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The Mammals. Fred Searcy Zoology. Mammals. Kitti’s Hognosed Bat of Thailand 1.5 g Blue Whale 130 metric tons Ubiquitous 4600 species Compared to 9000 birds 24,600 fish 800,000 insects. Evolution. Evolution. Synapsid ancestor Excellent fossilization and preservation

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The mammals l.jpg

The Mammals

Fred Searcy

Zoology


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Mammals

  • Kitti’s Hognosed Bat of Thailand 1.5 g

  • Blue Whale 130 metric tons

  • Ubiquitous

  • 4600 species

    • Compared to

      • 9000 birds

      • 24,600 fish

      • 800,000 insects



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Evolution

  • Synapsid ancestor

  • Excellent fossilization and preservation

  • Herbivorous and carnivorous pelycosaurs

  • Lead to carnivorous therapsids

  • Lead to cynodonts (faster metabolic rate)

    • Musculature of jaw muscles for stronger bite

    • Facilitated capture of prey and feeding

    • Turbinate bones in nasal cavity retain body heat by warming air prior to entry

    • Secondary bony palate to breather while eating (and nursing young to feed and breathe)

    • More upright posture

    • Muscular diaphragm for breathing


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Characteristics

  • Hair

  • Integument with sweat, scent, sebaceous and mammary glands

  • Skull with 2 occipital condyles; secondary palate; turbinate bones; middle ear with incus, malleus, stapes; 7 cervical vertebrate; pelvic bones fused

  • Diphyodont dentition (2 sets of teeth); lower jaw a single, large bone

  • Moveable eyelids; fleshy external ears

  • 4 chambered heart; persistent left aorta, non-nucleated erythrocytes

  • Lungs with alveoli; larynx, secondary palate to separate food passage from respiratory passage; muscular diaphragm

  • Metanephric kidneys with ureters into bladder

  • Highly developed brain with well developed cerebral cortex; 12 pairs cranial nerves

  • Endothermic and homeothermic

  • Devolution of cloaca (found only in monotremes and marsupials)

  • Separate sexes with specific organs for fertilization; male determines sex

  • Embryo in utero with placenta (except monotremes); fetal membranes: amnion, chorion, allantois

  • Young nourished by milk from mammary glands


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Integument & Its Derivatives

  • 1st line of defense against

    • Infections

    • Toxins

    • Retards water loss

    • Cools body

    • Weatherproofing chemicals (keratin, cellulose)

  • Thicker where no hair

  • Epidermis, dermis


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Epidermis

  • Mostly stratified squamous epithelia

  • Large amounts of keratin

  • Sloughed off as new formed

  • Non-keratinized cells may contain melanin


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Dermis

  • 0.6 to 3mm in thickness

  • Irregular connections with epidermis via papillae (papillary layer). Underneath lies the:

    • Dermal layer composed mostly of dense connective tissue (reticular layer)


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Hair

  • Originates in epidermis

  • Two forms:

    • Pelage (underhair – soft, dense, insulation)

    • Guard hair (coarse, wear and tear, coloration)

  • Composed of dead keratinized epidermal cells

  • From an epidermal follicle

  • Three layers:

    • Medulla

    • Cortex – may contain pigments

    • Cuticle – keratinized scales


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Hair Continued

  • Eventually stops growing

  • Replaced with new hair

  • Periodic molts

    • Humans molt year round

    • Foxes once a year

    • Some may molt up to 3 times

    • White coats in winter an example of leukemism (not albinism)

  • Types:

    • Sensory hairs on snout (vibrissae – cat’s whiskers)

    • Quills of porcupine are hair


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Horns & Antlers

  • True horns

    • arise from a core of bone from the skull

    • Enveloped in sheath of epidermis

    • Not shed

    • Cattle and sheep

  • Antlers

    • Shed after each breeding season

    • Outgrowths from skull

    • Temporarily covered in epidermis (velvet stage)

    • Deer, antelope, caribou (except for caribou, only males produce antlers

  • Rhino “horn” is actually fused hair


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Glands

  • Methods of classification

    • Mode of secretion

    • Method of discharge

    • Unicellular or multicellular

    • Structural geometry


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Mode of Secretion

  • Exocrine – secrete their product to an internal or external surface

  • Endocrine – secrete their product into blood stream and lymph system

  • Mixed – combination of both


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Method of Discharge

  • Merocrine – release product through their membrane and cell remains intact

  • Apocrine – material released also includes a portion of the cell’s cytoplasm

  • Holocrine – results in the destruction of the cell when product is released


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Composition and Structural Geometry

  • Single cells

  • Multicelluar

    • Ductless

    • Ducted

      • Tubular

      • Alveolar (acinar)

      • Tubulalveolar

      • Saccular

      • Other variations


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Categories

  • Sweat glands

  • Scent glands

  • Sebaceous Glands

  • Mammary Glands


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Sweat Glands

  • Tubular, coiled

  • Located all over body

  • Specific to mammals

  • Produce fluid (mostly water) to cool the body (evaporation)


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Scent Glands

  • Various functions

    • Communication

    • Marking territories

    • Warning

    • Defense


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Sebaceous Glands

  • Sebum (fatty material)

    • Keeps skin and hair pliable and glossy

    • Associated with hair follicles

    • Holocrine type

    • Usually doesn’t sour or turn rancid


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Mammary Glands

  • Origin in epidermis of embryo

  • Two milk lines form along abdomen

  • Mammaries develop along milk lines

  • 10 mammary glands in mammals (including humans)


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Food and Feeding

  • Variety of strategies

    • Herbivorous

    • Carnivorous

    • Omnivorous

  • Variations of these strategies

    • Coprophagy (rabbits)

    • Insectivorous

    • Herbivorous

      • browsers,

      • Grazers

      • Gnawers

  • Diet tied to physical structure and metabolism of animal


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Teeth

  • Heterodont Dentition – differentiated according to function

    • Incisors – cutting & biting

    • Canines - piercing

    • Premolars – shearing, crushing, grinding

    • Molars – shearing, crushing, grinding

  • Diphyodont Dentition (two sets)

    • Baby or deciduous

    • permanent


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Dental Formulas

  • Provides numbers of specific teeth for upper and lower half of the jaw


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Body Weight & Food Consumption

  • Smaller the animal, faster the metabolic rate, the more the food required


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Migration

  • Not all migrate

  • Few seasonal migrations

  • Most migrations center around home ranges

    • Based on food abundance

  • Longest are marine mammals

    • Gray whale 18,000 km (11,2500 miles) from Alaska to Baja California and back


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Flight & Echo Location

  • Bat – only flying mammal

    • Nocturnal and crepuscular (active at twilight)

    • Echolocation

      • Pulses emited 5-10 millisecs

      • Modulated at beginning with high frequency of 100,000 hz then down to 30,000 hz (ultrasonic range)


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Reproduction

  • Majority have estrous cycles

    • Monestrous vs polyestrous

    • Old World monkeys and humans have menstrual cycles



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Estrous Cycles

Source: University of Wyoming at http://www.uwyo.edu/wjm/repro/tab4-4.htm


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Reproductive Patterns

  • Oviparous Mammals (Prototherians)

  • Viviparous Mammals with pouches (Metatherians)

  • Viviparous Mammals with Placenta (Eutherians)


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Prototherians – The Monotremes

  • Gr monos = single, trema = hole)

  • Egg layers

    • Duck-billed platypus

    • Echidnas

  • After hatching, young feed on milk of mammary glands

  • No nipples


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Therians – the Marsupials

  • Pouched animals who give live birth

  • Young crawl into pouch

    • 235 days in case of kangaroos

  • Not true placentals

    • Have an ephemeral choriovitelline placenta

  • While nursing, mother often becomes pregnant again

    • Undergo embryonic diapause where embryos don’t develop until first brood leave pouch

  • Not all have embryonic diapause – not all have pouches

  • O’possum is only North American marsupial – does have pouch

    • Birth occurs 13 days after fertilization

    • Young in pouch for 2-3 months

    • Remain on mother’s body for additional 1-3 months


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Eutherians – The Placental Mammals

  • Marsupials have prolonged lactation; placentals have prolonged gestation

  • Embryo remains in uterus and nourished until live birth in the placenta

    • From either choriovitelline placenta or a chorioallantoic placenta



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Growth

  • Some mammals are precocial

  • Human growth is slower than any other mammal

  • # of progeny tied to mortality rate – the higher the number of progeny, the higher the mortality rate


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