General Characteristics• Bilaterally symmetrical• Hair• Mammary glands (produces milk)–Nurse young
• Endothermic (warm blooded)• Unique inner ear – Incus, Malleus, Stapes• Dioecious - Internal fertilization• Diphyodonty – Two teeth (replace teeth once)• Lower Jaw – Made of one bone attached directly
to head (improved power)
• Heterodont dentition– Specialized teeth with different function
• Birth to live young• Produce a placenta (usually) – nourishing fetus
(similar to yolk sac in reptiles/birds)
Mammalian Orders 6 Major Orders:
1.) Order Rodentia2.) Order Artiodactyla3.) Order Carnivora4.) Order Cetacea5.) Order Primates6.) Order Monotremata
Order Rodentia Rodents!
Mice, squirrels, gophers, beavers, & guinea pigs
Many have been pests Have continuously growing incisors
Incisors = front teethMust gnaw to keep short
• Have a short breeding cycle• Largest group of mammals
Order Artiodactyla• Pigs, hippos, camels, deer, sheep, etc.• 220 species• Means “even-toed” – they lost the first (many
have shortened the 2nd and 5th
Order Carnivora
• Meat eaters!• Canines, cats, bears, raccoons,
seals, otters, walruses, etc.• 260 species• Are predatory
Order Cetacea
• Whales and dolphins• Have blubber for insulation• Up and down movement of tail
(unlike side to side by fish)• All aquatic• Highly intelligent
Order Primates• Gorillas, chimps, orangutans,
humans, monkeys, lemurs• Bipedal – stand on two feet• Adaptations for tree-living–Strong limbs with opposable
digits
Order Monotremata
• Duck Billed Platypus and Echidnas (spiny anteater)• Only mammals to lay eggs• Have a single opening called a cloaca for
urination, defecation, and reproductive• Platypus has a poisonous barb on the
back foot
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