#4: Mammals Flashcards
Fossil record for mammals
very complete
Beginning of Tertiary, 70 MYA started age of mammals, coinciding with the extinction of many reptiles.
Synapsid branch
Amniotes diverged 320 MYA during carboniferous era.
Synapsid skull
Possesses:
1.one lateral temporal opening allowing for advanced muscles for diverse diets
What is nature of evolutionary lineages
IT branches; not linear
The KT boundary
divide between Cretacious & Tertiary eras wherein the former dinosaurs die out and mammals started to thrive
Characteristics of ancient mammalian ancestors
- more vertical limbs than reptiles
- possess a synapsid skull vs diapsid skull in reptiles
- seperation of moracic and abdominal cavity
- possession of mammary gland
- probably ectothermic
- oviparous
- no fur
Characteristics of typical mammal
- endothermic
- fur
- vivaparity (nourishes the embryo inside the body)
Characteristics of therapsids
- hindlimbs directly beneath the body, moved parellel to long axis
- seperation of trunk into thoracic and abdominal regions
- Breathing mechanisms similar to mammals
- most became extinct; only few cynodont therapsids survived
First true mammals
Jurassic era
mostly nocturnal
Later cynodonts
smaller
mammal-like with hair and endothermy
specialized teeth
changes in middle ear/brain improved hearing/olfaction
Additional characteristics of mammals
- mammary glands
- sweat, sebacaceaous, scent glands (all epidermal in origin)
- diaphragm
- three middle ear ossicles
- Four-chambered heart
- large cerebral cortex
Subclass: Protheria
Monotremes
Oviparous, w/ cloaca present
ie duck-billed platypus, spiny anteater
Only mammals that lay eggs
Subclass: Theria consists of what two infraclasses?
Metatheria & Eutheria
Infraclass: Metatheria
Characteristics:
Marsupials
1. Viviparous w/ short gestation period; young often premature
2. marsupium (protective pouch) covers mammary glands; young feed & complete development inside it
3. ie opposums, kangaroos, koalas, wombats
Infraclass: Eutheria
Characteristics:
- Placental mammals.
- Born at advanced stage of development after nourishment in uterus
- Placenta: structure thru which maternal and fetal circulatory systems exchange nutrients & wastes thru diffusion
- Elephants, manataees, anteaters, shrews, bats, otters, horses, giraffes, whales, rabbits, lemmings, monkeys
External structure of mammals
- Skin: epidermis & dermis; protects, regulates temp, helps in sensory perception, excretion
- Hair is keratinized derivative of epidermis; composed of dead cell and periodically molts. Aid in sense of touch; may be modifed into vibrissae (whiskers); traps air, provides insulation
- Sebaceous glands of hair follicles lubricate, waterproof skin. Sweat glands release water for cooling and salt excretion
- Scent glands: secrete pheromones for territorial behavior
- Mammary glands: milk in females
Skull and teeth
- One bone of lower jaws allows jaws to close together.
- Secondary palate separates nasal & oral passages; allows breathing while chewing
- Specialized teeth for different functions and diet (heterodont); reptilian teeth uniformly conical (homodont)
- Milk teeth develop into permanent teeth
5.
adult mammals teeth
4 kinds: 1. anterior incisors for gnawing 2. canines for tearing 3&4. premolars, molars for chewing Mammalian species have characteristic numbers of each, described by dental formula
Nutrition and Digestion
classified into:
Carnivores (fox), omnivores, insectivores (mouse), herbivores
Ruminant Herbivores
Enlarged cecum (pouch w/ microorganisms) for digesting cellulose Ruminants possess extra stomach before actual stomach, used to ferment plant-based matter prior to digestion (ie deer)
Non-ruminant herbivore
Simple stomach, large cecum
ie rabbit
carnivore
Short intestine & colon, small cecum ie fox
insectivore
shore intestine, no cecum ie common shrew
Circulation, gas exxchange
- Four chambered hearts with seperate pulmonary & systemic circuits
- Placenta allows diffusion of nutrients, gases and wastes bet fetal & maternal blood supplies w/out mixing
- Seperation of nasal & oral cavities & long snouts: increased surface area for efficient gas exchange
- inspiration & expiration occur by expanding & contracting volume of thoracic cavity using a muscular diaphragm
Temperature regulation
- Heat production by shivering thermogenesis (muscle activity w/ little movement & non-shivering thermogenesis (metabolism).
- Changing peripheral blood flow
- insulation
- countercurrent heat exchange systems (hands and feet)
- Controlled hypothermia (ie hibernation where hypothalamus slows down the metabolic, heart and respiratory rates.
- Evaporative cooling from sweat glands or respiratory surface.
Excretion and Osmoregulation
- excrete urea (water soluble, cannot be excreted in semi-solid form like uric acid) so leads to some H2O loss
- Water also lost thru sweat glands and respiratory surfaces
- Kidneys reabsorb H2O, produce concentrated urine
- Several behavioral & physiological mechanisms to reduce water loss. Low protein diets reduce urea production; metabolic oxidation of carbs makes H2O
Reproduction & development
- Highly developed viviparity. Allows females to roam but expends > energy.
- Most females undergo estrus cycle when sexually receptive; mediated by hormonal changes that stimulate maturation and release of ova. Uterus also changes to prepare for receiving developing embryos.
- Monestrus: bears; diestrus (domestic dogs); polyestrus (rats)
Monotremes
- oviparous
- nourishment through yolk
- ie platypus
Marsupials
- nourish come from uterine milk (a primitive placenta)
- short gestation period, long lactation period
- ie kangaroo
Eutherians
- embryo implanted into uterine wall
- nourished thru placenta
- ie human
Primates
- Late Cretaceous Era, 65 MYA
- Insectivores were probable ancestors
- Arboreal, diurnal habits favored color vision
- Eyes on front of head, providing overlapping view, depth perception
- Center of gravity shift to hind limbs
- sensitive foot and hand pads for exploration
- Medial digits of hands opposable to allow grasping.
Suborders of primates
- Lemurs & bush babies
2. Tarsiers, New & old world monkeys, gibbons, apes (gorilla, chimpanzee, orangutan, humans)
Evolution of hominins
- First apes 25 MYA
- 5-7 MYA, Hominids diverged from other apes when African apes became terrestrial, and upright posture provided better view and freed the hands.
- Bipedal locomotion w/ changes in skeleton and skull (ie curved vertebral column, shorter pelvis, reduction in size of jaws, teeth, etc.)
First Hominid: Australopithecus (Lucy) 4 MYA
show pelvis and leg structure typical of bipedalism
Six Homo species, starting to appear 2.5 MYA
Homo sapiens, arising in Africa 195K years ago.
