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 1 st 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: 4 th upper premolars and 1 st 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 1 st 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
Senses Nervous and Sensory Functions 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 welldeveloped color vision
Homework Take notes Hearing p 423 Smell p 427 Vision p 429 Remember that you are focusing on MAMMALS!!!!!