lec 18- amniotes

Question 1

how did the skull change in amniotes?

Answer 1

-changes in jaw muscle attachment to the skull
-several lineages developed openings in the skull called temporal fenestra

Question 2

what did temporal fenestrae allow for?

Answer 2

-allowed the jaw muscles to exit the skull and attach to the outer surface of cranium
-allowed for stronger jaw and made it more sufficient

Question 3

did temporal fenestrae evolve independently several times?

Answer 3

yes

Question 4

what did cranio-vertebral joints allow for?

Answer 4

head movement

Question 5

how is the head movement in fish?

Answer 5

-amphicoelus vertebrae
-cranial-vertebral joint had little mobility

Question 6

how is the head movement of amphibians?

Answer 6

-have a convex pair of occipital condyles which insert into concave vertebrae (atlas)
-allows up and down head movement

Question 7

how is the head movement of amniotes?

Answer 7

-increased flexibility and movement
-atlas and axis + other modifications of cranio-vertebral joint

Question 8

what is the cranio-vertebral joint?

Answer 8

a joint between two vertebrae

Question 9

what is the proatlas?

Answer 9

-a modified vertebrae which is basically a neural arch
-is the remainder of vertebrae fused to the skull, seen in reptiles but absent in most mammals

Question 10

what is the atlas? what does it contain

Answer 10

-vertebrae 1
-contains neural arch and intercentrum

Question 11

is the intercentrum only found in the atlas?

Answer 11

yes, absent in other vertebrae

Question 12

what is the axis? what does it contain?

Answer 12

-vertebrae 2
-contains pleurocentrum from the atlas (vertebrae 1, absent in atlas)
-contains neural arch
-cotains pleurocentrum of axis

Question 13

what is the odontoid process?

Answer 13

the fusion of the pleurocentrum of the atlas into the axis

Question 14

what are higher vertebrates?

Answer 14

-birds, reptiles, and mammals

Question 15

what does interlocking of elements in the skull, atlas and axis joint provide?

Answer 15

-more strength and stability to vertebrae
-maintain flexibility and rotation of skull

Question 16

what are the advantages of the increased flexibility of the cranio-vertebral joint?

Answer 16

-increased feeding oppurtunities
-repositioning head improves the use of sensory organs

Question 17

what are stem reptiles similar to?

Answer 17

-similar to non-amniotic tetrapods

Question 18

what were the type of limbs stem reptiles had and how were they positioned? how did they move?

Answer 18

-short legs
-proximal element of limb at right angles to body
-movement by thrust of limbs and body undulation

Question 19

did amniotes evolve appendicular skeletons more suitable for terrestrial environments?

Answer 19

yes

Question 20

Was there a reduction in the number of bones in the pectoral girdle? what did this help with?

Answer 20

yes
-helped with less weight and more mobility

Question 21

the pelvic girdle improved Anchorage of what?

Answer 21

the hind limbs

Question 22

how many vertebrae was the pelvic girdle originally attached to?

Answer 22

1

Question 23

in amniotes, did more vertebrae attach to the pelvic girdle over time?

Answer 23

yes

Question 24

what are the three bones in the pelvic girdle? what does sit provide?

Answer 24

-ilium, ischium, pubis
-ilium and pubis face downward
-provide greater leverage for muscles and greater range of movement

Question 25

what was the benefit to limbs being below the body? what two ancestors had the limbs below the body?

Answer 25

-more efficient support and locomotion -therapsids (ancestor to mammals) -archosaurs (dinosaurs, ancestors to birds)

Question 26

how is locomotion in advanced amniotes like birds and mammals and how is it in reptiles?

Answer 26

-advanced: elbows face backwards and knees face forwards to allow feet to face forward and provide faster and more efficient locomotion -reptiles: locomotion similar to early amniotic tetrapods (limbs face outward)

Question 27

what did scales allow for?

Answer 27

keratinized scales increased the ability of amniotes to live in terrestrial environments

Question 28

what are the 2 layers of skin in vertebrates?

Answer 28

-epidermis (outer layer, has several layers, derived from ectoderm) -dermis (deeper layer, derived from mesoderm)

Question 29

what are the 2 layers in the epidermis?

Answer 29

-stratum corneum: dead outer layer made of keratin -stratum germinativum: living inner layer

Question 30

what is fish skin made of?

Answer 30

-epidermis -dermis: acellular bony scales embedded in the layer (derived from ostracoderms)

Question 31

what is amphibian skin made of?

Answer 31

-lacks bony plates -epidermis is thin -stratum corneum is thin with little keratin -mucus gland -needs moisture

Question 32

what is reptile skin made of?

Answer 32

epidermis forms a complete body covering of keratinized scales -epidermis consist of both stratuses with the stratus corneum being very thick

Question 33

what occurs during molting?

Answer 33

-stratum germinativum proliferates to form a new set of inner epidermal layers -outer epidermal layer separates at the separation zone -outer skin is shed -upper cells die, dry out and form the new scales

Question 34

how is the formation of scales done?

Answer 34

folds in the outer layer form scales -each bump consists of epidermis and underlying dermis called papilla -papilli have different growth with outer layer growing faster then inner resulting in stratum corneum becoming thicker and one scale overlapping on the next

Question 35

what is the function of scales?

Answer 35

-thick layer of keratin reduces water loss resulting in less dependence on moisture in the environment -protection from abrasion

Question 36

what is the stem amniote family? what did it lead to?

Answer 36

-cotylosauria -lead to amniotia and diadectomotphs

Question 37

what is an amniotic egg?

Answer 37

several extra-embryonic membranes which allows development independent of water

Question 38

is the development of the amniotic egg as significant as jaw evolution in vertebrates?

Answer 38

yes

Question 39

what are the characteristics of a reptile telolecithal eggs?

Answer 39

-large amount of yolk that is unevenly distributed -snall amount of protoplasm in germinal disc -cleavage only occurs in germinal disc (meroblastic cleavage)

Question 40

how does development of the amniotic egg occur?

Answer 40

-periphery of disc spreads out over yolk -eventually covers entire yolk (yolk sac) -yolk sac is infiltrated by blood vessels for nutrients -other extra-embryonic membranes expand over the embryo to form coelom between the two layers (coelom is the space between embryo and membrane layers)

Question 41

what are the 4 membrane layers in amniotic eggs?

Answer 41

-yolk sac -amnion which envelopes the embryo -chorion which is the outer layer -allantois

Question 42

are cavities in the amniotic egg fluid filled?

Answer 42

yes

Question 43

what are the 3 advantages of the layers in the amniotic egg?

Answer 43

1. provides the embryo with fluid medium for development (embryo floats, no compression from gravity) 2. protects the embryo from dessication 3. fluid is a shock absorber (even pressure on all sides)

Question 44

what are some problems for the embryo?

Answer 44

-isolates the embryo from the environment -chorion and amnion prevent embryo from being near surface so no access to oxygen -problems with gas exchange -no means of disposing of nitrogenous wastes

Question 45

what does the allantois do? how does it develop?

Answer 45

-stores wastes -develops from hind gut of embryo -forms the allantoic sac -expands very rapidly to fuse with chorion -develops blood vessels on the surface which are connected to the umbilical cord -also the respiratory organ for the embryo

Question 46

what are the 6 successes of amniotic tetrapods?

Answer 46

1. amniotic egg ended the dependence on water for reproduction 2. keratinized epidermis 3. better jaw operation (jaw muscle attachment) 4. better locomotion 5. changes to head articulation for better hunting 6. dominate vertebrate life on land during mesozoic era