Final Exam

Question 1

What are the synapomorphies of Rhipidistia (lungfishes)?

What about this may create a constraint on respiration in the amphibians?

Answer 1

• Molecular support
• “Heart with separated pulmonary and systemic circulation”
• With pulmonary and systemic systems…
  
  • Generally need high BP to body and low BP to lungs, but limited separation of systemic and pulmonary prevents this
  • Because of undivided ventricle, some oxygenated blood can get to pulmonary arteries. Need to keep overall low BP to reduce this and maintain gas exchange in the lungs
  • This may constrain respiration rate in amphibians

Question 2

What is the ventilation system in most amphibians?

How is this a disadvantage?

How might this be a constraint?

Answer 2

• Most amphibians use “mixed-air 2-stroke buccal pumping” for lung ventilation (positive pressure system - air is forced into and out of the lungs)
  
  1. Air into nares (nares open; glottis closed)
  2. Glottis opens
  3. Air forced into lungs with buccal pump (nares closed)
  4. Exhalation aided by hypaxial muscles (glottis closed; nares open)
• Disadvantage because it is relatively ineffecient with mixed air and no ribs or costal musculature
• May be an anatomical constraint for whole group:
  
  • Low metabolic rates –> constraing on evolution and ecology of group in general?
  • Flat skull acts as “bellows” in ventilation –> constraint on skull morphology –> jaw musculature, skull fenestration, etc…

Question 3

What is the lung respiration system in the following bony fishes and lungfishes?

Gars and bowfins

Lungfishes

Bichirs and reedfish

What about amniotes?

Answer 3

• Gars and bowfins have “4-stroke buccal pump” with passive exhalation
• Lungfishes with 2-stroke system like amphibians
  
  • Mouth opens, sternohyoideus expands
  • Mixed air into sternohyoideus; glottis opens; elastic recoil and smooth muscles
  • Mouth closes; branchial constricts
  • Glottis closes; lung is under pressure
• Bichirs and reedfishes have an “aspiration (negative-pressure) pump”
  
  • Recoil of ganoid scales creates negative pressure
  • Dorsal ribs are not involved
  • “Recoil aspiration”
    
    • Escaping spent air - lung contracts
    • Inward buckling of ventral wall
    • Fresh air sucked in by aspiration - elastic recoil
• Amniotes have negative pressure pump system

Question 4

List six amniote synapomorphies

(Amniotes = reptiles and mammals)

(Lissamphibia = caecilians, salamanders, frogs)

Answer 4

1. Amniotic egg
2. Single erectile penis
3. Astragalus in ankle
4. Costal ventilation/skull fenestration/pterygoideus muscle
5. Thick epidermal keratin and lipids in skin –> relatively impermeable
6. Loss of lateral line system and larval stage

Question 5

Describe the amniotic egg

Answer 5

• 3 “new” extraembryonicmembranes (outside actual embryo but derived from embryonic tissue)
  
  • Chorion, amnion, allantois (plus yolk sac)
• Protection from physical dessication
• Nutrients, waste, respiration
• Leathery or rigid shell membranes in most
  
  • Laid down by mother after fertilization
  • Internal fertilization required
• Yolk sac and allantois develop into mammalian placentae

Question 6

Describe the single erectile penis in amniotes (which groups is it lost in and what do they replace it with?)

Answer 6

• Lost in lepidosaurs and birds
• Lepidosaurs with “hemipenes” and birds with external cloaca

Question 7

Describe the astragalus bone in the ankle

Answer 7

• “Talus” bone in ankle
• Fusion of 2-4 tarsals in ankle
• Increases mobility
• Unique astragalus in atriodactyl mammals = “double pulley” astragalus - leg bones stay perfectly straight, gives it a lot of strength

Question 8

Describe costal ventilation in the amniotes

Answer 8

• May facilitate evolution of a long neck (allows for complex brachial plexus to form, which contributes to complex control of the forelimb) - need strong costal ventilation to get air all the way down the neck
• All amniotes use aspiration (negative pressure) pump ventilation system (along with bichirs and reedfish)
  
  • Buccal pump in Actinopterygii; Dipnoi
  • Expiration pump in Caudata, gymnophiona, anura
  • Aspiration pump (Amniotes)
    
    • ​Inhalation: Axial muscles (negative)
    • Exhalation: Axial muscles (positive)

Question 9

Describe amniote skull fenestration (function, origin, evolutionary trajectory)

Answer 9

• Evolved independently in synapsids and diapsids
• Ancestral fenestra modified in most modern amniotes
• Current function: Origin, passage, and room for jaw adductor muscles
• Origin?
  
  • Changing skull bones shift stress points –> bone gets thin where there is no stress and where bones meet
  • OR simple developmental change –> adjacent bones fail to meet
• Evolutionary trajectory?
  
  • Costal ventilation develops in amniotes
  • Skull shape not constrained –> becomes more domed (selection for fenestration?)
  • Change of musculature –> new pterygoideus and flange on palate (unique muscles to amniotes)
  • Selection for strong jaw dynamics (new muscles, e.g., adductor)
  • Shift from inertial to static pressure feeding
  • Loss of labryinthodont dentition

Question 10

What are the Sauropsida?

What are their synapomorphies?

Answer 10

• Sauropsida = turtles, lizards, snakes, etc.
• Synapomorphies
  
  • Beta-keratin –> scales and feathers (alpha keratin in all vertebrates)
  • Complex faveolar lungs
  • Single centrale (tarsal) bone in ankle
  • Maxilla separated from quadratojugal
  • Single coronoid bone in jaw

Question 11

What are the Testudines/Chelonia?

Discuss their phylogeny

Answer 11

• The turtles (worldwide, not at high elevations and latitudes; terrestrial, freshwater, or marine)
• Phylogeny
  
  • Are turtles closer to basal anapsids or derived diapsids?
  • Anapsids?
    
    • Turtles close to several extinct anapsid groups (e.g., Parareptilia) –> sister to all extant reptiles
  • Diapsids?
    
    • Turtles closer to lepidosaurs –> anapsid skull evolved independently from diapsid ancestor
    • Supported by some molecular and extinct Odontochelys
    • But new (2012) molecular analysis has turtles closer to Archosaurs

Question 12

What are the two lineages of turtles?

When did the turtles evolve?

Answer 12

• Earliest turtle 220 Mya (Triassic)
• Two lineages in late Jurrasic
  
  • Cryptodira (hidden neck)
    
    • Retract neck in vertical “S”
    • 10 families, everywhere except Australia
    • Most species are in this clade, all with a common ancestor (but don’t know much about evolution)
  • Pleurodira (side neck)
    
    • Retract neck horizontally (sideways)
    • 3 families, southern hemisphere
    • All freshwater

Question 13

What are the three major synapomorphies of turtles?

Answer 13

• Loss of caniniform teeth
• Unique adductor muscles
• Shell

Question 14

What did turtles replace caniniform teeth with?

Answer 14

• Caniniform teeth replaced with a keratinous beak (some fossil forms have teeth)

Question 15

Describe the unique adductor muscles in turtles

Answer 15

• No temporal fenestra, but emarginations for head retraction
• Emarginations force origin of adductor mandibulae posterior on skull
• Unique “pulley system” provides jaw strength
  
  • ​Pivot point differ in Cryptodira and Pleurodira (trochlear processes differ - Pleurodira with more posterior otic capsule and anterior trochlear process)
  • Independent evolution

Question 16

Describe the turtle shell

Answer 16

• Dermal bone covered in keratinous scales or leathery skin
• Dorsal carapace and ventral plastron
• Trunk vertebrae and ribs fused to inside of carapace (top of shell)
• Both girdles are “inside ribs”

Question 17

How did the shell develop?

Answer 17

• Broadening of ribs and dorsal neural spines
• Ribs develop anterior and posterior to engulf girdles
• Plastron (bottom) only as ancestral –> supported by embryology
• “Evolution of turtle body plan by the folding and creation of new muscle connections” - examined development in Chinese soft-shelled turtle
  
  • Carapace ridge causes anterior ribs to grow forward –> engulfs girdle
  • Supports Odontochelys as ancestral (plastron and incomplete carapace region)
• Developmental changes cause big morphological change

Question 18

Why might the turtle shell be a constraint on evolution?

Answer 18

• In most lepidosaurs (tuataras, lizards, snakes)
  
  • ​Inhalation: Contraction of intercostals: negative pressure draws in (aspiration)
  • Exhalation: Contraction of hypaxials: positive pressure forces air out
• Ventilation in turtles
  
  • The ribs and the dorsal surface of lungs are attached to the shell…ribs can’t be used for ventilation
  • Viscera attached to ventral surface of lung
  • Move viscera up and down
  • Cannot breathe when limbs are drawn into shell –> apnea and blood shunting!

Question 19

What are the circulatory adaptations in turtles (and lepidosaurs)?

Answer 19

1. Ventricle partly separated by septum
2. Tripartite aorta: pulmonary, right, and left systemic arches
   
   • Still around equal pressure in pulmonary and systemic
     
     • Systemic: 30-40 mmHg
     • Pulmonary: 15-20 mmHg
   • But…allows for intracardiac blood shunting
   • Can maintain different volumes in pulmonary and systemic

Question 20

What are the functions of blood shunts in turtles and lepidosaurs?

(Left to right shunts; right to left shunts)

How does the right to left blood shunt help?

Answer 20

1. Left to right “shunt”
   
   • ​​Normal breathing –> lungs under low pressure
   • Blood into both systemic arches
   • Some oxygenated blood back to lungs
   • Up to 60% of blood back to pulmonary
2. Right to left shunt
   
   • ​​Diving, during apnea –> pulmonary pressure higher
   • More deOxy blood to left and right systemic

• How does this help?
  
  • Stabilizes oxygen in blood during apnea/breathing
  • “Bohr effect” –> high carbon dioxide –> low pH –> Hb releases O₂
  • Also enhances digestion (releases gastric acid)

Question 21

Describe turtle reproduction

Answer 21

• All oviparous
• Internal fertilization with erectile penis
• Elaborate courtship and mate guarding, but no parental care
• “Slow life histories”
• Low juvenile recruitment, adults long-lived
• Turtle embryos coordinate development with metabolic rates to synchronize hatching time –> the “hurry up” hypothesis
  
  • Hatching synchrony - hatch at same time and stage; embryos detect and respond to HR and metabolic rates in nest, and can adjust metabolic rates accordingly (increase metabolism)
• Temperature dependent sex determination in 11 families
  
  • ​Usually females at higher temperatures
  • Testosterone –> Aromatase (temp. dependent) –> Estrogen
    
    • Aromatase also affected by Atrazine (feminization in frogs)
  • Moms could potentially choose egg-laying sites based on this

Question 22

What do turtles use to guide their massive migrations?

Answer 22

• Odour plumes and South Atlantic equatorial current
• Have keen chemoreception (use 3-D info from earth’s magnetic field to know which currents to follow)

Question 23

What are the Lepidosaurs?

Answer 23

• The “scale lizards”
• Terrestrial, secondarily aquatic
• Sister group to Archosauria
• Lizards and snakes are “morphological groups”
• Iguania (3 lizard families) and Scleroglossa (lizard families and snakes) are phylogenetic groups (clades)
  
  • ​​​Molecular evidence has shattered Scleroglossa - snakes are monophyletic but closer to Iguania and Anguimorpha
  • Squamate phylogeny overhauled
  • Based on molecular evidence

Question 24

What are the five main lepidosaur synapomorphies?

Answer 24

1. Transverse cloacal slit with no erectile penis
2. Scaly skin with ecdysis (shed repeatedly)
3. Intravertebral break planes in tail (“caudal autonomy” or “urotomy”)
4. Hindlimb with astragalus fused with calcaneum (“astragalocalcaneum”)
5. Determinate growth

Question 25

Describe the transverse cloacal slit in lepidosaurs

Answer 25

• No erectile penis
• All other tetrapods with longitudinal slit
• Transverse cloacal slit considered derived

Question 26

Describe lepidosaur skin

Answer 26

• Scaly skin with ecdysis (shed repeatedly)
• Complex epidermis with thick outer layer of beta keratin
• May be brightly coloured with chromatophores

Question 27

What are intravertebral break planes in the tail of lepidosaurs?

Answer 27

• “Caudal autonomy” / “urotomy”
• Severed tail uses anaerobic metabolism to “twitch”
• Clean break from rest of the tail - new tail can regrow (but without intervetebral planes)
• Benefits obvious
• Costs?
  
  • Decrease growth rate
  • Loss of fat reserves
  • Decrease reproductive output
  • Some females use tail for storage

Question 28

Describe the hindlimb joint in lepidosaurs?

What does this have to do with ventilation?

Answer 28

• Hindlimb with astragalus fused with calcaneum (“astragalocalcaneum”)
  
  • Rigid with tibia and fibula
  • Strength for movement on land…but sacrifice speed
  • Ankle joint is “mesotarsal” (between astragalocalcaneum and distal tarsals)
  • Contributes to forward propulsion with sprawling gait
  • Some small lizards are “dynamic bipeds”
• Movement and ventilation are antagonistic (can’t run and breathe at the same time!)
  
  • Compression –> O₂ deficiency –> anaerobic glycolysis (constraint on sustained fast movement in lepidosaurs?)
• Monitor lizards have unidirectional pulmonary airflow patterns (increases metabolic efficiency - originally thought to be unique to birds and associated with endothermy)

Question 29

What is determinate growth in Lepidosaurs?

Which groups do not show this characteristic?

Answer 29

• Ends of long bones (epiphysis) ossify and growth stops
• Independent of determinate growth in mammals and birds
• Some snakes have indeterminate growth (secondarily evolved?)
• Turtles and crocs are also indeterminate

Question 30

What are the Sphenodontidae?

What is unique about them?

Answer 30

• Tuatara and Rhynocephalia
• Only diapsid to retain both ancestral temporal bars!
• Permanent heterodont dentition with some shearing action (convergent in carnivorous mammals)
• Internal fertilization with shallow cloacal outpocketing
• Temperature-depenent sex determination

Question 31

What are two major characteristics of the squamates?

Answer 31

1. Loss of lower temporal bar (quadratojugal) –> “cranial kinesis”
   
   • Frees quadrate from jugal –> allows for kinetic skull –> “STREPTOSTYLY”
     
     • Increases jaw leverage from pterygoideus muscle
     • Enhances static pressure feeding
   • Skull roof also kinetic in some - can change angle of pressure on prey (extreme kinesis in snakes, secondarily lost in others)
2. Limb reduction or loss (not derived for Squamata)
   
   • Evolved independently >60X
   • Hox genes (skinks!)
   • Complete limb and girdle loss in most snakes, many skinks, glass lizards, and most Amphisbaenians

Question 32

What are some characteristics of the Iguania? (Squamata)

Answer 32

• Amazing tongue for prey capture - ambush predators
  
  • Tongue can extend 2x snout-vent length
  • Captures prey up to 15% body weight
  • Circular accelerator muscle attaches to extension of hypobranchial skeleton (“processus entoglossus”)
  • Extreme contraction in longitudinal hypoglossus muscle
• Highly mobile eyes move independently
• Eyes with “telephoto lens” (enlarge images at a distance?)

Question 33

What are some characteristics of (the old) Scleroglossa? (Squamata - non-Iguanian lizards, amphisbaenians, and snakes)

Answer 33

• “Horny tongues” - hind tongue is heavily keratinized (chemosensory)
• Jaws used for prey capture
• Many “active predators”
• Many shared (convergent?) skeletal characteristics
• Major groups = the geckos, skinks, and snakes

Question 34

Describe Squamate reproduction

Answer 34

• Lack erectile penis, but have paired hemipenes (internal fertilization)
• Mating and fertilization don’t necessarily happen at the same time
  
  • Some garter snakes mate after hibernation in spring and females store sperm and fertilize eggs in summer
• Short growing season –> synchronize resource availability and production of young
• Most squamates are oviparous
• Clutch sizes from 1-100
• 20% are viviparous
  
  • ​Most lecithotrophic, some matrotrophic with allantoic placenta like mammals!
• Parental care in only around 100 sp.
  
  • ​Large, venomous species; mostly egg brooding and attendance and nest defence
  • Some care of young in viviparous species
• Temperature dependent sex determination in at least 2 families

Question 35

What are the costs and benefits of viviparity in the Squamates?

Answer 35

• Costs
  
  • Low reproductive rates
  • Increased risk of predation
  • Viviparity more common in ambush predator species (may be due to difficult time during pregnancy)
• Benefits
  
  • Evolved most often in cold climates with short growing seasons
  • Environment supports low reproduction output only (viviparity gives advantage in these environments)
    
    • Some with facultative viviparity (3-toed skink - viviparous in mountains; oviparous on coast)
  • Increases embryo development rate

Question 36

Serpentes - the snakes

Evolution?

Answer 36

• 3300 sp., 17-19 families
• Evolution
  
  • Most support for terrestrial burrowing ancestor or possibly aquatic extinct mosasaurs
  • Earliest fossils from early to late Cretaceous (100 Mya)
  • Large extant groups diversity in Cenozoic (35 to 5 Mya

Question 37

What are nine snake synapomorphies?

Answer 37

1. 100-400 precloacal vertebrae
2. Limb and girdle reduction
3. Loss of caudal autonomy
4. Lack of eyelids
5. Most with single row of ventral scales
6. Unique eye focusing mechanism
7. Sensory specializations
8. Indeterminate growth
9. Highly modified kinetic skulls

Question 38

Describe limb and girdle reduction in the serpentes

Answer 38

• Forelimbs and pectoral girdle absent and loss or reduction of pelvics - some with vestigial pelvics

Question 39

Describe snake eyelids

Answer 39

• No eyelids or scleral ossicles
• Bony orbit around eye

Question 40

Describe the eye focusing mechanism in snakes

Answer 40

• Unique focusing of lens with iris in snakes’ eyes
• Only tetrapods without muscles in “ciliary body”
• From reduced eyes of fossorial ancestor

Question 41

Describe some of the sensory specializations of snakes

Answer 41

• Sight well-developed in non-fossorial species
• No external ears –> substrate borne vibrations –> jaw-quadrate-stapes
• Taste and olfaction well developed
  
  • Paired vomeronasal organ (tetrapods) opens into mouth (squamate)
  • Forked tongue transfer from environment to vomeronasal
• Some detect infrared heat through skin on head
• Specialized “pit organs” in boas, pythons, and pit vipers (rattlesnakes) (can detect 0.003C changes and discern directionality)

Question 42

Describe the highly modified kinetic skulls in snakes

What have they lost that allows them to have this high kinesis?

What characteristics do they have that increases kinesis?

Answer 42

• Loss or reduction of hyoid elements and skull bones, including jugal
• Lower jaw of dentary and compound (articular and prearticulars)
• Loss of upper temporal arch (connection between postorbital and squamosal)
• “Kinetic links” in snake skull (creates “hinges”)
  
  • Loss of meso- and meta-kinesis due to enlarged brain case
  • Upper and/or lower jaw not attached by bone at front –> allows for lateral and independent movement
  • Can “walk jaws” over prey
  • Extreme kinesis in some derived forms (e.g., viperidae)
  • Left and right jaw segments can move independently

Question 43

Feeding specializations in the Macrostomata

Constriction

Answer 43

• Some primitive snakes, boas, and pythons use constriction
• Respond to heart rate of victims, use this as an indicator to determine whether or not to keep constricting
• Homodont teeth on maxillary, palantines, pterygoids, and dentary
• Most other snakes with solid/grooved fangs and venom

Question 44

How did venom evolve and contribute to diverse body types in snakes?

Answer 44

• Solid/grooved fangs and venom in many snakes
• Faciliated evolution of diverse body types?
  
  • Once you have venom, you are not constrained to use constriction
  • Evolutionary race between strong venom and prey adaptations
• Genes for venom often “co-opted” from other functions after gene duplications
  
  • Small changes to genes that code for other functions (e.g., blood coagulants, nerve damage repair, digestion, inflammation, muscle contraction)
• Same genes often used in many venomous taxa

Question 45

Type of dentition?

Description?

Answer 45

• Opistoglyphous (some Colubridae - e.g., garter snakes)
• Opisto = posterior; glyphous = groove
• Duvernoy’s (poison) gland and solid/grooved fangs on posterior maxilla
• Also anterior maxillary teeth
• Neurotoxic venom immobilizes prey and begins digestion
• Relatively poor delivery (50% transfer) –> may hold onto prey while venom works

Question 46

Type of dentition?

Description?

Answer 46

• Aglyphous
• Constrictors and others with no fangs
• Secondary evolution of constriction (e.g., rat snakes and king snakes - not boas etc.)
• Non-venomous or reduced venom gland

Question 47

Type of dentition?

Description?

Answer 47

• Proteroglyphous
• Elapidae (sea snakes, cobras, mambas)
• Hollow fangs at front of maxilla; small and permamently erect
• Usually other posterior teeth
• Fangs start at same place as Opistoglyphous, but move forward during embryological development (homologous with opistoglyphous fang)
• Powerful neurotoxic venom delivered by venom gland (90% delivery)
• Active predators with slim bodies (some elapids have some fang mobility)

Question 48

Type of dentition?

Description?

Answer 48

• Solenoglyphous
• Viperidae
• Large hollow fangs at front of highly mobile maxilla - fangs rotate 120 degrees
• No other maxillary teeth
• Rapid strike with deep penetration
• Venom kills and begins digestion of prey - ambush predators!
• Kill large prey - stout bodies, elastic skin, highly kinetic skull
• Ligaments help with jaw mobilty

Question 49

What are the Archosauromorphs?

What are some of their characteristics?

Answer 49

• The Archosaurs and many extinct Mesozoic species
  
  • “Thecodonts” (extinct)
  • Crocodilians
  • Pterosaurs (extinct)
  • “Dinosaurs”
  • Birds
• Dominant amniotes in Mesozoic
  
  • Laterally compressed, serrated teeth; loss of palate teeth; antorbital fenestra; orbit inverted triangle; elongation of pubis and ilium; trochanter on femur (muscle attachment for highly mobile limbs)
• Many traits associated with bipedalism
• Unique articulation of astragalus and calcaneum
• Elongated calcaneal ankle, foot directed forwards

Question 50

Describe the Crocodilians

Answer 50

• Mid-Triassic (225 Mya)
• Indeterminate growth
• Thecodont teeth - firmly in sockets
• Nostrils on dorsal snout with valves
• Secondary palate - eat and breathe simultaneously
• Flexible “crurotarsal” ankle - unique astragalus-calcaneum articulation (allows crocs to walk upright or sprawling)

Question 51

What are some crocodilian adaptations for efficient breathing?

Describe their ventilation

Answer 51

• Adaptations
  
  • Diaphragmatic breathing
  • Unidirectional airflow
  • Separate ventricles
  • Foramen of Panizza (blood shunting)

1. Retain ancestral costal aspiration with bony gastralia (bony bars on ventral body floor that allows a better ability to open thoracic cavity)
2. Uses liver as plunger (acts like mammalian diaphragm - likely reflects selection for need for increased energy)
3. Rotate pubic bones ventrally (like birds)
4. Unidirectional airflow in lungs

Question 52

Describe crocodilian circulation

Answer 52

• Complete ventricular septum (complete separation of circulation and ventilation)
• Pulmonary and left systemic from right ventricle
• Right systemic from left ventricle
• Foramen of panizza between right and left systemic - connects systemics (allows blood shunts)
• Left to right: Active, left ventricle pressure high; both systemics get oxygen
• Right to left: Diving, apnea, resting; lung pressure up (bypass); more blood to body; bohr effect
• Facultative adjustment of systemic and pulmonary circulation

Question 53

Describe crocodilian reproduction

Answer 53

• All oviparous
• Temperature-dependent sex determination
• No viviparity (no temperate species?)
• Extensive maternal care

Question 54

Ornithodira: Pterosaurs, “dinosaurs”, birds

Characteristics?

Answer 54

• Many modifications on both girdles
  
  • Interclavicles lost; clavicles reduced
  • Tibia elongated - longer than femur
  • Metatarsals 2-4 elongated
• Tendency toward higher mobility and bipedalism

Question 55

Name these dinosaur pelvic girdles (top left going clockwise)

Answer 55

• Ancestral archosaur
• Quadraped saurischian (–> derived theropods and modern birds)
• Derived ornithischian (bipedal and quadrapedal)
• Early ornithischian (with protractors and retractors)

Question 56

What are Theropods and Dromaeosaurs?

What are the “avian characteristics” seen in these groups?

Answer 56

• Theropods - mostly small, bipedal carnivores
• Dromaeosaurs - small, fast bipeds
• Avian characteristics?
  
  • Mobile, s-shaped neck
  • Bones: thin-walled, hollow with internal struts (very dense)
  • Tridactyl, digitigrade foot (digit 1 posterior; digits 2,3,4 anterior)
  • Posterior pubis
  • Fused sternum and clavicles
  • Kinetic shoulder and flexible wrist
  • Symmetrically vaned feathers on 2nd digit and tail
  • Assumed not capable of flight
  • Mesotarsal ankle (intertarsal) - non-avian dinosaurs, birds
    
    • Ankle is raised up off the ground (between tibiotarsus and tarsometatarsus)

Question 57

Characteristics of Archaeopteryx?

What happened after Archaeopteryx?

Answer 57

• Jurassic (150 Mya)
• Primary and secondary feathers
• Asymmetrical vanes
• Large furcula
• Modified sternum (no keel though)
• After Archaeopteryx - many transitional Cretaceous forms
  
  • Pygostyle and shortened tail
  • Alula and more mobile wrist and shoulder
  • Deeply keeled sternum
  • Skeletal fusion; strut-like coracoids
  • Centre of gravity forward
• Modern birds by mid to late Cretaceous

Question 58

Evolution of flight?

Answer 58

• Feathers (hindlimbs and forelimbs) well before flight
• Insulation, social interactions, incubation?
• Top-down or bottom-up evolution?
  
  • Bottom-up –> cursorial ancestry
    
    • Bipedal cursorial predators ancestral
    • Assisted in prey capture, predator avoidance, and/or climbing
  • Top-down –> Arboreal ancestry
    
    • Arboreal gliders
    • But limbs for arboreal not suited for powerfu downstroke

Question 59

What are the avian skeletal characteristics?

What are their other key characteristics?

Answer 59

• Pneumatic bones (thin-walled, hollow core; internal struts; theropod characteristic)
• Respiratory air sacs extend into spaces (birds no lighter than mammals for size!)
• Most weight in pectorals and hindlimbs
• Centre of gravity is over feet in terrestrial species
  
  • Centre of gravity over “knee”
• Other key characteristics?
  
  • Toothless bill
  • Synsacrum
  • Pygostyle (fused final caudal vertebrae)
  • Short tail
  • Furcula (absorbs stress and pressure during flight)
  • Fused coracoids
  • Keeled sternum

Question 60

How is thrust generated?

Answer 60

• Flapping flight
• Strongest thrust during the downstroke
• Supracoracoideus passes through foramen trioseum
• Contraction of supracoracoideus in upstroke
• Additional thrust from twisting asymmetrical primaries - act like a propeller

Question 61

How do birds increase lift?

Answer 61

1. Increase angle of attack
   
   • Moderate angle
   • Too steep and turbulence occurs
2. Alula
   
   • Decreases turbulence and maintains lift
   • Used in takeoff and landing
3. Slotting primaries
   
   • Turbulence greatest at wingtips
   • Slotting redirects air over wings
   • Increases wind speed and lowers turbulence
   • Act as individual wings (“winglets”)
4. Use wind speed –> soaring
   
   • Static soaring (rising air currents, slow air speed - broad wings for high lift; slotted primaries)
   • Dynamic soaring (use wind speed gradients, high wind speeds, long wings separate tip turbulence)

• More thrust from primaries; more lift from secondaries
• Cambered wings also create lift!
• **Wing proportions reflect flight type!

Question 62

What is wing loading?

Answer 62

• Wing loading = bird weight / wing area
  
  • High loading –> diving
  • Low loading –> static soaring

Question 63

What is aspect ratio?

Answer 63

• “Lift-to-drag” or length to width ratio
  
  • High aspect = dynamic soarers
  • Low aspect = maneuverable with fast take-off
• Can have high-aspect ratio, dynamic soaring, high lift, and elliptical wings

Question 64

Describe avian ventilation

Answer 64

• Move sternum and pelvis to change volume of thoracic cavity
• Flight muscles also do this - locomotion and ventilation are complimentary
• Also have unique air sac system associated with complex faveolar lungs
• No tidal ventilation
• “Original guys” with one-way flow over lungs
• No “dead anatomical space”

Question 65

Describe avian circulation

Answer 65

1. Complete separation of pulmonary and systemic (convergent in mammals)
   
   • Continuous lung ventilation (no shunts)
   • Right atrium and ventricle gets oxygen from coronary arteries
   • Separation allows different pulmonary and systemic pressures
   • Highly muscularized left ventricle and high systemic pressure
   • Thought to have contributed to development of endothermy
2. ​Loss of one systemic arch (independent in mammals)
   
   • Birds with right arch
   • Mammals with left
   • Why lose an arch? Increase pressure??

Question 66

Describe avian reproduction

Answer 66

• Most lack external genitalia (erectile penis lost)
• Internal fertilization with cloacal apposition
• Some with erectile cloacal modifications (e.g., corkscrew penis in ducks)
• Phylogeny unclear - driven by sperm competition
• Sex determination is genetic
• Parthenogenesis in turkeys, chickens, zebra finch - all young are males
• All birds are oviparous
• Clutch sizes vary with:
  
  • Ability to feed and incubate young
  • Risk of predation
  • Costs to future predation
  • Latitude - bigger clutch sizes in the North

Question 67

Difference between precocial and altricial

Answer 67

• Precocial (ancestral, most basal groups)
  
  • 70% yolk in eggs
  • Little parental care
  • Hind limbs well developed
• Altricial (evolved several times)
  
  • 15% yolk in eggs
  • Parental care common
  • Well-developed wings and flight

Question 68

Why is there no viviparity in birds?

Answer 68

• Not because of flight (bats are viviparous), not because of endothermy (no thermal benefits to retaining egg in oviducts), selection for large eggs, incubation, and shared parental care?

Question 69

Describe the evolution of mammals

Answer 69

• Synapsids (early Carboniferous - 350 Mya)
• Theraspids (late Carboniferous - 325 Mya)
• Cynodonts (mid-Permian - 275 Mya)
• Mammals (late Triassic - 200 Mya)?

Question 70

What are the cynodonts and what are their characteristics?

What are the characteristics of their skull?

Answer 70

• Derived Theraspids - sisters to the mammals
• Characteristics:
  
  • Modified girdles (limbs under body)
  • Calcaneal heel (free from astragalus)
  • Loss of lumbar ribs (diaphragm)
  • Hard secondary palate
  • Double occipital condyle
  • Heterodont dentition (more specialized teeth)

1. Large temporal fenestra and temporal fossa
2. Zygomatic arch
3. Coronoid process and coronoid fossa on dentary
4. Reflected lamina of angular bone

• Complex jaw musculature
• Selection for food processing, activity –> assumed high MR and endothermic

Question 71

Describe synapsid ventilation

Answer 71

• Two major changes from ancestral

1. Limbs become less “splayed”
   
   • ​​Decreases impact of locomotion on ventilation
   • Running may increase efficiency
2. Loss of lumbar ribs and evolution of muscular diaphragm
   
   • ​​Diaphragm separates pulmonary and abdominal cavities
   • Powerful negative pressure for inhalation
   • Elastic recoil aids in exhalation

Question 72

What are the key changes associated with endothermy in mammals (and in birds)?

(Info in brackets is for birds)

Answer 72

1. Locomotion/ventilation –> upright posture, limbs under trunk, running (or flying) synergistic
2. High energy demands –> complex alveolar (or faveolar) lungs, separation of pulmonary and systemic; evolution of diaphragm and secondary palate (air sacs and one way air flow in birds)
3. Retention of heat and water during breathing –> turbinate bones (or cartilages); incoming air is warmed and humidified; outgoing air is cooled and dried
4. Food processing –> complex teeth (or muscularized gizzard)
5. Heat retention –> fat, hair, (feathers)

Question 73

Describe temporal fenestration and jaw musculature in the sphenacodonts (basal synapsids) and derived cynodonts

Answer 73

• Sphenacodont
  
  • Small fenestra
  • Simple adductor mandibula
  • Reflected lamina of angular for insertion of pterygoideus muscle
• Derived cynodont
  
  • Large fenestra and temporal fossa
  • Adductor mandibula modified into temporalis and superficial and deep masseter
  • Pterygoideus (amniote synapomorphy)
  • Area that moves the most because of contraction of muscle is called the insertion
  • Both masseters (deep and superficial) originate along zygomatic arch

Question 74

Who do these skulls belong to?

Describe their characteristics

Answer 74

• Anapsid (first)
  
  • No fenestra
  • Complete dermal roof lateral to muscles
• Early cynodont (second)
  
  • Small fenestra
  • Muscles originate on top of skull; strong jaw adduction
  • New dermal roof develops medial to muscles
• Mammal
  
  • Large fenestra
  • Complete dermal roof encases enlarged brain

Question 75

What is the zygomatic arch?

What is its function?

Answer 75

• Squamosal and jugal bone - part of temporal fenestra
• Delimits ventral margin of fenestra
• Opening is now continuous with eye orbit
• All that remains of ancestral skull roof

Question 76

Where is the temporalis located?

Where are the masseters located?

In which types of mammals are these areas well developed in?

Answer 76

• Temporalis on the inside of coronoid process (medial, lingual)
• Masseters on outside of coronoid fossa (lateral, buccal)
• Carnivores have well-developed temporalis and coronoid process (jaw articulates on the dentary condyle - jaw articulation is at the tooth level; bite force to incisors and canines)
• Herbivores have well-developed masseters and coronoid fossa (jaw articulation well above teeth - leverage for masseters; bite force to cheek teeth (molars))

Question 77

Describe the evolution of the mammalian middle ear

Answer 77

• Articular and quadrate become incorporated into the middle ear
  
  • Reflected angular –> tympanic bone (auditory bulla)
  • Articular –> malleus
  • Retroarticular process –> manubrium of malleus
  • Quadrate –> incus
• This is consistent with “early hearing hypothesis” that cynodonts used articular and quadrate to conduct sound to stapes

Question 78

What are some of the characteristics of “true” mammals?

Answer 78

• Dentary-squamosal jaw articulation with dentary condyle, glenoid (squamosal) fossa
• Quadrate articular do not have to be incorporated into middle ear
• Three middle ear ossicles
• Diphyodonty (deciduous and permanent teeth) - lactation assumed
  
  • Lactation –> diphyodonty –> occlusion –> specialization of teeth
• Precise dental occlusion with transverse chewing and shearing
• Led to extreme specialization in dentition among mammalian orders
• Very complex “**tribosphenic” **teeth by late Jurassic/early Cretaceous

Question 79

What are four dental modifications in mammals?

Answer 79

1. Quadrate or bunondont
   
   • 4 grinding cusps
   • Omnivores, frugivores
   • Pigs, primates (humans)
2. Lophodont
   
   • Cusps extended by ridges - helps with grinding
   • Herbivores, omnivores
   • Rodents, elephants
3. Selenodont
   
   • Ridges in anterior/posterior crescents
   • Herbivores
   • Ungulates, camels, koalas
4. Carnassial
   
   • Extreme shearing in carnivores
   • Canids, felids

Question 80

What are some other mammalian characteristics?

Answer 80

• Mammary glands and other skin glands
  
  • Sweat (water) and sebaceous (oil)
  • Suckling developed complex face musculature - allowed for facial expressions?
• Hair
  
  • Unique to mammals, NOT homologous to feathers or scales
  • Original tactile function, secondary function is insulation
• Large comlex brain and well-developed sensory system
  
  • Neocortex associated with enhanced intelligence and sensory function
  • Larger forebrain
• Mammalian sensory systems
  
  • Olfaction
    
    • Highly developed in many groups (esp. nocturnal)
  • Hearing
    
    • Highly developed in most (primary sense in 20% species)
    • Esp. nocturnal
    • Long, coiled cochlea and external pinna unique in Therian mammals
  • Sight
    
    • Depressed in insectivores and cetaceans
    • Tetrachromatic colour vision may have been lost in some with nocturnal burrowing ancestors
• Anucleate RBCs
  
  • Increases oxygen carrying capacity and gas exchange
• Complete separation of pulmonary and systemic
  
  • One (left) systemic arch

Question 81

Describe reproduction in the Prototheria

Answer 81

• Prototheria = oviparous monotremes
• Has primitive amniote/synapsid and derived mammalian characteristics

1. Cloaca and weird penis
   
   • Erectile penis for semen only from ventral cloacal tissue
   • Intestinal and urogenital with separate openings in all others
   • Penis is 2-lobed (platypus) or 4-lobed (echidna)
2. Egg laying
   
   • Leathery, permeable shells
   • 1-3 eggs
   • Young very altricial at birth (hatch around 10 days; wean for 2-4 months)
3. Mammary glands
   
   • But no nipples in platypus; nipple-like in echidna
4. Plarypus with strange sex chromosomes
   
   • Female with 5 pairs X; male with 5X + 5Y

Question 82

Describe the differences in reproduction between metatheria and eutheria

Answer 82

Question 83

Difference between choriovittelline and chorioallantoic placenta?

Answer 83

• Chorioallantoic is way more developed, invasion of embryonic tissues into maternal tissues is much higher

Question 84

What are the ways that metatherian reproduction might be a constraint on diversification?

Answer 84

1. Choriovitelline placenta and no trophoblast
   
   • In most metatherians, outer shell membranes protext embryo
   • Birth soon after membrane shed - is this tissue rejection?
   • Constraint = lack of trophoblast limits length of gestation?
     
     • In Eutherians, trophoblast develops into placenta and protects from immunorejection
2. Short gestation - altriciality
   
   • Forelimbs well developed to help young climb to pouch
   • Constraint = limits adult morphology?
     
     • Limits evolution of specialized forelimbs
     • Cannot exploit adaptive zones
   • Only hindlimbs specialized for speed in large species
3. Short gestation - most energy to young from milk
   
   • Marsupial young grow more slowly and wean much longer
   • Constraint = slow reproductive rates, population growth?
     
     • Outcompeted by introduced eutherians to Australia?
     • But lower cost/time may be advantageous
4. Marsupium morphology
   
   • Constraint = limits evolution of aquatic forms with young in pouch