8: Mammals

Earth has an iron core

• Solid iron in center

• Molten iron above that

Above the iron core is hot, molten rock called the mantle

• Moves in circular pattern  causes movement of outer layer of crust (plate tectonics)

The heat of the interior of the earth comes mostly from radioactive decay of uranium, potassium, and thorium isotopes

The outermost layer of cold, hard rock is called the crust

Note:

• bya = billion years ago

  mya = million years ago

Amino acids and nucleotides bind to certain clays and, when heated, form proteins and nucleic acids

First living things: prokaryotes, then eukaryotes, then plants and animals appear in the 3rd Eon

• Prokaryotic cells evolved internal membranes which increased their ability to capture energy of food molecules

• Mitochondria and chloroplasts have their own DNA (resembles those of bacteria) 

Cellular evolution took about 3 billion years to accomplish

• This time period is called the Precambrian 

Prokaryotes – single-celled organisms (ex: bacteria)

Eukaryotes – cells have a nucleus; multicellular organisms

Precambrian (4.6 bya - 543 mya)

• Eukaryotic cells

• Photosynthetic organisms

• Formation of the ozone layer

• Some of the oldest rocks on Earth are at the bottom of the Grand Canyon

Paleozoic era (543 - 251 mya)

• Pangaea

• Evolution of major groups of animals

• Coral reefs – marine animals, insects, first vertebrates

• Stabilization of Earth’s climate

• First plants and fungi on land

Mesozoic era (251 - 65 mya)

• Triassic period – breakup of Pangaea, first dinosaurs

• Jurassic – age of dinosaurs, no polar ice

• Cretaceous – flowering plants, mammals and birds

• 65 mya – meteor impact causes mass extinction (Yucatan, Mexico)

Cenozoic era (65 mya - present)

• Rise of the mammals

• Primate evolution

• Human evolution

Mesozoic Era:

• Large reptiles being replaced by mammals

• Some egg-layers (monotremes)

• Many pouched opossum-like mammals (marsupials)

• Very few placental mammals, most small (ranging from size of mouse to medium sized dog)

• Large, grass-eating placental mammals like cattle and wildebeest absent (no grasslands yet)

• Not many flowering plants

Cenozoic: Paleocene

• Emergence of grazing and browsing mammals with tough hoofs, grinding teeth, and specialized digestive tracts

• Lead to evolution of carnivorous mammals specialized to eat the herbivorous mammals

• First proto-primates appear

• None of the placental mammals reached Australia yet

• South America began to drift away from Africa and eventually becomes connected to North America

• Placental mammals then reached South America

First true primates (euprimates)

• 50 mya

Placental mammals with larger bodies and bigger brains appear (possibly because the amount of oxygen doubled)

• Brains have especially high oxygen requirements

Coinciding with increase in atmospheric oxygen was a global warming

• No polar ice, higher sea levels

• Rapid evolution of animals and plants

• Climates were much warmer  Crocodiles in the Arctic, pine forests in the Antarctic, and palm trees in Wyoming

Primate evolution

• Nearly 4 times greater prosimian diversity than today

  • No competition with monkeys and apes

Hair

Homeothermy

• Ability to regulate internal temperature (“warm-blooded”)

Dietary trends

• Heterodontism: having different types of teeth

Longer infancy, learning development period, and lifespan

Higher energy, bigger brains

Specific reproductive patterns

• Lactation

• Internal gestation (depends on the type of mammal)

R-selection

• Reproductive strategy where parents produce many offspring and invest little in offspring

• Offspring have high probability of mortality, faster growth and development rate, and early independence

• More often occurs in less competitive environments

• Ex: mice, several fish and insect species

K-selection

• Reproductive strategy where parents invest heavily in offspring

• Offspring are entering in competitive world

• Fewer offspring

• Often have longer lifespans, slower growth and development rates, rely on learning from parents

• Ex: elephants, whales, primates

Monotremes

• Ex: platypus, echidna

• Egg-laying mammals

• More similar to reptiles

• Lactate through pores in skin

Marsupials

• Ex: kangaroos, koalas, wombats, opossums, bandicoots

• Give birth to offspring that aren’t fully developed; transfer to external pouch

Placentals

• Most mammals 

• Complete embryonic development internally