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Lecture 1.1_What is a Mammal?

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greetings Intrepid ABS 470 online

students this is Professor Jared Rachel

and I welcome you to lecture 1.1 the

very first lecture in our course the

life history of mammals

so what I want you thinking about today

is what unites these seemingly disparate

species from the animal here on the top

left which is an egg laying species with

no teeth

to this one here in the center an

arboreal species that's going to carry

its young in an abdominal pouch

the species on the top right highly

carnivorous species lives in the

Himalayan Mountains some 15 000 feet

above sea level

here uh we have a feces within which 1.5

million individuals are going to migrate

over 300 miles chasing spring rains to

get to Greener calving grounds

you see here in the bottom middle this

is a pelagic open ocean species that we know

know

transmits its hunting techniques from

one generation to the next as a cultural heritage

heritage

and then finally let's get these on the

bottom right

this one is 99 genetically identical to

you and I it's seen here uh fishing with

a rod that it crafted fishing for termites

termites

so my question to you today is what

unites all of these organisms in the

class mammalia

so allow me to point out right from the

start that while there are certainly

diagnostic or distinguishing characteristics

characteristics

common traits that are shared by all mammals

mammals

we Define this lineage by its

evolutionary ancestry not necessarily by

any particular characteristic

so when you think about mammals probably

one of the first characteristics that

you think of is hair or fur

but consider the naked mole runs

so it's clearly a mammal and yet it's

almost completely hairless

so the hairlessness or almost complete

hairlessness is secondarily derived in

ABS 470 we're going to define the class

mammalia following row 1988.

uh the most recent common ancestor right

here of the monotremes which are the

duckbilled platypuses and the spiny echidnas

echidnas

the most recent common ancestors are the

monotreme and the theory which includes

the metatherea or the approximately 272

species of marsupials as well as the

true theory or that you Theory u means

true which is all of those placental

mammals as well as all of these extinct lineages

lineages okay

let's think about what exactly is a

mammal and let's use uh linnaean

taxonomy to kind of help us hone in okay

so we're going to go from the most

inclusive taxonomic category okay from

domain all the way down to the most

inclusive category in this case class

okay the class mammalia so we know that

mammals consist of eukaryotic cells that

is to say large at least larger than

bacterial cells which are only one to

ten microns large complex cells that are

made from

membrane-bound organelles like a nucleus

that has a nuclear envelope a nuclear

membrane around it

so this includes the eukaryotes are the

protists the plants the fungi as well as

the animals

so the kingdom Animalia represents mobile

mobile

multicellular and heterotrophic species

eliminating the mostly single-celled

protists although not also and the

relatively immobile fungi as well as the

photo synthetic plants mammals are

members of the phylum chordata which

means they have multiple

synapomorphies including the development

of a flexible Rod structure named the

notochord which develops into the

vertebrae and vertebrata

they also had a dorsal Hollow nerve cord

which will develop into your central

nervous system

they have a post-anal tail ours is

highly truncated and lastly the chordata

have pharyngeal gill slits or pouches or

arches which will become the jaw and the

inner ear in mammals

so this is going to eliminate the vast

majority of animals including the most diverse

diverse

biologically diverse lineage on the

planet The Beatles remember 60 of

animals are beetles the subphylum

vertebrata or the craniates is going to

exclude the tunicates

but it's going to include the jawless

fishes the cartilage is the shark Rays

the Bony fishes the amphibians reptiles

and the star of our show the mammals so

all of these animals develop a cranium

and vertebrae with the exception of the

hagfish which has a rudimentary

vertebral column

normals are Petra pods Tetra meaning for

and pode is foot in Greek so that of

course is going to eliminate both our

cartilaginous and bony fish the

tetrapods that is to say amphibians

reptiles birds and mammals represent the

descendants of something akin to the

lobe-finned fish like salamander-like

fossil named titalic this is a

375 million year old transitional

species the amniotes represent

vertebrates that lay eggs that are

impermeable to water and have three

extra embryonic membranes the amnion the

Korean and the allentos so this is going

to eliminate our amphibians which have

to lay their eggs in water thus they're

tied to living in or near water or in

really wet environments like the

tropical rainforest so our tree frog is

now out so I know you're probably saying

to yourself

um you know wait a minute with the

exception of the Platypus and the

echidnas mammals do not lay eggs and you

are correct but the amniotic egg has

been highly modified in mammals so for

example in the placental mammals the

embryo is surrounded by the amnion which

is filled with the amniotic fluid so

doctors will often check out this fluid

in developing uh fetuses just to check

on the health of the unborn child

meanwhile the Alan towis and the yolk

Sac become the umbilical cord which of

course is the connection between mother

and fetus it's going to provide a

glucose and oxygen and then remove

nitrogenous waste and CO2

so together with the Korean

um these membranes are going to make up

the placenta which physically attaches

the embryo to the uterine wall of mom

and around the hole is the fluid-filled

Corian which when it breaks the water

has broken and labor begins so fear not

we're going to return to this uh in our

lecture on the evolution of mammals but

in short

mammals are what we call synapses which

means they only have a single and plural fossa

fossa

on each side of their skull whereas

reptiles are

biptoe die meaning who so we're going to

have two of these temporal fossa or

openings on the skull

so the diapids are now eliminated the

Komodo dragon is out but other synapses

are included uh like this guy down here

this is dimetrodon and again we're going

to to come back to him

and finally this brings us to this

adorable red panda here on the bottom right

right

so mammals are distinguished from their

synapsid relatives uh by their large and

heavy dinkery bone right down here the

lower jaw okay you can see that it's all

one bone

bone in mammals is going to form a joint

with the cuomoto bone and again we're

coming back uh to these Concepts so

apart from linnaean taxonomy what other

key adaptations help us distinguish

mammals from other taxa

mammals are endothermic as opposed to

ectothermic meaning they're going to

maintain a higher body temperature than

that of the external environment recall

that ectotherms are going to have highly

variable body temperature that's going

to fluctuate as the external environment fluctuates

fluctuates

many mammals are not only endothermic

they're homeothermic meaning they're

going to maintain a relatively constant

body temperature even as environmental

temperatures fluctuate so consider us

humans living in the Sonoran Desert

right it could be 115 degrees or below

freezing and we're training to keep at about

about

98.6 so we're going to return to thermal

regulation during our fifth unit in the

endothermy has allowed mammals to

exploit an incredible array of habitats

from the open ocean to high in the Himalayas

Himalayas but

but

endothermic comes at a massive energetic

cost resulting in higher metabolic rates

and so therefore mammals they're going

to need to eat frequently

so in my in my lab as I may have

mentioned I house a lot of different

reptiles and the star of our show is a

six foot Sonoran gopher snake so this

massive snake Delilah she only eats

twice a month

whereas this baleen whale is constantly

on the hunt

so I love this a concise but very

accurate way to describe mammals is

veritable eating machines

at least relative to other vertebrates

many of the traits that we associate

with mammals ultimately serve this

purpose of being eating machines

together they form this correlated Suite

of adaptations adaptations like complex

teeth or heterodontentition

whole array of foraging strategies

locomotor specializations

and relative to fish and reptiles

mammals have very large brains

these large brains in fact all of these

attributes the complex teeth the uh

foraging strategies they're all about

meeting feeding those voracious

appetites of these high energy animals

so initially the brains likely enlarge

to support olfaction

um the sense of smell uh the mammalian

sense of smell is very keen and it's key

in helping many mammals identify their Foods

Foods

likewise hair or fur it was present in

the more recent synapsid ancestors and

it's also probably pretty obviously

correlated with endothermia so hair and

fur is going to provide insulation to

trap and conserve body heat that body

heat that was so expensive to generate

so not only do mammals requiring large

amounts of energy to maintain themselves

but they also invest heavily

energetically invest in their offspring

so we're going to cover mammalian

reproduction in well next week and then

we'll cover uh mating systems and

parental investment in week four but for

now what I need you to recognize is are

these terms here so over parity refers

to species where the females lay eggs

with little or no other embryonic

development within the mother like the

amount of trips the Platypus and the echidnas

echidnas

although the production of those eggs is

very energetically expensive so there's

still you know relative to other taxa

investing heavily in their offspring

viviparity has evolved in the marsupials

which have altricial or undeveloped

relatively undeveloped Young And as well

as the placentals which are going to

have precocial or well-developed young

in both of these cases the females give

birth to live young like these very real

photos of a giraffe birth and then

female mammals are going to produce this

wondrous highly nutritious High caloric

high fat food this liquid known as milk

in their mammary glands mammary mammal

so it's the namesake of mammals we'll

return to the placenta uh next week when

we talk about reproduction but in

placenta mental mammals the suckling

period at the mammary glands is preceded

by this period it's a long period in

which the fetus develops in utero and

this period is known as gestation so

while humans have an approximately nine

month gestation time the gestation

period for an African elephant which has

considerably larger body size is 22 months

months

that's going to conclude chapter one

part one called mammals in your text so

next I want you to skip ahead to chapter

four part seven and I want you to read

that short verb entitled characteristics

of mammals it's just two pages so I'm

going to really quickly summarize that

so endothermic mammals with high

metabolic rates are variable eating

machines as we've already established if

they're eating machines we know they're

doing lots of cellular respiration

they're breaking down that glucose to

get ATP they're doing cellular

respiration so they need oxygen thus

mammals have evolved a very efficient

pump to move blood so mammals have a

four chambered heart if I get my cursor

to come up here uh mammals have two

atria on the top which receive the blood

and then two ventricles on the bottom

which are gonna pump the blood the

ventricles are separated by a wall that

wall is called the septum and this is

what makes that heart solely so

efficient because it's going to separate

the deoxygenated blue blood from the

oxygenated red blood okay if we look at

other vertebrates with lower metabolic

rate fish only have two Chambers one

Atrium and one ventricle uh most

amphibians and reptiles are going to

have three chambers two atria and one ventriclem

ventriclem

and then uh some of the more derived rep

house the crocodilians uh as well as

Birds which of course evolved from feral

pods uh Birds uh crocodilians and

mammals have the four chambered heart

and we think about birds they too have a

very high metabolic rate so they need

um lack of oxygen moving to those cells

if we zoom in on the mammalian blood

cells we find that the red blood cells

have lost their nucleus and further

their biconcave meaning on both sides

they have this Con uh concave shape

which is going to allow them the ability

to carry bukus of oxygen what do I mean

by that each red blood cell has approximately

approximately

270 million hemoglobin molecules and

each of those hemoglobin molecules can

bind four molecules of oxygen so we've

already discussed the production of milk

by the mammary glands or Mame the plural

that's beautifully shown here uh by this

female Basset Hound

and then finally mammals have this flat

parachute shaped muscle called the

diaphragm which is going to contract

and allow the volume of the lungs to

increase creating a negative pressure

and air flowing in and then when it

relaxes it's going to decrease that volume

volume

forcing air out so again this is high

respiration High metabolic rate because

we're all about feeding the machine

right the eating machine

so in conclusion when we talk about

mammals what do we mean

mammals are smart big brains mobile

eating machines that exhibit great

maternal care lots of energy invested in

our young like this female orangutan and

her babe

so I look forward to joining you for

lecture 1.2 when we discuss why should

we even study mammals so we'll get into

the importance of mammology and the

importance of mammals uh to ecosystems

and to our lives I appreciate uh your

time and attention and I'll see you next

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