EARTH HISTORY UNIT 4 PALEOZOIC ERA

EARTH HISTORY UNIT 6 STUDY GUIDE
THE PHANEROZOIC EON BEGINS WITH THE PALEOZOIC ERA
(Revised 7/11)
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Introduction
- We have reviewed the first 4 BY (Precambrian) of our Earth’s 4.56 BY of existence
- We examined the Earth for the Hadean Eon, the Archean Eon, and the Proterozoic Eon.
- During the Precambrian, we saw continental masses being created
- Then plate tectonics really “kicked in” to create and tear apart two supercontinents - Rodinia and
Pannotia
- Earth had two ice ages during this period
- Bacteria ruled the Earth for billions of years and they created the free oxygen for our atmosphere
- At the end of the Precambrian, we saw oxygen levels reach 3% - 10% and a few primitive life forms
in the shallow seas
- On a 24 hour “Earth existence clock”, it is now 9:00 PM
- The Precambrian Proterozoic Eon was the beginning life eon”
- We now enter the last eon – The Phanerozoic (visible life) Eon
- With this unit we will examine the Paleozoic (early life) Era of the Phanerozoic Eon
- The Paleozoic (early life) Era of the Phanerozoic (visible life) Eon represents almost 50% of the time
since the Precambrian (a total of 291 MY).
Determining the Precambrian-Cambrian Boundary
- Original boundary was based on what was thought to be the appearance of the first shelly metazoans.
- Date for the beginning of the Cambrian was originally estimated at 590 MY.
- Today’s date for the beginning of the Cambrian is about 542 MY.
- Traditionally the Cambrian boundary was picked to represent the appearance of the first body fossil
of the trilobite Olenellus
- Testing found the original boundary was actually at 525 MY, not 590 MY, so a new boundary had to
selected.
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- In 1991, an international committee selected the Chapel Island Formation at Fountain Head, SE
Newfoundland Canada to represent the Cambrian-Precambrian boundary.
- This boundary strata (chosen in 1991) corresponds to the first appearance of distinctive trace fossils
and not body fossils. A fossil boundary in Siberia that correlated to the Newfoundland boundary was
radiometrically age dated at 542 MY.
Early Paleozoic Era (542 MY – 416 MY)
- The Early Paleozoic Era lasted for 126 MY.
- It is subdivided into the Cambrian Period, Ordovician Period, and Silurian Period.
Late Paleozoic Era (416 MY – 251 MY)
- The Late Paleozoic Era lasted for 165 MY.
- It includes the Devonian Period, Mississippian Period, Pennsylvanian Period and the Permian Period.
- In Europe they use the Carboniferous Period instead of the Mississippian and Pennsylvanian Periods.
Paleographic Maps
- One of the goals of historical geology is to provide paleographic reconstructions of early Earth.
- The maps can be constructed by synthesizing all of the pertinent paleoclimatic, paleomagnetic,
paleontologic, sedimentologic, stratigraphic and tectonic data available.
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Geography of the Early Paleozoic Era (542 MY – 416 MY)
- North America was one of the 5-6 continental land masses at that time.
- Ancestral North America is named Laurentia.
- For most of the Early Paleozoic, Texas would have been found south of the equator.
- Only during the Late Paleozoic would Texas again be north of the equator.
Period Maps
- Period maps can sometimes be confusing (used as an example maps of the Cambrian)
- The maps are interpretations of the geography of an area for a particular time in the geologic past.
- All of these maps can be plausible for their exact point in time
- The North American continental outlines shown on these maps won’t exist for millions of years
- The US and North American outlines are for “reference only” on all the maps
Paleozoic Sea Levels
- Eustatic (world-wide) sea levels were higher throughout most of the Paleozoic than the levels of
today.
- The Paleozoic Era had long periods of no large continental glaciers which would equal to a higher sea
level.
- Rapid sea floor spreading and submarine volcanism can make a significant portion of the sea floor
shallower.
- Twice during the Paleozoic, there would be extensive continental glaciation which would cause sea
levels to drop.
- Sea level changes would be most strongly felt over continental land masses.
- (Returned to a Cambrian Period map as an example)
- Epicontinental (Epeiric) sea: widespread, shallow seas that transgress or regress over a craton.
- This was a common feature of the various periods of the Paleozoic Era, especially over Laurentia
(North America).
- Transgressive: describes a rise in sea level, generally over a craton (left map).
- Regressive: describes a fall in sea level, generally off a craton (right map).
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Transgressive Seas (Using a Cambrian Period map as an example)
- Transgressive: describes a rise in sea level, generally over a craton, this would leave behind a
stratigraphic sequence.
- This situation (rocks) can provide a record of the rising sea level: sandstone overlain by shales
overlain by limestone.
- Transgressive sequence: deep-water, sedimentary-rock sequence that overlies shallow-water,
sedimentary-rock sequence.
Regressive Seas
- Regressive: describes a fall in sea level, generally off a craton; this would leave behind a stratigraphic
sequence.
- This situation (rocks) can provide a record of falling sea level: limestone overlain by shale overlain
by sandstone.
- Regressive sequence: shallow-water sedimentary-rock sequence that overlies deep-water,
sedimentary-rock sequences.
FYI: Walther’s Law: can be used to identify transgressions and regressions.
- This law states that the sequential vertical changes in sedimentary rock types will equal horizontal
sequential changes in rock types.
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CAMBRIAN PERIOD (542MY – 488 MY)
- Epicontinental seas cover a large portion of the North American craton.
- On each side of the craton, we can find a transgressive sequence of sediments.
- There is no life on land at this time
- To the southwest of the craton are a series of islands
- Transcontinental arch: a series large, late Cambrian island arcs that extended to southern New
Mexico (bottom tip of land mass on above map).
- Erosion of the craton produced a lot of clean sandstone (good glass sand) in Wisconsin
- We can find examples Cambrian sand within the Bliss Sandstone (El Paso area)
- We also know that the Enchanted Rock area (Central Texas) had islands because of the Hickory
Sandstone (Mason, Texas)
Cambrian Climate
- During the Cambrian, the temperatures would have been warmer than today
- There would not have been advancing glaciers during this time
- There would have been no life on land at this time
Cambrian Big Bang Evolution
- At the Cambrian (542 MY), many different life forms suddenly appeared in the fossil record.
- This period represents the fundamental mysteries of the history of life on Earth and the fossil record.
- For billions of years, life was represented by simple life forms such as bacteria and algae.
- Then for a hundred million years, somewhat complex life forms appeared in the Upper Precambrian
Ediacaran Period (630 MY – 542 MY).
- There is some recent evidence that a few Ediacaran life forms may have survived beyond the
Cambrian 542 MY boundary
- Remember that this 542 MY boundary is based on trace fossils and the appearance of “small shelly
fauna” (advanced life)
- In 1993 Cambrian fossils were been found at Yakutat, Siberia to be older than (or before) the first
Cambrian trace fossils, yet younger than (or after) the Ediacaran fauna
. The fossils found here were primitive ancestors to sponges, mollusks and brachiopods.
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- The Cambrian boundary has not yet been adjusted to fit this new location.
Complex Life Forms
- The Cambrian Big Bang continued with the rather sudden appearance of other diversified shelly
metazoans.
- For the first time, complex animals appeared with protective shells.
- New adaptations included: legs, claws, antennas, other appendages, eyes and mouths with teeth.
- All of these changes can be attributed to adaptive radiation
- Adaptive radiation: rapid speciation of a single or a few species to fill any ecological niche
- This is an evolutionary process derived by mutation and natural selection.
- Possibly either environmental with genetic causes
Environmental Changes Driving the Cambrian Adaptive Radiation
1 - Continued continental breakup allows more shallow water habitats to develop.
2 - Oxygen levels need to reach a critical level.
- A certain oxygen level is required to aerate tissues and to make structural components like teeth and
bone.
3 - Evolution of predators would favor species that have protective shells.
4 - Chemistry of the oceanic water may have changed to favor the precipitation of calcareous shells.
- Most of the ocean’s iron had been removed and placed into banded iron formations.
- Dolomite supply and deposition decreased.
- More dissolved oxygen in the water column
5 - Widespread submarine volcanism increased availability of energy and nutrients.
Genetic Causes of Cambrian Adaptive Radiation
- The various forms of mutations drive the process of evolving organisms that survive the changing
environments.
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Chengjiang China
- The best Early Cambrian fossils are found in China
- In 1984, a large number of diverse Early Cambrian fossils were discovered here.
- The fossils here are really complex considering that complex life is just beginning on Earth.
- This implies that the Cambrian explosion may have occurred in as little as 10 MY.
- (Video clip of life in the Cambrian Chinese sea)
Sirius Passet, Greenland
- Also in 1984, fossils were discovered here which have the same age as fossils found in China
Burgess Shale Biota
- No discussion of Cambrian life is complete without discussing the Middle Cambrian Burgess Shale
biota
- The Burges Shale was discovered in 1909 near Field, British Columbia, Canada
- This Middle Cambrian shale (515 – 520 MY) contains some of the best period examples of soft
bodied flora and fauna.
- The shale provides fossil examples of Earth’s complex animals.
- These animals had shells, heads, mouths, eyes, claws, legs and other appendages
- Many animals of the Burgess shale are “unknown phyla” - have no living organisms with their basic
body plan.
- This biota of invertebrates represents the root stock and basic body parts from all present day
invertebrates (and vertebrates).
- Life was much more diverse in terms of phyla during the Cambrian than today.
- The biota here suggests the Cambrian big bang or explosion occurred over a relatively short period of
geologic time.
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Life Body Plans
- The pattern for the rest of the history of animal life was set in the Cambrian Period (542 MY – 488
MY).
- By the end of the Cambrian, ancestors of all living phyla of shelly invertebrates had appeared (except
bryozoans).
- No new shelly phyla have appeared since that time.
- The Early and Middle Cambrian fossils seem to imply early experimentation and then later
standardization.
Phylum Chordata
- All chordate are bilateral animals related by possessing notochord: something resembling a backbone
- A notochord will eventually evolve into a backbone
Earliest Known Chordates
- Cathaymyrus diadexus age is 535 MY from China
- The chordate Yunnanozoon, figure 21.14, page 617 of text, has been reassigned to Phylum
Hemichordata.
- Next oldest known chordate (not vertebrate) found at the Burgess Shale, at 520 MY, is the 2-3 inch
Pikaia, a filter feeder (above).
Oldest Known Vertebrate
- Vertebrates: animals with backbones (covered notochord)
- Earliest known vertebrates are fish.
- Myllokunmingia is one of two of the oldest known vertebrate fish at 530 MY, found at Chengjiang,
China.
- Haikouichths is also found at 530 MY
- (Video clip of Cambrian fish)
Trilobites
- Cambrian is also known as the Age of the Trilobites
- All orders of trilobites would evolve in the Cambrian
- Trilobites would make up +50% of the Cambrian fauna (542 MY – 488 MY).
- There would be more than 15,000 species
- The trilobites would have a wide variety of eye types.
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- They are the world’s most popular fossil to collect.
- Trilobites would roll themselves up when faced with danger.
- Quite a few trilobites can be found near Llano, Brownwood and El Paso, Texas.
- Present day sow bugs and horse shoe crabs are not related to trilobites.
End of Cambrian
- The end of the Cambrian would be marked by colder temperatures and mass extinction of most of the
trilobites
Ordovician Period (488 MY – 444 MY)
- As during the Precambrian, ancestral North America will again be subjected to tectonics and many
colliding land masses
- Such a tectonic collision is called an orogeny
- Orogeny: an episode of mountain building, usually associated with convergent zones.
- The results of an orogeny is intense crustal deformation accompanied by metamorphism and igneous
intrusions and thickening of the Earth’s crust.
- This is directly associated with colliding tectonic plates at convergent plate boundaries or subduction
zones
- (Mountains form along convergent zones.)
Taconic Orogeny of the Appalachian Mountains (oldest)
- At 510 MY (Cambrian), the eastern US continental shoreline extended from New York to the
Carolinas
- During the Ordovician, Laurentia would remain south of today’s equator.
- Before this event, the Eastern US shoreline extended only from the Carolinas to New York.
- Offshore, an island arc called the Taconic Arch is headed toward Laurentia during the Early
Ordovician
- The Taconic Island Arc would first collide with the Canadian Maritime provinces
- The arc finished its collision (convergence) by 450 MY, extending the US coastline from New
England to Georgia.
- Remember that with convergent (subduction) zones, we find related igneous intrusions and the
Taconic Orogeny is no different
- The igneous intrusions from Georgia to New York all have similar age-dating of intrusions -460 to
440 MY (Taconic Orogeny).
- Later, two large masses begin approaching Laurentia from the eastern coast of the Iapetus Ocean –
the continent of Baltica and the Avalonia Islands (Acadian Orogeny)
- But we will have to wait for the Devonian for the US collision
- The early Appalachian Mountains created by the Taconic Orogeny will erode downwards before the
Acadian Orogeny
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- Why is it that, over time, most mountains do not erode to a totally flat sea level plane?
- Mountains are characterized as rising above surrounding area; for this to happen, mountains must
have deep roots
- Mountains and mountain roots are a property of isostasy.
- Isostasy: the concept of the Earth’s crust floating on a dense underlying layer.
- This concept can be illustrated by a cork in floating water.
- As mountains erode, isostatic adjustments push the mountain roots upward.
- Isostatic rebound: the phenomena in which unloading (erosion) of the crust (mountains) causes the
crust to rise until it attains equilibrium.
- Thus older mountains will always be higher than the surrounding plains
- This is why mountains persist over millions of years.
- Ordovician sea levels were very high with transgressive seas over the North American craton, until
the end of the period
- The (Appalachian) Taconic Highlands now begin to erode downwards
- Thick sediments were deposited opposite the eastern subduction zone
- This would create the Queenstown Clastic Wedge
West Texas
- In the Early Ordovician, a large deposit of sand-grained filled dolostone were deposited by the seas,
called the sandy El Paso Formation in the El Paso area.
- In the Middle Ordovician, large deposits of dolostone were deposited by advancing seas, called the
Montoya Formation in the El Paso area.
- East of the El Paso area is found the Lower Ordovician Ellenberger Formation – a deep, thick
dolostone that has an associated 90 large oil fields and 50 major gas fields. Outcrops can be found
near Llano Texas.
Marine Life in the Ordovician
- Cephalopod mollusks grew to more than 18 feet in length.
- Brachiopods would increase in importance.
- Some trilobites survived into the Ordovician
- Plants would become well established in the seas
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Class Agnatha – Fish of the Ordovician
- These are jawless fish that became common during the Ordovician Period
- These are some of the most primitive fish - they lack both a jaw and paired fins.
- There were six major groups called including Ostracoderms, a bony-skin fish that was about 10
inches long and lived only from the Cambrian to the Devonian (542 MY – 416 MY).
- Modern day examples include lamprey eels and hagfish
Ordovician Land Plants
- There is some evidence that primitive algae and lichens invaded the land masses
An Ordovician Ice Age and a Mass Extinction
- The third extensive continental glaciation will occur at the end of the Ordovician Period
- This will cause sea levels to drop (regressive seas)
- The glaciation also lowered water temperature
- The temperature and sea level drops will have a catastrophic effect on life; this probably lad to the
mass extinction of many life forms.
- About 12% of Earth’s life forms would become extinct.
- Most of the extinctions occurred in shallow tropical waters
- This would include more than 100 families of marine invertebrates.
- There were basically no land forms of life yet.
Silurian Period (444 MY – 416 MY)
- Ancestral North America will soon again be subjected to tectonics by an approaching land mass
- Two other large land masses began approaching Laurentia from the western coast of the Iapetus
Ocean – the continent of Baltica and the islands of Avalonia
- Let’s begin the process at 450 MY in which the plates are approaching one another
- Baltica has collided with Canada and Avalonia is headed toward the eastern coast of the US
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- But Avalonia will not yet collide with the US during the Silurian Period
- Meanwhile, the earlier Appalachian Mountains by the Taconic Orogeny are beginning to erode
downwards
Silurian Seas and Deposition
- Another period of high sea levels (transgressive seas) will cover most of North America (Laurentia).
- In the Michigan basin, large reefs would block seawater, resulting in thick salt deposits within the
Michigan basin.
- In Texas, large deposits of sandy dolostone (El Paso area) were deposited by the seas, called the
Fusselman Dolostone.
- To the east of El Paso, the Fusselman Dolostone is a major oil and gas producer in the deep wells of
West Texas.
Silurian Fish
- Sea life would now be filling as many niches as possible and we even have fresh water fish
- Silurian fish will take a major evolutionary step forward
- To develop further, fish needed to develop a jaw.
- Some suggest that the vertebrate jaw began with modifications of the first 2 or 3 gill arches.
- The first fish with jaws would develop during the Silurian Period
- Class Acanthodii were the first fish with jaws, known as spiny fish that grew up to 6 feet in length.
- Lived from Silurian to the end of the Paleozoic (444 MY – 251 MY).
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- Class Placodermi is a Silurian armored fish that became extinct after only 50 million years of
existence.
- Group Arthrodires: was a giant predator that grew more than 20 feet long and had a giant head.
- Group Antiarchs: grew up to two (2) feet long and had over 100 species.
Insects
- The Silurian saw the development of large sea scorpions up to three feet long
- (Video clip of jawless fish and large sea scorpions)
- Later sea scorpions up to 10 feet long would evolve
- (Video clip of a giant sea scorpion)
First Invasion of Life on Land
- Even with the transgressive seas, there would be enough land available for life to invade
- Before there can be animal life on the land, there must be some kind of a food supply for them
- The first invasion of living organisms would take place during the Silurian
- And this occur about 430 MY ago by algae and vascular plants.
- Earliest known vascular plant is Psilopsids
- (Video clip of Silurian plants)
Insects (Arthropods)
- The earliest animals on land would be insects
- Oldest known fossil insect is the millipede (Silurian Age); we have found fossil footprints of some
giant millipedes.
- Also, there were many bizarre giant, scorpion-like insects that invaded the shorelines.
- (Video clip of scorpions on land)
Age of Corals
- The Silurian Period is often called the Age of the Corals because of the great abundance
End of Silurian Period
- The end of the Silurian Period is marked by a few groups of small marine creatures becoming extinct
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Devonian Period (416 MT – 359 MY)
- We are now moving to the Late Paleozoic
- Life and Earth will undergo some major changes during this period
- The components for the Acadian Orogeny started at 450 MY (Ordovician) in which the plates of
Laurentia and Baltica and the island arc of Avalonia are converging
- The early Appalachian Mountains created by the Taconic Orogeny have eroded downwards
(Ordovician – Silurian)
- Baltica had converged with Canada and Avalonia was converging toward the eastern US coast
(Silurian)
- The final convergence or Acadian Orogeny created a very tall Appalachian Mountains in the
Devonian Period
- Now we have the second generation Appalachian Mountains
Determining Ages of Mountains
- There are three different methods used to give the age of mountains
- 1) Age of mountains determined by the age of the rock deposition
- This is the time that the rocks actually formed but we have a problem: What if the deposition covered
several ages? Do you use the latest age?
- 2) Age of mountains determined by the orogeny that formed the mountains
- This represents the timing of the orogeny event. What if there was more than one orogeny?
- 3) Age of the mountains as determined by the topography
- What if the present topography was created by a renewed uplift?
- One or all three methods have been used to age-date a mountain
Antler Orogeny of Western US
- What else is going on that would eventually converge with Laurentia during the Devonian
- The Antler Highland mini-continent has been moving toward Laurentia
- But this Antler Orogeny will not occur until the end of the Devonian
Gold and the Antler Highland
- This ancient landmass forms a greater portion of the outcropping rocks of the state of Nevada.
- Some of the largest and richest US gold mining districts are found within this ancient Antler
Highland
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Euramerica
- There is now a larger landmass created by the Taconic, Acadian and Antler orogenies
- We would now have a new huge continent called Euramerica (or Laurasia)
The Devonian Seas and Potash
- We will have mostly transgressive seas during the Devonian along with some times of regression
- Only a thin layer of Devonian rocks is found in Texas, the Canutillo Limestone in the El Paso area.
- Reefs blocked off most of the seawater from the Williston Basin in Canada which is the site of large
salt and world class potash deposits. (Potash is used for fertilizer)
Plants
- Land plants become widespread, large and diversified
- Forests first began along the river banks with shallow roots
- This will provide even more food for more animals to invade the lands
- Finally, tall trees (seed-bearing gymnosperms) with deep roots will evolve toward the end of the
Devonian
- Earth is becoming slightly more familiar
Life in the Devonian Seas
- There will still be a few trilobite species in the seas
- Major changes were occurring in the shallow Devonian Sea especially with fish
- The Devonian Period is also known as the Age of the Fish
- All five (5) classes of fish would be alive at this time and there would be no new classes.
- Before we continue the lobe-finned fish, let’s review some of the fish that we have studied up to now:
acanthodians and Placodermi
- Let’s examine Devonian cartilaginous fish
- Class Chondrichthyes includes all of the cartilaginous fish (sharks, rays, etc.)
- This class includes a number of extinct but very weird shaped sharks including: Cladoselache,
Heliocoprion, Scissor-tooth shark, Stethacanthus and Farukatasu
- (Video clip of sharks and big fish)
-Let’s examine the remaining fish types that evolved during the Devonian
- Class Osteichthyes (bony fish) have two types of bony fish: lobe-finned fish and ray-finned fish
- Order Crossopterygii includes the lobe-finned Coelacanth, that first appeared in the Devonian and
was thought to be extinct 75 MY ago; but was rediscovered as a living fish in 1938.
- We can see some evolutionary changes with the lobe-finned fish
- They have articulated bones within stubby fins.
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- They have muscles that extend into the fins.
- This is important because this would be the beginning of tetrapod limbs.
- Tetra is Greek for four and Podos is Greek for foot
- Tetrapod: Vertebrate animals having 4 feet or leg-like appendages (excludes fish)
- A lungfish is with the Order Dipnoi that was first seen in the Devonian.
- This is a living fossil that took another evolutionary step forward with external nostrils and lungs as
well as gills
- Lungfish have articulated bones in fins with muscles in the fins
- This includes the Devonian Panderichthys (416 MY – 359 MY) that had long frontal lobe-fins
- Let’s examine a freshwater fish that some scientists had earlier thought was the first tetrapod ancestor
of amphibians (found in the Devonian Period)
- Acanthostega at one time was thought to be an amphibian. But they probably had no lungs – just gills
like fish.
- Let’s also examine a present day tetrapod-like fish – the mudskippers of today
- “Mudskippers” are examples of modern day tetrapod fish (front limbs more developed than rear).
- (Video of a mudskipper battle)
- Other lobe-finned fish in the Devonian were showing their presence and may have been feeding
onshore
- It is suspected that Eusthenopteron fed out of the water along shoreline.
- Recent discovery of an air-breathing fish with front legs has been hailed as the missing link to
amphibians – Tiktaalik roseae
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- Why do we suspect that fish may have walked on land?
- From a shallow water basin, we find +365 MY something large was walking in shallow water with
their widely separated footprints, preserved in today’s rocks.
- (Video clip of a walking fish Eusthenopteron)
- The first tetrapod ancestors of amphibians is found in the Devonian Period
- The labyrinthodonts called Ichthyostega had seven toes on its back fins (feet).
- We reviewed how the original fins of various creatures as they rapidly evolved into feet
- (Video showing possible evolution of fish into amphibians)
- At the end of the Devonian, another mass extinction would affect about 14% of Earth’s life forms.
- This resulted in the near collapse of all massive reef communities and one class of fish.
- Almost all warm water environments were affected but not the cool water environments.
- The primitive land plants were not affected by this event.
- The Devonian mass extinction may have taken a few million years to complete
- Causes: global cooling? Oceanic volcanoes? Other?
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Mississippian Period (359 MY – 318 MY)
- Earth is preparing for its largest collision ever.
- Now at 327 MY, Euramerica (Laurasia) is headed toward Gondwana which will produce the Pangaea
supercontinent
- With this convergence, we will suture these masses together
- In the next period, tectonics will create the third generation of the Appalachian Mountains when
Africa will converge here
- The Mississippian Period is the last very widespread transgressive epicontinental sea.
- Many parts of “North America” will be covered by vast shale deposits
- We are not sure why so much mud was deposited here
- The Barnett Formation of Central and West Texas is one of such shale deposit
- Oil and gas wells are widespread within the Bartlett Shale.
- These wells will contribute +$100 Billion to the Texas economy
- Although the Mississippian is part of the “Carboniferous Period”, very little coal is associated with
this age in the US
- The epicontinental seas will contain abundant forms of life.
- The Mississippian is also called the Age of the Crinoids
- Blastoids became very common
- We know that amphibians were walking near water at this time
- 350 MY Mississippian footprints (probable amphibian) have been found in Canada.
- Amphibians had a major problem in that they had to lay gelatinous eggs in water.
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- The next evolutionary step for vertebrates will be the development of the amniotic egg.
- These amniotic eggs (whether hatched inside the mother or in nests on the ground) provide the
parents (reptiles) greater opportunity for expanding their environment.
- (Video of the transformation of eggs)
- The first suspected reptile is a small lizard-like Westlothiana (350 MY) in Scotland
- Although we find a possible reptile here, the real “Age of the Reptiles” is the Permian Period (299
MY – 251 MY and different than the Age of Dinosaurs).
- The step from amphibian to reptile would take less than 60 MY
- At the end of the Mississippian Period, CO2 levels dropped from 1800 ppm to 300 ppm and world
temperatures dropped
- The Mississippian Period would end with a minor extinction of a few sea creatures
Pennsylvania Period (318 MY – 299 MY)
- This is the period of the “big collision”
- We will begin with the Allegheny Orogeny
- Now the latest Appalachian Mountains are part of the supercontinent Pangaea (PennsylvanianPermian Periods)
- It will be Permian times before the convergence with Africa will end
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- Meanwhile, South America is converging with North America – the Ouachita Orogeny
- The results include the formation of the Ouachita Mountains of Arkansas and Oklahoma
- During the Allegheny Orogeny, the Llano area of central Texas will be uplifted from great depths
- Epicontinental seas are still present but less extensive than previous periods.
- These regressive seas will expose a series of islands in the western US
- The formation of Pangaea is nearly complete.
- Major coal deposits would form in the Eastern US and Texas.
- Evaporation would cause thick salt and potash deposits in New Mexico and Utah.
- Outcrops of Pennsylvanian limestone can be found in north-central Texas.
- During the Pennsylvanian Period, the craton (North America) would be part of Pangaea
- The Appalachians, Ouachita and Antler Mountains are present
- Major swamps are located along the equator, which will become vast coal deposits
- Even Texas has vast coal resources from these swamps
- (Video about the coal swamps)
- Trapped seas would collect in the basins
- Large deposits of potash would be created in New Mexico and Utah
- Pennsylvanian Period rocks can be found in central Texas
- With a large land mass and ongoing evolution near the equator, some changes are going on
- The first undisputed reptile is a small lizard-like Hylonomus that has been found in the 300 MY
(Pennsylvanian) Joggins Formation, Nova Scotia in Canada.
- The first mammal-like animals will appear now; we will discuss mammal-like in the Permian Period
- The Pennsylvanian Period is also known as the Age of Plants and Age of Giant Insects.
- New evidence suggests that insects may have developed wings in the Devonian Period
- Winged insects are common in the Pennsylvanian Period
- Dragonflies became giants, some with wingspans of 36 inches
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- This period could also be called the Age of the Cockroaches since more than a thousand species were
present and they grew to be giants
- (video about insects – spiders, dragonflies, and centipedes)
- Earth will enter its fourth ice age at the end of the Pennsylvanian Period
- This will cause a minor extension with some marine fauna
Permian Period (299 MY – 251 MT)
- The Allegheny Orogeny will be completed and we now have the supercontinent of Pangaea
- And the Appalachian-Caledonian Mountain ranges were created
- For half of the Permian Period, Earth will endure its fourth ice age- Fewer swamps will be around for
most of the Permian
- Glaciers and deserts are common for most of this period
- There were fewer transgressive seas
- And the Appalachian- Caledonian Mountains will present a barrier for biodiversity
- During this period, only the western 1/3 of the US was under shallow seas.
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- In West Texas, there is a large evaporate basin
- In this basin, the thick Castile Gypsum will be deposited
- The West Texas Permian Basins would be inland seas with the seawater coming from the west
- Large reefs (shelves) would surround these seas
- El Capitan in the Guadalupe Mountains is actually a world famous Permian reef.
- The Permian Basin is famous for its huge oil and gas deposits
- In the Utah area is the Phosphoric Sea where valuable deposits of phosphates (fertilizer) will be
deposited.
- There are extensive Permian deposits of sandstone and limestone in North-central Texas.
- Animal life expanded on the lands
- Large primitive amphibians lived along the shorelines of Texas:
- Seymouria baylorensis, from Baylor County, (North) Texas
- Eryops and Cacops from Archer County, (North) Texas
- Diplocaulus from near Abilene, Taylor County, Texas is a famous Texas fossil.
- We should mention the freshwater reptile mesosaurs of African and South American rivers
(remember continental drift)
- The Permian Period is also known as the Age of the Mammal-like Reptile (not dinosaur)
- And we will see that at the end of the Permian – this will be a failed life form for Earth
- The finned-back Pelycosaurs are mammal-like reptiles
- This includes the carnivorous Dimetrodon and Edaphosaurus an herbivore
- Dimetrodon skeletons have been found Archer County, North Texas.
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- Cynogathus are mammal-like reptiles of African- South American fame (continental drift fame)
- (Video on big reptiles and video on mammal-like reptile)
- What do we mean by mammal like?
- The mammal-like animals had several mammalian skeletal characteristics”
- Primitive differentiation of teeth, like mammals (all other animals have same style teeth)
- They have several mammalian skeletal characteristics.
- No true mammals have been found before the Mesozoic Era.
- (Video on teeth)
- Now the therapsids will evolve
- (Video – Late Permian)
- The world environments become largely deserts
- (Two videos on changes)
- The end of the Permian Period would result in the largest mass extinction event ever recorded on
Earth
- (Video clip)
EXTINCTIONS
Late Ordovician (444 MY) Mass Extinction
- There were times when Earth was not a very friendly place for many forms of life.
- At the late Ordovician, about 12% of Earth’s life forms would become extinct.
- This would include more than 100 families of marine invertebrates.
- There were basically no land forms of life yet.
Late Devonian (359 MY) Mass Extinction
- At the end of the Devonian, another mass extinction would affect about 14% of Earth’s life forms.
- This resulted in the near collapse of all massive reef communities and one class of fish.
- Almost all warm water environments were affected but not the cool water environments.
- The primitive land plants were not affected by this event.
Late Permian (251 MY) Mass Extinction
- This event would mark the largest mass extinction event ever recorded on Earth.
- More than 52% of Earth’s “families” became extinct.
- This event marks the end of the Permian Period and Paleozoic Era.
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Permian Life Forms That Became Extinct by 251 MY Ago
- 90% -95% of all marine invertebrate species died out (shallow water).
- Only one of the many species of Crinoids survived (shallow water).
- All blastoids disappeared (shallow water).
- 80% of all brachiopods disappeared (shallow water).
- Almost all gastropods (sea snails) disappeared (shallow water).
- 8 out of 27 orders of insects disappeared (land environment).
- Two orders of coral disappeared (shallow water).
- 75% of all reptiles disappeared (land environment)
- 67% of all amphibians disappeared (water and land environments)
- Another entire class of fish disappeared (marine environment)
- All trilobites disappeared (all water environments).
Timing of the Permian Period Mass Extinction
- This extinction was not instantaneous but occurred over a period of less than 8 million years.
- Succeeding Mesozoic life forms would have a very low diversity but the surviving species would
tend to be very abundant and widespread.
Probable Cause of the Permian Mass Extinction
- We do not know for certain.
Types of Extinctions
- Extinction: the planet-wide disappearance of a species or higher taxonomic group.
- This is the ultimate fate of all species.
- This is a continuous process as recorded in the fossil records.
- Looking back at the Phanerozoic Era, we have noticed five severe mass extinctions.
- Background Extinctions: continued extinction of species.
- Mass Extinctions: twice the background rate
- Minor Mass Extinction: same as above (mass extinction); a good example would be the decrease in
many species at the end of the last Ice Age.
Time to Complete A Mass Extinction
- From a few months to a few million years.
Significance of a Mass Extinction
- This signifies a planet-wide environmental or ecological problem.
- For one species, a mass extinction is bad but for another species – a mass extinction of their
competitors is good.
- The extinction of a large number of dominant species is instrumental in the expansion of “minor”
species to fill the niche left open by the mass extinction.
Theories of Mass Extinctions
- Most are related to catastrophic changes in the atmosphere; or
- Catastrophic changes in the hydrosphere
- Many geologic events can severely affect either one or both of these spheres.
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Meteorite Impacts
- These can have a major impact on Earth’s atmosphere, with the addition of gas, dust and chemicals.
- The hydrosphere and atmosphere could be severely impacted by sudden global heating and global
cooling.
Related to Massive Volcanism
-Flood basalts: huge flows (thousand of cubic miles) of basalt from fissures.
- These add huge quantities of greenhouse methane and CO2 gases to the atmosphere
- The Permian Siberian flood basalts added 500,000 cubic miles of basalt to the Earth’s surface.
Continental Glaciation
- This can cause major changes in sea levels that affect cooler ocean water and world temperatures.
Tectonics
- The formation of a super-continent can cause major changes in ocean currents and on climate.
Others
- Also postulated are problems with magnetic reversals and supernovas.
- However, there has never been a total extinction during the Phanerozoic Eon.
END OF UNIT 6
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