Mammals

1. Mammals Chapter 28

2. I. Diversity • Only 4600 living species but most highly differentiated of all animal groups • Many domesticated to use as food, clothing, pets, beasts of burden, and in research • Habitat destruction is the cause of 300 species and subspecies being listed as endangered

3. II. Origin A. Synapsids • First amniotes to radiate into fully terrestrial habitats • Pair of openings in skull roof • Over 150 million years small, hairless ectothermic ancestors evolved into today’s furry endotherms • Herbivorous and carnivorous pelycosaurs

4. B. Therapsids • Arose from carnivorous synapsid lineage • Only synapsid group to survive beyond Paleozoic • Efficient erect gait with limbs beneath body • Cerebellum expanded to coordinate more muscles • Most died out in Permian extinction

5. C. Cynodonts • Therapsid subgroup that survived into Mesozoic • Higher metabolic rate to support more active lifestyle • Skeletal changes improved flexibility, agility, and muscle attachment • Developed secondary palate that allowed animal to breathe while eating prey; important innovation that allowed later mammals to breathe while suckling

6. D. Diphyodonts • Early mammals evolved in Triassic, small and shrewlike and nocturnal • Diphyodonts means teeth replaced once with permanent teeth • Endothermic but cooler than placental mammals • Hair with sebaceous and sweat glands • Hatched from eggs and relied on mammary milk • Radiated in Eocene after extinction of many amniote groups at end of Cretaceous

7. III. General Characteristics • Hair; even in aquatic forms may be few but present • Mammary glands to nourish young • Most specialized placenta to feed embryo • More advanced nervous system

8. IV. Skin • Thick • Dermis much thicker than epidermis • Thin epidermis protected by hair

9. V. Hair A. Structure • Hair follicle sunk in dermis of skin • Cells divide in follicle; as they grow away from source of nourishment, they die, forming hair shaft • Made of protein keratin • Three layers: pith center surrounded by cortex of pigment, then outer cuticle made of scales

10. B. Function • Protection against wear or attack (quills) • Concealment—spots , stripes, salt-and-pepper disrupt coloration • Waterproofing • Buoyancy • Signaling & sensing--coarse long guard hairs and whiskers • Thermal insulation--dense soft underhair

11. Hair

12. C. Molting • Usually twice in spring and fall • Some have winter coat which is heavier and may be white for camouflage; condition called leukemism which also includes dark eyes, dark ear tips, noses , etc

13. VI. Horns & Antlers A. Horns • Found in ruminants such as sheep and cattle • Hollow sheaths of epidermis surrounding a core of bone from skull • Not shed or branched, but may be greatly curved • Found in both sexes and grow continuously

14. B. Antlers • Deer family, males only • When, mature composed of solid bone • Covered in spring by highly vascular skin called “velvet’ • Before breeding velvet drops off; after breeding antlers drop off • New set bigger than last

15. VII. Glands A. Sweat • 1. Eccrine • Watery fluid evaporates heat from surface of skin • Found in hairless areas • Absent in rodents, rabbits, and whales

16. 2. Apocrine • Larger than eccrine and open onto hair follicle • Forms film on skin • Related to reproductive cycle • In humans, develop at puberty in armpits, groin, ear canals

17. B. Scent • Found in all mammals though vary in location • Used for communication, warning, defense, and marking territory • Stronger during breeding season to attract mates • Skunks, minks, and weasels have very strong glands near anus

18. C. Sebaceous • Associated with hair follicles but some open directly onto skin; all over body • Fats and oils that keep skin soft, and hair flexible and glossy

19. D. Mammary • Modified apocrine glands • Rudimentary in males; occur on all females • Swelling when pregnant or nursing • Humans, develop at puberty with fat; further development at pregnancy

20. VIII. Teeth A. General • Heterodont (diphodont) dentition—differentiation of teeth for cutting, seizing, gnawing etc • Structure reveals life habits of animals; some are specialists and others generalists • Primitive mammal arrangement—3 incisors, 1 canine, 4 premolars, 3 molars • 1 baby set and 1 adult set of teeth; generally molars only appear in adult set

21. Primary Teeth

22. B. Types • Incisors—sharp edges for snipping, biting • Canines—piercing • Premolars—compressed crowns with 1-2 cusps for shearing, slicing • Molars—large bodies, variable cusp arrangements for crushing, grinding

23. Feeding SpecializationsA. Insectivores • Shrews, moles, anteaters, bats • Short digestive tract because eat few plants • Other mammals may eat insects but not exclusively

24. B. Herbivores • Browsers, grazers-- horses, deer, antelope, cattle, sheep, goats, camelids; Gnawers– rabbits, rodents • Reduced or absent canines; molars broad and high crowned • Rodents have chisel-shaped incisors that growth throughout life • Long digestive tracts; ceca add additional absorptive area • Fermentation chambers in stomach to aid in digestion of cellulose • Ruminants 4-chambered stomachs; food regurgitated and passed back through • Rodents eat fecal pellets to add to fermentation • Some use size and defensive behaviors to avoid predation; others keen senses and escape behavior

25. C. Carnivores • Feed mainly on herbivores; some switch to fruits, berries when food scarce • Many specializations to kill prey; more intelligence, stealth, and cunning used • Short digestive tract • More leisure time because do not have to continuously graze • Humans have exterminated many carnivores from areas; led to more crop pests in these areas

26. D. Omnivores • Eat plant and animal tissue—pigs, raccoons, rats, bears, primates • Migration, hibernation, food caching used in temperate areas where food supplies become scarce during certain seasons

27. X. Metabolism • Smaller the animal, greater metabolic rate and more must eat per unit size • Small animals end up spending more time hunting and eating than larger animals • Small shrews weighing 2 g. must eat more than this each day; if deprived of food for a few hours will die • Mountain lions need to eat an average of 1 deer a week

28. XI. Migration • Most remain in a home range, but some migrate and most located in North America • Caribou migrate100-700 miles; gray whales 11, 250 miles

29. XII. Flight • Bats fly; some mammals glide • All bats nocturnal so use echolacation to find food • Echolocation uses high frequency sounds in pulses that bounce off objects • Large ears help collect “echos and bat forms mental image of object • Some moths have coevolved to have ultrasonic detectors to avoid bats

30. ReproductionA. Cycles • Mating seasons timed to coincide with favorable time to rear young • Estrous Cycle—mating restricted to fertile period in females (estrous or heat) when ovulation occurs; 1 mating/year (monoestrous); multiple (polyestrous) • Sometimes blastocyst remains dormant for implantation until a more favorable season—delayed gestation • Menstrual Cycle—old world monkeys and humans; cycle terminated by menstruation when uterine lining is shed

31. B. Patterns • Egg-laying—montremes only; egg fertilization and formation similar to birds but eggs are leathery; laid once a year in burrow and incubated; young hatch and nursed from milk • Pouched—marsupials only; short gestation with early birth of embryos; mother usually immediately becomes pregnant with suckling young still in pouch but development of embryos arrested (embryonic diapause); long lactation period • Placental—long gestation, short lactation period; embryo in uterus nourished by placenta; humans slowest developing animal

32. Forms of Reproduction

33. Humans & MammalsA. Domestication • Dogs were probably first; derived from wolves • Cats from African wildcat • Subdued horses, oxen, reindeer, camels, elephants, and llamas • Wild versions of llamas and dromedary camels no longer exist • Traits have been modified through selective breeding

34. B. Pests • Rodents and rabbits major pests of crops; elimination of natural predators has heightened problem • Diseases such as Tularemia, Lyme disease, and Rocky Mountain spotted fever transmitted by ticks on animals such as rodents, dogs, and deer • Tapeworms and trachina worms transmitted by eating infected meat

35. Human EvolutionA. Evolutionary Groups • Primates—grasping fingers, flat fingernails, forward facing eyes; split into prosimians & simians • Prosimians—dental comb, more projecting face; lemurs, tarsiers, lorises • Simians—opposable thumb, some tool use, large cerebrum; split into monkeys and apes • Monkeys—Old World located in Africa & Asia, close set nostrils, advanced dentition (baboon, mandrill, colobus); New World located in South America, grasping tail • Apes--tailless • Hominids—bipedal, larger cranium, speech

36. Primates

37. B. First Hominids • Grasslands and drought appeared about 8 mya; thought to be selective pressure that pushed apes out of trees. • Ardipithecus ramidus—appears about 4.4 mya with combination of ape/hominid traits • Australopithecus afarensis—appears about 4 mya; short bipedal hominid; brain size and facial features similar to chimp • Australopithicus africanus—appears about 2.2 mya; maybe descendant of A. afarensis and ancestor to Homo

38. A. afarensis H. habilis and A.africanus H. erectus

39. C. Emergence of Homo • Found in Africa • Homo habilis—first fully erect hominid that used stone and bone tools; appeared 2 mya and disappeared 1.5 mya • Homo erectus– appeared 1.5 mya; larger head and height; spread throughout Africa, Europe, and Asia; complex culture;disappeared about 300,000 years ago

40. D. Homo sapiens • Homo erectus disappeared about 300,000 years ago • H.neanderthalensis—some consider it a subspecies; emerged about 130,000 years ago; proficient hunters and tool users; large nose, big brow ridges, sloping head; big bones; disappeared about 30,000 years ago • H. sapiens—appear about 100,000 years ago; more tool using culture; rounded head, finer features; current people today

41. H. Erectus and H. sapiens

42. Neanderthal Man

43. XIV. Class Mammalia

44. A. Order Monotremata • Duck billed platypus, spiny anteater; Australia, New Guinea & Tasmania • Egg laying mammals • Oviparous

45. B. Order Marsupiala • Viviparous • Pouched (marsupium) • Young nourished by yolk-sac placenta • Short gestation • Australia and North America • 260 species

46. C. Order Insectivora • Insect eaters • Pointy snout • Live part of time underground • Shrews, hedgehogs, tenrecs, and moles • All over except Australia and New Zealand • 419 species

47. D. Order Chiroptera • Flying with modified forelimbs with membrane between elongated fingers • Bats • Worldwide • 925 species

48. E. Order Primates • Large cerebrum • Most arboreal • 5 digits with flat nails on fore- and hindlimbs; fore- used for grasping • Prosimians, monkeys, apes, humans • Worldwide • 223 species

49. F. Order Xenarthra • Toothless or simple peg teeth • Anteateaters, armadillos, sloths • South and Central America • 29 species

50. G. Order Lagomorpha • Long constantly growing incisors • Additional pair of peglike incisors growing behind 1st set • Herbivores • Hares, rabbits, pikas • Worldwide • 80 species