Chapter 8

Living on Land

IntroductionTetrapods are believed to have arisen

from SarcopterygiansChallenges to adapt to land conditions:

Dryness is most obvious changeVertebrates are mostly waterRegulating salt/water balance on land is very

different from in waterRequires investments in water conservation

mechanisms including switching to Ureotely and uricotely

Challenges to life on LandGravity becomes an impediment to

support, locomotionDon’t have buoyancy of water to support bodyRequires major changes to skeletal system and

muscle system, to support bodyGas exchange with air vs. water

Oxygen availability is far much betterExposing thin permeable gas exchange

surface to air means potential for water lossSuction feeding is no longer an option

Can’t suck in food with water, so need new feeding mechanisms

Adaptations: Bone structure (figure 8.1)Skeletal system is composed of bone

which is rigid to resists force of gravityBone made up of Haversian systems

the basic unit of structure in compact bone, consisting of a Haversian canals and the concentrically arranged lamellae of bone surrounding the canal.

Within the Haversian canals lie the neurovascular components supplying the bone.

Adaptations: Bone structureLamela bone

Form the external of bone– concrete" of the bone, dense compact– A lamellar unit is composed of five sub layers. Each

sub layer is an array of aligned mineralized collagen fibrils.

Cancellous boneInternal structure of bone; lighter and spongyThe spongy, or Trabecular, tissue in the

middle of bone and at the end of the long bones.

Adaptations: Bone structureBone joints

Bone ends are cancellous bone are are covered by cartilage

Reduced friction as the joint movesJoint is enclosed in a joint capsule containing

synovial fluid for lubrication

Axial Skeleton System: Vertebral ColumnVertebral column

For most vertebrae, the contacts between the centra alone do not provide enough stability, so there are extra articular surfaces between adjacent vertebrae. These are called the zygapophyses (sometimes just called ``zygs'' for short).

Thus the vertebra are locked together by articular processes (bones) called zygapophyses

Vertebral Column (zygapophyses)

There are two pairs of zygapophyses on each vertebra, all of them located above the centrum.

The prezygapophyses are in front on the neural spine (one each on the left and right), and their articular surfaces face forward, upward and inward (or craniodorsomedially, if you like).

The postzygapophyses are behind the neural spine, with their articular surfaces facing backwards, downward and outward (or caudoventrolaterally).

Vertebral Column (zygapophyses)The zygs allow the vertebral column to act

like a suspension bridge, bearing the weight of the animal and transferring it to the limbs

Allow vertebral column to resist gravity

Cervical VertebraeOperculum that connects the pectoral

girdle to the skull is lost.Tetrapods developed a neckSo the cervical vertebrae

Support headAllows head to move independently of body

for feedingAllows head to remain stationary while

animal is walkingAtlas and Axis: most anterior cervical

vertebrae that confer function to neck vertebrae

Cervical vertebraeThe atlas is the first cervical (neck) vertebra

which is just under the head;The axis is the second cervical vertebra; it

has what is called the odontoid process about which the atlas rotates.

The joint between the atlas and axis is a pivot type of joint. It allows the head to turn from side to side. It is also called the atloaxoid joint.

Other parts of the vertebral columnThoracic vertebrae

These bear the ribsVery large in

Lumbar vertebraeLost ribs

Other parts of the vertebral columnSacral vertebrae

Connect to the pelvic boneProvides bony connection of hind limbs to vertebral

columnEnhances weight bearingLets pelvic transmit propulsion from legs to trunkExtant amphibians have a single sacral vertebraMammals have 3-5 and dinosaurs had many

Caudal VertebraeTail end of the vertebral columnSimple in structure

Axial MusclesSpecialized for support of postureVentilation of lungsHighly differentiatedEpaxial muscles

Primary role is posturalHypoxial muscles

Differentiated into 3 layers

Epaxial and Hypoxial MusclesThe epaxial muscles of the trunk in tetrapods

provide support only and become reduced in later vertebrates;

In the shark for example the epaxial and Hypoxial muscles mainly assist in locomotion.

The Hypoxial muscles are less segmented than the epaxial muscles and are more developed than in earlier vertebrates.

The Hypoxial muscles include the subvertebrals, that contract the vertebra; the rectus abdominis, that gives support to the abdomen; and the lateral group, which serves to compress the abdomen.

Coastal musclesRib cage musclesFor breathing Formed by hypoxial muscles

Hypoxial musclesRectus abdominus

On ventral side, extends from pelvic to pectoral girdle

6-pack in humansRole is primarily postural as it supports the

abdomenTransverse abdominus

Used for exhalation of air from lungs

Appendicular skeletonIncludes limbs and limb girdles

strong pectoral and pelvic girdlesAll tetrapod limbs are characterized by jointed

limbs bearing Forward pointing kneeBackward pointing elbowDigit bearing hands & digit bearing feetWrist and ankle joints or mesotarsal jointsFeet used as holdfasts in primitive amniotes and or

used as levers to propel the animal

Basic Tetrapod skeleton: Pelvic GirdleJoined to sacral vertebraeMade up of three bones on each side of the

body that unite & attach firmly in a bone to bone connectionIlium- connects pelvis to vertebrae (figure

8.5)PubisIschium

Femur articulates from the joint

Basic Tetrapod skeleton: Pectoral GirdleTetrapods show loss of the skull bone,

freeing the shoulder from skull, thus allowing a flexible neck

In bony fishes, the PG & forelimbs are attached to the back of the head via the opercular and gular bones which are not present in tetrapods

Pectoral girdle is freed from dermal skull roof

Basic Tetrapod skeleton: Pectoral GirdleScapula & Coracoid main PG

endochondral bonesHumerus (upper arm bone) articulates the joint

of these two bonesHumerus is also articulates the elbow joint with

two more distal bones the Ulnar and radiusMinor bones of the PG: post opercular

bonesClavicle (collar bone in humans): Cleithrum: only in extinct tetrapodsInterclavicle: absent in birds & most mammals

but present in monotremes

Basic Tetrapod skeleton: Pectoral GirdleSternum

Formed from endochondral boneVery ossified in birds and mammalsLinks lower ends of right and left thoracic ribs

in amniotesAlso called breast boneClavicle connects with sternum (e.g. in

humans) or Sternum also connects to interclavicle in

other animals that still possess the interclavicle

Basic Tetrapod skeleton: Pectoral GirdlePectoral girdle joined to vertebral column

through muscles and connective tissue.No direct link with vertebral column

Locomotion on LandEarly Modes of locomotionWalking trot

Opposite limbs move as a unitRight front/left hind

Primitive gait seen in sharks as they move their fins

Early Modes of locomotionAmble

Elephant & horsesEach leg moves independently in successionSpeeded up walk with at least one foot on

the ground and 3 or 2 feet off the ground at any one time

Fast TrotDistinct jump from off the walking trotDiagonal pairs of limbs are moved together

with a period of suspension between each pair of limb movements when all four feet are off the ground

Early Modes of locomotionBound

Jumping off the hind legs and landing on the forelimbs (figure 8.9)

GallopModified bound seen in horses & elandsSee figure 8-9

RespirationWell developed lungs in amniotesLungs of amphibians are simple: cutaneous

respSubdivided to increase surface areaLong trachea seen in amniotes

Branches in a series of bronchiDevelopment of larger necks

Air sucking through creation of a negative pressure in lungsExpansion of the rib cage by intercostal muscles

causes air pressure to drop in lungs, leads to sucking in of airDiaphragm & intercostal muscles contracting humans

CARDIVASCULAR SYSTEM Lymphatic system well developed

Transport lymph back into the bloodComposed of lymph nodes (concentration of

lymphatic tissues ) WBC found in lymph vessels

Double cardiovascular system (Figure 8.11)Pulmonary Circulation

Gas exchange between lungs and heartSystemic circulation

Heart and body circulation

CARDIVASCULAR SYSTEMMajor aortic arches are retained

Carotid arch---- supplies headSystemic arch----supplies bodyPulmonary arch---- supplies Lungs

CARDIVASCULAR SYSTEM Skin of amphibians: loss of scales for

cutaneous respirationPrimary importance in exchange of O2 and

CO2Pulmonary arch is a pulmocutaneous arch

Has a major cutaneous artery that branches off the pulmonary artery to supply the skin: carries O2 poor blood to skin

Cutaneous vein carries oxygen rich blood from the skin to the systemic circulation heart’s via left and right atrium into ventricle which is undivided.

CARDIVASCULAR SYSTEMVentricular Septum

Divides L & R ventriclesAbsent in non-amniotesSeen in all amniotesPermanent in mammals

CARDIOVASCULAR SYSTEMBlood pressure low in modern amphibians and

non-avian reptilesVentricles allow mixing of O2 rich and O2 poor

bloodNo coronary arteries. Enough O2 diffuses into

the heart musclesCoronary arteries present in birds & mammals

Supply O2 to ventricles & musclesHigher blood pressureO2 rich and O2 poor blood do not mix due to

permanent septum

Sensory System: VisionTetrapods have flatter lenses than fishesCornea used to focus light on retinaTetrapods focus by changing lens shape,

but fishes focus by moving the position of lens

Eyes characterized byEyelids, lubrication glands, tear producing

lacrimal glands, nasolacrimal glands to drain eye tears into nose

Sensory System: HearingLateral line system lost in all tetrapodsTympanum (ear drum) receives soundPasses sound to oval window through a

series of bones (stapes) that will vibrate (middle ear) to the Cochlea (or lagena)

organ of Corti is housed in cochlea and contains hair cells that send impulses to CNS

Sensory System: HearingMiddle ear is not air tightPassage that connects middle ear to the

mouth or pharynx is called the Eustachian Tube.derived from spiracles of fishesAllows passage of air in out of the middle earCan get blocked and cause pain plus

reduction in auditory sensitivity

Sensory System :OlfactionOlfactory epithelium

Smell receptors on nasal cellsWell developed in some mammals but poor

in primates (e.g. humans)Turbinates: small bones in nasal passages

that increase surface area of Olfactory epithelium. Covered by moist tissue that warm and humidify inspired air.

Poor sense of smell due to small snouts which are too short to accommodate large turbinates and more olfactory epithelium

Sensory System :OlfactionJacobson Organ/Vomeronasal Organ

An olfactory organ in the roof of the mouth of tetrapods

Sensitive to chemicals in the airSnakes flick tongues in and out of their

mouths to capture molecules in the air and transfer them to this organ

Hoofed male animals sniff or taste the urine of females to assess stage of reproductive cycle

May result in flehman (see pages 186- 187)

Sensory System: ProprioreceptionA neural mechanism that senses the

position of the limbs in space. A derived character is tetrapods

Set of senses that monitor body and limp position-determine posture and balance

Can touch our nose with eyes closed due to proprioreception in our arms

Mostly found in limbs. Include muscle spindles that determine amount of stretch in muscles, tendons and organs

Water conservation in a dry environment: SkinEpidermal cells make keratin that fills

the cells ( keratin = Insoluble protein)Cell layers of keratinized epidermal cells

Form the stratum corneum Many layers deep in amniotes, but thin in

amphibiansResist physical wear & tear, waterproofing

effectsBut lipids in skin limit water loss

ThermoregulationUsually internal body temperatures > air

tempHeat produced through endothermy or

ectothermyHeat exchange with the environment is

important in both cases

Heat exchange with Air Radiation

Animals gain solar radiation directly from sunIndirectly when reflected from atmosphere and other

objects in the environment (fig 8-18) Infrared radiation

ConvectionHeat exchange between animals and airAnimals gain or lose depending on relative

temperature of airUsually loose heat through convection since their body

temperature is higher than air temperaturesInsulation with fur & feathers reduced convective heat

loss

Heat exchange with AirConduction

Animals can loose or gain heat from ground or other objects in which they are in contact depending on relative temps

Animals lose heat when warmer than contacted object

Animals gain heat when colder than contacted object

Lizards gain heat from warm ground

Heat exchange with AirEvaporation of water from body surface

Always results in heat loss from the animalSweating, panting, and bathing are

adaptations to increase evaporative heat loss to prevent overheating

Heat exchange with AirMetabolic Heat Production

Trivial in ectothermsDerive heat (in) directly from solar energyEndotherms derive heat mostly from

metabolism but their routes of energy exchange with the environment are same as ectotherms, thus must be balanced to maintain stable body temperature

Thermoregulation by ectothermsThrough their behaviorsMovement back & forth between shaded

and sunny sportsSeen in lizards. Bask in sun early morning,

avoid windy areas. Seen in shade in mid hot days

Orienting body toward sunTo capture max solar radiationLizards either spread ribs to gain heat or fold

ribs to minimize heat gain

Thermoregulation by EctothermsColor change

Lizards darken or lighten by moving dark pigment in their skin

Melanophores are adjusted in terms of their position under skin

Activity Temperature RangeThis is the body temperature maintained by

an ectothermal animal when it is thermoregulatingLizards: 33-38 degrees CelsiusSnakes: 28-34 degrees Celsius

PHYSIOLOGICAL EFFECTS ON TEMP REGULATIONRead on effects of the following

Nutritional StatusPregnancyInfections

Read last 2 sections on pages 192-195