Lecture 21 Flashcards
What makes mammals unique? (3, with that one where other animals have it as well)
Hair (all mammals), milk (only mammals nurse young with milk), placenta
Other animals have a placenta or similar structures but major innovation; important for long gestation periods
Class Mammalia
- 5000 species
3 unique features:
- Hair: insulation, camouflage by modifying color patterns, sensory & defense
- Sweat glands: mammals only ones to sweat; major thermal regulator = evaporation generate sweat that evaporates heat from body to cool
- Mammary glands (milk production): only females
- Divergence between reptilian & mammalian-like amniotes during Carboniferous (350 MYA)
Skull Morphology (4 sids, key difference (3))
- Key to compared relatedness amniotes
a. Anapsids (turtles, no hole)
b. Synapsids (therapsids & mammals, one hole)
c. euryapsids (extinct marine reptiles, one hole)
d. Diapsids (dinosaurs & birds, two holes)
Key Different btwn skulls is presence, size, number of temporal fenestrae = holes on side of skulls, provide more surface area of muscle attachment)
Mammalian Evolution (When? Characteristics? First mammal?)
- True mammals evolved - 225 MYA (Triassic) before dinosaur extinction
At first, small arboreal, shrew-like insectivores, nocturnal, improvements to middle ear (increase hearing)
First mammal: Hadrocodium Wui (large brain for their body size) (middle ear bones derived from jaw)
Didn’t radiate until after dinosaur extinction (65 MYA)
- Coexisted with Saurs
- became dominant group upon “saurs” extinction
- diversified
- filled empty terrestrial & marine niches (large herbivores & carnivores)
- return to ocean
Ambulocetus (5, ancestor, characteristics (3), evolution)
ancestor to whales (50MYA) - ear similar to whales - can hear well underwater - similar teeth to cetaceans Whales evolved: terrestrial, amphibious, fully aquatic
Megatherium (3)
- herbivorous
- elephant-sized giant ground sloth
- 2 MYA to 8,000 years
Smilodon (3)
- saber-tooth cat
- 1.5 MYA to 1,000 year Pleistocene
- Argued most large fruits & trees in North America specialised for dispersal by extinct large mega herbivores
Why did Smilodon & megatherium go extinct?
by humans
Mammalia (other features) (5)
- Endothermic
- Advanced nervous system
- Internal fertilization: egg implants in mother’s reproductive tract when develops & nourished by placenta
Unlike reptile & fish: show heterodonty (different teeth in mouth specialized for different tasks) (specialization among species reflects varied diets; incisors, canines, molars) - 4 chambered heart
Mammal Brain Body Size
- increase complexity of nervous system: evidenced by larger brain
Man: largest brain for body size, others = dolphins & chimps
Largest brain = sperm whale
Bats = small brain since heavy & energetically expensive - Energetic, oxygenic, or weight limits brain size
Sexual Dimorphism (Not only in mammals)
- different sexes: size, color, morphology
- competition among males coz of monopolized mating opportunities, females make choices for evolution of these traits in male
- influence mating opportunities independent of ability to produce offspring
Mammalian Groups
- monotremes (Prototherians)
- Eutherian (therians)
- Marsupials (therians)
Prototherians
- eggs laying (oviparous)
- egg incubation until hatching
- females lack placenta
- have mammary glands, no nipples, young suck milk from fur
Marsupials
- pouch
- early birth, fetus, completes development in pouch
- do not lay eggs
- short gestation, long nursing period
- birth after short internal development
- Newborns crawl over mother’s body to pouch (attach to nipple in pouch, complete development)
- 350 species
- S America, Australia
Echidna (Prototherians)
- short & long nose
- insectivores
- sticky tongue
- temporary pouch for eggs
- Hatch 8 days, in pouch, spines form (3 weeks), live 50 years
Platypus (Prototherians)
- echidna (Australia)
- Use bill to dig crustaceans & worms (electro sensory); build nests in river banks
Males: poisonous spine on back foot
Largest marsupial carnivore
Tasmanian Devil (scavengers)
- extinct on mainland due to hunting & dingos
Contagious Tasmanian facial cancer
Marsupial Evolution
- diverged from early placentals - 100 MYA
- most of NA marsupials are extinct
Tasmanian Tiger (Thylacine)
- not tiger
- example of convergent evolution that looks like dog but those haven’t been related
Eutherians: Placental
- embryo retained in female reproductive tract
- 94% species: most speciose group is rodents
- Capybara: biggest modern rodent
- Viviparous: no pouch or shelled egg (amniotic egg retained in female reproductive tract: embryo nourished by mother via placenta)
Placenta
- organ formed by embryo & mother after implantation
- Formed by extraembryonic membrane & uterus lining of mother
- Site of gas, nutrient & water exchange btwn mother & embryo; makes hormones needed to maintain pregnancy
- Substances pass btwn mother & fetus via diffusion: 2 separate blood systems with no mixing of blood cells or plasma
- Placenta blood supply (3 fetal blood vessels in umbilical cord): 2 arteries carry deoxygenated blood to mother (away from fetus); 1 vein carries oxygenated blood towards fetus
Look at the notes coz I’m not sure if u included everything
