Post-Midterm Material Flashcards
(130 cards)
1
Q
What is a cleidoic egg?
A
- A key feature of an amniote.
- Has a semi-permeable shell which allows gases to pass (oxygen and carbon dioxide), but keeps fluids inside.
- Has extra-embryonic membranes.
2
Q
What is the purpose of the extra-embryonic membranes of a cleidoic egg?
A
- Protection and gas transfer: chorion surrounds the embryo and yolk sac, amnion surrounds the embryo with water.
- Respiration and waste storage: Allantois fills with waste as yolk proteins are used.
3
Q
What is the importance of the cleidoic egg?
A
- Allowed for the full development of an organism on land.
- Allowed the embryo to become larger before hatching, allowing more energy to be invested in each egg.
4
Q
What are some derived features of amniotes (besides the cleidoic egg)?
A
- Low skin permeability
- Greater variety of skin elaborations.
- Presence of a lipid. - Costal (rib) ventilation of the lungs
- allows for a long neck (buccal pump muscles not
needed).
- space for elaboration of nerves that supply the
forelimb.
5
Q
Describe the amniote axial skeleton.
A
- Regionalization of the vertebral column is expanded.
- Lumbar ribs lost in some amniotes.
- No ribs in the way of hindlimb movement.
- Allowed vertical plane flexion of the column.
- Easier limb oscillation.
- Rapid locomotion.
6
Q
Describe the atlas and axis vertebrae in amniotes.
A
- Atlas and axis have reduced centrum and processes.
- Skull-atlas joint: Vertical nodding and horizontal tilting of the head.
- Atlanto-axial joint: twisting movement.
- Maintains bony strength of neck while allowing cranial mobility.
7
Q
How are trunk vertebrae positioned in amniotes?
A
Trunk vertebrae are held in a archer’s bow-like arch by abdominal muscles and sternum.
8
Q
How are cervical vertebrae positioned in amniotes?
A
Cervical vertebrae are held in a violin-bow-like reversed arch by neck ligaments.
9
Q
How has gravity changed body support in amniotes?
A
- Body is suspended between legs with vertebral column as a “bridge” between support posts.
- Requires a firm vertebral column.
- Direction and height of vertebral neural spines modified to deal with mechanical forces acting on the vertebral column.
10
Q
How did limb posture change in early amniotes?
A
- In many mammals and dinosaurs, limbs are situated under the body for increased efficiency of limb swing during locomotion.
- Digits and limbs rotated inward, made forward thrust better aligned with the direction of movement.
11
Q
What is anapsid fenestrae?
A
No temporal fenestrae present (earliest amniotes and turtles).
12
Q
What is synapsid fenestrae?
A
One lower temporal fenestra (extinct synapsids and mammals).
13
Q
What is diapsid fenestrae?
A
Two temporal fenestrae (reptiles and birds).
14
Q
What is euryapsid fenestrae?
A
One upper temporal fenestra (marine dinosaurs).
15
Q
Describe the parallel evolution of and differences between the two approaches to terrestrial life (Synapsids vs Sauropsids).
A
Parallel Evolution:
- fast-moving predators
- flight
- endothermy
- extensive parental care and complex social behaviour.
Differences:
- solutions to repiratory/locomotion conflict.
- solutions to high rate of gas exchange/conserve water conflict.
- body insulation
- excretory system
16
Q
How can amphibious fish survive in air for months?
A
- Gas exchange through skin.
- Air gulping.
- Gills non-functional.
17
Q
What is sauropsida?
A
- A group of amniotes known as “lizard faces.”
- Includes anapsids (turtles) and diapsids.
18
Q
Describe the testudine group of anapsids (turtles).
A
- Present by the late Triassic.
- Hard shell and toothless skull hasn’t changed.
- Dorsal carapace and ventral plastron attached on the sides.
19
Q
What is the origin of the turtle body plan?
A
Shell: [vertebrae + ribs + osteoderms] + scutes (keratin)
Position of scapula: inside of rib cage.
Two hypotheses:
- The classic transformationalist view
- gradual transformation - The emergentist view
- rapid evolution via changes in developmental regulation.
20
Q
Describe the Sauropsid first diapsids.
A
- Origins in Carboniferous period.
- Includes Petrolacosaurus
- Smaller head, longer limbs and neck than earliest amniotes.
- skull has larger orbits and two fenestrae.
21
Q
Describe the Lepidosauromorphs/Lepidosauria Sauropsids.
A
- Extinct forms leading to Squamates (lizards and snakes).
- Oldest lizards present from mid-Jurassic, snakes from early Cretaceous.
- Relationship between legless forms (snakes) and lizards is uncertain.
- Origin of snakes is still debated.
22
Q
Describe the skull adaptations in squamates.
A
- Lower temporal bar absent in lizards, upper and lower absent in snakes (improved jaw mobility and swallowing).
- Cranial kinesis (mobility) in lizards modified jaw mechanics.
- Snout tips up when jaws open, tips down when jaws close.
23
Q
What is lateral undulation?
A
A form of crawling locomotion (limbless). Moving waves push sideways against contact points (min. 3), generating a reaction force with a forward component.
24
Q
What is concertina movement?
A
A form of crawling locomotion (limbless), but costly, and only used in narrow spaces (tunnels). Stationary coils wedge the animal into place while free body parts move forward.
25
What is sidewinding?
A form of crawling locomotion (limbless), used over sandy soil. Body contacts 2-3 straight tracks at a time with different segments in succession as they are released from the previous track.
26
What is rectilinear movement?
A form of crawling locomotion (limbless) used by many snakes and all amphisbaenians. Requires specialized muscles progressively lifting and bringing forward ventral scutes to peg them onto the ground. Where the body is not in contact with the ground, the body is moved forward within the distensible skin.
27
Describe the Sauropterygia Sauropsids.
- Aquatic reptiles of the Mesozoic with euryapsid skulls.
| - Plesiosaur locomotion: swims using "paddles."
28
Describe the Ichthyosaur Sauropsids.
- Mesozoic group of fish/dolphin-like predators.
- Euryapsid skull.
- Dominant in Jurassic seas, but phylogenetic position is uncertain.
29
Describe Archosauromorph Sauropsids.
- Small groups and the archosaurs ("ruling reptiles"), a very large group.
- Archosaurs include crocodilians, dinosaurs, birds and related groups.
30
Describe the Pterosaur group of Archosaurs.
- First group of vertebrates to evolve powered flight using membranous wings supported by an elongated forelimb.
- Late Triassic.
- Early forms had long tails and teeth.
- Later forms lost teeth and got a crest on their head.
31
Describe the Dinosaur group of Archosaurs.
- Radiation started in late Triassic.
- Two major groups, Saurischia and Ornithischia, distinguished by structure of pelvic girdle.
- Saurischians: girdle bones radiate outward from centre.
- Ornithischians: ischium and part of pubis are parallel and project backward.
32
What are the main groups of Saurischians (group of dinosaurs)?
1. Sauropodomorphs: mostly herbivorous (e.g. Diplodocus).
2. Theropods: mostly carnivorous, bipedal (e.g. Tyrannosaurus and Velociraptor).
3. Birds likely evolved from therapods.
33
What are some skeletal adaptations of giant dinosaurs?
- Shortened, pillar-like limbs (weight support).
- Reduction/shortening of wrists/fingers and ankles/toes.
- Elongated necks (more, longer, and lighter cervical vertebrae).
34
What are the main groups of Ornithischians (group of dinosaurs)?
1. Thyreophorans: e.g. anklyosaurs and stegosaurs.
2. Ornithopods: e.g. duck-billed dinosaurs (able to chew).
3. Pachycephalosaurs: 'head-butting' dinosaurs.
4. Ceratopsians: e.g. triceratops.
(All groups are herbivorous).
35
Why were dinosaurs so successful?
- Their evolutionary rivals, Crurotarsans, died out by chance.
- Dinosaurs filled the ecological niches with their specialized adaptations.
36
What are the hypotheses for the origin of flight?
The classics:
1. Arboreal Hypothesis: gliding from tree to tree.
2. Cursorial Hypothesis: running start and lifted off the ground for insect foraging.
New ideas:
1. Used wings to scale inclined objects and trees.
37
What are the skeletal adaptations of birds?
1. Skull: Reduced number and thinner bones, no teeth, light weight.
2. Exceptional flexibility of neck: Compensates for loss of forelimbs, heterocoelus cervical vertebrae.
3. Very rigid backbone: Minimizes number of muscles needed to maintain streamlined body during flight, reducing energy consumption.
4. Pelvic girdle fused with synsacrum: bipedal, no symphysis, large pelvic outlet for massive eggs.
5. Sternum: ossified and well pronounced keel to provide attachment for flight muscles.
38
Compare reptile glands to bird glands.
Reptile: Fewer glands and all are granular (pheromones).
Bird: One large integumentary alveolar gland, and uropygial glands (secrete oil for feathers).
39
Compare reptile scales to bird scales.
Reptile:
- Well developed epidermal keratinized (horny) scales.
- Shed regularly.
- Functions: locomotion, protection.
Birds:
- Epidermal scales confined to places without feathers.
- Claws derived from scales.
- Beaks derived from scales.
- Feathers for locomotion and thermoregulation.
40
Describe the evolution of synapsids.
Pelycosaurs => Therapsids => Cynodonts => Mammals
41
Describe the early Pelycosaurs.
- Arose in late Carboniferous, radiated in early Permian.
- Dominant carnivores, some herbivores as well.
- Single temporal opening and posterior orbit.
42
What is the difference between carnivorous and herbivorous Pelycosaurs?
Carnivorous:
- Moderate size (0.5-3 m), large sail along the back.
- e.g. Dimitredon.
Herbivorous:
- Blunt teeth.
- Laterally expanded rib cage suggesting a large gut used in fermentation of plant material.
- e.g. Edaphosaurus
43
Describe early Therapsids.
- Evolved in early Permian and radiated in late Permian, replacing Pelycosaurs.
- Dominant until the end of the Triassic.
- Earliest forms displayed enlarged fenestrae and reduction of palatal teeth.
44
What are the two main groups of Therapsids?
1. Dinocephalians
- Large animals with heavy skulls (head-butting).
- Began a trend towards more erect limbs.
2. Gorgonopsians
- Dominant carnivores of late-Permian after extinction of dinocephalians.
- Varied from dog to rhino-sized.
- More terrestrial than Pelycosaurs and greater diversity in body design.
45
Describe Cynodonts.
- Arose in late Permian, radiated mostly in Triassic.
- Changes in jaw muscles allowed chewing.
- Adductor differentiates into masseter and temporalis muscles, expand and invade larger areas of skull.
- Semi-erect hind limb closer to the body.
46
Describe early mammals.
- Arose in late Triassic from Cynodont ancestors.
- Small shrew-like animals in Jurassic and Cretaceous.
- Characteristics:
- Feed young milk from mammary glands.
- Extended parental care of young.
- Large brain to body size ratio.
- Hair
47
What are the two types of integument glands in mammals?
1. Sebaceous glands: alveolar, oil secretion, often for hair. They waterproof hair and prevent thin skin from drying.
2. Sweat glands: tubular, secret water, salt and urea. Used for thermoregulation.
48
What are the parts of the mammal middle ear?
Malleus, incus, and stapes.
49
What are the parts of the mammal lower jaw?
Only a single bone, the dentary.
50
What are the parts of the mammal jaw joint?
Dentary and squamosal bones.
51
What is the regional differentiation of vertebrae in mammals?
- Cervical: reduction of ribs, 7 cervial vertebrae, best at rotation.
- Thoracic: ribs.
- Lumbar: below ribs/no ribs attached.
- Sacral: articulate with pelvic girdle.
Caudal: presence of hemal arch (tail).
52
Describe the living group of mammals, Monotremes.
- Platypus and echidnas.
| - Shair hair, endothermy and sucking of young with other mammals, but don't have nipples or external ears, and lay eggs.
53
Describe the living group of mammals, Marsupials.
- Predominantly in Oceania, but some in the Americas.
| - Young grow in mother's pouch.
54
Describe the living group of mammals, Placentals.
- Most diverse and widespread group of mammals.
- Radiated in Palaeocene after K-T event.
- Prolonged gestation of embryo in uterus.
55
What are the four groups of Eutherians?
1. Afrotheria.
2. Xenarthra.
3. Euarchontoglires.
4. Laurasiatheria.
56
Describe the living group of mammals, Afrotheria.
- Evolved in Africa after breaking from South America.
| - Extant species: elephants, golden moles, aardvarks.
57
Describe the living group of mammals, Xenartha.
- Diversified in South America after breakup.
- Extant species: armadillos, sloths and ant-eaters.
- Extinct species: giant armadillo-like creatures and giant ground sloths.
58
What are some characteristics of primates?
- Agile in trees (grasping hands and feet, sensitive finger pads).
- Large brain to body size ratio.
- Good binocular vision.
- Enhanced parental care.
59
How did humans evolve from primates?
- Bipedalism
- Sideways hip joint.
- Straight knee joint.
- Longer leg bones.
60
Describe cutaneous respiration in amphibians.
- Low keratinization of skin allows for efficient gas exchange, but causes water loss in air.
- Water or moisture needed to maintain integument.
- Blood capillaries at surface of exchange and increased SA.
61
Describe tetrapod lungs.
- Generally: paired, high surface-to-volume ration, joins gut via trachea.
62
Describe the buccal pump of amphibians.
(a) Air is taken in through nares by depression of the throat.
(b) Glottis opens, deoxygenated air in lungs is expelled.
(c) Nares close, throat floor brought up, pushing air into lungs.
(d) Glottis closes, keeping air in lungs, repeated pumping flushes the buccal cavity.
63
Describe the aspiration pump of amniotes.
- Ribs and intercostal muscles power pump in most reptiles.
- Diaphragmaticus muscles posterior to liver act as piston for pump in crocodiles.
- Diaphragm is anterior to liver in mammals, where diaphragm and rib cage participate in lung ventilation.
64
Describe bird lungs.
- Use an aspiration pump.
- Unidirectional air flow.
- Gas exchange in small air capilaries in walls of parabronchi.
65
What is the difference between bird lungs and mammal lungs?
- Mammal lungs have tidal flow, bird lungs have unidirectional flow.
- Blood in mammals encounters constant gas concentrations.
- Blood in avians encounters increasing gas concentrations within lungs.
66
What are the special adaptations of bird lungs?
1. Unidirectional flow.
2. Cross-current exchange.
3. Large exchange surface (10x more than mammals).
4. Relatively fixed lung volume.
5. Two cycles of inspiration ans expiration to move air through the system.
67
Describe the heart in tetrapods.
- Blood passes through the heart twice.
- Double-Circuit pump (mammals):
- Heart to body - systemic circulation.
- Heart to lungs - pulmonary circulation.
68
Describe the anuran heart.
- Ventricle is undivided.
- Atrium separated by septum.
- Conus partly divided by spiral valve, guiding blood flow to systemic and pulmocutaneous routes.
- Interatrial septum and spiral valve reduced or absent in lungless salamanders.
69
Describe the facultative heart of reptiles.
- Turtle/squamate heart has divided atrium and ventricle.
- Ventricle has 3 interconnected compartments, allowing transfer of deoxygenated blood to lungs when breathing air and lung bypass when saving energy.
- Crocodiles have different heart organization for similar function.
70
Describe the heart of birds and mammals.
- Four-chambered hearts with similar design but different origins.
71
Describe the aortic arches in embryonic jawed vertebrates.
Have 6 pairs, but the 1st pair disappears in adults.
72
Describe the aortic arches in sharks.
Have five pairs, the 1st pair disappears.
73
Describe the aortic arches in teleosts.
Have 4 pairs, the 1st and 2nd disappear.
74
Describe the aortic arches in tetrapods.
1st and 2nd disappear, have a unique carotid system to the head which is derived from the ventral aorta and 3rd aortic arches.
75
Describe the aortic arches in amphibians.
4th - becomes systemic arch to posterior body.
6th - becomes pulmonary arches to the lungs.
Anurans lose the 5th.
Salamander with adult gills: 5th and 6th supply gills.
76
Describe the aortic arches in reptiles.
Same as anurans, but the two systemic arches run independently from the heart.
77
Describe the aortic arches in mammals.
Similar to reptiles, but only retain the left systemic arch.
78
Describe the aortic arches in birds.
Only retain the right systemic arch, internal carotids replace common carotids in the long neck.
79
What is the role of teeth in the digestive system?
- Derived from bony dermal armor.
- Composed of dentin, surrounded by enamel.
- Used to eat and/or for defense.
80
What are the types of teeth attachments?
1. Acrodont dentition: teeth attached to outer surface of jawbone (teleosts).
2. Pleurodont dentition: attached to inner side of jawbone (anurans, salamanders, many lizards).
3. Thecodont dentition: teeth occupy sockets (some fish, crocodilians, birds and mammals).
81
What are the two types of tooth variation?
1. Homodont: teeth all same size and shape.
| 2. Heterodont: teeth vary morphologically.
82
What type of teeth do mammals have?
Heterodont dentition with species-specific number of teeth, evolved with the ability to chew.
83
What is the role of the stomach in the digestive system?
- Muscular chamber at the end of the esophagus that utilizes gastric glands to break down food.
84
How is the stomach modified in birds and crocodiles?
Split into two parts:
1. Glandular Proventriculus: secretes digestive enzymes.
2. Muscular Gizzard: tough horny layer inside, grinds and mizes food with gastric secretions, that makes up for the lack of teeth.
85
How is the stomach modified in some mammals?
Modified into reuminants (4 compartments).
1. Rumen: stores and churns, residence for bacteria that produce cellulose.
2. Reticulum: receive food from rumen and form cud, then regurgitate for further chews.
3. Omasum: temporary holding site.
4. Abomasum: the only place with gastric glands.
86
What is the role of the intestines in the digestive system?
- Secretes mucus and enzymes used to further break down food.
- Selective absorption of nutrients and water.
- No differentiation between large and small intestine in many tetrapods.
- Small: digests food and absorbs nutrients.
- Large: recovers water.
87
What is the structure of the gut wall?
Four layers:
| Serosa, Muscularis externa, Submucosa, and Mucosa.
88
What are the strategies used to increase surface area in the digestive system?
1. Caeca: extensions of gut.
2. Spiral valve: forces food through a spiral route to increase path length.
3. Foldings: canals, folds, villi and microvilli on internal surface.
89
What is the first part of the kidney?
Pronephros
- Segmented, usually first four segments of the kidney.
- Appear in all vertebrates then degenerate quickly.
- Functional in fish larvae, adult hagfish and some teleosts.
90
What is the middle part of the kidney?
Opisthonephros/Mesonephros
- Reduced segmentation.
- Opisthonephros in late larval and adult anamniotes, and is all of the mesomere posterior to the pronephros.
- Mesonephros in amniotes, is the middle part of the nephrogenic cord, it is only present in fetuses, then it degenerates.
91
What is the last part of the kidney?
Metanephros
- Never segmented, it is the kidney of amniotes.
- The posterior nephrogenic cord that replaces the mesonephros.
- Dual origin: origin of ureter, urine drain from ureter.
- Old mesonephric duct degenerates in females, but carries sperm in males.
92
What are the differences in nephron variation?
- Desert rodents need many loops in the medulla for highly concentrated urine.
- Aquatic mammals have no need for concentrated urine, only have a few loops.
93
How do the gonads develop?
From two sources:
1. Mesomere genital ridges: supporting tissue of gonads (sex cords).
2. Primordial germ cells that become gametes arise from ectoderm, then migrate to the gonad early in development.
94
What are the principal urogenital ducts?
1. Nephric ducts.
2. Muellerian (=paramesonephric) ducts.
3. Opisthonephric ducts.
4. Ureter.
5. Other accessory ducts.
- all vertebrates have nephric and muellerian ducts.
95
Describe the female urogenital ducts.
1. Muellerian ducts become oviduct in ova except in teleosts.
2. Opisthonephric ducts are for urine in anamniotes, mesonephric ducts generates so the ureter is used for urine in amniotes.
3. Open system: egg => body cavity => oviduct.
4. Teleosts: Oviduct is derived from folding in ovary, not homologous to muellerian ducts.
96
Describe the male urogenital ducts.
1. The fetal muellerian ducts always regress (reduce).
2. Efferent ductules derived from anterior tubules carry sperm from testis to nephric duct.
3. Nephric duct becomes named the deferent duct when carrying sperm, or sperm and urine.
4. Closed system.
97
What are some accessory organs of the urogenital system?
- Bladder
- Cloaca
- Male copulatory organs
98
What are the types of cells in the nervous system?
1. Neurons
| 2. Glia cells
99
What are neurons?
- Type of cell.
- Classified according to function (sensory, motor, interneuron) or morphology (unipolar, bipolar or multipolar).
- Receives information and sends impulses.
100
What are glia cells?
- Two types (oligodendrocytes and Schwann cells).
| - Involved in structural and metabolic support, microglia are part of the immune system.
101
What is the central nervous system composed of?
The brain, spinal cord, neurons and interneurons.
102
What is the peripheral nervous system composed of?
Nerves and ganglia outside the CNS. Two kinds of neurons:
- Afferent/sensory fibres: impulse from receptor organ to CNS.
- Efferent/motor fibres: CNS to receptor organ.
103
What is the somatic nervous system?
Innervates skin and voluntary muscles.
104
What is the visceral nervous system?
Innervates involuntary muscles and glands.
105
What is the autonomic nervous system?
- monitors internal environment.
- controls cardiac, smooth muscles, urogenital system and intrinsic eye.
- Two divisions:
- Sympathetic (alertness, excitement).
- Parasympathetic (rest, digestion).
106
What is the prosencephalon?
- The forebrain, split into two parts:
- Telencephalon: cerebral hemispheres, olfactory.
- Diencephalon: thalamus, hypothalamus.
107
What is the mesencephalon?
- The midbrain.
| - Includes the optic lobes.
108
What is the rhombencephalon?
- The hindbrain, split into two parts:
- Metencephalon: cerebellum.
- Myelencephalon: medulla oblongata.
109
How is the brain organized?
1. Brainstem: central axis, includes meten-, dien-, mesen-, and myelen-.
2. Cerebellum: derivatives of meten-, coordinates motor function.
3. Cerebrum: derivative of telen-, dominates brain in size and function.
110
How does the body control chemoreception?
1. Olfactory organs
- ectodermal origin, located in nasal pit.
- filaments to increase SA.
- used to discriminate chemicals in the environment.
2. Taste organs
- Endodermal origin.
- Less sensitive than olfactory.
- Receptor cells in taste buds.
- Taste buds are exposed, worn, and replaced.
111
What are photoreptors?
- Cells capable of phototransuction.
| - Neurons in the retina of the eyes.
112
How are eyes accommodated in water?
- Cornea is flat and not involved in focusing light.
| - Focusing: Change in lens position by contraction of the retractor lentis muscle.
113
How are eyes accommodated on land?
- Cornea is rounded, also involved in focusing light.
- Focusing: Change in lens shape by relaxation of ciliary muscle which attaches suspensory ligaments between the eye and lens.
114
What is the lateral line system?
- Neuromasts dispersed on body surface or in lateral line canals.
- Can detect weak electrical stimuli, allows fish to detect underwater movement.
- Neuromasts provide spatial and temporal information.
115
What are the functions of the ear?
1. Equilibrium: vestibular system.
| 2. Hearing: middle ear and cochlea.
116
How do the middle and inner ear allow for hearing?
- Typanum (eardrum) receives air-borne sound waves, middle ear bones mechanically transmit the vibration to the oval window.
117
What are the modifications of the ear?
- Fish can hear, sometimes very well.
- Amphibians: Very specialized, stapes and operculum connect with pectoral gurdle, basilar papilla + amphibian papilla.
- Reptiles: Some snakes have no middle ear. Stapes joins the mandible or quadrate for reception of vibration from the substrate.
- Birds: Many rows of hair cells.
- Mammals: Very long cochlea, external ear.
118
What is the square-cube law?
If you double the size of an object, its surface area increases 4x and volume increases 8x.
119
How do animals interact with a fluid-filled environment (lake)?
- Drag acts against animals in fluids.
- Pressure drag: from pushing fluid aside.
- Friction drag: friction of fluid against the animal.
120
What are some advantages of living in an aquatic environment?
- Low impact of gravity.
- Relatively constant environment with plenty of food available.
- Good avenues for dispersal and migration.
- Escape from terrestrial predators for secondary swimmers.
121
How do animals reduce the effect of drag?
- Spindle-shaped bodies.
- Reduction of body appendages or retraction alongside body.
- Surface covered in slime.
122
How do swimming animals generate propulsive force?
- Thrust of fin against water (Ft) causes equal push in opposite direction (Fw) due to water inertia.
- Two components: forward (Ft) and lateral (Fl).
- Forward movement faces little resistance compared to lateral movement.
123
How does the strength of body materials assist in underwater movement?
- Bones resist force (provide compressive, tensile and shear strengths, allows them to withstand normal stresses).
- Bending: compressive forces act on the inside, bend and tensile forces on the outside, causes greater stress to be at the surface.
- Cartilage is lighter than bone.
124
What is Symmorposis?
A theory of economic design. Structural design should be matched to (but not exceed) functional demand.
125
Describe the shape of horses.
- Barrel-shaped trunk.
| - Long skinny legs.
126
Why is the gut of horses so large?
- Fermentation occurs in the gut.
- Cellulose present for fermentation.
- Horse is a hindgut fermenter (modification of dentition, cecum and ascending colon).
127
Describe horse teeth.
- Herbivore teeth.
- Made for grinding.
- Able to break down cell walls.
128
Describe horse legs.
- Built for
- Speed: long and rapid strides.
- Stamina: energy efficient motion.
- Standing: fatigue resistance at rest.
(Speed = stride length x stride frequency)
129
How is stride length maximized in horses?
- Lengthened legs.
- Cover ground while in air.
- Lost collar bone (clavicle) adds length to the leg.
- Lengthen legs by changing foot posture.
- Lengthened leg bones themselves.
130
How do horses maintain stride frequency?
- Disproportionate bone length saves energy.
- Losing toes saves energy.
- Folding the leg saves energy.
- Can stand without tiring.
