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Lecture 4.1_Mammalian Modes of Locomotion

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hello again ladies and gentlemen and

welcome to module four the first lecture

in module 4 lecture 4.1 is entitled

mammalian modes of locomotion so today I

will be describing the Myriad of

different ways by which mammals have

evolved to move from point A to point B

I will detail some of the anatomical

adaptations that are characteristic of

cursorial or running species like these zebras

zebras

saltatorial Locomotion like this jumping

red kangaroo

brachiation like this Gibbon swinging

from the tree limbs

fossorial species like this mole

Roland Locomotion like the true uh

powered flight we see in the chiroptera

like this fruit bat and then I'll end

with the fully aquatic marine mammals

like this harp seal lecture 4.1 aligns

with chapter 6 in your textbook which is

entitled integument support and movement

that said you are only responsible for

the third section entitled modes of

locomotion that's what you'll be tested

over you can totally skim over

integument basic skeletal patterns and muscles

muscles

to begin with many mammals use walking

as their primary means of locomotion

walking is probably the Primitive

pattern of locomotion the first means by

which mammals move from one place to the

next most mammals are quadrupedal

meaning they move on for limbs although

there are some notable exceptions namely

us mammals that are bipedal walking on

two limbs

species that move predominantly by

walking are called ambulatory like this

polar bear and then there are species uh

who are exquisitely adapted for blazing

fast speeds like this cheetah and

they're considered cursorial the running

species the Primitive walking gait is

associated with plan to grade foot

posture in plan to grade foot posture

all or most of the Palm on the forelimb

or the Soul on the hind limb is in

contact with the substrate so that's

clearly evident here the soul of the

human's foot is totally in contact with

the sand so this is plan to grade

football posture also evident here in

the bear another plan to grade species

this is the bear hind foot here uh there

you can see the bear hind foot and

that's the Bear's forefoot so that's the palm

palm

in plan to grade foot posture these

these

metatarsals as well as the phalanges the

toes of the hind foot and then the

metacarpals and the fingers the

phalanges of the front foot they're

oriented parallel to the ground so

examples of plant a grade species

obviously include humans bears as well

as rodents skunks raccoons and hyraxes

in digital grade species uh like this

cat we see that the metacarpals here in

the forelimb as well as the metatarsals

in the hind limb they've been elevated

off the ground to an acute angle leaving

only the phalanges in contact with the

substrate so this is the metatarsal here

in Gray those are the phalanges shown in

that kind of yellowish color and then

the brownish color that represents the

claws most digital grade species have

reduced uh their digits leaving only

four functional toes for Locomotion and

then in the angula grade mammals we're

going to take this carsorial foot

posture even further so we're talking

about the ungulates now or the hooved

mammals and in the ungulates we see now

that even the phalanges again shown in

yellow as well as the metatarsals and

metacarpals shown in Gray are all

elevated so only the tips of the

phalanges are in contact with the ground

that said those tips are covered by

these keratinized Hooves as exhibited by

this zebra and we've got increased

lengths now of metatarsals and phalanges

so you can see this Evolution here in

the plantagrade species the metatarsals

are parallel and in contact with the substrate

substrate

in the digit of grade species those

metatarsals are now elevated at that

acute angle and now in the angular grade

species the metatarsals and the

phalanges are both elevated so

increasing specialization for a

cursorial Locomotion along with their

foot posture ungulates have further

reduced the number of toes of digits on

uh their feet so for example there are

three digits in the tape ears

there are just two digits in the audio

dactyls like this deer and then there's

just the one digit this one toe uh with

this keratinized hoof in the horse's and

zebras in his 1985 publication which is

cited at the end of this lecture

Hildebran identifies four functional

requirements for animals that are either

going to walk and or run number one

there needs to be support and stability

even though those feet are only making

intermittent contact with the substrate

so walking is obviously the most stable

of gates because of the prolonged

contact of the feet with the ground

however when running particularly when

Galloping the animal must ensure that

the front and the hind limbs do not

interfere with one another I.E become

all tangled up

number two the walking running mammal

must have forward propulsion it's got to

move its body forward so models of

animal movement are based on the idea

that the legs Swing below the body like

a pendulum

jointed Limbs and their Associated

muscles tendons and ligaments work like

levers further tendons and ligaments

that cross the joints like the knees can

function like Springs when the joints

are flexed storing energy that is

released during the subsequent extension

number three walking and running mammals

require maneuverability that's the

capacity to change direction during

Locomotion it's required by both

predators and prey most cursorial

mammals they can alter their gait

momentarily such that both legs on the

same side strike the ground

simultaneously resulting in an angular

shift in the direction of the movement

some mammals can even turn their bodies

by flexing their spines while in the air

thereby altering their directions and

then lastly number four Hildebrand

argues that walking and running mammals

require endurance

endurance is going to result from the

integration of the animals

musculoskeletal systems as well as the

physiological adaptations so the

appendicular muscles of cursorial

mammals they tend to be very rich in

these fast twitch muscle fibers that are

capable of rapid and Powerful

contractions but in order to fuel those

contractions those mammals need robust

respiratory and cardiovascular systems

to support those muscles that require

that oxygen for respiration with respect

to number one support and stability

large heavy species of mammals like

elephants and uh this rotund Hip Hop

autonomous they are Grava portal meaning

that their legs are directly under the body

body

further their leg bones are columns and

their ankle and knee joints are nearly vertical

vertical

collectively this skeletal Arrangement

allows the skeleton to Bear most of that

large body mass taking the burden off of

the postural muscles that would

otherwise require large amounts of

energy to support and stabilize this

massive hippopotamus while lighter

mammals such as this deer can

energetically afford to have their limbs

positioned slightly outside of the trunk

axis it's clearly demonstrated here

they're going to rely more on these

muscles uh for their posture for their

support and stability during Locomotion

it's more energetically expensive but

it's possible because they're lighter

and it's going to provide them with much

greater maneuverability than the

hippopotamus with respect to forward

propulsion there are different

strategies different approaches to

propelling your body forward in other

words there are different Gates that

mammals are going to use for different

situations and by Gates I mean

oscillation patterns of the limbs during

forward movement so walking

pacing and trotting are all considered

symmetrical Gates as they all involve

equal spacing of the feet making contact

with the substrate with the footfalls

evenly spaced in time however in Darla

Bean like this Greyhound dog as well as

bounding the footfalls are now unevenly

spaced in time and thus are considered a

symmetrical at moderate to high

velocities these Gates can entail having

all four feet off the ground

simultaneously for a portion of the

stride as shown here so I think the best

way to Envision these different Gates is

to look at this really wonderful video

which was created uh for animators it's

one minute and 47 seconds but it's going

to clearly demonstrate the different leg patterns

patterns

as well as the footfalls used by

cursorial or running mammals to walk to

amble Pace Trot Cantor gallop and run so

please take a minute and check this out

I think you'll find it quite helpful speed

speed

is a crucial aspect of locomotion in

cursorial mammals an ability to move

faster may increase success in hunting

or escaping Predators running speed is

controlled by two components The Stride

links the distance traveled in a single

step cycle as well as the stride

frequency the rate at which one step

follows another

both stride length and stride frequency

are related to body size with larger

animals tending to take fewer but longer

strides than smaller species these

differences are going to compensate for

one another to some extent because

stride length increases with increasing

body size more rapidly than stride

frequency decreases

meaning larger animals generally run

faster than smaller ones with some

notable exceptions some of the swiftest

animals that we see the cheetah the

pronghorn antelope here in Arizona as

well as the red kangaroo the saltatorial

jumping kangaroo

they achieve stride lengths well beyond

what might be expected by looking at

their body size alone so they're hurling

themselves into this aerial phase of

Galloping and greatly increasing the

distance traveled in each step cycle

so it's one thing to have me describe

cheetah speeds of up to 80 miles per

hour it's another thing to see it so

please take the two minutes and check

out this cheetah hunting it shows great

persistence in taking out this juvenile

wildebeest please check it out jumping

and ricocheting are both forms of

saltatorial locomotion jumping involves

the use of all four feet as exhibited by

these rabbits whereas ricocheting also

known as bipedal hopping involves

propulsion using only the hind limbs

such as in kangaroos as well as the

kangaroo rats and the jumping mice

mammals that employ uh this ricochettle

motion spend much of their lives in a

bipedal position and they're going to

use those Four Paws only occasionally

for slow short distance movements if you

remember way back to my lecture on

marsupials I showed you that diagram uh

that broke down the different ways in

which kangaroos move so it might make

sense to take a look at that the forums

uh they are important uh they're

employed for manipulating objects like food

food

most mammals uh actually most

vertebrates that use saltatorial

Locomotion are jumping and ricocheting

they're actually small bodied animals

the exception being these red kangaroos

at right which can top out at close to

200 pounds

a saltatorial movement has evolved in

quite a number of different lineages the

anatomical similarities shared by

jumping and or ricocheting species are

the result of convergent evolution

recall we discussed evolutionary

convergence when we discussed fossorial

species and lecture 2.4 at that time we

were focused on gold and moles remember

convergent evolution we're going to talk

about it again and again throughout this

course is when different lineages

independently evolve

morphologically similar adaptations in

response to similar selection pressures

so species that show convergence on the

same morphology they may look similar

superficially but they may not be

genetically very closely related at all

so the principal adaptation uh when we

think about

saltatorial species is the lengthening

of one or more segments of the hind

limbs usually the tibia as well as the

development of long elastic tendons that

stretch across the knee as well as the

ankle joints

especially in the large Hoppers energy

is stored in these tendons as the limbs

recover from one jump I.E there's energy

stored when the kangaroo lands that's

released on the next propulsive jump forward

forward

small bouncing species tend to store

relatively less energy in these tendons

and ligaments but they have much uh

reduced costs of propulsion uh they have

lower uh propulsion angles in other

words they have a more vertical hop so

this is awesome some arboreal or tree

dwelling species that leap amongst the

trees when they're on the ground they're

going to use

ricocheting Locomotion so examples of

ricochetal locomotion include lemurs

like this cockerels safaka lemur here

almost looks like he's dancing as well

as Tarsiers and the white-faced sake

which is a new world primate so these

ricocheting uh arboreal uh mammals will

cling to a tree trunk with all four

Limbs and then they'll drop down to the

ground land on their hind feet and then

bound back up to another tree

primates that leap and Ricochet have

long femurs uh much longer than other

primates allowing them to make these

long leaps by increasing the lever

action of their hip muscles so please

put me on pause and check out this

unique form of locomotion for yourself

this is ricochettle Locomotion on the

ground it's going to begin at about 40

seconds into this video but really cool

to see

declining mammals use their limbs to

move about in trees that is to say they employ

employ

arboreal Locomotion and as such are

going to display a whole Suite of

corresponding adaptations uh for this

arboreal Locomotion so in species that

also spend a substantial portion of time

on the ground in addition to in trees

climbing is accomplished primarily by

the use of claws these are keratinized

claws here on this black bear

small or arboreal mammals such as

squirrels gain a steadfast hold on tree

bark with those shark Claws and they're

able to maneuver on Trunks and branches

with considerable agility larger species

such as this black bear they're going to

use their claws in a similar manner but

they're much less agile than squirrels

all of these species possess foot pads

to provide friction in gripping tree

limbs securely as well as an increased

number of sensory receptors on their

palms and souls and the ventral surfaces

of these digits

so black bears may not be as agile of

climbers as squirrels I'll give you that

but they are much better climbers than

us humans who have to use climbing gear

and climbing ropes like myself

um I may have mentioned it uh when I did

my instructor introductory video but

back in Spring of 2005 I was the uh

field crew leader for a U.S fish and

wildlife service team that was focused

on capturing and translocating

threatened Louisiana black bears that's

a subspecies of black bear with an

elongated Rostrum that's evolved to eat

acorns we were capturing these bears in

bottomland hardwoods in uh Cyprus bald

cypress swamps uh in the tensaw National

Wildlife Refuge and then we were moving

them several hundred miles to the South

and a bit to the west to the chefilia

River Basin these bears are incredible

climbers as you can see they climbed

straight up this vertical surface on

this massive bald cypress tree all the

way up to there that is the entrance to

their den right there it's about 100

feet off the ground these pictures were

shot with films so the resolution is not

great and then here this is me I've made

it up the climbing rope and now I'm

peering inside of that tree and with my headlamp

headlamp

and there's a sow down here a female

black bear she's curled up and her Cubs

are suckling but you can look down

inside this tree den and see that it's

about 10 feet deep down inside the tree

so again my point being these bears are

very good climbers this is a very good

and safe place to hibernate and have

your Cubs and and nurse your Cubs for

several months here's uh one of those

sounds uh that we collared and

translocated you can tell uh she's

obviously anesthetized we used ketamine

uh to anesthetize the Bears uh for

transport well to get them out of the

tree dens and then move them down uh to

Three Rivers in the Atchafalaya River

Basin and then here is one of the

translocated Cubs and you can tell even

at you know six weeks old these Cubs are

already very well equipped with a sharp

claws for climbing as I'm sure many of

you are aware uh many of the primates

are amazing climbers they're gonna put

those black bears to shame so with the

arboreal primates uh their digits are

more flexible they have mobile joints

but between the phalanges in the hand

which is going to allow them to grasp

branches old world monkeys and apes have

also evolved an opposable thumb which

can be rotated towards the tips of the

other digits again for grasping while

climbing there's a specialized form of

swinging through the branches called

brachiation This is particularly well

developed in the Gibbons

um so Gibbons have very large clavicles

collar bones that are actually anchored

to their sternum they have really long

for limbs obviously grasping hands they

have great big opposable toes they have

a really Stout uh pectoral girl which is

going to stabilize that shoulder joint

allowing the forelimb to Bear the weight

of the animal as it brachiates as it

swings in the trees we actually have uh

the same structure uh in our pectoral

girdle and this is a reflection of our

arboreal ancestry this is some beautiful

footage of a brachiating gibbon it's

truly impressive so when I was thinking

when making this slideshow this given

would absolutely kill it at the Spartan Race

Race

many arboreal species like primates have

long tails that they're going to

primarily use for balance uh when

maneuvering about on tree branches

however in a few species of South

American monkeys like this aptly named

spider monkey

the tail has become a prehensile

appendage used to grasp branches in the

spider monkey tail the distal portion of

the tail the end the tip of the tail has

developed these friction pads and an

increased number of tactile receptors

like the gripping hands and feet of

other climbing mammals mammals that dig

in the soil to find food or create

shelters for themselves are called

fossorial so it's useful at this point

to distinguish between the terms fossil

and fully subterranean

refers to animals with adaptations for

digging like this wombat pictured at

bottom left whereas a Subterranean

species refers to species that live

virtually their entire lives underground

like this African naked mole rat among

mammals there are far more fossorial

than Subterranean species regardless the

limbs of digging species tend to be

short and they're powered by strong

appendicular muscles to power that

digging so digging is usually

accomplished by scratching at the soil

with the Four Paws to excavate a hole or

a tunnel large enough to accommodate the

animal's body

however many fossorial rodents are going

to use their teeth their incisors as

digging tools as shown at right so

phosphoryl species that use their

incisors to dig include root rats bamboo

rats blind mole rats the pocket gophers

and the African mole rats as pictured

here they have these large incisors that

are external to the lips that are going

to allow them to dig with their teeth

while their mouths remain closed because

as we're digging we don't want to get a

big mouthful of dirt

further the eyes of subterranean species

are very small

oftentimes they're non-functional

they're vestigial meaning they're

evolutionary leftovers they have tactile

receptors uh in the snout that are very

well developed and they're going to have

the Bruce these whiskers that often will occur

occur

um all over their bodies including their

the tail the body wall the legs and then

lastly they have Subterranean mammals

have very acute senses of hearing and smell

smell

gliding has evolved independently in

several lineages of mammals including

the gliding possums which we discussed

when we went over marsupials the kalugos

which is what is pictured here kalugos

are in the order

dermoptera the uh skin wings and we're

going to talk about uh dermoptera next

in lecture 4.2 and there are also

gliding members in the order rodentia

the rodents such as the Flying Squirrels

flying in quotation marks in each of

these groups the gliding species are

arboreal and they use their gliding

ability as a means of moving uh from

tree to tree

the principal morphological adaptation

for gliding species is the patagium this

is an extension of skin that stretches

from the lateral neck and the body wall

all the way to the wrists and to the

ankles as well as the tips of the

fingers and the toes and even the tail

and the kalugos

so the animal leaps from a perch it

extends its Limbs and tail such that

this pathogium is going to act as an airfoil

airfoil

aerodynamic control during gliding and

Landing is accomplished by adjusting the

position of the limbs you can never have

too much David Attenborough can you so

this species is incredible this is the

Sunda kalugo or also called the kubong

and this guy is capable of gliding for

over 100 meters uh please check out this footage

footage

among mammals only bats the order

chiroptera have evolved true powered

flight or Volant Locomotion

interestingly with the exception of

swimming flying is actually the most

energetically efficient means of moving

a mammalian body from point A to point B

in other words you're going to cover

more ground

calorie per calorie burned when flying

compared with running or jumping or

certainly burrowing which is

energetically expensive a bat's Wing is

also a pathogium it's got this thin

membrane of skin like in the gliders but

now it's going to have skeletal support

from these really impressive

metacarpals and phalanges so the bats

are highly modified

for flight in comparison to the gliders

uh further the bats have this Broad and

slightly keeled uh sternum much like a

bird which is going to serve as the

point of attachment uh for uh the flight

muscles the pectoralis muscles the

shoulder includes a very Stout clavicle

a collarbone with a locking mechanism to

keep the joint at an appropriate angle

the radius of the bats right here is

thin and very uh elongated comparatively

but the ulna now it is reduced distal to

the Elbow meaning out here far distal

from the elbow so you can see the ulna

is only from here uh to here

at the wrist the number of carpal bones

in the wrist is reduced and those

remaining carpels have all fused into a

single bone which is going to provide a

lot more stability for the rigors of flight

flight

the first digit here is relatively

unmodified and it Bears a claw but

digits two three four and five have

greatly elongated

metacarpals as shown here

um as well as uh two or three phalanges

that are oval in cross section

the radius

and the bones of Digit two right here

those are going to support the Leading

Edge of the bat's wing while digits uh

three four and five form struts for the

trailing edge of the wing so this is a

fascinating 39 seconds it really shows

the bats Wing thrusts in slow motion so

really check this out so you can see the

mechanics of powered flight in the

chiroptera so all mammals that spend a

significant portion of time in water

like whales Dolphins manatees they

evolved from terrestrial ancestors

because water is generally cooler than

average mammalian body temperatures and

it's also more thermally conductive than

air Aquatic and marine mammals must

conserve heat when they are in the water

so most species of aquatic mammals have

thick coats of fur and or thick layers

of body fat that serve not only for

insulation but also for buoyancy in the water

water

amphibious species that are

semi-aquatic so the polar bear I think

platypuses uh the monotreams uh beavers

and muskrats the water shrew which I

showed you a video of

otters uh even moose are considered

semi-aquatic they spend a lot of time in

lakes and ponds most of these animals

these semi-aquatic mammals are equally

at home in the water as they are on land

webbing between the toes of many of

these species like in this polar bear

the webbing is going to increase the

surface area in contact with the water

which is going to Aid in propulsion the

pinnipens like seals sea lions and

walruses are fully aquatic they're only

going to move on to Terra Firma dry land

in order to breed and to give birth to

their pups the limbs of the pennipads

have evolved into flippers where all

five of the digits are encased in a

single sheath of integument of skin

in the pinnipeds their tails are absent

or rudimentary

anatomical specializations for fully

Aquatic Life reach their Pinnacle among

the marine mammals those mammals that

never come on land not to breed or to

give birth they're going to do all of

their life cycle in the water and those

include two groups the cetacea which

we'll cover later in the semester and

the Serenia the manatees and dugong

which we've already covered in the

marine mammals like the satacia this

baleen whale we see that the axial

skeleton has become simplified the

cervical vertebrae those in the neck

have become partial really fused for

stability and then the interlocking

facets uh between the trunk and the tail

vertebrae have been lost allowing for

more flexibility in that tail

the sacrum as well as the hind limbs the

femur the tibia they're gone and the

pelvic girdle uh that's all that's left

this tiny little vestigial pelvis so I

always use slides of whale skeletons in

my evidence for evolution lab and my

general biology 2 class

because of course whales evolved from

terrestrial vertebrates and this is the

evolutionary leftovers of their

terrestrial past this little vestigial pelvis

pelvis

the world Tales are modified into

horizontal flukes so they're going to

propel themselves like this uh that type

of propulsion is called dorsal ventral undulation

undulation

they're full limbs are modified into

flippers uh much like the pinnipeds

they're going to show an increase in the

number of phalanges

but these flippers they're not used for

propulsion the tail is doing all of the propulsion

propulsion

um the flippers are merely stabilizers

and they're going to allow that whale to

bank and turn so that finishes Marine

Mammal Anatomy for now we're coming back

to the whales and the Dolphins I promise

they're just too much fun

only a couple of references cited in 4.1

Hildebrand remember

um the four requirements for walking and

running next up we have lecture 4.2

which are the orders scandentia and

dermoptera so we're going to come back

to those kalugos I hope you enjoyed it

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