chapter 22 · • skull with 2 occipital condyles, secondary bony palate, middle ear with 3...
TRANSCRIPT
Chapter 22
Mammals: Specialized Teeth, Hair, Endothermy, and Vivparity
Evolutionary Perspective
• Fossil evidence – Mammals evolved from reptilian ancestors – Tertiary period (70 mya) - Age of Mammals
• Extinction of many reptilian lineages • Allowed for adaptive radiation of mammals • First mammals were small
– 10 cm – Delicate skeleton – Some herbivores, others hunted – Good hearing – May have been nocturnal
What is a mammal?
• Endothermic and homeothermic – Permits high levels of activity at night – Allows them to stay in one place year
round • Placenta and mammary glands
– Nourish developing young – Give parental care
• Specialization of teeth / secondary palate – Allows for diversified diet – Palate allows for breathing while chewing
• Highly evolved brain – Enlarge neocortex – Allows for memory and fast learning – Elaborate sense organs
Diversity of Mammals
• Characteristics of modern mammals – Hair – Mammary glands – Specialized teeth – endothermy
• When was the 1st evidence of hair? • About 60 mya
• When is it believed that hair actually appeared?
• 130 mya
• Why is evidence of mammalian relationships hard to study? – Mammals evolved very rapidly after the
extinction of the dinosaurs
• Kingdom: Animalia • Phylum: Chordata • Class: Mammalia
– Order Insectivora: • Small, primitive mammals, 3rd largest
mammalian order • Hedgehogs, moles, shrews
• Order Chiroptera – Long, slender bones in arms and hands – Flight membranes extend from body – Mostly insectivorous – bats
• Order Carnivora – Predatory, highly developed sense of smell – Canines well developed – Dogs, cats, bears, raccoons, minks, sea lions, seals,
walruses, otter
• Order Perissodactyla – Hoofed, elongate skull – Odd number of toes – Horses, rhino, zebra, tapir
• Order Artiodactyla – Hoofed, grazing and browsing mammals – Even number of toes – Pigs, hippos, camels, deer, giraffes, cattle
• Order Cetacea – Streamlined, nearly hairless – Insulated by blubber – Paddlelike flippers – Whales, dolphins, porpoises
• Order Xenarthra – Incisors and canines absent – Prominent toes and claws on forelimb – Limbs adapted for climbing or digging – Anteaters, tree sloths, armadillos
• Order Lagomorpha – 2 pairs of upper incisors, one pair lower – Teeth never stop growing – Feed on vegetation – Rabbits, pikas
• Order Rodentia – Largest mammalian order – Upper and lower jaws have one pair of ever-growing
incisors – Squirrels, chipmunks, mice, rats, beavers,
porcupines, woodchucks, lemmings
– Order Primates • Adapted for agility and tree-dwelling • Unspecialized teeth • Grasping digits • Nails on digits • Lemurs, tarsiers, monkeys, gibbons, apes,
humans
• Order Proboscidea – Long, muscular proboscis (trunk) – Second incisor on each side of upper jaw modified
into tusks – African and Indian Elephants
• Order Sirenia – Large, aquatic herbivores – Nearly hairless with thick skin – Flipperlike forelimbs, no hindlimbs – manatees
• Order Monotremata – Egg-laying – Duck-bill platypus, spiny anteater, echidna
• Order Marsupialia – Viviparous pouched mammals – Opposums, kangaroos, koalas, Tasmanian wolves,
wombats, bandicoots, numbats
Mammal Characteristics
• Body covered with hair • Integument with sweat, scent,
sebaceous and mammary glands • Skull with 2 occipital condyles,
secondary bony palate, middle ear with 3 ossicles, 7 cervical vertebrae, pelvic bones fused
• Mouth with diphyodont teeth (no permanent), teeth heterodone in most, single enlarged jaw bone
• Moveable eyelides and fleshy external ears
• 4 limbs adapted for many forms of locomtion
• Circulatory system with 4 chambered heart
• Respiratory system with lungs, voice box and muscular diaphragm
• Excretory system with metanephric kidneys and bladder
• Brain highly developed
• Endothermic and homeothermic • Cloaca present only in monotremes • Separate sexes • Internal fertilization • Young nourished by mammary glands
Tibetan Fox
Mammal Adaptations
• What is the purpose of: – Endothermy? – Hair? – Glands? – Hibernation? – Teeth?
• How have these things increased the survival of mammals?
Evolutionary Pressures
• Mammals naturally found on all continents (except Antarctica) and live in all oceans
• Adaptive radiation made this possible
• External Structure and Locomotion – Skin – Consists of epidermal and dermal layers – Protects from mechanical injury, invasion
by microorganisms and sun – Also important in temperature regulation,
sensory perception, excretion, water regulation
– Hair • Keratinized derivative of the epidermis • Held in hair follicle • Pelage (coat of hair) consists of 2 kinds of hair
– Short, insulating hair – Longer, outer hairs
• Hair must be shed (molting) • Important for sense of touch • Guard hairs (vibrissae)
– Thick – Found around legs, nose, mouth, eyes – Very sensitive to movement
• Almost no hair: – Naked mole rats
• Reduced hair: – Large mammals in warm climates – Aquatic mammals
• Hair color – Depends on amount of melanin in the hair – Most coats are dark above and light underneath
Homework
• Take Notes on Skin – Page 390-391
• The skin of mammals – Features
• Hair • Variety of epidermal glands • Stratified, cornified epidermis • Dermis may be thicker than epidermis
– Epidermis • Composed of stratified squamous epithelium • Rapid cell divisions push skin to surface • Dead cells become keratinized • Keratinized cells make out outer layer (stratum
corneum) • Keratin is water-proof
• Dermis – Thickest portion – Contains blood vessels, lymphatic vessels,
nerve endings, hair follicles, small muscles and glands
• Hypodermis – Loose connective tissue, adipose tissue
and skeletal muscles
• Sweat pores – Regulates body temperature – Found in humans and horses – Sudoriferous glands (sweat)
• Produce sweat for cooling • Can produce pheromones
• Sebaceous glands (oil) – Connected to hair follicles – Secrete sebum – Keep skin soft – Secrete protective layer from
microorganisms – Can also act as pheromone
• Hair – Keratin-filled cells from the epidermis – 2 parts
• Shaft – outside of skin • Root – holds hair to skin
– Arrector pili muscles controls hair position
• Nails – Modifications of epidermis – Variety of forms
• Nail – flat plate of dorsal surface of digit • Claw • Hoof • Horns • Baleen plates (found in toothless whales)
Homework
• P. 403 • Read the summary of chapter 23 • Write down the points that pertain to
mammals • Do this on a separate sheet of paper to
be turned in
• Complete Ch 22 notes outlines
• Glands – develop from the epidermis of the skin – Sebaceous glands are associated with hair
follicles and lubricate and waterproof the skin
– Sudoriferous (sweat) glands release water secretions for evaporative cooling
– Scent or musk glands located around face, feet or anus, secrete pheromones
– Mammary glands functional in females, produce milk
• The Skull and Teeth – Jaw articulation distinguishes reptile from
mammal skulls – a single bone articulates the mammalian
lower jaw – mammal secondary palate extends
posteriorly by a fold of skin called the soft palate • almost completely separates nasal passages
from mouth cavity – mammal teeth are specialized for different
functions. heterodonts
– most mammals have 2 sets of teeth in their life • 1st set called deciduous or milk teeth • these teeth are lost, permanent teeth replace
them – adult mammals have up to 4 kinds of teeth
• Incisors most anterior teeth, used for gnawing • Canines long, stout, conical, used for catching,
killing, tearing • Premolars next to canines, have 1 or 2 roots,
used for chewing • Molars have broad chewing surface, 2 to 3
roots
– Zoologists use a dental formula to characterize mammals
– Human Beaver •
– some mammals have no teeth, example armadillo and giant anteaters
– omnivores feed on a variety of plants and animals • Posterior teeth flattened for grinding • Anterior teeth with sharp ripping surface
– mammals that eat plants have flat, grinding posterior teeth and incisors, sometimes have canines
– predatory mammals use canines and incisors for catching, killing and tearing prey
– order Carnivora: 4th upper premolars and 1st lower molar for shearing surface called carnassial apparatus
• The Vertebral Column and Appendicular Skeleton – vertebral column divided into 5 regions – first 2 cervical vertebrae: atlas and axis – exceptions: tree sloth has 6 or 9 cervical
vertebrae, manatee has 6
– trunk divided into thoracic and lumbar regions • thoracic region contains ribs • ribs protect the heart and lungs • Lumbar vertebrae interlock for support, but give
little freedom of movement – appendicular skeleton rotates so
appendages are usually directly beneath the body
– joints limit movement of appendages – bones of pelvic girdle fused in adult
• Muscles – skeleton bears the weight of the body – muscle mass concentrated in upper
appendages and girdles – many running mammals have little muscle
in lower leg – tendons run from muscles high in leg to
cause movement in joints
• Nutrition and the Digestive System – feeding habits of mammals reflect the
ecological specializations that have evolved
– carnivores: • Order Insectivora (shrews) • Order Chiroptera (bats) • Order Edentata (anteaters)
• herbivores – Order Artiodactyla (deer) – Order Perssodactyla (zebras)
– specializations in digestive tracts • herbivores digest food rich in cellulose • some have enlarged cecum at junction of large
and small intestine • cecum is a fermentation pouch where
microorganisms aid in cellulose digestion • ruminants include sheep, cattle, and deer • ruminant stomachs modified into 4 chambers
– 1st 3 chambers for storage and fermentation
• Circulation, Gas Exchange, and Temperature Regulation – eutherian mammals must distribute gases
and nutrients to fetus – maternal and fetal blood are exchanged
across the placenta – nutrients, gases and wastes diffuse
between fetal and maternal blood supplies
– Gas Exchange • high metabolic rates require efficient gas
exchange • mammals have a muscular diaphragm that
separates the thoracic and abdominal cavities • inspiration results from contraction of
diaphragm and expansion of rib cage • expiration is from elastic recoil of lungs and
relaxation of inspiratory muscles
– Temperature Regulation • mammals are widely distributed • nearly all face temperatures that require them
to dissipate excess heat and conserve and generate heat at other times
• 2 categories of heat-producing mechanisms – Shivering thermogenesis is a muscluar activity – Non-shivering thermogenesis involves heat
production by general cellular metabolism and the metabolism of brown fat
– mammals are insulated by pelage and/or fat deposits
– counter current heat-exchange systems help regulate heat loss from exposed areas
– excess heat is radiated into the air from vessels near the surface of the skin
– evaporative cooling occurs in sweat glands or surfaces during panting
– animals in hot environments can radiate heat from ears(jackrabbits and elephants)
– small mammals avoid heat by burrowing
• Winter Sleep and Hibernation – Winter sleep is when an mammal becomes
less active, but could easily be woken up • example: bears and racoons retreat to dens in
the winter – Hibernation is a period of winter inactivity in
which the hypothalamus of the brain slows the metabolic, heart and respiratory rates • example: Orders monotremata, insectivora,
rodentia and chiroptera have true hibernators
Nervous and Sensory Functions
• Senses – Well developed sense of touch
• Receptors associated with hair follicles – Olfaction
• Locates food, recognize members of same species, avoid predators
– Auditory • External ear (pinna) developed • Sensitive to pitch and volume
– Vision • Color vision poorly developed • Early mammals may have been nocturnal • Primates, squirrels and few others have well-
developed color vision
Homework
• Take notes – Hearing p 423 – Smell p 427 – Vision p 429
– Remember that you are focusing on MAMMALS!!!!!