Mammals!!! NB #159 Write this on your own paper. Mammal Taxonomy Kingdom: Animalia Phylum: Chordata...
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Transcript of Mammals!!! NB #159 Write this on your own paper. Mammal Taxonomy Kingdom: Animalia Phylum: Chordata...
Mammals!!!NB #159
Write this on your own paper
Mammal TaxonomyKingdom:
Animalia◦ Phylum: Chordata
Subphylum: Craniata Infraphylum:
Vertebrata Class: Mammalia
Evolution of Mammals Began evolving 320 mya “Age of Mammals” began 70
mya◦ Flourished after the extinction of
many reptiles The early group of mammal
ancestors were part of the “synapsid branch”◦ Large sails- raised body
temperature at night◦ Lacked hair◦ Egg layers (oviparous)◦ Either herbivores or carnivores◦ Large anterior teeth
Gap between these teeth and the posterior teeth allowed the jaw to close
◦ Arched palate- strengthened the upper jaw and allowed air to pass over prey in the mouth
Evolution of Mammals Therapsids
◦ Predators- teeth mostly in the front of the mouth to hold & tear prey
◦ Herbivores- large space separating anterior & posterior teeth Posterior teeth specialized to shred plants
◦ Hindlimbs directly beneath body◦ Changes in ribs allowed for mammalian
breathing methods Over 185 my, mammals evolved as
small (size of domestic cats) and nocturnal◦ Development of hair and endothermy◦ Teeth specialized to facilitate digestion◦ Brain specialized for hearing and
smelling◦ First “true mammals” present in the
Jurassic Period (oldest fossil is 160 myo)◦ Mammals began to flourish 65 mya after
the Cretaceous-Tertiary mass extinction (caused by the meteorite)
Characteristics of Mammals
Mammary glandsHairDiaphragmThree middle-ear
ossiclesHeterodont dentitionSweat glandsSebaceous glands (oil)Scent glandsFour-chambered heartLarge cerebral cortex
Diversity of Mammals5,400 speciesDominant terrestrial
animals on every continent (even extended to the oceans)
Two lineages◦ Prototheria-
monotremes◦ Theria- marsupials &
plancental mammals
External StructureBody covered in two-layered
skin (epidermis & dermis)◦ Used for protection &
temperature regulationHair- unique to mammals
◦ Grows from a follicle in the skin◦ Pelage- coat of hair◦ 2 Types:
Long guard hairs- protection Short underhairs- insulation
◦ Periodically molt old hairs◦ May grow a thicker pelage in
the winter and/or change pelage color
External StructureOther hair functions:
◦ Sense of touch◦ Insulation
Air spaces Arrector pili muscle
Muscle around hair follicle that contracts & allows the hair to stand upright
Amount of air trapped in the pelage increases, which provides more insulation
Also contract in response to threat (fight-or-flight) Allows the animal to look bigger
◦ Camouflage- color due to melanin
◦ Hair reduced in large mammals in hot climates (hippo) and aquatic mammals (whales)
External Structure Claws- used for locomotion &
offensive/defensive behavior◦ May modify to form nails or hooves
Sebaceous glands- secretes oil to waterproof & lubricate the hair & skin
Sudoriferous glands- secretes sweat that aids in cooling
Scent or musk glands- secrete pheromones for defense, recognition, & territory
Mammary glands- present in all mammals, but only functional in females◦ Secrete milk to nourish young◦ Secreted through nipples or teats in most
mammals◦ Monotremes secrete milk from the skin
and into depressions on the belly
Skull & TeethHeterodont- teeth are
specialized for different functionsTeeth are set in sockets of the
jab2 sets of teeth throughout life
◦ 1st- deciduous or milk teeth◦ 2nd- adult/permanent teeth
4 kinds of teeth-◦ Incisors- front teeth, used for
gnawing or nipping◦ Canines- long & conical, used for
catching, killing, and tearing prey◦ Premolars- truncated for chewing◦ Molars- broad surface, used for
chewingDental formula- each mammal
species has a set # of teeth
Dental Formula
Teeth of the upper jaw above teeth of the lower jaw in the order: incisors, canine, premolars, & molars
Nutrition & DigestionDigestive tract
specialized for dietMany different diets
◦ Insectivores- anteaters◦ Omnivores- bears◦ Carnivores- lions◦ Herbivores- horses
Enlarged cecum in the intestines to digest cellulose (thanks to microorganisms)
Circulation, Gas Exchange, & Temperature Regulation
Four chambered heartCirculatory system allows
maternal and fetal blood exchanges across the placenta
Breathe with lungsDiaphragm allow air to
enter the lungsMaintain temperature
with insulating fat layers & cool with longer appendages and/or sweating
Winter Sleep & Hibernation
Winter sleep – burrowing under the snow and become less active (still alert)
Hibernation- hypothalamus of the brain slows the metabolic, heart, & respiratory rates◦ “True hibernators”-
Monotremes, moles, shrews, rodents, & bats
◦ Lose around 1/3-1/2 of body weight during hibernation
◦ Aroused from hibernation occurs by metabolic heating (takes several hours)
Nerves & SensesComplex brainMay communicate
over long distances through olfaction (smelling)
Vision is an important sense◦ Color vision not as
developed as reptiles (except for primates)
Reproduction & Development Internal fertilization
Most mammals are viviparous (give birth to live young)◦ Advantage: allows the mother to remove
ties to a nest◦ Disadvantage: growing a fetus requires a
lot of energy Oviducts are modified into one or two
uteri Reproductive cycles: Most have
definite times during the year to mate◦ Usually determined by the season◦ Estrus cycle- when females are receptive
to males Determined by hormones
◦ Some mammals begin ovulating post copulation
Gestation period- length of time young develop within the female reproductive tract
Altricial young- helpless at birth Precocial young- walk and run shortly
after birth