21. Mammals I: Hair, milk, placenta Flashcards
(42 cards)
Role of hair?
Like feather, except flight
Insulation, camouflage, sensory/defence
3 unique features of mammalia?
1) Hair
2) sweat glands
3) mammary gland
Which evolved first - mammals or birds?
Mammals
Split reptilia/mammals before split reptilia/bird?
Yes - 350 mya
What is diagnostic of different groups?
Holes in skulls
- Presence, size, numbers, temporal fenestrae
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
When did mammals evolve?
225 mya (Triassic) - Very small insectivores nocturnal (not many fossile possibilities)
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
Brain size of first mammals?
Bigger for body size than other groups
When did mammals became dominant group?
When dinosaurs become extinct - opened up a bunch of opportunities (empty terrestrial and marine niches).
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)
Size of past mammal?
There existed giant ground sloth “dinosaur size” (megatherium) - bigger than dinosaur in redpath museum
Size of elephant
Smilodon?
Saber-toothed cat (1.5 mya - 11 000 ya)
- Contemporary with humans, mammoths and giant ground sloths
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.
Teeth of mammalia?
Heterodonty: Different teeth specialized for different tasks (unlike reptiles and fish)
Different teeth depending on diet
Humans and dolphins have largest….
Brain by body size
Largest brain?
African elephants, blue whale, sperm whale
But human compared to body size
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)
3 mammalian groups?
- Protoherians (monotremes)
- Marsupials
- Eutherians
Specific of prototherians?
LAY EGGS!!!
Typic of marsupials?
Pouches - early birth, fetus completes development in pouch
Typic of eutherians?
Embryo in female reproductive tract - born much more advanced state
Placenta in prototherians?
Lack placenta
Why prototherians are still mammals?
Produce milk - but no nipples, young suck milk from fur
