The Cenozoic

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TheCenozoic
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Tectonics
Tectonics of the Mesozoic and Cenozoic
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Major Mammal Groups

• Multituberculates - now extinct - rodent-like
  mammals who lived from Jurassic to Oligocene and
  were probably outcompeted by modern rodents
• Monotremes - only three species still alive,
  duck-billed platypus and two species of echidna
  (long-nosed and short-nosed spiny anteaters), all
  found in Australia and New Guinea

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Major Mammal Groups

• Metatheria (Marsupials) - Important group of
  mammals - originated in Middle Cretaceous as
  opossum-like organisms. They give birth to live,
  immature offspring.
• Eutheria (Placental mammals) - Give birth to live
  young, often very mature functional organisms.
  Provide support for developing offspring through
  placenta connecting it to mothers blood supply.

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Echidna - a Monotreme
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Platypus - a Monotreme
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Platypus - a Monotreme
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Monotremes

• A mix of primitive, standard mammal, and advanced
  features
• They lay eggs like birds or reptiles
• They support their young with milk
• They have standard mammal skull structure
• They have very specialized parts (e.g. nose
  parts, webbed feet)
• Platypuses are even venomous!

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Monotremes

• Monotremes have no teeth as adults (some have
  teeth as young)
• Eggs are small (1/2 to 3/4 inch in diameter) and
  leathery in platypus only the left ovary works
• Probably split from other mammals sometime in
  Mesozoic - the earliest fossil is from the
  Cretaceous
• Some possible monotreme fossils found in
  Argentina - could they have been widespread at
  one time?

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Kangaroo - a Marsupial
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Tasmanian Wolf - a Marsupial
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Marsupials

• Originated in North America around Middle
  Cretaceous
• Rapidly spread to South America and then to other
  parts of the world (scattered fossils found in
  Europe, Asia, the Americas), but faded away from
  North America by the Miocene when placental
  mammals entered the scene
• Marsupials recolonized the Americas during the
  Pliocene.

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Marsupials

• Young are born after only 8-40 days of gestation
• What is the problem they are trying to solve?
• Rejection by mothers immune system
• Whats better, marsupial reproduction or
  placental?
• Not clear, but placentals have outcompeted
  marsupials most places where they have been in
  conflict

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Marsupials

• Lots of forms of marsupials which are parallel to
  placental forms have existed at various times
• There have been big marsupial grazers, marsupial
  dogs, cats, rodents, even a lion-like marsupial
  with retractable claws
• Kangaroos and their relatives are an exception -
  no known parallel among other mammals. Theyve
  been more diverse in the past too - one ten-foot
  high species existed.

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Placental Mammals

• Includes most mammals we think about - whales,
  bats, elephants, shrews, and armadillos
• All give birth to live offspring after extended
  gestation
• Sometimes offspring are fairly helpless for long
  periods after birth other times offspring are
  fairly mobile
• All require mothers milk for support for at
  least a while (like other mammals)

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Placental Mammals

• First showed up no later than Upper Cretaceous,
  possibly earlier (early fossils havent been
  definitively split between marsupials and
  eutherians)
• Eutherians were widespread in Asia by the K-T
• Many modern groups were around at or near the
  start of the Cenozoic, and all modern groups were
  in place by the end of the Miocene.

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How do we fit into all of this?

• Humans are placental mammals, evolved from a
  small subgroup of rodent-like ancestors
• Before we continue, lets make sure we know our
  taxonomic address...

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Kingdom Animalia
Animals are a very diverse group. Most are
mobile at some level, but not all can relocate
(e.g. sponges, bryozoans). All must consume
external nutrients to survive, although some have
developed symbiotic relationships with plants or
algae.
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Phylum Chordata
All chordata share the following
characteristics pharyngeal slits - a series of
openings that connect the inside of the throat to
the outside of the "neck". These are often, but
not always, used as gills. dorsal nerve cord - a
bundle of nerve fibers which runs down the
"back". It connects the brain with the lateral
muscles and other organs. notochord -
cartilaginous rod running underneath, and
supporting, the nerve cord. post-anal tail - an
extension of the body past the anal opening.
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Subphylum Vertebrata
All vertebrates share the following
characteristics vertebrae - all vertebrates have
a hard spinal column encasing their
notochords neural crest cells - these cells
migrate throughout the body during development,
distributing nerve bundles everywhere cartilage -
all vertebrates have cartilage in addition to or
in place of bone dermal and endoskeletal bone -
all vertebrates have bones made of calcified
tissue or cartilage in their bodies well-defined
head centrally-located heart acute sensory organs
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Tetrapoda
Tetrapoda, including all reptiles and mammals,
have four limbs. In some (like snakes and
dolphins), the four limbs have been highly
modified, but they are still present in the
skeletal structure. All tetrapoda have digits at
the end of their main limbs
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Synapsida
Synapsida is a group which includes some mammals
and some mammal-like reptiles. They are
distinguished by having a single cavity in their
skulls through which muscles from the jaw
pass. Most reptiles are diapsids and have two
such cavities.
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Class Mammalia
Almost all mammals share the following
characteristics Warm blooded - regulate
temperature from within Hairy covering - for
insulation and protection takes various forms in
different species Mammary glands - secrete milk
to nourish young
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Subclass Eutheria
Eutheria are the placental mammals, those which
develop in the uterus of the female and obtain
liquid nourishment from a placenta.
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Order Primates
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Order Primates
Primates include all of the monkeys, lemurs,
tarsiers, apes, and humans. To be a primate, you
need a big head, acute sight, binocular vision,
and well-developed manipulative hands (and often
feet).
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Family Hominidae
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Family Hominidae
Hominids are the human-like apes, different from
the other living apes. They radiated from
existing ape species about 5-10 million years ago.
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Lemur (Prosimian)
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Loris (Prosimian)
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Tarsier (Prosimian)
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Marmoset (New World Monkey)
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Atelinae(New World)
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Cappuchin (New World)
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Squirrel Monkey (New World)
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Baboon (Old World)
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Rhesus (Old World)
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Vervet(Old World Monkey)
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Langur (Old World Monkey)
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Gibbon (Lesser Ape)
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Orangutan(Great Ape)
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Gorilla (Great Ape)
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Chimpanzee (this ones a bonobo)(Great Ape)
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Human(this ones named Brianna)
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Australopithecus (Early upright hominids)
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Hominid evolution

• Humans and living apes used to be thought to have
  split 15-20 Ma, or even up to 30-40 Ma.
• Some apes occurring within that time period, such
  as Ramapithecus, used to be considered as
  hominids, and possible ancestors of humans.
• Later fossil finds indicated that Ramapithecus
  was more closely related to the orangutan, and
  new biochemical evidence indicated that the last
  common ancestor of hominids and apes occurred
  between 5 and 10 million years ago.
• -Talk.origins FAQ

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Australopithecus

• Lived primarily in grasslands, seldom in forest
• Had many grinding teeth, some large, and had
  small canines
• Habitual biped (walked on two legs)
• Brains were probably slightly larger than modern
  apes

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Australopithecines
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Australopithecines

• Ardipithecus ramidus - oldest known human-like
  hominid (4.4 Ma). About 4 tall, possibly
  bipeds. Probably forest dwellers.
• Australopithecus anamensis - 4.2-3.9 Ma. 21
  fossils (teeth, fragments) found in Kenya.
  Primitive skull, advanced body - probably
  bipedal. Very human-like limbs.

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Australopithecines

• Australopithecus afarensis - 3.9-3.0 Ma. 4-5
  tall. Apelike face (low forehead, bony ridge
  over eyes, no chin, protruding jaws). Brain size
  about 1/3 of human. Bipedal but not fast very
  muscular.
• Australopithecus africanus - 3-2 Ma. Bipedal,
  slightly taller, bigger brain (about chimp size).
  Teeth larger than human but similar in form.

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Australopithecines

• Australopithecus aethiopicus - 2.6-2.3 Ma - known
  from one skull plus some other bits. Earliest
  robust australopithecine. Confusing mix of
  traits.
• Australopithecus robustus - 2-1.5 Ma. Similar
  body to africanus, but bigger head. Flat face,
  smaller teeth except for molars - indicating
  coarse, tough food. May have used digging tools.

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Australopithecines and Homo

• Australopithecus boisei - 2.1-1.1 Ma. Similar to
  robustus but even bigger face and teeth, some
  almost an inch across. 530 cc brain, possibly
  same species as robustus.
• Homo habilis - - 2.4-1.5 Ma. Handy man
  definitely used tools. Form is like
  Austalopithicines but bigger brain. 5 tall,
  100 lbs. Brain has more human structure - may
  have had rudimentary speech.

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Genus Homo

• Homo erectus - 1.8-0.3 Ma. Protruding jaw with
  large molars. Thick brow ridges, larger brain
  (900-1100 cc). Probably more muscular than
  earlier Homo species. Better walker than us -
  pelvis not so wide. Habilis and
  australopithecines found only in Africa, but
  erectus found in Asia, Africa, and Europe.
  Probably used fire, had sophisticated stone tools.

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Genus Homo

• Homo sapiens - 500,000 years ago to present.
  Started with 1200 cc brains but got bigger.
  Started with bigger teeth, but got smaller. Also
  lost brow ridges.
• Neanderthals - 230,000 - 30,000 yrs ago - Larger
  brains than us (1450 cc) but they were larger.
  Protruding jaw, receding forehead, but very
  similar to modern humans (even considered same
  species as us sometimes). Thick bones, heavily
  muscled. Lots of weapons and tools.

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