Mammals

Overview of Mammals

Overview of Mammals

• Sister to Reptiles
• ~5,300 species

Characteristics

• Mammary glands: produce milk for offspring
• Milk is rich in fats, sugars, proteins and minerals
• Hair
• Fat layer under skin
• Provides insulation to conserve water and heat
• Kidney: reduces water lost in urine
• Endothermic
• Efficient circulatory and respiratory system
• Parental care
• Teach learned behaviors
• Variable jaw and tooth structure
• Synapsid: Only one hole behind eyes in skull

Evolution of mammals

• Synapsids evolved into herbivores and carnivores ~300-250 MYA
• Mammal-like synapsids diversified at the end of the Triassic period (250 - 200 MYA)
• First true mammal occurred during the Jurassic period (200-150 MYA)
• Three major lineages of mammals around by the end of the Cretaceous period (140 MYA)

Diversity of Mammals

Monotremes

• Platypus and echidnas
• In Australia and New Guinea
• Characteristics
• Lay eggs
• Have hair
• Produce milk (but lack nipples)
• milk secreted from mothers belly

Marsupials

• Opossums, kangaroos, koalas etc.
• High metabolic rate
• Have nipples for milk
• Give birth to live young
• Placenta: structure that provides nutrients to embryo from mothers blood
• Marsupials born very early in development
• Marsupium: pouch where very small young develop
• Used to exist worldwide
• During Pangaea marsupials spread
• Only remain in Australia which has not had secondary contact with other lands
• Most marsupials replaced by eutherians outside of Australia

Eutherians

• Placental mammals
• Have a more complex placenta than marsupials
• Longer pregnancy
• Young complete embryonic development in uterus
• Diversification occurred in a burst

Primates

• Also Eutherians
• Lemurs, tarsiers, monkeys and ape Example: Humans are within the ape clade

Characteristics

• Hands and feet
• Digits have flat nails
• Larger brains, shorter jaws
• Forward facing eyes close together
• Complex parental care and social behavior
• Opposable thumb: thumb that is opposite the fingers, for grasping
• Humans have additional bone for precise dexterity

Living primates

• Three main groups
• Lemurs, lorises, bush babies
• Tarsiers
• Anthropoids: monkeys and apes
• Monkeys
• Old world monkeys
• Arboreal and ground dwelling
• New world monkeys
• All are arboreal
• Apes
• Gibbons, orangutans, gorillas, chimpanzees and bonobos, humans

Humans

Overview of Humans

• Characteristics
• Stand upright
• Much larger brain
• Language, art, tools
• DNA is 99% similar to chimpanzees
• 1% represents substantial changes
• Early Hominins: extinct species that are more closely related to humans than chimps
• Earliest fossil ~6.5 MYA
• Show gradual progression to more upright

Australopiths

• 2-4 MYA
• "lucy" discovered in africa
• Bipedalism: walking on two legs
• Became more efficient, fewer limbs required
• Tool use
• Found cuts on bone ~2.5 MYA
• Indicates stone knives

Homo

• Genus that contains humans
• Homo habilis
• "Handy man"
• 2.4 - 1.6 MYA
• Sharp stone tools
• Homo ergaster
• 1.9 - 1.5 MYA
• Larger brain
• Decreased sexual dimorphism
• Used to be considered Homo erectus
• Homo neanderthalensis
• Neandrathals
• Larger head than modern humans
• Buried dead
• Tools from stone and wood
• 350,000 - 30,000 YA
• Gene flow with humans
• Homo sapiens
• Modern humans
• Oldest fossils from Africa 195,000 - 160,000 YA
• More slender, less pronounced brows

Human Migration