Biodiversity – Oct. 15/12
- Class Mammalia (mammals) – synapomorphies: Have hair growing from follicles in the skin. Have
three middle ear bones used in hearing, allowing exceptional hearing ability. Have a neocortex region
in the brain, allowing enhanced cognitive skills, memory, thinking, and language in primates. Females
have mammary glands, which produce milk to feed to offspring.
- Mammal main groups: Monotremes – Modern day representatives of early mammals. Lay eggs.
Marsupials – Short-lived placenta (specialized organ to nourish embryo). Give birth to live young.
Females have pouch and carry young. Placentals – Long-lived placenta. Give birth to live young. Have
- Modern monotremes are a surviving species of an early branching of the mammal tree. Includes
echidna and platypus, which are indigenous to Australia and New Guinea. They lay eggs.
- Marsupial mammals are found in Australia, New Guinea, North America, and South America. The
North American opossum is the only marsupial mammal found north of Mexico. It is fairly common in
the US, but is now found in London, ON. It has been forced to expand its range due to habitat
disturbance from humans.
- Placental mammals (most mammals): There are 4000 described species, with most of them being
rodents and bats. There are also dogs, cats, cows, pigs, horses, whales, elephants, armadillos, shrews,
monkeys, and humans.
- Cetaceans: Includes whales, dolphins, and porpoises. They are land mammals adapted to life in
water. Their ancestor was a land mammal. Their closest living relatives are hippopotamus and deer.
They have forelimbs modified into flippers, which move up and down. They have vestigial hindlimbs.
Vestigial means reduced in form and having lost most or all original function. They breathe air. They
are highly intelligent. There are 90 cetacean species. They are all marine except for freshwater