In This Lesson:
Vertebrates and
Invertebrates
(Lesson 2 of 3)
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?
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.
Multicellularity
ANCESTRAL PROTIST
Specialized Tissues
Bilateral Symmetry
Body Cavity
Segmentation
True Coelom
Chordata
(Backbones)
Echninodermata
(Sea Stars)
Arthropoda
(Insects/Spiders/
Crustaceans)
Annelida
(Segmented Worms)
Mollusca
(Mollusks)
Nematoda
(Roundworms)
Platyhelminthes
(Flatworms)
Cnidaria
(Sea Jellies)
Porifera
(Sponges)
Animal Evolution Overview
Backbone
Endoskeleton
“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.
Tube Sponge
(Cribrochalina olemda)
– Sponges bring water in through porocytes,
then into the spongocoel, then out through
the osculum.
http://www.mbgnet.net/salt/animals/1sponge.jpg
Video Break!
• Porifera
– Sponge Dye
Peanut Butter and Jellyfish
• 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 oneholed cavity, this time called a gastrovascular
cavity.
– They also tend to have stinging cells called
nematocysts for feeding. Eww.
Moon Jellyfish
(Aurelia aurita)
• Lastly, they have a hydrostatic skeleton for
support.
– Such skeletons are not bony but instead use
fluid in the coelom or gastrovascular cavity.
http://www.terraspirit.com/memories/11
0810_moonjellyfish.jpg
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:
Blood Fluke
(Schistosoma)
– 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
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).
Chambered Nautilus
(Nautilus pompilius)
http://www.aqua.org/~/media/Images/Animals/Chambered%20nautilus/animals-nautilus-slide1-web.jpg
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)
Leeches
(Hirudo medicinalis)
http://media3.s-nbcnews.com/j/msnbc/Components/
http://featuredcreature.com/wp-content/uploads/2013/02/6667475015_6f03b67401.jpg Photos/040628/040628_leeches_hmed.grid-6x2.jpg
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).
Amblypygi
(Phrynus whitei)
– 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/pict
ures/phrynus_whitei01.jpg
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).
Brittle Star
(Ophiothrix fragilis)
• DEFINING CHARACTERISTIC:
Spiny exoskeleton with a water
vascular system (water canals
that help them move and eat).
– They also have a hydrostatic
skeleton.
http://
http://www2.estrellamountain.edu/faculty/farabee/BIOBK/adultseastar.gif www2.estrellamountain.edu/faculty/farabee/BIOBK/adultseastar.gif
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).
Neural Tube
Notochord
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.
European River Lamprey
(Lampetra fluviatilis)
• 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.jpg
Pacific Hagfish
(Eptatretus stoutii)
http://www.wired.com/wpcontent/uploads/2014/05/hagfish-getty-01a.jpg
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 rayfinned 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.
Humerus
Femur
Tibia Pelvis
Ulna
Lobe-finned fish
Fibula
Pelvis
Fibula
Femur
Humerus
Tibia
Early amphibian
Ulna
Shoulder
Radius
Shoulder
Radius
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
buccal
cavity
glottis
closed
Amphibians
Anura
Urodela
Fun Fact: There are
lungless species of frogs
Apoda 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 threechambered 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
lung
anterior
air sacs
posterior
air 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 Line
From 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.
Gray Short-Tailed Opossum
(Monodelphis domestica)
http://upload.wikimedia.org/wikipedia/commons/b/b5/Monodelphis_
domestica.jpg
http://s110.photobucket.com/user/corsiphoto/media/photos-part2/Image1-1.jpg.html?t=1204759648
Mammals
Primates
• Primates range from the
prosimians (lemurs and lorises) up
through the new/old world
monkeys and great apes.
Bonobo
(Pan paniscus)
– And those pesky humans.
• DEFINING CHARACTERISTIC:
Opposable thumbs, nails (instead
of claws), good depth perception.
Pygmy Slow Loris
(Nycticebus pygmaeus)
http://rewireyourbrainforlove.com/wpcontent/uploads/2013/02/bonobos.jpg
Human
(Homo sapiens)
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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 “inbetween” 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.