21. Mammals I: Hair, milk, placenta Flashcards Preview

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Flashcards in 21. Mammals I: Hair, milk, placenta Deck (42):
0

3 unique features of mammalia?

1) Hair
2) sweat glands
3) mammary gland

1

Role of hair?

Like feather, except flight
Insulation, camouflage, sensory/defence

2

Which evolved first - mammals or birds?

Mammals

3

Split reptilia/mammals before split reptilia/bird?

Yes - 350 mya

4

What is diagnostic of different groups?

Holes in skulls
- Presence, size, numbers, temporal fenestrae

5

Skull types of amniotes?

Anapsids (turtles) - no holes
Synapsids (therapsids, mammals) - single hole begins to fuse with eye orbit (through which muscle can go through - in turtles, outer bone covers it - mammals lost that outer bone)
Euryapsids (extinct marine reptiles) - single hole
Diapsids (dinosaurs + birds) - two holes

6

When did mammals evolve?

225 mya (Triassic)
- Very small insectivores nocturnal (not many fossile possibilities)

7

Characteristic of first mammals in Triassic?

Improvements to middle ear (bones we hear with) - modern mammilial way of earing. not in the same way that other animals hear

8

Brain size of first mammals?

Bigger for body size than other groups

9

When did mammals became dominant group?

When dinosaurs become extinct - opened up a bunch of opportunities (empty terrestrial and marine niches).

10

What is the return to the ocean of the mammal?

Mammals return to ocean when dinosaurs disappeared. Ambulocetus, ancestor of whales (because of teeth structure and ear structure)

11

Size of past mammal?

There existed giant ground sloth "dinosaur size" (megatherium) - bigger than dinosaur in redpath museum
Size of elephant

12

Smilodon?

Saber-toothed cat (1.5 mya - 11 000 ya)
- Contemporary with humans, mammoths and giant ground sloths

13

Why did Smilodon and Megatherium go extinct?

Hunting by humans! (not end of ice age)

- Why large in Africa? Evolved together. Animals learned to avoid humans. When humans arrived in NAmerica, these animals were not accustomed to humans.

14

Teeth of mammalia?

Heterodonty: Different teeth specialized for different tasks (unlike reptiles and fish)

Different teeth depending on diet

15

Humans and dolphins have largest....

Brain by body size

16

Largest brain?

African elephants, blue whale, sperm whale
(But human compared to body size)

17

Sexual dimorphism

In animal sexes appear different (not so much for humans, but a lot in lions, eg.): size, colour, morphology

Most impressive: elephant seal
Why: gender roles (female lion hunt; male lion chill and look impressive at each other)

18

3 mammalian groups?

- Protoherians (monotremes)
- Marsupials
- Eutherians

19

Specific of prototherians?

LAY EGGS!!!

20

Typic of marsupials?

Pouches - early birth, fetus completes development in pouch

21

Typic of eutherians?

Embryo in female reproductive tract - born much more advanced state

22

Placenta in prototherians?

Lack placenta

23

Why prototherians are still mammals?

Produce milk - but no nipples, young suck milk from fur

24

Example of prototherians?

- Platypus
- Echnidna

25

Platypus?

- Australia
- Bill to dig for crustaceans & worms
- Build nests in river banks
- Lay eggs, hatch in days, nurse for 5 mos

26

Only poisonous mammals?

Platypus - male have poisonous at the back of leg (sexual dimorphism - could be in sexual selection, competition for mates - but usually not lethal? - we don't know why - prof will let us know)

27

Echidna?

"Spiny anteaters"
Insectivores, sticky tongue, temporary pouch for egg (hatch 8 days, spines form in pouch, live for 50 y!)

28

Marsupials?

Short gestation, long nursing period
HAVE A PLACENTA (though non uterian)
Kangaroos, loalas, opossums

29

Thyosine?

Extinct dog-like marsupials - but not at all related to dog (eg. of convergent evolution)

30

Marsupial diverged from early placentals...

100 mya

31

NA marsupials?

Most extinct, except opossum

32

Eutherians make .... species

94%

33

Eutherians - amniotic egg?

Retained in female reproductive tract

34

Eutherians - nourrishment of embryo?

Mother placenta

35

Most speciose group of mammals?

Rodents

36

Placenta formed by?

- Embryo and mother after implantation - formed by extraembryonic membranes and uterus lining of mother

37

Placenta is site of...

Gas, nutrient & waste exchange betwen mother and embryo

38

Placenta produces...

Homrones necessary to maintain pregnancy

39

Substances pass between mother and fetus by ...

Diffusion (two separate blood systems, no mixing of blood cells or plasma)

40

Placental blood supply?

3 blood vessels in umbilical cords
- 2 arteries carry de-oxygeneated blood to mother (AWAY from fetus)
- 1 vein carries O2 blood towards fetus
(opposite of adult)

41

Catch up last slides.

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