The Paleozoic Book chapters 1012

1
The Paleozoic(Book chapters 10-12)

• 570 Ma - 245 Ma
• Includes Cambrian, Ordovician, Silurian,
  Devonian, Carboniferous, Permian
• Started with simplest multi-celled life
• Ended with the biggest extinction in the fossil
  record

2
Paleozoic Time and Environments

• The Paleozoic can be divided into two cycles,
  each very similar
• Early Paleozoic - Cambrian, Ordovician, Silurian
• Late Paleozoic - Devonian, Carboniferous, Permian

3
Paleozoic Time and Environments (continued)

• Both Early and Late Paleozoic began with marine
  transgressions - shallow seas invade continents
• Both ended with a cyclic regression - more land
  exposed, less shallow marine habitat
• QUESTION What controls sea level?
• First, some definitions...

4
Sea Level

• There are two kinds of sea level change
• Eustatic Global sea level change - e.g.
  add/remove water or increase/reduce ocean
  basin size
• Isostatic Local sea level change - e.g.
  raise or lower local landmass - post-glacial
  rebound in Alaska

5
Eustatic Sea Level Change

• Add or remove water - e.g. ice meteorites,
  volcanic activity,
• Ice sheets - the more ice there is on land, the
  less water there is in the oceans.
• Temperature - the warmer the ocean is, the less
  dense the ocean water is, and the higher sea
  level will be

6
Eustatic Sea Level Change

• Plate Tectonics - a big factor in the Paleozoic
  transgressions and regressions
• How does plate tectonics affect sea level?
• Oceanic crust is hot when formed
• Hot crust is less dense, so it rides up higher on
  the asthenosphere due to isostasy
• Crust cools at a fairly constant rate upon
  exposure to the ocean

7
Eustatic Sea Level Change and Plate Tectonics

• If the oceanic crust is spreading rapidly (e.g.
  East Pacific Rise), then the oceanic crust will
  be less dense, and the ocean bottom will be
  shallower. This forces water up onto land.
• If the oceanic crust is spreading slowly (e.g.
  Mid-Atlantic Ridge), then the oceanic crust will
  be more dense, and the ocean bottom will be
  deeper. This draws water back down into the
  ocean basin

8
Eustatic Sea Level Change and Plate Tectonics

• What if you have a single supercontinent (e.g.
  Rodinia, Pangea) rather than a bunch of smaller
  continents?

• Typically, more continents mean more ocean
  ridges, and a younger average age for oceanic
  crust. That means you have shallower ocean
  basins and higher sea level.

9
Paleozoic Time and Environments (continued)

• Paleozoic contained both steady, slow
  sedimentation and also orogeny - episodes of
  mountain building
• Much of the Appalachians were built during the
  Paleozoic through a series of orogenies

10
Isostatic sea level change

• Sometimes the land moves up or down, usually
  through isostasy
• Remember, isostasy is when a plate floats higher
  or lower due to changes in thickness, density, or
  mass
• Examples of isostatic change include areas of
  sediment accumulation offshore (land sinks) and
  areas where ice was recently removed (land rises)

11
Paleozoic Plate Tectonics

• The Proterozoic ended just as an early
  supercontinent (Rodinia) was breaking apart
• Oceans proceeded to widen and become better
  established as the Early Paleozoic passed
• Plate Tectonics Movie - Here

12
Major Tectonic Events of the Appalachian Region

• Grenville Orogeny - 1.1 billion years ago -
  occurred when North America collided with another
  continent (Laurasia). Formed mountains, but only
  their roots still exist.
• Iapetus Ocean - 650 million years ago - North
  America pulled apart from the rest of Laurasia,
  creating an earlier version of the Atlantic.

13
Major Tectonic Events of the Appalachian Region

• Iapetus lasts for about 200 million years. As it
  is closing, a subduction zone and island arc form.

14
Major Tectonic Events of the Appalachian Region

• Taconic Orogeny - 445-435 million years ago -
  Iapetus closes, and an off-shore volcanic island
  arc (related to subduction - like Japan today)
  slams into North America, creating more
  mountains. These mountains begin to erode,
  creating thick sediments (4000 feet thick in some
  places - Catskill delta) across the east coast.

15
Major Tectonic Events of the Appalachian Region

• Acadian Orogeny - 375-355 million years ago
  -Iapetus begins closing for good, and a new
  mountain range is forced up east of the
  fast-eroding Taconic mountains.

16
Major Tectonic Events of the Appalachian Region

• Acadian mountains continue to erode, producing
  tons of sediments across the east coast.
• Alleghenian Orogeny - 320-220 million years ago
  -Iapetus finally closes completely as the
  northwestern part of Africa rams into North
  America (forming part of Pangea). This creates
  our modern Appalachian mountains.

17
Major Tectonic Events of the Appalachian Region

• After the orogenies - 220 million years ago to
  the present - Pangea breaks up, forming the new
  Atlantic. The rifting of Africa and North
  America produces pull-apart basins which fill
  with sediments from the new mountains. There is
  also basaltic volcanism as dikes come up through
  the fractures in the rifting crust.

18
Latest Proterozoic Life

• At the end of the Proterozoic (Precambrian) life
  was just shifting toward multicelled forms -
  remember Ediacaran fauna
• Here are some pictures...

19
Vendian organisms
Dickinsonia - Ediacara Hills - from UCMP web
site Worm (Annelida) or coral (Cnidaria)?
20
Vendian organisms
Tribrachidium - Ediacara Hills - from UCMP web
site Annelida? Echinodermata? Something
completely weird?
21
Vendian organisms
Kimberella - White Sea (Russia) - from UCMP web
site Was thought to be jellyfish at first, now
new structures and symmetry point to mollusc
22
Vendian organisms
Arkarua - Ediacara Hills - from UCMP web
site Echinodermata? Has the right symmetry
23
Cambrian Life

• Base of the Cambrian is easy to spot in most
  places - set at the place where you first get
  shelled fossils
• There were a few Precambrian shelled species, but
  the Cambrian Explosion produced many more
• All phyla with hard parts (except Bryozoa) began
  in Cambrian, and many without hard parts too.

24
Cambrian organisms
Trilobite - from UCMP web site Dominant animal of
the Cambrian (and much of Paleozoic)
25
Cambrian organisms
Remember, these guys had stalks
Brachiopods - from UCMP web site Dominant animal
of the Cambrian (and much of Paleozoic)
26
Burgess Shale

• Rich fossil beds in British Columbia
• Whats good about organic-rich shale for fossils?

• Shale has small clay-sized grains, which means
  the area was low-energy - less destruction of
  dead organisms, even soft ones

• Organic rich means the area where the organisms
  landed was anoxic - reduces decay and breakdown
  of dead organisms

27
Walcott Quarry Burgess life discovered
1909Quarry began 1910
Photo by Andrew MacRae from University of Calgary
Burgess Shale web page http//www.geo.ucalgary.ca
/macrae/Burgess_Shale/
28
Burgess Shale

• Walcott initially described the burgess species
  by fitting them in to existing phyla
• Not a stupid thing to do - thats how taxonomy
  works
• However, it turns out that the Burgess organisms
  represented a number of forms not seen before or
  since

29
Burgess Shale Animals
Anomalocaris claw - organism was up to 60 cm long
Photo by Andrew MacRae from University of Calgary
Burgess Shale web page http//www.geo.ucalgary.ca
/macrae/Burgess_Shale/
30
Burgess Shale Animals
Anomalocaris - about 60 cm long
From National Museum of Natural History
(Smithsonian)
31
Burgess Shale Animals
Marella
Photo by Andrew MacRae from University of Calgary
Burgess Shale web page http//www.geo.ucalgary.ca
/macrae/Burgess_Shale/
32
Burgess Shale Animals
Ottoia - worm-like organism
Photo by Andrew MacRae from University of Calgary
Burgess Shale web page http//www.geo.ucalgary.ca
/macrae/Burgess_Shale/
33
Burgess Shale Animals
Paediumias clarki
Rendering by necrosis http//www.bekkoame.or.jp/
necrosis/html/pageframe.htm
34
Burgess Shale Animals
Marella
Rendering by necrosis http//www.bekkoame.or.jp/
necrosis/html/pageframe.htm
35
Burgess Shale Animals
Wiwaxia - from 0.3-5 cm long
From National Museum of Natural History
(Smithsonian)
36
Burgess Shale Animals
Amiskwia - about one inch long
From National Museum of Natural History
(Smithsonian)
37
Burgess Shale Animals
Opabinia - Had five eyes! About 3 inches long 1
inch tube nose
From National Museum of Natural History
(Smithsonian)
38
Burgess Shale Animals
Hallucigenia - about 1 cm long - which end is the
head?
From National Museum of Natural History
(Smithsonian)
39
Burgess Shale Animals
Hallucigenia - incorrect reconstruction Its
walking on its protective spines
From National Museum of Natural History
(Smithsonian)
40
Burgess Shale Animals
Hallucigenia - actual photograph - note that it
shows only one set of legs
From National Museum of Natural History
(Smithsonian)
41
Concepts from Burgess

• Cambrian was a time when many new forms appeared,
  many soft-bodied and not well preserved, but only
  a few survived
• Sparked a debate between punctuated equilibrium
  (Punk Eek) and continuous evolution
• What is the role of contingency versus fitness?
  How do we define fitness?

42
What is our concept of evolution?
43
What is our concept of evolution?
44
What is our concept of evolution?
45
What is our concept of evolution?
46
Rise and fall of great faunal groups
Families
47
Wikipedia image
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Wikipedia image
49
PeriodicitySepkoski and others discovered a 62
million-year periodicity to their extinction
records (R and W are background estimates)
Rhode and Muller, 1994. Cycles in Fossil
Diversity.
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Some were 6-8 feet long - yikes