The Mammals

1. The Mammals Fred Searcy Zoology

2. 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

3. Evolution

4. 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

5. 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

6. 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

7. Epidermis • Mostly stratified squamous epithelia • Large amounts of keratin • Sloughed off as new formed • Non-keratinized cells may contain melanin

8. 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)

9. 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

10. 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

11. 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

12. Glands • Methods of classification • Mode of secretion • Method of discharge • Unicellular or multicellular • Structural geometry

13. 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

14. 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

15. Composition and Structural Geometry • Single cells • Multicelluar • Ductless • Ducted • Tubular • Alveolar (acinar) • Tubulalveolar • Saccular • Other variations

16. Categories • Sweat glands • Scent glands • Sebaceous Glands • Mammary Glands

17. Sweat Glands • Tubular, coiled • Located all over body • Specific to mammals • Produce fluid (mostly water) to cool the body (evaporation)

18. Scent Glands • Various functions • Communication • Marking territories • Warning • Defense

19. 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

20. 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)

21. 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

22. 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

23. Dental Formulas • Provides numbers of specific teeth for upper and lower half of the jaw

24. Body Weight & Food Consumption • Smaller the animal, faster the metabolic rate, the more the food required

25. 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

26. 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)

27. Reproduction • Majority have estrous cycles • Monestrous vs polyestrous • Old World monkeys and humans have menstrual cycles

28. Estrous Cycles

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

30. Reproductive Patterns • Oviparous Mammals (Prototherians) • Viviparous Mammals with pouches (Metatherians) • Viviparous Mammals with Placenta (Eutherians)

31. 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

32. 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

33. 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

34. Gestation

35. 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