Class Mammalia Flashcards
What kind of skull do they have ?
all mammals are synapsids
Why this type of morphology for the skull?
- associated with attachment of mandibular muscles (important for chewing , biting)
Mammals have various skeletal changes
1) turbinate bones in nasal cavity (retain body heat)
2) bony secondary palate ( can breathe & chew at same time )
3) loss of lumbar ribs but evolution of diaphragm (more spinal flexibility)
Which lineage give rise to early mammals?
One cynodont lineage
What were early mammals like ?
-small & mouse-like but important adaptations nonetheless
- diphyodont dentition (teeth replaced only once)
former bones of jaw become incorporated into middle ear
-quadrate & articulate bones become malleus
& incus
- what are the 3 major lineages by end of mesozoic
monotremes, marsupials and eutherians.
what characterize the modern mammal lineage ?
1) Mammary glands
2) Hair
3) Fat layer
4) 4 chambered heart
5 ) Usually shell-less embryo
mammary glands
milk (fat, sugar, proteins mineral vitamins)
relative composition varies
Fat layer
Under the skin
to retain heat
endothermic
4 chambered heart
everything separated .
- dont mix oxygenated & non oxygenated blood.
- support high metabolic rate
Shell less embryo
embryo avoid desiccation by developing inside mother.
Integumentary tissue
- all vertebrates have dermis and epidermis
- but generally thicker skin in mammals with presence of hair & many glands.
Hair growth
- hair grows from a hair follicle
- epidermal cell but sunk into dermis
- growth by cell proliferation in follicle – dead once out of follicle
- hair shafts become filled with keratin (sound familiar?)
2 kinds of hair forming the pelage (fur coat)
underhair: dense & soft for insulation
guard hair: coarse & long for protection & colouration
Does it stop growing ?
Yes, hair typically stops growing once it reaches a certain length
- normally stays in follicle until a new growth starts – then falls out.
Molting
some only molt once/year (every summer)
most molt twice/year (spring & fall)
Hair isn’t just for isolation
camouflage or warning colouration
vibrissae
whiskers
modified as sensory structures
Horns or horn like structure
- Mammals are the only animals that are able to grow it.
-true horn are hollow sheaths of keratinized epidermis surrounding core of bone arising
from skull
both sexes, grow continuously, not branched,
e.g. sheep, cattle
Antlers
- antlers are composed of solid bone when mature
-covered with vascularized soft skin (Velvet) during growth
grown by males , shed annually after breeding season
-only in deer family
Glands
derivatives of epidermis separated into 4 types : 1) sweat glands 2) Scent glands 3) Sebaceous glands 4) mammary glands
Sweat glands
-tubular & coiled
- occur over much of body surface but absent in other vertebrates
-eccrine glands secrete watery fluid
-usually in hairless regions
function in evaporation cooling
-apocrine glands always open into a hair follicle in specific body regions
- fluids not involved in cooling
- correlated with reproductive cycle
Scent glands
- locations & functions vary
- communication, marking territory,attracting mates, defence
- also in humans (but tend to dislike own scent!)
Sebaceous glands
-mostly associated with hair follicles
-gland cells discharged along with fatty mixture (sebum)
-keeps hair & skin pliable & glossy
very important for waterproofing in marine mammals.
Mammary glands
- occur on all females & accompanied by adipose tissue
- rudimentary on all males
- monotremes have these glands but lack nipples
4 types of teeth
incisors
canines
premolar
moalrs
Incisors
simple crowns & sharp edges
- snipping / biting
canines
long, conical crowns
-piercing
premolars
compressed crowns, cusps, shearing, slicing, crushing, grinding
molars
same as premolars
Large masseter
large masseter for side-side movement
-articulation best for grinding motion
Diastema
gap to fit large tongue
in herbivores
Large temporalis
- large temporals for up-down movement
- articulation best for providing strong downward force
grazers and browsers
- ingest a lot of cellulose
- diets rich in carbon but low in protein
How do herbivore digest cellulose
- lack enzyme needed to digest cellulose
- depend on specialized bacteria & protozoa in digestive tracts
- bacteria concentrate in foregut or hindgut
- aerobic respiration replaced by fermentation converts sugars
What part of intestine is part in cellulose digestion ?
-digestion takes place less efficiently in
hindgut
-long intestinal tract slows food passage
-well-developed caecum to allow fermentation by mutualistic bacteria
Where is the cellulose most digested.
- most digestion in foregut
4 - compartment stomach
ruminants
The rumen and reticulum are inhabited by what?
The function of it ?
- inhabited by anaerobes and function as fermentation vats
cud
regurgitate fermented material
finer material (digestion of herbivore) enters…
the reticulum , then omasm and obomasum
microorganism in rumen produce what?
produce fatty acids
carnivores stomach
commonly large , expandable stomachs
Why is it useful to have an expandable stomach ?
- can’t be sure when next meal will be
- takes a lot of energy
is the gut of carnivore long or short ? why?
- carnivores have relatively short gut
- animal material easier to break down & assimilate
Cecum present in carnivores ?
very reduce or absent
Omnivores
- omnivores ingest both plant & animal material
- dependent upon season & needs
- very opportunistic feeders
longest migration are made by …
marine mammals (seal and whales)
Migration is cause by…
temperature and other environmental factor with seasonal variations ( rain fall)
Mammalian flight
-while bird & bat wings are homologous, flight evolved independently
-flight also evolved independently in several
groups of mammals
-but only bats capable of powered flight
-others actually glide , not fly
How do bats stay competitive against the
much more dominant birds?
mostly nocturnal – occupy largely unoccupied niche
success are attributable to 2 features in bats
flight and echolocation
echolocation , how does it works
- emit short sound pulses of very high frequency (ultrasonic)
- spaced so receive echo of each before next emitted (prevent jamming)
- pulse bounces off prey & is received back by ears
- creates mental image of surroundings
Other types of bats
dont use echolocation .
fruit bats
- vampire bats : secrete anticoagulant
Mating season
- Most mammals have definite mating seasons
- birth & rearing of young during most conditions
- seasonal reproduction in deer levels of hormone melatonin goes up as daylength goes down
- stimulates reproductive hormones
Fertility restrcited to
certain time of estrous cycle
- female only receptive to mating while in estrus ( heat)
estrus
heat
Subclass Prototheria
aka monotremes
- egg-laying (oviparous)
- embryos develop 10-12 days in uterus
- thin, leathery shell secreted prior to laying eggs
- hatch relatively undeveloped after ~12 days
- feed on milk produced by mother’s mammary glands
subclass theria
contain 2 subgroups
Both are viviparous ( no egg)
1) Metatheria
2) Eutheria
Infraclass Metatheria
a.k.a marsupials
-most embryonic development completed in a pouch (not the uterus)
- only have a transient type of placenta (choriovitelline or placenta)
-early embryo floats freely in uterine fluid while encapsulated in shell membranes
- “hatch” from membranes but do not implant
- erode depressions in uterine wall to lie in & absorb nutrient secretions from yolk sac placenta
- brief gestation – birth to embryonic young
young crawl into pouch for prolonged period of lactation & parental care
Infraclass Eutheria
a. k.a. true plancental mammals
- prolonged period of gestation
- yolk sac placenta replaced by chorioallantoic placenta
- highly vascularized with close connections between embryo & mother (diffusion of nutrients, wastes, respiratory gases)
Why would a longer gestation
period confer an advantage?
eutherians have a longer gestation period but generally have to spend less time in total
caring for their young
-less time until next bout of mating – more offspring -more genes passed on
-but enormous variation among mammals in condition of young at birth (all are altricial but vary in how much)
Subclass Prototheria
key traits: a.k.a. monotremes
-egg-laying (oviparous)
-members: only one order found in Australia, Tasmania & New Guinea
ex : platypus
Subclass Theria infraclass Metatheria
key traits: -most embryonic - development completed in a pouch members: a.k.a. marsupials not just found in Australia! (but most diversity & largest ) -marsupial lineage in Australia has been separated from eutherians for very long time - much convergent evolution – marsupials fill ecological niches usually held by eutherians elsewhere
ex: Kangaroo
Koala
North america = opossum
Infraclass Eutheria (key traits)
key traits:
- true placental mammals
- members: distributed worldwide
- greatest diversity
Order Cetacea (trait)
Think about dolphin and whales
- aquatic
- no hind limbs (no pelvic fins like fish)
- blowhole for gas exchange into lungs
- produce sounds (echolocation)
- lower jaw receives and transmit
- conical teeth (dolphin)
porpoises
no melon
Flat teeth
whales
also communicate vocally & use echolocation (but no melon )
some have tooth
- others are filter feeders (toothless)
whales are closely related to…
And share some characters with…
hoofed mammals t
- some characters with ungulates
Order Rodentia (key traits)
think mice & rats , beaver, squirrels key traits: -2 prominent upper & lower incisors - grow continually -adapted for gnawing members: most numerous of all mammals (number & diversity)
Order perissodactyla (traits)
key traits:
- hoofed with an odd number of toes
- 1 or 3 toes enclosed in keratinized hoof
- all are herbivorous
members: a.k.a. ungulates
e. g. horses, zebras, rhinoceroses
Order artiodactyla
key traits:
- hoofed with an even # of toes
- 2 or 4 toes enclosed in cornified hoof
- many have horns or antlers
- most are ruminant herbivores
- members: many domesticated species
e. g. pigs, cattle, sheep, goats, deer
Order Carnivora
key traits: -consumption of flesh prominent canine teeth – tearing members: mainly larger predators but vary in degree of carnivory ex : cats, bears, wolves
Order Primates
many adaptation to life in trees A. modified hand b. modified feet C. relatively large brains D. close -set eyes
A. modified hands
mobile thumb that is fully opposable in monkeys & apes – 5 digits
- allows for grasping
- flat nails (instead of claws)
- skin ridges on fingers (fingerprints)
B. modified feet
- opposable big toe
- use like a grasping hand
- humans are the exception
- not good for bipedal lifestyle
C. relatively large brain
also more folding
increases surface area
D. close set eyes
- binocular vision
- brain takes information from each eye & unites into 1 picture
- interprets slight differences between each view as depth
- produces a 3-D picture (stereoscopic)
Monkey and ape form a clade called
Anthropoidea
Apes clade
Hominoids
Old world monkey
-tail not used for gripping
-tree and ground dwelling
- nostrils open downwards
old world (africa and asia)
New world monkeys
prehensile tail (grasp things)
- tree dwelling
- nostrils open to the sides
Ne world= South america
Hominoids traits
non-human hominoids only in old world
- all except gibbons are larger than monkeys
- relatively long arms
- short legs
- no tail
- larger brain in proportion to body size more complex behaviors
Homo sapiens
- relatively largest brain
- bipedalism
- reduced jawbones (flat face) and muscles , teeth
Human evolution
- humans descended from extinct hominoids more closely
- related to humans than to chimps
- earliest hominid fossils from 6-7 MYA
- had some, but not all, derived characters of humans
e. g. reduced canines, more upright & bipedal
Mosaic evolution
different rates of evolution for different features . -characters did not evolve in tight unison
e.g. bipedalism while brains still relatively small
Autralopiths
- hominids from time of increased diversity 2-4 MYA
- fossils indicate full bipedalism
- “lucy”
- brain size similar to chimpanzee long lower jaw
Selective pressures towards bipedalism
-changes in leg bones, pelvic structure, muscles - long distances on 2 legs only -more arid environment - less energy for bipedal walking than on all fours
Use of tools
- earliest accepted evidence from 2.5 MYA
- cut marks on animal bones
- suggests stone tool use before large brains evolved
Early members of genus Homo
substantially larger brain
brain shape suggests limited speech possible
more complex culture – used fire
-reduced sexual dimorphism
-perhaps more pair-bonding & biparental care
Homo neanderthalensis
- a.k.a. Neanderthals
- once considered to be ancestors of H.sapiens in Europe
- DNA analyses indicate Neanderthals form a clade while living Europeans more closely related to living Africans & Asians
- migrating H. sapiens may have been superior competitors.
- ancestor of all humans originated in africa.
