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
