Amniotes and Mammals lecture Flashcards
What is a crown group? Give a course-relevant example
A derived monophyletic group; Amniota
What are the Amniota synapomorphies?
Amniotic egg
Claws or nails at the end of digits
Egg tooth
Genitalia for internal fertilization
At least 2 sacral vertebrae
Formation of astragalus
Loss of water breathing and lateral line system
What structures are conserved between the amniotic egg and amphibian/fish egg?
Yolk and chorion
What structures does the amniotic egg have that the amphibian/fish egg doesn’t?
Allantois, amnion, and chorioallantoic membrane
What limits the fish/amphibian egg from moving onto land?
Lacks an outer shell to avoid desiccation. It is dependent on water for gas exchange, waste management, and moitsure
What is the function of the yolk sac?
Nutrition
What is the function of the amnion?
Encapsulates embryo, protective against mechanical forces
What is the function of the chorion?
Encapsulates embryo and extraembryonic tissues (including amnion), protection for embryo, gas exchange, and provides structure for the yolk sac
What is the function of the allantois?
Storage of metabolic waste and gas exchange, ‘mini bladder’
What is the chorioallantoic membrane?
It is synthesized from an old character (chorion) and new character (allantois) for gas exchange and waste storage
Why do amniotes require an allantois?
Embryos are unable to diffuse metabolic waste into their surroundings like fish/amphibians can. Also necessary for gas exchange for the same reason
What germ layers make up the yolk sac? Outside to inside
Mesoderm and endoderm
What germ layers make up the allantois? Outside to inside
Mesoderm and endoderm
What germ layers make up the chorioallantoic membrane? Outside to inside
Ectoderm, mesoderm, and endoderm
What germ layers make up the amnion? Outside to inside
Mesoderm, ectoderm
What germ layers make up the chorion? Outside to inside
Ectoderm, mesoderm
Why is declawing a cat considered unethical?
Claws and nails have a tight connection/association with the end of the digit through lots of connective tissue, so removing them is like amputating the most distal phalange
What germ layers make up the egg tooth?
Ectoderm and neural crest
What tissue makes up the caruncle?
Keratin
Why do (most) squamates have an egg tooth rather than a caruncle?
Egg teeth are much harder, which is needed to break free of the leathery shell that encapsulates the embryo
What is the Shh gene?
Sonic hedgehog, it is analogous to HOX genes and allows for symmetry of tissues
Which clade does not have Shh expression?
Tuatara
What are the steps for penile development?
External genital initiation, Shh expression, and cloacal separation
Which two clades do not have external penises?
Anoles and Tuataras
Where is the penis housed in amniotes?
Inside of the cloaca
The development of (at least) 2 sacral vertebrae suggests what?
More emphasis on terrestrial movement and less on using the tail for locomotion
Which hypothesis best demonstrates the formation of the astragalus?
3 largest wrist/ankle bones fused and smallest one fused with adjacent bones
Which hypothesis for the formation of the astragalus is least likely? Why?
Wrist bones disappeared and the astragalus appeared in its place; very unlikely for new bones to develop de novo
The sacral vertebrae articulate with the _____
Pelvic girdle
What is the difference between amphibian nostrils and amniote nostrils?
Amphibian nostrils face upwards while amniote nostrils face forwards, they are also larger
What features of an early amniote suggest its independence from water?
Highly fused skull, larger zygomatic arch, increased area for olfaction (dorsally expanded), larger forward-facing nostrils and eyes
Why was the fusion of skull bones necessary for early amniotes to specialize for living on land?
Structure fights gravity
What systems might be pressured to change if water is not a requirement for larval stages or sensory systems anymore?
Respiratory (costal vs diaphragmatic), muscular (change in density of medium), reproductive (desiccation avoidance, internal fertilization), loss of cutaneous system (can no longer breathe through skin)
How does rib anatomy reflect the breathing strategy of amniotes?
Ribs extend to pelvic girdle = costal respiration
Ribs extend to midsection = diaphragmatic respiration (room for intercostal muscles)
Diaphragmatic respiration changes respiration how?
Allows for a faster metabolism and movement due to less restriction of the ribcage
What is the theme in the cardiovascular anatomy following amniote diversification?
Reduction of unnecessary characters due to loss of gills and cutaneous system, as well as increased efficiency
What is ammonotelism? What is its toxicity and metabolic cost of synthesis? What groups use it? What limits it?
Ammonia (NH3) excreted in its raw form; high toxicity and no metabolic cost; most fishes, amphibians, turtles, and some aquatic reptiles use it; dependence on water
What is ureotelism? What is its toxicity and metabolic cost of synthesis? What groups use it?
Convert ammonia to urea and store in water (makes urine) to then release; moderate toxicity and low metabolic cost; sharks, sarcopterygians, mammals, amphibians, and turtles
What is uricotelism? What is its toxicity and metabolic cost of synthesis? What groups use it? What limits it?
Convert ammonia to uric acid and release and/or integrate into shell; low toxicity and high metabolic cost; birds and reptiles; requires significant amounts of water
Synapsids have ____ fenestra
One
Diapsids have _____ fenestra
Two
Anapsids have ____ fenestra
No
Synapsids later developed into what clade?
Mammalia
Diapsids developed into what clade?
Sauropsida
What bones make up the amniote skull?
Postorbital, squamosal, jugal, and quadratojugal
Where is the postorbital located?
Caudal to the orbit (eye socket)
Where is the squamosal located?
Caudal to the postorbital
Where is the jugal located?
Ventral to the postorbital
Where is the quadratojugal located?
Caudal to the jugal and ventral to the squamosal
Which bar(s) do synapsids have? Where is it (are they) located?
Lower temporal bar; ventral to the lower temporal fenestra
Which bar(s) do diapsids have? Where is it (are they) located?
Postorbital bar and lower temporal bar; Ventral to the upper temporal fenestra and lower temporal fenestra, respectively
What is the purpose of fenestration?
Allows for more room for jaw muscles which gives the ability for a snapping mechanism
Why is it important that synapsids and diapsids have more muscular jaws?
Able to resist gravity when catching prey, which was unnecessary in the water
What groups are included in Synapsida?
Monotremata and Theria (Marsupialia and Placentalia)
List the important features of early synapsids
Small temporal fenestra
Dentary makes up half of the lower jaw
Large pectoral girdle
Sprawling posture
Ribs on all trunk vertebrae
Vertebral interlocking restricts lateral undulation
Two sacral vertebrae
Large processes on caudal vertebrae for caudofemoralis muscle
Vertebral interlocking is caused by what structure?
Zygapophyses
What features contribute to limited lateral movement seen in early synapsids?
Large clavicle, interclavicle, and coracoid
Sprawling posture
Ribs on all trunk vertebrae
Vertebral interlocking
What are large processes on the caudal vertebrae used for in early synapsid movement?
Large attachment points for the caudofemoralis, which is the major hind limb retractor. This suggests they used tail muscles to aid in locomotion
Why are pelycosaurs, like dimetrodon, not considered dinosaurs?
Different time period and were synapsids, while dinosaurs were diapsids. Differebt pelvic anatomy
What may the long processes on the vertebrae of pelycosaurs have been used for?
Holding a sheet of skin for thermoregulation, attracting mates, warning predators, sexual dimorphism, etc. Not currently known
True/False? Pelycosaurs showed the first signs of heterodonty
True
What changed from early synapsids to early therapsids?
Enlarged temporal fenestra
Well-defined dental regions (incisors, canines, and cheek teeth)
Reduced clavicle and interclavicle
Upright posture
Three sacral vertebrae (+1)
Reduced processes on caudal vertebrae
Intertarsal ankle joint between calcaneus and astragalus
What kind of breathing did pelycosaurs and therapsids lack? Why?
Diaphragmatic ventilation due to ribs on all trunk vertebrae
What do the reduced processes on caudal vertebrae imply (therapsids)?
Less dependent on tail for locomotion
The development of the ankle joint in therapsids caused what? Why?
Upright posture. The change in orientation of the girdles caused selection pressures
List the important features of cynodonts
Enlarged temporal fenestra
Secondary palate
Complex cheek teeth
Olecranon process
Calcaneal heel
Short and flattened lumbar ribs
Four or more sacral vertebrae
Expansion of the ilium
Reduction of the pubis and ischium
What are derived therapsids commonly referred to as?
Cynodonts
Why was the development of a secondary palate important?
Allowed for the division of respiration from consumption, so breathing and eating at the same time was possible. This is seen in mammals, specifically when breastfeeding milk
What is sandboxing?
“Setting up” the development for something later
The secondary palate is an example of what?
Sandboxing
What defines “complex” cheek teeth?
Multiple cusps
What about the Cynodont skeleton suggests diaphragmatic breathing? Why?
Short and flattened lumbar ribs; gives room for costal muscles and a diaphragm
What is the purpose of an olecranon process and calcaneal heel?
Muscle attachment points for locomotion
What does the reduction of the pubis and ischium reveal about cynodont locomotion?
Less tail muscle attachment points, so do not rely on the tail for locomotion as much
The pelvic girdle (and articulated vertebrae) of the Cynodont skeleton allow for what?
Increased stability and muscle attachment
Why are tails reduced in derived therapsids?
Rely less on the tail for muscle attachment and more on the pelvic girdle
Why are derived cynodonts not considered mammals despite them having one jaw bone?
They have a quadrate-articular jaw joint. Mammals have a dentary-squamosal jaw joint
What is the sister taxon to mammals?
Derived cynodonts
Holes can be seen in the rostral portion of the derived cynodont skull. Why?
Allow for nerve endings to poke through for whiskers
List the features of mammaliaformes
Dentary-squamosal jaw joint
Clavicle, interclavicle, and coracoid reduced
Mammal-like dentition
Describe how mammaliaform dentition is similar to mammals
Teeth have prismatic enamel
Two generations of incisor, canine, and premolar teeth
Molars have two roots
True/False? Mammaliaformes generally had a low metabolic rate
False. Their efficient locomotive abilities actually allowed for a higher metabolism
True/False? Mammals typically avoided dinosaurs
False. Despite their small size, they fought back (fossil evidence)
True/False? Mammals have always been a diverse clade
True. We can see this in the fossil record
Describe the development of muscles for mastication
Started out as a singular muscle in early synapsids that allowed for up and back motion of the lower jaw
In cynodonts, the masseter allowed for up and forward motion, while the temporalis allowed for up and back motion, so the jaw could move up as well as forwards and backwards
Basal probainognathids divided the masseter into a superior and deep portion. The superior allowed for up and forward, deep allowed for up, back, and laterally. The temporalis allowed for up and back motion
How many jaw muscles were there from early synapsids to basal probainognathids?
1 (early synapsids), 2 (cynodonts), 3 (basal probainognathids)
What did the early synapsid jaw look like?
Dentary and angular made up the lower jaw and the jaw joint was between the quadrate and articular
What did the cynodont jaw look like?
Dentary and reduced angular made up the lower jaw. Quadrate and articular were reduced and associated with the tympanum but still make up the jaw joint
What did the probainognathian jaw look like?
Dentary and reduced angular made up the lower jaw. Quadrate and articular are also further reduced and have increased association with the tympanum.
What does the mammal jaw look like?
Dentary is the only lower jaw bone. Tympanum, angular, quadrate, and articular now make up middle ear. Dentary-squamosal joint
What did the tympanic bone derive from?
The angular bone
What did the incus bone derive from?
The quadrate
What did the stapes bone derive from?
The hyomandibula
What did the malleus bone derive from?
The articular
What structure in the middle ear is the one to not change its classification upon the evolution of mammals?
The tympanum
Why are there so many apomorphies for mammals?
They are an incredibly diverse clade, especially after the dinosaurs went extinct
What are the synapomorphies of Mammalia?
3 ear ossicles
Dentary (one jaw bone)
Hair
Mammary glands
Double-rooted cheek teeth
Prismatic tooth enamel
Crurotarsal ankle joint
Calcaneal heel
True/False? Hair and mammary glands are dermal organs
False. They are ectodermal organs formed by the ectoderm and neural crest cells
What is a sebaceous gland?
A gland associated with a hair follicle that secretes oil
What is the difference between an eccrine gland and apocrine gland?
Eccrine is not associated with a hair follicle while apocrine is
What do eccrine/apocrine glands secrete?
Sweat and pheromones (apocrine specifically)
What is a key feature of sebaceous glands that lead researchers to the current hypothesis of laction development
Look very similar to mammary glands, which suggests that mammary glands were derived from sebaceous glands
Why are double-rooted cheek teeth important for mammals to have? Why specifically cheek teeth and not incisors/canines?
They chew their food (mastication) which creates a lot of pressure from any direction on their back teeth, so double roots provide extra stability; incisors and canines are not used for chewing, but molars and premolars are
What is the advantage of having prismatic tooth enamel?
It distributes force throughout the entire structure, rather than just where the force is being applied. This increases the tooth’s strength overall, making teeth the strongest mineralized tissue in mammals
What do the calcaneal heel and crurotarsal ankle joint provide for mammals?
A muscle attachment point for locomotion
What happens to interactions with the environment as the movement arm increases?
Decreases
What happens to locomotion as the movement arm increases?
Increases
A plantigrade ankle joint has the _____ interaction with the environment and _____ movement arm
Most; smallest
A digitigrade ankle joint has _____ interaction with the environment and a(n) _____ movement arm
Intermediate; intermediately-sized
A unguligrade ankle joint has the _____ interaction with the environment and _____ movement arm
Least; largest
What is unique about monotremes relative to therians in terms of reproduction?
Oviparity instead of viviparity
What separates marsupials from placentals in terms of reproductive strategy?
Marsupials favour lactation > gestation and placentals favour gestation > lactation
What are the synapomorphies of Monotremata?
Cloacal opening
Oviparity
Lactation field
Edentulous
5 pairs of sex chromosomes
True/False? Female Monotremes have only one ovary
True
What is a cloaca?
A multipurpose opening for waste excretion and reproduction. Houses the penis inside of a sheath within the cloaca
What is the only clade that has both an egg tooth and caruncle?
Monotremata
What is a lactation field?
An area on the stomach of a monotreme that secretes milk
Why is the lactation field important when it comes to the development of the milk gland?
Basically shows the intermediate step for how milk glands developed from sebaceous glands due to their similar morphology
What does edentulous mean?
Missing teeth
True/False? All monotremes lack teeth
False. While modern monotremes do, fossil evidence suggests ancestors had rooted teeth
A karyotype for monotremes reveals they have 5 X and 5 Y chromosomes. They also lack the SOX9/SRY complex on their Y chromosomes. Explain why this is relevant
Their 5 pairs are a synapomorphy for this group. What is confusing is that the SRY/SOX9 complex is involved in the development of the testes, yet their genes can be found on autosomal chromosomes in monotremes (not the Y chromosome), which both males and females have. So does this mean there is another level of regulation preventing females from developing testes?
What is SRY?
A transcription factor that enables SOX9 transcription
What is SOX9?
A gene usually found on the Y chromosome (autosome in monotremes) that, when transcribed, allows for the development of the testes
What is an Ornithorhynchidae?
Platypus
Do platypuses have ampullae of lorenzini?
No, but they do still have weak electroreception via an analogous structure
What is a Tachyoglossidae?
Echidna
Describe the features of a Tachyoglossidae
Long tongue (gloss- part of the name)
Limited electroreception
Backwards-facing feet only on hindlimbs for digging
What are the synapomorphies of Marsupialia?
Testes cranial to penis (do not descend)
2 lateral vaginae + pseudovaginal canal
Favour lactation over gestation
Only the third premolar is replaced
Retention of epipubic bones
Why do the ureters not loop over the vas deferens in Marsupialia?
The testes are above the penis, so the ureters and vas deferens do not need to cross each other
How many ovaries do marsupials have?
2
Why are twins so common in marsupials?
Females have 2 uteruses that can be occupied at the same time
What is the function of the pseudovaginal canal? Where is it located?
Birthing canal, located between the lateral vaginal cavities
How do we know that only the third premolar is replaced in marsupials?
When looking at a developmental diagram (?), there are two branches that emerge from the P3 spot whereas only one branch forms at P1, M1, and M2. Each branch develops into a tooth
What are epipubic bones?
A muscle attachment point for tail muscles
Are marsupials the sole owners of epipubic bones?
No, monotremes and placentals have them too, except reduced
What clade of marsupials is the most diverse? What are a couple features about them?
Diprotodontia; lower incisors jut outwards and have syndactyly
What animals are within Diprotodontia?
Wombats, koalas, kangaroos, sugar gliders
What clade are considered new world marsupials?
Ameridelphia
Why are new world marsupials paraphyletic?
Microbiotheria (new world) is a sister taxa to Diprotodontia (old world)
Australidelphia importance
It represents the clade of marsupials that wildly diversified after the split of Pangea
Why are there so few new world marsupials?
Biogeography
Explain why marsupials are divided based on geography
Therians split into marsupials and placentals before the split of Pangea, so both continents had marsupial ancestors after the divide
Explain the Great American Biotic Interchange (GABI)
When the Isthmus of Panama solidified, it allowed many North American placentals to cross into South America, allowing for competition and niche filling between new world marsupials and placentals
What is the Isthmus of Panama?
The bridge connecting South America and North America
Explain why competition isn’t the only cause for the low new world marsupial diversity
Global temperatures were already dropping before the Isthmus solidified, which decreased diversity before niche competition from placentals also decreased marsupial diversity (niche emptying caused by decrease in temperature, filled by placentals)
Explain how carbon isotopes can be used to evidence the GABI
Before the southern migration of placentals, their diets consisted of C3 dominant plants, which can be found in closed landscapes. After the migration, a mix of C3 and C4 is observed, which is indicative of a generalist diet. C4 can be found in grasses and sedges, plants of the open landscapes found in South America
Why are C4 dominant species less common after the GABI?
C4 can be found in plants from open landscapes, which do not allow for much diversity. As such, not many clades have a C4 diet
What feeding strategy was favoured after the GABI? What are the associated carbon isotopes?
Generalist; C3 and C4
Provide 7 examples of members of Placentalia that exemplify the diversity of this clade
Manatees
Sloths
Rodents
Primates
Chiropterans (bats)
Ungulates
Cetaceans
Perissodactyla vs Artiodactyla
Odd vs even number of toes
Are cetaceans perissodactyls or artiodactyls?
Artiodactyls
What muscles are used in dorsoventral movement? How does this differ from lateral movement?
Hypaxial and epaxial; in dorsoventral, hypaxial muscles contract, then epaxial muscles contract. In lateral, both hypaxial and epaxial contract at the same time, just opposing sides (left vs right)
Why is there an increase in vertebrae in cetaceans?
Allows for more muscle attachment and flexibility for the movement of the tail
True/False? Cetaceans evolved from carnivorans
False. Fossil evidence suggests they evolved from Artiodactyla
What are the specimens used as fossil evidence for the evolution of cetaceans from artiodactyls?
Protocetid and pakicetid whales
What fossil discoveries provided the evidence for the evolution of cetaceans from artiodactyls?
Similarities in the skull
Ankle bones share distinct morphological similarities with artiodactyls
Morphology of the lungs (2 rather than 3 bronchi) and penis
What is a synapomorphy of artiodactyls that led scientists to believe cetaceans descended from this line?
Proximal and distal indent in the ankle bone
What is the carnassial apparatus? What family is it present in?
The upper last premolar and lower first molar overlap when the jaw is closed, which allows for tearing of meat; Carnivora
Bats and rats are the most speciose clades of mammals and have a nearly global distribution. What does this say about their lifestyles?
Global distribution allows for adaptation to many ecological niches, both generalist and specialist
Give an example of a generalist rodent
Rat
Give an example of a specialist rodent
Beaver
Give an example of a generalist bat
Omnivorous bats
Give an example of a specialist bat
Vampire bat
Why are rats so successful? Are they geographically isolated?
They can eat pretty much anything, have a global distribution, are hardy, fast reproducing, able to survive in most climates, can swim and climb, which all come together to result in less direct competition; no, they avoided geographic isolation
Describe how geographic isolation is a strong selective force for mammals
Geographic isolation usually means that there is high competition and limited niches available for occupation. In rodents, this led to many species in which some filled very specific roles
Discuss the impact that geography has had on mammalian evolution
Allows for diverse speciation, generalist vs specialist strategies, etc
If an organisms body temp doesn’t fluctuate with the environment, it is a ___________
Homeotherm
If an organisms body temp fluctuates with the environment, it is a ___________
Heterotherm
If an organisms primary heat source is internal, it is an _____________
Endotherm
If an organisms primary heat source is external, it is an _____________
Ectotherm
What is resting metabolic rate?
The lowest level of metabolism without spending extra energy
What is specific dynamic action?
BMR + energy expended for digestion
What is activity in terms of metabolic rate?
Movement
When is activity advantageous vs disadvantageous?
Advantageous: colder climates (produces heat)
Disadvantageous: warmer climates (already hot organism gets even hotter)
What is the relationship between metabolism and body temperature?
Positive and linear
As mass increases, standard metabolic rate ________________
Increases
Mammals with a low resting metabolic rate and body temperature have a ______ standard metabolic rate and _______ body mass
Low, low
On average, birds and mammals have a ______________ metabolic rate than amphibians, fishes, and reptiles
Higher
If body temperature falls, what happens in the body to compensate?
Increase in metabolic rate by:
Vasoconstriction
Hormonal thermogenesis
Thermogenesis
If body temperature rises, what happens in the body to compensate?
Decrease in metabolic rate by:
Vasodilation
Evaporative cooling
What is hormonal thermogenesis?
Increasing body temperature using hormones (inhibiting cortisol to burn fat, etc)
What is vasoconstriction?
Blood vessels close to the skin are constricted to decrease blood flow there and increase blood flow to the core which keeps heat in
What is thermogenesis? Ex?
Using metabolism to generate heat; shivering
What is vasodilation?
Increasing blood flow to the skin to exchange heat with the environment
What is evaporative cooling? Ex?
Using vaporization to exchange heat with the environment; panting and sweating
What is the lower lethal temperature?
The minimum body temperature that can be tolerated by an organism
What is the upper lethal temperature?
The maximum body temperature that can be tolerated by an organism
What is the lower critical temperature?
The minimum body temperature that requires the minimum amount of metabolism
What is the upper critical temperature?
The maximum body temperature that requires the minimum amount of metabolism
When do we see metabolic heat production?
From the lower lethal temperature to the lower critical temperature
What is the thermoneutral zone?
The temperature range with the minimum metabolic rate (BMR), so no energy is spent on thermoregulation
What are the bounds of the thermoneutral zone?
Lower and upper critical temperatures
When do we see evaporative cooling?
Upper critical temperature to upper lethal temperature
Why is the temperature range for metabolic heat production larger than the range for evaporative cooling?
It is easier to get hotter than cooler, so organisms that follow this basis of thermoregulation cannot tolerate warmer temperatures as well as they can cooler temperatures
Explain why whales migrate from the productive regions at the poles to the equator
Whale calves are not able to survive well at the poles because they lack blubber, and would expend lots of energy just staying warm rather than putting that energy into growing. Adults migrate down to the equator where it’s warmer so their calves can feed on lipid-dense milk without worrying about thermoregulation. Here, they are able to build up a layer of blubber so they can survive and eat at the poles
What tradeoff do whale calves face at the poles?
Thermogenesis vs growing
What is a vascular plexus?
Veins are intertwined with arteries near the core
For an endotherm that lives in a cold environment, what happens to their blood vessels as activity increases?
Warm blood is shunted to the veins closer to the exterior to allow for better heat dissipation
For an endotherm that lives in a cold environment, what happens to their blood vessels as activity decreases?
Warm blood is shunted to the veins closer to the interior (vascular plexus) to reduce heat dissipation
What are some behaviours endotherms exhibit when in a cold environment?
Cuddling and building nests and digging holes
A cold receptor senses ______. Which layer does it terminate in?
Cold; dermis
A heat receptor senses ______. Which layer does it terminate in?
Heat; dermis
Meissner’s corpuscle senses __________
Pressure
Pacinian corpuscle senses _________
Touch
List the dermal layers from outside to inside
Epidermis, dermis, hypodermis
What is the function of the undercoat?
Insulation
What is the function of guard hairs?
Protects the undercoat, is associated with sebaceous glands which aid in waterproofing
Where is the end of a hair follicle located?
Hypodermis
What is the hypodermis?
A layer of fat beneath the dermis
What is an erector pili muscle?
When cold, this muscle contracts to make hairs stand straight up, creating an insulative layer of warm air
Describe the differences between a white fat cell and a brown fat cell
White: One huge lipid droplet and one mitochondria, fat storage
Brown: Many small lipid droplets, multiple mitochondria, thermogenesis
Why is it more efficient for brown fat cells to have multiple fat droplets instead of one big one?
Increased SA:V ratio, easier to break down for thermogenesis
What is the correlation between hair length and insulative value?
Positive and linear
Why is an arctic fox’s metabolic rate so low at low ambient temperatures?
It has thick, long fur that keeps the fox warm so a high metabolism isn’t needed to maintain their body temp
What happens to body temp as an organism enters torpor? Metabolic rate?
Drops 5-10 degrees C; decreases
What happens to Tb as an organism exits torpor? Metabolic rate?
Rises until normal Tb is restored; increases
How to calculate energy saved by going into torpor?
Area above the curve (BMR vs Time) during torpor minus energy cost of arousal
A lot of energy is saved by going into torpor. Why?
Not as much energy is spent on regulating body temperature
What does a Temperature vs. Time graph look like for a hibernating mammal?
Tb increases periodically when the mammal wakes up to go pee, then back down again to 1 degree C above Ta
What is the relative Tb - Ta difference between torpor and hibernation?
Tb - Ta is smaller in hibernation because Tb is maintained closer to Ta during sleep as it is held for longer periods of time = less metabolic waste per unit time = able to sleep longer without needing to pee
Why cant large mammals hibernate but small mammals can?
Large mammals cannot generate heat as quickly as small mammals due to smaller SA:V ratio, so instead they rely on fat stores to last them through cold months
True/False? Large mammals, much like small mammals, have lots of brown fat cells
False
What is done during hibernation to limit BMR?
Oxidative metabolism reduced
Temp regulation set to a lower point
Slowed respiration and heart rate
Vasoconstriction in peripheral tissues (most heat kept in the core)
How do we conserve water in hot environments?
Reduced sweating and increasing urine concentration
Where is the renal cortex? Which structures of the nephron does it house?
Outer layer of the kidney; glomerulus, PCT, DCT
Where is the renal medulla? Which structures of the nephron does it house?
Inner layer of the kidney; loop of Henle and collection duct
Which hormone controls urine concentration? What secretes it?
ADH; posterior pituitary
Which structures of the nephron have variable permeability to water? How does it change with dehydration vs excess water?
Collecting duct and terminal portion of the DCT;
Dehydration: more permeable
Excess water: less permeable
Solute concentration of the renal medulla vs cortex. Why?
Medulla has a very high concentration to pull out as much water as possible from urine
What is the function of ADH?
Retains water by increasing collecting duct and terminal DCT permeability to water
Glomerulus function
Produces ultrafiltrate that is isosmosal with blood plasma
PCT function
Actively pumps sodium, glucose, and amino acids back into blood. Chloride and water passively exit
Descending loop of Henle function
Diffusion of water out of filtrate
Ascending loop of Henle function
Actively pumps sodium out of filtrate, mitochondria rich
DCT function
Water passively leaves filtrate
Collecting duct function
Water passively leaves filtrate
To get more concentrated urine, what happens to the cortex/medulla ratio?
Decreases (cortex decreases, medulla increases)
To get more dilute urine, what happens to the cortex/medulla ratio?
Increases (cortex increases, medulla decreases)
Why must the brain take cool blood as opposed to warm blood?
Warm blood will kill the animal
How is blood cooled in endotherms in hot environments?
Increased venous surface area leads to more heat dissipation to surroundings
What are the synapomorphies of Placentalia?
Vas deferens folds over ureters, allowing for descent of testes
Testes caudal to penis
Uterine horns
Dental formula: I3C1P4M3
All teeth but molars replaced
Corpus callosum
What is a bihornate uterus?
Has 2 horns
Why do the testes fold over the ureters in Placentals?
Because the testes descend, unlike in marsupials
What is the maximum amount of horns a uterus can have?
2
Why are twins more common in some placentals but not in others? Ex.
Have bihornate uteruses, which allows for more than one fertilization event; rabbits vs humans
Describe the diversity of the uterus in placentals
Can have varying numbers of horns, cervices, uterine bodies, etc. Hyenas have a very unique reproductive tract (look it up)
What does diphyodont mean?
Teeth are replaced once throughout the lifetime
Which teeth are diphyodont in placentals?
All incisors, canines, and premolars (antemolar teeth)
Which teeth are diphyodont in marsupials?
The third premolar
What is the corpus callosum?
A structure in the brain that connects the two hemispheres together, allowing for communication between active parts of the brain
Why is placentation not a synapomorphy for placentals?
There are some viviparous species of sharks and squamates that also use a placenta
What is the difference between placentas of placentals vs. other placenta-using animals?
Placentals have a much higher diversity of placenta-mother association
Why is a hemochorial placental association dangerous if the pregnancy is terminated incorrectly?
The placenta is directly attached to the mother’s blood vessels. If incorrectly terminated, this could lead to the mother bleeding out if the placenta is removed
Explain how a retrovirus is responsible for the placenta
The retrovirus has immunosuppression capabilities, which are important for the development of a fetus in utero. If not for this suppression, the fetus would be attacked by the mother’s immune system. This suppression would be highly selected for, as it allows for the fetus to be carried by the mother for a much longer period (gestation > lactation)
What is the correlation between the retrovirus and placental association?
Positive (stronger connection to retrovirus = stronger association of the placenta to the mother)
Laurasia consisted of these contemporary countries/continents:
North America, Greenland, Europe, and Asia
Gondwana consisted of these contemporary countries/continents:
Africa, Antarctica, Australia, India, and South America
What is allopatric speciation?
Speciation caused by geographical isolation
Why was Gondwana important for marsupial diversity?
Old world marsupials had little competition with placentals, allowing for extreme niche filling
Which four life mechanisms must be optimized in the face of selection pressures for mammals?
Digestion, endothermy, reproduction, and energetics
Which two traits optimize endothermy in mammals?
Blubber and hair
Which three processes go into reproduction?
Estrus, gestation, and lactation
What are the two mechanisms for digestion?
Physical and chemical
What is needed for physical digestion?
Teeth
Explain the selection pressures of endothermy
Endothermic organisms operate within a specific temperature range. If too much energy is spent on heat production, not enough will be spent on reproduction, growth, and digestion. So, in order to optimize endothermy, they use insulative layers to keep their body heat in, thus not needing to spend the extra energy
Explain the selection pressures of digestion
Physical digestion requires teeth. In order to optimize the energy gain from good, teeth are required to help catch and consume prey items much easier
Explain the selection pressures of reproduction
The life history strategies of mammals heavily depend on optimization. If gestation is focused on, for example, the organism can’t put as much energy into lactation, and vice versa. Energy must be allocated efficiently to ensure the highest survival for the mother and offspring
What are some ectodermal organs we can see in amniotes?
Hair, feathers, teeth, skin, scutes
Why do some tumors have teeth and hair?
Anywhere the ectoderm contributes to, ectodermal organs are able to grow there. If the tumor contains ectoderm, then they can grow
Describe the development of patterning in ectodermal organs
At first, the signals for activators and inhibitors was random. Self-activation caused a spike in activator concentration, which then caused a spike in inhibitor concentration in the same space. This increase and diffusion of the inhibitor decreased the activator around it, which in turn decreased the inhibitor in those same spaces, giving way to high spikes of activator and inhibitor in some spaces, and low drops of activator and inhibitor between the spikes. This is what causes the patterns we see in ectodermal organs
What does the molecular pre-pattern look like?
Spots high in activator surrounded by a gradient of inhibitor, strongest at the border between the two and weakest the farther it diffuses
What follows the molecular pre-pattern?
Morphogenesis, which follows the template of the pre-pattern
What is morphogenesis?
The biological process that causes cells, tissues, or organisms to develop their shape and structure
True/False? The base-patterning cascade for tooth development occurred after vertebrates
False. Before vertebrates
What are some examples of animal classes that show the development of tooth-like structures that occurred before dermal denticles?
Conodonts, chelicerates (spiders, horseshoe crabs), and arthrodires (dunkleosteus)
What was the traditional belief of tooth origins?
Tooth-like structures evolved independently of ectodermal organs (teeth and mouth are separate from ex. placoid scales)
What is the inside-out hypothesis?
Teeth originated from internal pharyngeal structures like gill arches consisting of endoderm
What are the 4 points that evidence the inside-out hypothesis?
- Argument focuses on teeth as endodermal organs exclusively
- To bring teeth into the jaw, the mechanisms to make teeth must have come from the endoderm (jaw is endodermal)
- Skin denticles form from ectoderm
- Unique patterning mechanisms of teeth are inclusive to the oropharyngeal endoderm that were co-opted from endoderm
What is the caveat to the inside-out hypothesis?
It requires that the earliest vertebrates with teeth would have dental precursors within endodermal organs without superficial precursors
What is the outside-in hypothesis?
Teeth originated from external dermal structures, such as skin denticles, which later migrated into the mouth (ectodermal)
What are the 6 points that evidence the outside-in hypothesis?
- Placoid scales look and develop like teeth
- Odontodes form both teeth and denticles
- Odontodes are ectodermal organs, not endodermal organs (pattern the same way and have the same structure as placoid scales)
- Pharyngeal teeth only found in species that had gill slits during development or during life-direct support of neural crest cells as contributors
- Neural crest migration operates with both ectoderm and endoderm for teeth using localized gene regulatory networks (HOX)
- No fossils to date that have been found with teeth exclusively within endodermal organs
What is an odontode?
Developmental precursor in tooth-like structures
Where could odontodes be located in sharks?
On the skin (forms placoid scales) and in the mouth (forms teeth)
What is the caveat to the outside-in hypothesis?
It requires some mechanism to transfer odontode patterning into the oropharyngeal cavity from the outside
What may be a potential mechanism to support the outside-in hypothesis caveat?
Neural crest migration
Why is the outside-in hypothesis generally more supported than the inside-out?
It takes a more developmental approach, so has an evolution-development link (evo-devo)
Why are teeth so important in studying mammalian evolution?
They are extremely variable and fossilize well
Why is constructing phylogenetic trees of tooth development based on tooth characters not entirely useful?
We see a lot of convergent evolution
If a tooth was used for crushing, how might the wear appear?
Uneven surface
Generalist mammals tend to have more ________ because:
Hypsodont; able to ingest tougher vegetation
If a tooth was used for shearing, how might the wear appear?
Lines across the shearing surface
What does tribosphenic mean?
Three-wedge
Describe haplodonty. Which animals had them?
Upper molars were buccal to the lowers, all monocuspid; Pelycosaurs and cynodont therapsids
Describe triconodonty. Which animals had them? What changed from haplodont teeth?
Premolars and molars were established, multi-cusped teeth, determinate growth, and no interaction between uppers and lowers; Sinoconodon and Morganuconodon; addition of mesial and distal cusps
Sinoconodon teeth
Deeply rooted, and showed indeterminate growth (replaced teeth like sharks do)
Morganucodon teeth
Diphyodonty, determinate growth
What is diphyodonty?
Teeth are replaced once
Sinoconodon is the sister taxa to what?
Mammalia
Describe Symmetrodonty. What changed since triconodonty?
Triangulation of main cusps from triconodont pattern, slight interaction between uppers and lowers, converged on many many times through the Mesozoic; shearing interactions between teeth
The slight interaction between the uppers and lowers seen in symmetrodonty suggests what?
A shearing surface (meat eating)
The primary cusp of the trigonid moves _____ in symmetrodonty
Buccally
The primary cusp of the trigon moves _____ in symmetrodonty
Lingually
The cones of the upper teeth have this suffix:
-cone
The cones of the lower teeth have this suffix:
-conid
Describe pre-tribosphenic teeth. What animals had them?
Experimentation of how the uppers and lowers interact, most common mode of interaction = shelf of upper trigon interacts with a new cusp of the lowers, weakly developed talonid (talonid shelf); Cladotheria
Cladotheria is the sister taxon to:
Monotremata
A pulping surface seen in pre-tribosphenic teeth is allowed by:
The addition of a cusp located distally to the rest of the tooth (talonid shelf)
Describe tribosphenic teeth. What animals can these be found in? What’s special about these two clades?
Evolution of protocone to talonid basin connection, evolution of talonid basin, has evolved twice; Boreosphenidans and Australosphenidans; show convergent evolution of tribosphenic molars
The talonid basin serves as a:
Pulping surface
What are the two modern extremes of the tribosphenic molar? Provide an animal example for each
- Enhance grinding function for herbivorous diet; horse
- Enhance cutting function for carnivorous diet; lion
Describe the architecture of the tribosphenic molar in the grinding extreme
Addition of another cusp, pulping-focused
Describe the architecture of the tribosphenic molar in the cutting extreme
Loss of a cusp, shearing-focused
Extremes of tribosphenic molar architecture arised from what?
Optimization of energy from environmental pressure
Are the two extremes of the tribosphenic molar the only two structures we can see in mammals?
No. Adaptive radiation seen in Cenozoic mammals, so it’s more of a spectrum
What is the Cope-Osborn model?
The protocone and protoconid evolved as the primary cusp in both the uppers and lowers. It is based on the function of the protocone and protoconid and works backwards from most complex
What is the current model for tribosphenic tooth development?
Protoconid evolved as primary cusp in lowers only, does not evolve in the uppers until the development of the tribosphenic tooth. It is phylogeny based
Describe why the Cope-Osborn model is less accurate than the current model
C-O relies more on human inference than biology, whereas the current model relies on phylogeny
