11 - Mammals Flashcards
Mammals and ancestral amniotes
most closely related group to ancestral amniotes1
Premammalian synapsids
present during mid-triassic
Bad thermoregulation so probably not true homeotherms (dimetrodon and cynognathus)
Evolutionary perspective mammals
- first amniote lineage
- started 200 mya with therapsid subgroup
Therapsid subgroup
- mammal-like teeth
- hindlimbs directly beneath body
- separation of thoracic and abdominal regions
- near extinction 240 mya (dinos took over)
During dinosaurs
- mammals survived nocturnally (bad colour vision)
Mammalian radiaton
- 65 mya
- mass extinctioin of dinos and other taxa
- tertiary period “age of mammals”
- mammals were able to be outside during the day
2 subclasses of mammals
- prototheria
- theria
Subclass prototheria
- cloaca, oviparous
Subclass prototheria infraclass
ornithodelphia (monotremes)
Subclass theria 2 infraclasses
Metatheria (marsupials)
Eutheria (placental mammals)
Monotremes
- 6 species
- found in australia/new zealand
- eggs
- ex: echidnas and platypus
Marsupials
- around 250 species
- viviparous but short gestation periods
- born early but not developed so feed and develop in marsupium (pouch)
- ex: koalas, kangaroos
Biogeography of mammals
Movement of continents explains the current distribution of mammals
Hair
- guard hairs
- insulating underhair
- whiskers provide sense of touch
Glands
- sebaceous (oil)
- sudoriferous (sweat)
- scent (pheromones)
- mammary (nutrition for offspring)
Teeth
- heterodonts (unlike homodont in reptiles where they’re uniformly conical)
- specialized for different functions
- deciduous (milk) teeth and permanent
- single replacement of teeth is the diphyodont condition. reptiles are polyphydont
diphyodont
single replacement of teeth
4 types of teeth
- incisors
- canines
- premolars
- molars
humans teeth
2,1,2,3 on each side
incisors, canines, premolars, molars
Diastema
missing teeth section separates the biting teeth at the front of the jaw, from the chewing teeth at the rear
Skeleton
- vertebral column
- appendicular skeleton
Vertebral column 5 regions
Cervical thoracic lumbar sacral caudal
Appendicular skeleton
- rotates under body
- appendages move in anteroposterior plane (makes them faster than reptiles)
Digestive systems
Adapted for diverse feeding habits that reflect ecological specializations
Herbivores/ruminants: rumens, cecums and spiral loops (long digestive system)
Carnivores: much smaller, no storage/fermenting compartments
Heart, circulation
- complete separation of pulmonary and systemic circuits
- similarities with bird hearts result from convergence within synapsid and archosaur lineages (adaptations to active lifestyles)
Fetal circulation
- nutrients/gases/wastes exchanged by diffusion across placenta
- in fetus, blood shunted away from lungs until inflated at birth
2 structures involved in shunting
- foramen ovale (shunt between left and right atria)
- Ductus arteriosus (most blood in pulmonary artery bypasses lungs)
These close off after birth
Respiration
- respiratory passageways highly branched with large surface areas
- thin membranes and high surface area
- larynx, trachea, bonchi (1,2,3) bronchioles, alveoli
Heat producing mechanisms
- shivering thermogenesis
- nonshivering thermogenesis (metabolism of brown fat: hibernation)
Heat conservation
- insulating pelage and fat deposits (ex: hair, and blubber)
- shunt blood from surface to core to keep it warm in water
- heat conserving postures
- countercurrent heat-exchange systems
Cooling
Radiation into air Evaporative cooling (sweat glands/panting)
Winter sleep
- less active and metabolic rates drop somewhat
- easily aroused/periodically wake
- body temperature doesn’t change much
- bears/raccoons
Hibernation
- metabolic rates drop substantially
- hypothalamic thermostat reset
- not easily aroused
- insectivores, rodents, bats
Conserving water; kidneys
- very efficient kidneys
- long loop of nephron (loop of henle)
- concentrates urine and conserves water
- countercurrent exchange system!
- longer loop = better water usage
More strategies for water conservation
- Dry feces
- Nocturnal habits
- Water condensation in respiratory passages
- Low protein diets
2 reproductive cycles
- estrus cycle
- menstrual cycle
Estrus cycle
- Female behaviourally and physiologically receptive to male
- hormonal changes stimulate maturation of ova and ovulation
- uterine lining proliferates
- vaginal swelling and discharge
Males show heightened interest in females
Menstrual cycle
- humans, apes, monkeys
- periodic proliferation of uterine lining that correlates to maturation of ovum
- Sloughing of lining occurs in absence of fertilization
Delayed fertilization
Adaptation to winter dormancy in some bats.
suspended or slow growth of the embryo that can occur after implantation has occurred but prior to birth
Embryonic diapause
- Development arrested after fertilization
- development occurs when resources are most plentiful
Modes of development
- monotremes are oviparous
- all others are viviparous
Viviparous
marsupials: nourished via uterine milk following short gestation period
Eutherian mammals: form placenta and have long gestation periods
