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Living on Land
Chapter 8
Introduction
 Tetrapods are believed to have arisen from
Sarcopterygians
 Challenges to adapt to land conditions:
 Dryness is most obvious change
 Vertebrates are mostly water
 Regulating salt/water balance on land is very different from in water
 Requires investments in water conservation mechanisms including
switching to Ureotely and uricotely
Challenges to life on Land
 Gravity becomes an impediment to support, locomotion
 Don’t have buoyancy of water to support body
 Requires major changes to skeletal system and muscle system,
to support body
 Gas exchange with air vs. water
 Oxygen availability is far much better
 Exposing thin permeable gas exchange surface to air means
potential for water loss
 Suction 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 gravity
 Bone 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 structure
 Lamela 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 bone
 Internal structure of bone; lighter and spongy
 The spongy, or Trabecular, tissue in the middle of bone and at
the end of the long bones.
Adaptations: Bone structure
 Bone joints
 Bone ends are cancellous bone are are covered by cartilage
 Reduced friction as the joint moves
 Joint is enclosed in a joint capsule containing synovial fluid for
lubrication
Axial Skeleton System: Vertebral
Column
 Vertebral 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 Vertebrae
 Operculum that connects the pectoral girdle to the skull
is lost.
 Tetrapods developed a neck
 So the cervical vertebrae
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Support head
Allows head to move independently of body for feeding
Allows head to remain stationary while animal is walking
Atlas and Axis: most anterior cervical vertebrae that confer
function to neck vertebrae
Cervical vertebrae
 The 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 column
 Thoracic vertebrae
 These bear the ribs
 Very large in
 Lumbar vertebrae
 Lost ribs
Other parts of the vertebral column
 Sacral vertebrae
 Connect to the pelvic bone
 Provides bony connection of hind limbs to vertebral column
 Enhances weight bearing
 Lets pelvic transmit propulsion from legs to trunk
 Extant amphibians have a single sacral vertebra
 Mammals have 3-5 and dinosaurs had many
 Caudal Vertebrae
 Tail end of the vertebral column
 Simple in structure
Axial Muscles
 Specialized for support of posture
 Ventilation of lungs
 Highly differentiated
 Epaxial muscles
 Primary role is postural
 Hypoxial muscles
 Differentiated into 3 layers
Epaxial and Hypoxial Muscles
 The 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 muscles
 Rib cage muscles
 For breathing
 Formed by hypoxial muscles
Hypoxial muscles
 Rectus abdominus
 On ventral side, extends from pelvic to pectoral girdle
 6-pack in humans
 Role is primarily postural as it supports the abdomen
 Transverse abdominus
 Used for exhalation of air from lungs
Appendicular skeleton
 Includes limbs and limb girdles
 strong pectoral and pelvic girdles
 All tetrapod limbs are characterized by jointed limbs bearing
 Forward pointing knee
 Backward pointing elbow
 Digit bearing hands & digit bearing feet
 Wrist and
 ankle joints or mesotarsal joints
 Feet used as holdfasts in primitive amniotes and or used as levers to propel
the animal
Basic Tetrapod skeleton:
Pelvic Girdle
 Joined to sacral vertebrae
 Made up of three bones on each side of the body that unite &
attach firmly in a bone to bone connection
 Ilium- connects pelvis to vertebrae (figure 8.5)
 Pubis
 Ischium
 Femur articulates from the joint
Basic Tetrapod skeleton:
Pectoral Girdle
 Tetrapods 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 Girdle
 Scapula & Coracoid main PG endochondral bones
 Humerus (upper arm bone) articulates the joint of these two
bones
 Humerus is also articulates the elbow joint with two more distal
bones the Ulnar and radius
 Minor bones of the PG: post opercular bones
 Clavicle (collar bone in humans):
 Cleithrum: only in extinct tetrapods
 Interclavicle: absent in birds & most mammals but present in
monotremes
Basic Tetrapod skeleton:
Pectoral Girdle
 Sternum
 Formed from endochondral bone
 Very ossified in birds and mammals
 Links lower ends of right and left thoracic ribs in amniotes
 Also called breast bone
 Clavicle 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 Girdle
 Pectoral girdle joined to vertebral column through muscles
and connective tissue.
 No direct link with vertebral column
Locomotion on Land
 Early Modes of locomotion
 Walking trot
 Opposite limbs move as a unit
 Right front/left hind
 Primitive gait seen in sharks as they move their fins
Early Modes of locomotion
 Amble
 Elephant & horses
 Each leg moves independently in succession
 Speeded up walk with at least one foot on the ground and 3 or 2
feet off the ground at any one time
 Fast Trot
 Distinct jump from off the walking trot
 Diagonal 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 locomotion
 Bound
 Jumping off the hind legs and landing on the forelimbs (figure
8.9)
 Gallop
 Modified bound seen in horses & elands
 See figure 8-9
Respiration
 Well developed lungs in amniotes
 Lungs of amphibians are simple: cutaneous resp
 Subdivided to increase surface area
 Long trachea seen in amniotes
 Branches in a series of bronchi
 Development of larger necks
 Air sucking through creation of a negative pressure in
lungs
 Expansion of the rib cage by intercostal muscles causes air
pressure to drop in lungs, leads to sucking in of air
 Diaphragm & intercostal muscles contracting humans
CARDIVASCULAR SYSTEM
 Lymphatic system well developed
 Transport lymph back into the blood
 Composed 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 heart
 Systemic circulation
 Heart and body circulation
CARDIVASCULAR SYSTEM
 Major aortic arches are retained
 Carotid arch---- supplies head
 Systemic arch----supplies body
 Pulmonary arch---- supplies Lungs
CARDIVASCULAR SYSTEM
 Skin of amphibians: loss of scales for cutaneous respiration
 Primary importance in exchange of O2 and CO2
 Pulmonary 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 SYSTEM
 Ventricular Septum
 Divides L & R ventricles
 Absent in non-amniotes
 Seen in all amniotes
 Permanent in mammals
CARDIOVASCULAR SYSTEM
 Blood pressure low in modern amphibians and non-avian reptiles
 Ventricles allow mixing of O2 rich and O2 poor blood
 No coronary arteries. Enough O2 diffuses into the heart muscles
 Coronary arteries present in birds & mammals
 Supply O2 to ventricles & muscles
 Higher blood pressure
 O2 rich and O2 poor blood do not mix due to permanent septum
Sensory System: Vision
 Tetrapods have flatter lenses than fishes
 Cornea used to focus light on retina
 Tetrapods focus by changing lens shape, but fishes focus by
moving the position of lens
 Eyes characterized by
 Eyelids, lubrication glands, tear producing lacrimal glands,
nasolacrimal glands to drain eye tears into nose
Sensory System: Hearing
 Lateral line system lost in all tetrapods
 Tympanum (ear drum) receives sound
 Passes 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: Hearing
 Middle ear is not air tight
 Passage that connects middle ear to the mouth or pharynx is
called the Eustachian Tube.
 derived from spiracles of fishes
 Allows passage of air in out of the middle ear
 Can get blocked and cause pain plus reduction in auditory
sensitivity
Sensory System :Olfaction
 Olfactory epithelium
 Smell receptors on nasal cells
 Well 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 :Olfaction
 Jacobson Organ/Vomeronasal Organ
 An olfactory organ in the roof of the mouth of tetrapods
 Sensitive to chemicals in the air
 Snakes 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: Proprioreception
 A neural mechanism that senses the position of the limbs
in space. A derived character is tetrapods
 Set of senses that monitor body and limp positiondetermine 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: Skin
 Epidermal 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 amphibians
 Resist physical wear & tear, waterproofing effects
 But lipids in skin limit water loss
Thermoregulation
 Usually internal body temperatures > air temp
 Heat produced through endothermy or ectothermy
 Heat exchange with the environment is important in both
cases
Heat exchange with Air
 Radiation
 Animals gain solar radiation directly from sun
 Indirectly when reflected from atmosphere and other objects in the
environment (fig 8-18)
 Infrared radiation
 Convection
 Heat exchange between animals and air
 Animals gain or lose depending on relative temperature of air
 Usually loose heat through convection since their body temperature is
higher than air temperatures
 Insulation with fur & feathers reduced convective heat loss
Heat exchange with Air
 Conduction
 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 Air
 Evaporation of water from body surface
 Always results in heat loss from the animal
 Sweating, panting, and bathing are adaptations to increase
evaporative heat loss to prevent overheating
Heat exchange with Air
 Metabolic Heat Production
 Trivial in ectotherms
 Derive heat (in) directly from solar energy
 Endotherms 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 ectotherms
 Through their behaviors
 Movement back & forth between shaded and sunny
sports
 Seen in lizards. Bask in sun early morning, avoid windy areas.
Seen in shade in mid hot days
 Orienting body toward sun
 To capture max solar radiation
 Lizards either spread ribs to gain heat or fold ribs to minimize
heat gain
Thermoregulation by Ectotherms
 Color change
 Lizards darken or lighten by moving dark pigment in their skin
 Melanophores are adjusted in terms of their position under skin
Activity Temperature Range
 This is the body temperature maintained by an ectothermal
animal when it is thermoregulating
 Lizards: 33-38 degrees Celsius
 Snakes: 28-34 degrees Celsius
PHYSIOLOGICAL EFFECTS ON TEMP
REGULATION
 Read on effects of the following
 Nutritional Status
 Pregnancy
 Infections
 Read last 2 sections on pages 192-195