Platyhelminthes

• Flatworms live in either water (fresh or marine) or damp environments.

• They include trematodes, tapeworms, and planarians.

• Many are parasitic, like tapeworms or blood flukes.

• DEFINING CHARACTERISTIC:– Compressed top-to-bottom

bodies but still just a single mouth/anus.

http://www.nzdl.org/gsdl/collect/fnl2.2/archives/HASH60ea.dir/p146b.gif http://www2.estrellamountain.edu/faculty/farabee/BIOBK/01fluke.gif

Blood Fluke(Schistosoma)

Lophotrochozoa: Phylum Rotifera

• Rotifers are small (<3 mm) but multicellular with specialized organs.

• They are the simplest animals to have an alimentary canal, which is the tube connecting a separate mouth/anus.

• DEFINING CHARACTERISTIC: A mouth lined with cilia and simple jaws.

http://www.microscopyu.com/staticgallery/dxm1200/images/lecanerotifer.jpg

Loricate Rotifer(Lecane)

Lophotrochozoa: Phylum Mollusca• Not to be confused with

crustaceans, mollusks include:– Snails and slugs (Gastropoda)– Oysters and clams (Bivalvia)– Octopuses and squids (Cephalopoda)

• DEFINING CHARACTERISTIC: Their three main parts:– Foot – used for movement.– Visceral mass – most of the body.– Mantle – covering of visceral mass,

makes shell (if present).http://www.aqua.org/~/media/Images/Animals/Chambered%20nautilus/animals-nautilus-slide1-web.jpg

Chambered Nautilus(Nautilus pompilius)

Video Break!

• Mollusks:– Octopus Carrying Coconut– Octopus Pulls Cap Off Jar– Octopus Escapes Jar– Killer Cone Snails

Lophotrochozoa: Phylum Annelida

• Annelids are segmented worms.

• They include leeches, earthworms, and more obscure things like errantrians (marine plankton/algae predators).

• DEFINING CHARACTERISTIC: Segmented body sections, like you’ve seen on earthworms, along with a hydrostatic skeleton.

Giant Earthworm(Microchaetus rappi)

http://media3.s-nbcnews.com/j/msnbc/Components/Photos/040628/040628_leeches_hmed.grid-6x2.jpghttp://featuredcreature.com/wp-content/uploads/2013/02/6667475015_6f03b67401.jpg

Leeches(Hirudo medicinalis)

Video Break!

• Annelids– BBC – Giant Earthworm

Ecdysozoa: Phylum Nematoda

• Roundworms (nematodes) are found just about anywhere, and can be between <1 mm to 1 m in length.

• They include the often-studied Caenorhabditis elegans (or C. elegans) and Trichinella spiralis, which causes trichinosis.

• DEFINING CHARACTERISTIC: No segments and a cuticle (exoskeleton).

http://www.news.wisc.edu/newsphotos/images/Kimble_worm_c_elegans2_02.jpg

C. elegans(Caenorhabditis elegans)

Ecdysozoa: Phylum Arthropoda• Arthropods include insects, arachnids

(spiders), and crustaceans.– Eating lobster and crab means eating giant sea

insects.• DEFINING CHARACTERISTIC: A three-part

segmented body including head, thorax, and abdomen, plus an open circulatory system (no blood vessels – hemolymph washes over organs in cavities).– They molt their exoskeleton (which is made of

chitin – a carbohydrate) since it can’t grow with them.

– They are the first to evolve jointed limbs.– They are also the most numerous phylum.

http://www.panarthropoda.de/sub/galerie/pictures/phrynus_whitei01.jpg

Amblypygi(Phrynus whitei)

Video Break!

• Arthropods– Amblypygii – Actun Chek, Belize– TED: Sheila Patek – Fastest Animals EDITED

Deuterostomia: Phylum Echinodermata

• Echinoderms include the sea stars, sea urchins, sea cucumbers, and sand dollars.– Fun fact: the mouth and anus are

in the center but on opposite sides (top/bottom).

• DEFINING CHARACTERISTIC: Spiny exoskeleton with a water vascular system (water canals that help them move and eat).– They also have a hydrostatic

skeleton.http://www2.estrellamountain.edu/faculty/farabee/BIOBK/adultseastar.gifhttp://www2.estrellamountain.edu/faculty/farabee/BIOBK/adultseastar.gif

Brittle Star(Ophiothrix fragilis)

Video Break!

• Echinoderms– Sea Cucumber Fights with Guts

Deuterostomia: Phylum Chordata

• And now for something different: a backbone!• There are actually some distinctions when it comes to

backbones, and chordates have four defining characteristics:– A notochord (1) is a flexible rod that provides skeletal

support.• Vertebrates mainly only have these as embryos but others keep

them as adults. It’s not bone.

– A dorsal, hollow nerve cord (2) that becomes the central nervous system (spine and brain).• Dorsal means it’s located toward the back, not belly.• It’s solid and ventrally located in other animals.

Video Break!

• The importance of a backbone:– TED: Gregoire Courtine 2013 – The Paralyzed Rat

That Walked – Subtitled

Notochords and Nerve Cords

Remember this?

• During neurulation, the notochord and neural tube form.– The notochord will eventually become the spinal

column.– The neural tube will eventually become the central

nervous system (the brain and the spinal cord).

Notochord

Neural Tube

Other Chordate Features

• The pharynx is the region of the digestive tract just posterior (toward the butt) of the mouth.

• In chordate embryos, the pharynx develops slits known as…pharyngeal slits (3).– In vertebrates, these develop into either

gills or ear/head/neck parts.– In invertebrates, the pharyngeal slits

develop into filter-feeding organs.• Also note the muscular post-anal tail

(4).http://www.bio.miami.edu/dana/pix/chordate2.jpg

Chordates

• Chordates include the following subphyla:– Vertebrates (that’s us! And like, alpacas and stuff)– Urochordates (tunicates and sea squirts)– Cephalochordates (lancelets)

• FYI, subphyla are above classes but below…phyla.• Let’s start with the creatures that aren’t as

familiar…

Lancelets

• Lancelets (cephalochordates) are invertebrates with a notochord that persists throughout life and a head region.– (that’s the DEFINING

CHARACTERISTIC)– Lancelets are also known as amphioxi

(singular: amphioxus).

Tunicates

• Tunicates (urochordates) include the sea squirts, which are named for what they do with ocean water.

• DEFINING CHARACTERISTIC: They too possess a persistent notochord along with a tunic made of cellulose.

Vertebrates

• Ah, the vertebrates.• If you haven’t noticed yet, the phylum

Chordata includes invertebrates.– You can be an invertebrate and still have a

notochord.• We’re going to take a look at the various types

of vertebrates from the perspective of vertebrate evolution.

Agnathans• Possessing the most rudimentary of

backbones, the agnathans represent the most ancient of the true vertebrates – living fossils.– Their backbones are cartilage.– Technically “agnathans” are paraphyletic when

considering extinct species.• Who are the agnathans? Only two living

groups:– Lampreys (class Petromyzontida)– Hagfishes (class Myxini)

• DEFINING CHARACTERISTIC: Agnathans are jawless fish (the only vertebrates without jaws) and do not have paired appendages (limbs).

http://upload.wikimedia.org/wikipedia/commons/3/3f/Lampetra_fluviatilis.jpghttp://www.wired.com/wp-content/uploads/2014/05/hagfish-getty-01a.jpg

European River Lamprey(Lampetra fluviatilis)

Pacific Hagfish(Eptatretus stoutii)

Video Break!

• Agnathans– Lampreys – Dirty Jobs– Hagfish– Hagfish Slime

Transitions: Origin of Vertebrates

• Agnathans are so primitive they actually give us some hints as to the origin of vertebrates.– Seriously, hagfish today nearly identically match

hagfish fossils from 300 million years ago.• Here are some early transition species from

the Cambrian explosion:– Haikouella– Myllokunmingia– Conodonts

Haikouella and Myllokunmingia• Haikouella (~3 cm) had eyes, a brain, and muscles,

but no skull or ears (used for balance).

• Myllokunmingia had rudimentary ear and eye capsules, suggesting the beginnings of a head.– Alas, it still didn’t have vertebrae.

Conodonts

• Conodonts were a bunch of jawless vertebrates whose skeleton was cartilaginous.– They also had large, creepy eyes

for stalking food.• They lived about 500-200

million years ago, during which time other species appeared with simple bony structures.– Are you seeing the transition?

http://www.le.ac.uk/gl/map2/abstractsetc/conanimals.jpg

On the topic of transitions…

• Let’s explore “our inner animals.”• HHMI – Your Inner Animals – Click and Learn

Jaws!• Next to evolve were the gnathostomes, which are the so-

called “jaw mouths.”– So gnathostomes are everything from sharks through

amphibians, reptiles, birds, and mammals.• Jaws appear to have evolved from supports for those

pharyngeal slits we mentioned before.

Chondrichthyans

• After several more transition groups…– Placoderms and acanthodians were

armored, jawed vertebrates.• …there emerged the

chondrichthyans.– These include sharks and rays.

• DEFINING CHARACTERISTIC: A cartilaginous skeleton.– Chondrichthyans appear to have

branched off from other fish that were beginning to develop bone.

It gets fishier…and bonier…• True bone continued to develop with the rise

of the osteichthyans.– “Osteo-” is a root for bone-related things.

• Osteoporosis (when bones become brittle/weak)• Ossification (development of bone from cartilage)

• Osteichthyans technically include tetrapods (four-limbed creatures with feet), but is informally used to describe bony fish:– Ray-finned fish (Actinopterygii)– Lobe-finned fish (Sarcopterygii)

• BOTH bony fish and cartilaginous fish have a two-chambered heart.

Ray-Finned Fish (Actinopterygii)

• Ray-finned fish include sturgeon, cod, trout, carp, and mudskippers.– If you eat fish, you’ve probably

eaten a few ray-finned fish.• DEFINING CHARACTERISTIC:

“Rays” of bone that support their fins.

Mudskipper(Periophthalmus)

Wait…hold on a second.

• Mudskippers are fish?!– Yep. Amphibious ray-finned fish.• Remember I told you classifying animals can be hard?

• It’s time for mudskipper videos!– Fish That Walk– BBC – Mudskipper

• Wanna get a little weirder?– BBC – Flying Fish

• Wanna get a little funnier?– Fish Blooper – Asian Carp

In all seriousness…

• Think about what trends you’re seeing:– Cartilage turning to bone…– Marine creatures moving to land…– The development of heart chambers…– Progress toward the ability to fly…

• Watch for these to continue and to occur in more than just one group.

Lobe-Finned Fish (Sarcopterygii)

• Lobe-finned fish are a much smaller group than the ray-fins.– They mainly include the lungfish and

coelacanths.• Lungfish are so-named because they can

go dormant when bodies of fresh water dry up using lungs homologous to tetrapod lungs.

– HOWEVER (!) they are the precursors to tetrapods, including humans.

• DEFINING CHARACTERISTIC: Thick muscles in their lobed fins that allow them to “walk” along the bottom surface.http://animalia-life.com/data_images/lungfish/lungfish3.jpg

Spotted African Lungfish(Protopterus dolloi)

Video Break!

• Lobe-Finned Fish– Finding the Coelacanth

Transitions: Movement to Land

• As you might guess, and as we’ve discussed before, amphibians represent descendants of the earliest tetrapods.

• Transitional species exist, though the line between fish and amphibian is…blurry.

• Let’s take a closer look at Tiktaalik and Ichthyostega.

Tiktaalik roseae• Tiktaalik was discovered in

2006 by Neil Shubin (remember that name) on Ellesmere Island, Canada, and, as you might guess, made the biology world shudder with glee.– Why?

• Because it had fins, gills, and lungs.

• It also had ribs, shoulders, and a skeletal system much like modern land dwellers.

https://en.wikipedia.org/wiki/Ellesmere_Island#mediaviewer/File:Ellesmere_Island,_Canada.svg

Tiktaalik roseae

Ichthyostega• Ichthyostega also appears to be a transitional species,

possessing features common to both fish and to amphibians, yet did not possess gills.– Now’s a good time to remind you that by the time animals

finally crawled onto land, they were greeted there by plants.

Tibia

Femur

Fibula

Humerus Shoulder

RadiusUlna

TibiaFemur

Pelvis

Fibula Lobe-finned fish

Humerus

Shoulder

Radius

Ulna

Pelvis

Early amphibian

The Move to Land

It’s time for a movie!

• Like, a real, hour-long movie!– Okay fine, it was a mini-series on TV. Whatever.– Your Inner Fish with Neil Shubin.• The dude that discovered Tiktaalik, remember?

Amphibians• The word amphibian (Class Amphibia)

comes from “amphi-” (“two”) and “-bios” (“lives”).

• They are divided into three clades:– Salamanders (Urodela – “tailed ones”)– Frogs (Anura – “tailless ones”)– Caecilians (Apoda – “legless ones”)

• DEFINING CHARACTERISTIC: Amphibians– breathe through moist skin.– lay eggs/develop in water.– have three-chambered hearts.– are ectothermic.

lung

buccalcavity

glottisclosed

Amphibians

Anura

Apoda

Urodela

Fun Fact: There are lungless species of frogs and salamanders, and

some caecilians live underwater.

Amphibian Hearts

• There’s something interesting about the amphibian heart/circulatory system.– There’s one part that goes from the heart to the

lungs (like in us).• The pulmonary circuit.

– There’s one part that goes from the heart to the rest of the body (like in us).• The systemic circuit.

– There’s a third part that brings deoxygenated blood from the heart to the skin.• Pulmocutaneous circulation (NOT shown).

Hearts and Lungs• This is a good time to tell you a quick general

fact that’s hard to place elsewhere:– Key: Gas exchange requires moist membranes.– Since amphibians are generally “slimy,” they can

breathe through their skin or their lungs.• Hence the pulmocutaneous circuit.

– Reptiles, birds, and mammals only have moisture in their lungs – a product of land life.

– Fish are the moistest, hence gills.• I hope you’re seeing how strong the

evolutionary ties are between all these traits.

Hearts in General

• I’ll show you this again at the end of the lesson.

Amniotes

• As we continue to get more specific (and exclude more and more), we’re now at the amniotes.

• Amniotes are named for their amniotic egg (not present in amphibians) and include:– Mammals (Class Mammalia)– Turtles (Class Testudines)– Tuataras (Class Sphenodontia)– Snakes and Lizards (Class Squamata)– Crocodilians (Crocodiles and Alligators)– Birds (Class Aves)

Reptiles

More on the Amniotic Egg

• The amniotic egg includes a shell that facilitates exclusive life on land and the extraembryonic membranes:– Allantois– Amnion– Chorion– Yolk Sac

• Amphibian eggs, in contrast, need to develop in water.– As do their young.

Further Evolution

• Reptiles• DEFINING CHARACTERISTIC:

They are further evolved to life on land with– Scales (made of keratin protein)

prevent desiccation.• Air must therefore come from

lungs only.

– Fertilization is internal.• Like amphibians, they’re also

ectothermic and have three-chambered hearts.

Marine Iguana(Amblyrhynchus cristatus)

(Give me your) Reptilian Heart

• Okay, here’s the weird thing.• Reptiles don’t have the pulmocutaneous

circuit that amphibians do.• They have two defining features:– A shunt that diverts mixed blood to the

systemic circulatory system.– A partially-separated ventricle that very

nearly gives them four chambers.

Turtles• As you can see from the image at

the right, turtles are a bit of an outgroup from the rest of the reptiles.– DEFINING CHARACTERISTIC: They’ve

got, you know, shells.– They include the tortoises.

• Non-testudines (non-turtles) are the diapsids and are divided into:– Lepidosaurs (tuataras, lizards,

snakes, extinct marine reptiles)– Archosaurs (crocodilians,

pterosaurs, dinosaurs)

Archosaurs• Lepidosaurs are

straightforward (picture next slide).

• Archosaurs, however, are a bit more interesting.

• They’re divided into:– Pterosaurs– Dinosaurs, which are

divided into:• Ornithischia (extinct)• Saurischia (extinct except

for birds)

Lepidosaurs (including the Mososaurs)

https://loretoscience.files.wordpress.com/2012/01/mosasaur4.jpg

BIRDS!!!1• Birds (Class Aves) branched off

from reptiles around 150 million years ago.

• DEFINING CHARACTERISTIC: Birds have– hollow bones adapted for flight.– a four-chambered heart.– feathers and wings.

• They’re also endothermic.– Key: Their hearts and endothermic

metabolism is CONVERGENT evolution with mammals – they don’t have a recent common ancestor.

trachea

anteriorair sacs

lung

posteriorair sacs

Carnivorous Origins

• As we just saw, birds evolved from saurischian dinosaurs.

• More specifically, they evolved from a group of bipedal dinosaurs (walking on two legs) known as the theropods.– They were primarily carnivorous.– You may have heard of Tyrannosaurus Rex?

• That’s right, even those cute seed-eaters evolved from…– …CARNIVORES!

Transitions: Flight• You remember

Archaeopteryx, right?– The first flying birdreptilething?

• Flight appears to be a more common adaptation than you may realize.– Snakes That Fly video– Incredible Flying Snake video

Evolution Denial• At this point it may seem ridiculous, but evolution deniers

sometimes cite a lack of transition species or fossils.– Really? REALLY?!

• I hope you now realize there are plenty.• Then again, here’s the current top comment on one of those

Coelacanth YouTube videos from before (I have most of the conversation saved):

The Grand Finale?• For better or worse, usually depicted as the

pinnacle of evolution are the mammals.– Half-hearted whoo…cause we’re not the apex.

• Mammals got their start around 220 million years ago, but really got going when the dinosaurs kicked the bucket around 65 million years ago.

• DEFINING CHARACTERISTIC: Hair, specialized teeth, ear flaps, live birth, milk production, being endothermic, and a four-chambered heart.– Key: Having mammary glands is the only trait

that does not have exceptions.

Hearts in General

• I showed you this before…

Mammal Groups

• Mammals are split into three groups:– Monotremes (egg-laying mammals)• Platypus• Echidna

– Marsupials (underdeveloped young)– Eutherians (placental mammals)

Marsupials

• Marsupials appear to have split from the placental mammals (eutherians) around 125 million years ago.– Eutherians = North– Marsupials = South

• There’s been a great deal of convergent evolution since then, as seen at the right.

Reminder: The Wallace LineFrom Unit 1 Lesson 1

• Wallace noted that on the west side of the line, most species were “Asian-like,” (placental mammals), whereas east of the line animals were “Australian-like” (marsupials), though similar.

• The line, therefore, is a biogeographical boundary of genetic isolation.

http://1.bp.blogspot.com/-Qvvxbs1hN1c/UXqP8qTME8I/AAAAAAAABic/I0VIyTgiEl0/s1600/wallace+line.gif

Marsupials

• Marsupials are known for having a pouch, but that’s not always necessary.– The short-tailed opossum, for example,

has no pouch.• The young cling to their mother’s teats

instead.

• Sometimes marsupials can reproduce quickly.– Kangaroos give birth after 31-ish days of

pregnancy, so frequently there’s one in the womb, one in the pouch, and one on the ground.

http://s110.photobucket.com/user/corsiphoto/media/photos-part2/Image1-1.jpg.html?t=1204759648http://upload.wikimedia.org/wikipedia/commons/b/b5/

Monodelphis_domestica.jpg

Gray Short-Tailed Opossum(Monodelphis domestica)

Mammals

Primates• Primates range from the

prosimians (lemurs and lorises) up through the new/old world monkeys and great apes.– And those pesky humans.

• DEFINING CHARACTERISTIC: Opposable thumbs, nails (instead of claws), good depth perception.

http://rewireyourbrainforlove.com/wp-content/uploads/2013/02/bonobos.jpg

Bonobo(Pan paniscus)

http://lemur.duke.edu/wordpress/wp-content/uploads/2014/01/IO-moth-eating-frozen-apple-sauce.jpg

Pygmy Slow Loris(Nycticebus pygmaeus)

http://www.privatewifi.com/wp-content/uploads/2014/02/selfie.jpg

Human(Homo sapiens)

Video Break!

• Primates:– Things You Probably Didn’t Know About Cute

Bonobos– Human Fails

Homologous Structure Case-in-Point

• Now’s perhaps one last opportunity to talk about a homologous structure throughout the animal kingdom: keratin.– We heard of keratin as being that protein that makes

up reptile scales.– Know what else it makes up?

• Keratin is also a primary ingredient in hair, nails, and feathers.– So as you can imagine, it showed up in the animal

lineage a LONG time ago.

Closure: Egg Transitions• Turns out, even eggs have a number of “in-

between” transitional species.– Fish and amphibians strictly lay eggs.• So we call them oviparous.

– Reptiles mostly lay eggs.• Also oviparous.

– Some reptiles develop in eggs inside Mom, but they’re never laid.• So we call them ovoviviparous.

– One reptile has a placenta and takes care of its young.• It, like mammals, is viviparous.

Closure Part Deux

• In a single PowerPoint file we’ve experienced quite literally millions upon millions of years of evolution.

• Most of the evolution we’ve examined has been skeletal or reproductive in nature, with some hints toward the cardiovascular system.

• With all this evolution, there were also incredible developments into animal organ systems, and that’s what’s up next.– Stay tuned for the last lesson of AP Biology.