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LECTURE 8: Cenozoic Era65 mya - Present
What were the Significant Events of the Cenozoic Era?
• Age of Mammals (Adaptive Radiation)– Rodents, Hooved mammals, carnivores– First Primates– HUMANS!!!
• Adaptive Radiation of Birds and Angiosperms
• Continents move to Present Locations– Warm, Tropical Climates then cooler, drier
grasslands
What are the Mammal Groups?
• Differ in Reproduction• Monotremes
– Hatch from eggs- platypus
• Marsupials – Born before they are fully developed and continue
development outside the womb, often in a pouch -kangaroo and opossum
• Placentals– Develop completely in their mother’s wombs before
they are born- such as humans, horses, dogs, etc
What is Fossil Lake?
• Wyoming was once a warm, tropical lake
• Waters were rich in calcium carbonate, due to runoff from surrounding limestone and dolomite mountains
• Quick burial prevented the organisms’ bones, teeth, and sometimes even soft tissues such as scales and feathers from decaying
• Fossils are Holotypes– Used to classify fish fossils
• Diplomystus dentatus Leidyosuchus wilsoni
• Masillosteus janei Amphliplaga brachiptera
• Dragonfly Jumping Spider
What caused the Climate Change?
• Moving continents caused the Earth’s climate to begin shifting from warm and wet to cooler and drier- 45 mya
– New waterways created cold currents• As continents moved, new seaways opened at the poles. Cold polar
water flowed where it hadn’t before, cooling global temperatures
– New mountains interrupted rain patterns• Colliding continental plates buckled Earth’s crust, forming massive
mountain ranges. Mountains blocked moist air currents blowing in from the ocean, creating dry environments further inland
• This cooler, drier climate was just right for hardy grasses, which spread across—and transformed—the continents
What did Climate Change due to Mammal Evolution?
• Until now, mammals had been small• With large, open, grasslands: mammals were
able to roam large distances• Hooved Animals diversified and got larger and
started grazing– Taller teeth with more enamel can withstand
constant chewing of gritty grass without being worn away
– Longer limbs with fewer toes are better for outrunning predators and traveling long distances. (Fewer toes make for lighter feet.)
• Leptomeryx evansi Menodus
What is the Affect of Grazers?
• Coevolution: Carnivores!
• Cats/Dogs- 35 mya– Efficient Hunting
Techniques • Hunted in Packs• Surprise ambush
• Early Hyena
South America and Convergent Evolution
• Nimravid carnivoran skullHoplophoneus primaevus South Dakota
Saber-toothed marsupial skull Thyllacosmilus atroxArgentina- South America
Different Species, Same Tools
On separate continents, two predators from different sides of the mammal family tree faced the same challenge. They had to hunt large prey to survive. Though the two species were only distantly related, natural selection favored the same trait in both—saber-teeth—for meeting this challenge.
While the predator on the left is a North American carnivoran, the predator on the right is a South American marsupial—a completely different mammal group. Yet both of these predators have saber teeth, terrific for piercing thick hides of large prey
• Terror bird (theropod dinosaur)Andalgalornis ferox South America
• In most of the world, carnivoran mammals were the top predators. But in South America, lack of competition from mammals may have allowed terror birds like this one to play that role
•With their long legs, terror birds may have been able to sprint at speeds close to 40 miles per hour, catching and stunning prey with their sharp beaks
How did Whales Evolve?
• Fossils tell us these ancient whale ancestors were four-footed mammals with hooves – From land-dwelling ancestors, the first whales
evolved for life spent partly on land, partly in the sea• With webbed feet, they could swim; with long limbs, they
could move about on shore
• Within ten million years, whales were fully aquatic– Webbed front feet evolved into paddle-like flippers.
Hind limbs all but disappeared, as a broad tail fluke evolved for more powerful swimming
What were the First Primates?
• Altiatlasius – 60 mya
– Somewhat squirrel-like in size and appearance
– Grasping hands and feet that were increasingly more efficient in manipulating objects and climbing trees
– Developing effective stereoscopic vision
