Week 7

Precambrian: Archean, Lecture Materials + ch 8

Proterozoic: Ediacara Fauna, Lecture  Materials + ch 9

 
 

alligator gar: Lepisosteus osseus, Cretaceous to Recent
Reading Assignment:  Chapters 9, and 10
 Middle Paleozoic

Unit (Chapter) Plan:

Contents  (unit topics)

Activities  (things you must do)

Abilities Acquired (what you learned)

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Visit this web site: UCMP    to review the History of Life of  this interval of time

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Contents (course topics):

Phanerozoic Eonothem The Middle Paleozoic
Chronstratigraphic Divisions: Silurian System || Devonian System
  The Silurian System
            Biological Features:
          The Evolutionary Processes of Phanerozoic Biota; From Eukaryotes to Animalia
                Life recovered and expanded in aquatic habitats (textbook ch 10, p. 150-151)                 Paleogeography || Landmasses:  Laurentia and Baltica collide
           Paleoentological features:
          Divisions of time    The Devonian System: Age of Fish
            Biological Features:
                Coral-strome reefs
                New swimming invertebrates: ammonoids (cephalopods) Texbook ch 12, p. 182-186)
                Animals move ashore: the amphibians Tiktaalik (textbook ch 13, p. 198-204)
            Geological features:
                Paleogeography:
      Paleoentological features:
                 Faunas: Classification of Fishes (textbook, ch 10, p.186-190)
                    Jawless fishes: ostracoderms
                    Fishes with jaws: acanthodians
                        sharks and ray-finned fishes
                    Fishes with lungs
                Plants invaded the land (textbook ch 13, p. 193-195; ch. 14, p. 205-218)
                    Vascular plants
                    Spore plants
                    Seed plants
 
 

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Activities (things you must do):

Read Chapters nine and ten  of your textbook

Review the story of plate tectonics

For a more simplistic model visit this site <http://www.pbs.org/wgbh/aso/tryit/tectonics>

<http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml>

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Abilities Acquired (what you learned):

By the end of this chapter you should be able to:
 

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Phanerozoic Eonothem

Silurian System: 438 to 408  mya . From Latin Silures, an ancient people of southwest Wales, where the rocks were first identified. It is characterized by: the first terrestrial plants and animals.  The first jawed fishes and  uniramians  (like insects, centipedes and millipedes) appeared during the Silurian (over 400 million years ago). First vascular plants (plants with water-conducting tissue as compared with non-vascular plants like mosses) appear on land (Cooksonia  is the first known). High seas  worldwide.Brachiopods , crinoids, corals.

The Silurian was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it. The Silurian witnessed a relative stabilization of the earth's general climate, ending the previous pattern of erratic climatic fluctuations. One result of these changes was the melting of large glacial formations. This contributed to a substantial rise in the levels of the major seas.

Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws. It is also at this time that our first good evidence of life on land is preserved, including relatives of spiders and centipedes, and also the earliest fossils of vascular plants.

Biological Features:
The Silurian is a time when many biologically significant events occurred. In the oceans, there was a widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the oldest known fossils of coral reefs.

Horn and honeycomb corals were common. By mid-period, these same corals were building reefs in the warm seas.

The time period also marks the wide and rapid spread of jawless fish, along with the important appearances of both the first known freshwater fish and early jawed fish. Other marine fossils commonly found throughout the Silurian record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks.

Numerous brachiopods, worms, and shrimp lived on the muddy bottoms. The larger scorpions (eusarus) and sea scorpions (ptertogus) were less numerous but dominated the scene because of their larger size.

It is also in the Silurian that we find the first clear evidence of life on land. While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils (a group of fungi), as well as remains of the first arachnids and centipedes.

Perhaps most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cooksonia, a collection of branching-stemmed plants which produced sporangia at their tips. None of these plants had leaves, and some appear to have lacked vascular tissue. The Silurian was a time for important events in the history of evolution, including many "firsts," that would prove highly consequential for the future of life on earth.
 

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Devonian System: "The Age of Fishes" 408 to 360 mya . Devonian period (div?'n?un) [key], fourth period of the Paleozoic era of geologic time between 408 and 360 million years ago (see Geologic Timescale, table). It was named (1838) by the geologists Sir Roderick Impey Murchison and Adam Sedgwick for Devonshire, England, where they first investigated rocks formed during the period.
The Devonian period was a time of great tectonic activity, as Laurasia and Gondwanaland drew closer together.First amphibians, ammonites, fishes abundant. Fish and land plants become abundant and diverse. First  tetrapods  appear toward the end of the period. First amphibians appear. First sharks, bony fish, and ammonoids. Many  coral reefs, brachiopods, crinoids. New insects, like springtails, appeared. Mass extinction (345  mya) wiped out 30% of all animal families) probably due to  glaciation  or meteorite impact.

 
Biological Features:
By the Devonian Period life was well underway in its colonization of the land. Before this time, there is no organic accumulation in the soils, causing these soil deposits to be a reddish color. This is indicative of the underdeveloped landscape, probably colonized only by bacterial and algal mats.

The vegetation of the early Devonian consisted primarily of small plants, the tallest being only a meter tall. By the end of the Devonian, ferns, horsetails and seed plants had also appeared, producing the first trees and the first forests in swampy areas.

By the beginning of the Devonian  early terrestrial vegetation had begun to spread. These plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall. These plants included the now extinct zosterophylls and trimerophytes. The early fauna living among these plants were primarily arthropods: mites, trigonotarbids, wingless insects, and myriapods, though these early faunas are not well known.

Insects appeared during the middle of the system and were common by the end of the system. Most were small, but a few grew to sizes larger than the largest insects known today. Fossil remains include cockroaches up to 10 centimeters (4 inches) long and dragonflies with wingspans about 74 centimeters (29 inches) wide. Scorpions, spiders, and centipedes also were among the more than 400 species found as fossil remains.

Plants: By the Upper Devonian, lycophytes, sphenophytes, ferns, and progymnosperms had evolved. Most of these plants have true roots and leaves, and many are rather tall plants. The progymnosperm Archaeopteris was a large tree with true wood. In fact it is the oldest such tree known, and produced some of the world's first forests. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". Along with this diversification in terrestrial vegetation structure came a diversification of the arthropods.

Also during the Devonian, two major animal groups colonized the land. The first tetrapods, or land-living vertebrates, appeared during the Devonian, as did the first terrestrial arthropods, including wingless insects and the earliest arachnids. In the oceans, brachiopods flourished. Crinoids and other echinoderms, tabulate and rugose corals, and ammonites were also common. Many new kinds of fish appeared.

In warm seas, corals had become the dominant form of live. At least 700 different species of brachiopods lived on the ocean floor with lily-like crinoids which were scattered everywhere.

The Devonian seas were dominated by brachiopods, such as the spiriferids, and by tabulate and rugose corals, which built large bioherms, or reefs, in shallow waters. Encrusting red algae also contributed to reef building. In the Lower Devonian, ammonoids appeared, leaving us large limestone deposits from their shells. Bivalves, crinoid and blastoid echinoderms, graptolites, and trilobites were all present, though most groups of trilobites disappeared by the close of the Devonian.

The Devonian is also notable for the rapid diversification in jawed and bony fish. Benthic armored fish were common by the early Devonian. These early fish are collectively called "ostracoderms", and include a number of different groups. By mid-Devonian, placoderms, the first jawed fish, appear. Many of these grew to large sizes and were fearsome predators. Of the greatest interest to us is the rise of the lobe-finned fish, which eventually produced the first tetrapods just before the end of the Devonian. The lungfish developed the ability to breathe air at the surface. Some lungfish still survive today in Africa. The first amphibians developed from this group of animals by the end of the period. The footprint of a primitive salamander-like amphibian was found in Pennsylvania.
 
 

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