Historical Geology
INTRODUCTION
VERTEBRATE EVOLUTION
FISH
AMPHIBIANS—VERTEBRATES INVADE THE LAND
EVOLUTION OF THE REPTILES—THE LAND IS CONQUERED
PLANT EVOLUTION
¨Perspective 13.1: Palynology: A Link Between Geology and Biology
Silurian and Devonian Floras
Late Carboniferous and Permian Floras
SUMMARY
The following content objectives are presented in Chapter 13:
¨ Vertebrates first evolved during the Cambrian Period, and fish diversified rapidly during the Paleozoic Era.
¨ Amphibians first appear in the fossil record during the Late Devonian, having made the transition from water to land, and became extremely abundant during the Pennsylvanian Period when coal-forming swamps were widespread.
¨ The evolution of the amniote egg allowed reptiles to colonize all parts of the land beginning in the Late Mississippian.
¨ The pelycosaurs or finback reptiles were the dominant reptiles during the Permian and were the ancestors to the therapsids or mammal-like reptiles.
¨ The earliest land plants are known from the Ordovician period, whereas the oldest known vascular land plants first appear in the Middle Silurian.
¨ Seedless vascular plants, such as ferns, were very abundant during the Pennsylvanian Period.
¨ With the onset of arid conditions during the Permian Period, the gymnosperms became the dominant element of the world’s flora.
To exhibit
mastery of this chapter, students should be able to demonstrate comprehension
of the following:
¨ the characteristics of chordates, and which invertebrate group is most closely related to the chordates
¨ the characteristics and evolutionary history of the different fish groups
¨ the evolution of amphibians, advantages to terrestrial living, and relationship of amphibians to the crossopterygians
¨ the evolution of the reptiles and their advantages over amphibians
¨ the evolution of plants and the sequence of events leading to terrestrial habitation
¨ the necessary accommodations of both plants and animals for terrestrial life
¨ general patterns of Paleozoic plant evolutionary history
1. Chordates are characterized by a notochord, dorsal hollow nerve cord, and gill slits. The earliest chordates were soft-bodied organisms that were rarely fossilized. Vertebrates are a subphylum of the chordates. Echinoderms and chordates may have shared a common ancestor.
Figure 13.1 Three Characteristics of a Chordate
Figure 13.2 Yunnanozoon
lividum
Figure 13.3 Cell Cleavage
2. Fish are the earliest known vertebrates with their first fossil occurrence in Upper Cambrian rocks. They have had a long and varied history, including jawless and jawed armored forms (ostracoderms and placoderms), cartilaginous forms, and bony forms. It is from the lobe-finned fish that amphibians evolved.
Figure 13.4 Ostracoderm Fish Plate
Figure 13.5 Geologic Ranges of the Major Fish Groups
Table 13.1 Brief Classification of Fish Groups Referred to in the Text
Figure 13.6 Devonian Seafloor
Figure 13.7 Evolution of the Vertebrate jaw
Figure 13.8 Late Devonian Seascape
Figure 13.9 Ray-finned and Lobe-finned Fish
Enrichment Topic 1. The End of the Placoderms
The second
of the large mass extinctions occurred during the Late Devonian. In addition to brachiopods, trilobites,
ammonoids, and conodonts facing heavy losses, several fish went extinct as
well. Jawless fish were particularly
hard hit, as well as the top predator of the Devonian seas, the placoderm. One
hypothesis for the extinction involves the evolution of land plants, and the
subsequent increase in chemical weathering and soil formation. The increase of organic matter into the seas
resulted in accelerated weathering of silica on land, which resulted in increased
calcium and magnesium carbonate. This in turn removed carbon dioxide from the
atmosphere, which may have resulted in global cooling. Lucas, “25 Years of Mass Extinctions and
Impacts,” Geotimes, 2005, v.50 n.2 p.28-32.
3. The link between the crossopterygian lobe-finned fish and the earliest amphibians is convincing and includes a close similarity of bone and tooth structures. The transition from fish to amphibians occurred during the Late Devonian. During the Carboniferous, the labyrinthodont amphibians were abundant.
Figure 13.10 Rhipidistian Crossopterygian
Figure 13.11 Similarities between Crossopterygians and Labyrinthodonts
Figure 13.12 Late Devonian Landscape
Figure 13.13 Tiktaalik rosae
Figure 13.14 Carboniferous Coal Swamp
Enrichment Topic 2. Winged Insects
Insects
evolved and invaded land before the earliest amphibian set foot upon the terra
firma. However, new analyses are pushing
back our understanding of the emergence of flight in insects. Mandibles from a fossil dated at 400 million
years indicate an association with winged insects. (Only silverfish and winged
insects possess this type of mandible in the modern world.) This new analyses possibly pushes the
evolution of flight in insects back 70 million years earlier than previously
suspected. “Early Flight? Winged Insects Appear Surprisingly Ancient,” Science
News, 2004, v. 165 n. 7 p. 100.
4. The earliest fossil record of reptiles is from the Late Mississippian. The evolution of an amniote egg was the critical factor that allowed reptiles to completely colonize the land.
Figure 13.15 The Amniote Egg
Figure 13.16 Hylonomus
lyelli
5. Pelycosaurs were the dominant reptile group during the Early Permian, whereas the therapsids dominated the landscape for the rest of the Permian Period.
Figure 13.17 Evolutionary Relationships among the Paleozoic Reptiles
Figure 13.18 Pelycosaurs
Figure 13.19 Therapsids
Enrichment
Topic 3. Early Synapsids: Pelycosaurs and Therapsids
Pelycosaurs and therapsids are synapsids. Synapsids, classified because of the skull opening for the attachment of jaw muscles, include not only these extinct reptiles, but the living mammals of today. Although the pelycosaurs were dominant for 40 million years during the Permian, the evolving therapsids were more successful and supplanted these earliest synapsids at the end of the Permian. However, the reign of the therapsids was short, and prematurely brought to a close when the Permian mass extinction decimated their numbers. A synapsid overview can be found on the Palaeos website (http://www.palaeos.com/Vertebrates/Units/390Synapsida/390.000.html), with a more detailed discussion of Therapsids at http://www.palaeos.com/Vertebrates/Units/400Therapsida/400.000.html.
6. In making the transition from water to land, plants had to overcome the same basic problems as animals—namely, desiccation, reproduction, and gravity.
Table 13.2 Major Events in the Evolution of Land Plants
7. The earliest fossil record of land plants is from
Middle to Upper Ordovician rocks. These
plants were probably small and bryophyte-like in their overall organization.
8. The evolution
of vascular tissue was an important event in plant evolution as it allowed food
and water to be transported throughout the plant and provided the plant with
additional support.
Figure 13.20 Upper Ordovician Plant Spores and Cells
9. The ancestor of terrestrial
vascular plants was probably some type of green alga based on such similarities
as pigmentation, metabolic enzymes, and the same type of reproductive cycle.
Enrichment Topic 4.
Plant Lifestyles
Researchres investigated the fundamental choices faced by plants: Do you live fast and die young, or do you grow slowly and grow old? Ian Wright of Macquarie University discovered that both the risk-taking “day traders” and conservative “bondholders” are found in every type of modern climate. When plants invest energy into photosynthesis and little in defense, their leaves have large surface areas and they require a large amount of enzymes. However, they desiccate easily and are prone to disease. When plants invest more in defense, they are tougher and produce chemicals to deter potential consumers. They live longer, although they produce energy at a slower rate. “Risk and Reward,” Natural History 2004, v.113 n.6 p.14.
10. The earliest seedless vascular plants were small, leafless stalks with spore-producing structures on their tips. From this simple beginning plants evolved many of the major structural features characteristic of today’s plants.
Figure
13.21 Cooksonia
Figure 13.22 Early Devonian Landscape
11. By the end of the Devonian Period, forests with tree-sized plants up to 10 m had evolved. The Late Devonian also witnessed the evolution of the flowerless seed plants (gymnosperms) whose reproductive style freed them from having to stay near water.
Figure 13.23 Generalized Life History of a Seedless Vascular Plant and
Gymnosperm Plant
Figure 13.24 Chaleuria
cirrosa
12. The Carboniferous Period was a time of vast coal swamps, where conditions were ideal for the seedless vascular plants. With the onset of more arid conditions during the Permian, the gymnosperms became the dominant element of the world's flora.
Figure 13.25 Pennsylvanian Coal Swamp
Figure 13.26 Horsetail Equisetum
Figure 13.27 Late Carboniferous Cordaite Forest
Co-Evolution and
Evolutionary Novelties
1. It is important for students to understand not just the concept of evolution but also co-evolution. What interactive relationships determined the progression of some life forms? Discuss the food chain and levels of predators. What does each level on the food chain do for the organisms on the level above or below?
2. Each major event in evolution, such as the development of the amniote egg, represented an enormous opportunity for colonization and speciation. For each of these events, stress to students what the advantages were for each development and how that event changed the evolutionary history of that organism.
Evolution as a
“Branching Bush”
1. The evolution of amphibians from lobe-finned fish and the evolution from reptiles from amphibians provide excellent opportunities to discuss the nature of evolution. When amphibians evolved, did lobe-finned fish disappear from the Earth? When reptiles evolved, did amphibians disappear?
2. Discuss the advantages that amphibians had over lobe-finned fishes. Were amphibians in direct competition for resources with lobe-finned fishes after they moved onto land?
3. Discuss the advantages of reptiles over amphibians. Were reptiles in direct competition with amphibians? When amphibians and reptiles did compete in the same environment, which organism was victorious? Why?
4. Consider the environments in which amphibians and reptiles occupy today. In which environments are amphibians successful? Do reptiles occupy this same environment? Stress to students that these two groups of vertebrates can occupy the same environment when each occupies a particular niche.
Evolution and Diversity of Fish
1. The Devonian is called the Age of Fishes. Why were fish so prolific during the Devonian? Why didn’t fish maintain their diversity and their total domination as top predators in the world’s oceans after the Paleozoic? Have students predict what will happen in the Mesozoic and Cenozoic eras within the seas.
1. Why was it necessary for plants to populate the land before animals were able to? Discuss the role that plants play in the establishment of animal habitats and food sources. What types of animals might have been able to inhabit the land without plants being present?
2. The textbook noted the similarities in hurdles that plants and animals had to overcome before they successfully colonized the land. What are the differences in terrestrial occupation between these two kingdoms? What problems did plants encounter that animals did not? What problems did animals encounter that plants did not?
3. If the end of the Permian was accompanied by the greatest mass extinction of all time, what do you think the early Mesozoic Era looked like in terms of numbers of organisms and diversity? Which types of organisms do you think survived into the Mesozoic?
4. Consider the environment and organisms at the end of the Permian. If the Permian mass extinction had not occurred, how might evolution have proceeded?
|
amniote egg |
labyrinthodont |
seedless vascular plant |
|
bony fish |
lobe-finned fish |
therapsid |
|
cartilaginous fish |
ostracoderm |
vascular plant |
|
chordate |
pelycosaur |
vertebrate |
|
crossopterygian |
placoderm |
|
|
gymnosperm |
proterothyrid |
|
|
|
|
|
1. Insect Evolution, Evolution Video Library, Discovery Channel/FFH&S
2. Fossils: Plants and Tetrapods, Films for the Humanities and Sciences
3. Fossils: Reptiles and Mammals, Films for the Humanities and Sciences
4. Miracle Planet: New Frontiers, The Science Channel
5. Miracle Planet: Extinction and Rebirth, The Science Channel
6. NOVA: Ancient Creatures of the Deep, WGBH Boston
7. Walking with Monsters: Before the Dinosaurs, BBC
1. Fossils and their Living Kin, slide set, Educational Images, Ltd.
2. Evolution of Life on Earth, slide set, Educational Images, Ltd.
3. Ancient Animals, slide set, Educational Images Ltd.
|
1. c |
6. e |
11. c |
|
2. b |
7. b |
12. e |
|
3. c |
8. e |
13. b |
|
4. c |
9. c |
14. b |
|
5. a |
10. d |
|
15. In seedless vascular plants, the sporophyte generation produces spores
that germinate and grow into the gametophyte generation. This produces gametes
(spore and eggs) that come together to generate the next sporophyte plant. In
gymnosperms, both male and female gamete-producing bodies exist on the same
plant; gametes meet and merge to form a seed that can generate the next conifer
plant. Basically, seedless vascular plants require water for gamete transfer,
and have the intervening gametophyte generation before zygote production;
conifers have both gametes on one plant, without water transfer. Therefore,
gymnosperms could more efficiently colonize land, without the need for water
for reproduction.
16. Jawless fishes are found in Upper Cambrian rocks and provide evidence
that there were fish in the oceans in the early Paleozoic. Freshwater fish
appear in the Silurian. The first jawed fish are Lower Silurian. Armored fish
prevail through the Devonian; both bony and cartilaginous fish appear in this
period. Devonian bony fish include both the ray-finned and lobe-finned fish
(crossopterygians and lungfish). Crossopterygian lobe-finned fish invaded land
and salt water, and gave rise to the amphibians and coelacanths in the
Devonian.
17. Desiccation, reproduction (getting sperm to egg without a water medium),
and the pull of gravity were all problems that had to be overcome before
organisms could colonize the land.
18. Pelycosaur sails may have been used for sexual display, defense display,
and/or may have served as thermoregulatory mechanisms. In the latter
possibility, the sail could heat the animal by catching the sun’s rays, or
cooling the animal if it faced the wind.
19. Reptiles were more successful at expanding their habitat because
amphibians needed to return to the water to lay their eggs. With the evolution
of the amniote egg, reptiles could invade drier habitats, and were not bound to
water for reproduction...
20. During the Paleozoic, the continents were moving together to form the
supercontinent Pangaea. This was a time of mountain building and of a reduction
in the amount of coastline, although warm shallow seas were common during
marine transgressions. Over time, conditions became warmer and drier. There
were many available habitats and animals and plants evolved to fit into them.
Apply Your Knowledge
1. During the Mississippian, epeiric seas covered
the land, providing extensive shallow water, presumably warm environments in
which extensive carbonates (crinoidal limestones) were deposited. During the Late Mississippian, a major
regression created the unconformity between the Kaskaskia and the Absaroka
sequences. In the Pennsylvanian,
alternating marine and nonmarine strata with interbedded coals of cyclothems
attest to depositional environments present. The swampy lands that produced the
eventual coals were analogous to the swamps of Florida and the Louisiana delta.
These environments are warm with lush vegetation today.
Therefore, it seems likely that geology of the
Carboniferous was conducive to warm environments, such as those observed in the
Bahamas (Missisippian) and the Louisiana delta (Pennsylvanian) today. We know
from studies in diversity that speciation more commonly occurs in warmer environments,
with the majority of species at the tropical realms. In addition, the epeiric
seas and alternating swampy conditions created many new niches that
organisms—both plants and animals—could fill.
2. Student answers will vary. However, the vertebrate fossil record has
evidence of the move from sea to land: Panderichthys –a lobe
finned fish with a tetrapod-like head, Acanthostega—with gills and
lungs, but more suited for water, Tikaalik rosae—an intermediate
between lobe-finned fishes and amphibians, and Ichythostega—the
oldest known amphian. Reptiles evolved in the Pennsylvanian, and their amniote
eggs freed them from water for reproduction.
The argument can be made that although amphibians evolved from
lobe-finned ancestors, the lobe-finned ancestors did not disappear. (Consider
the Coelacanth.)
Likewise, although reptiles evolved from amphibians, amphibians did not go extinct. Not only do Paleozoic fossils provide evidence for evolution, but many Paleozoic vertebrate fossils represent forms that are extinct. Because we still have fish, amphibian, and reptile species, natural selection has operated over millions of years. The best-suited organisms to the environments have survived—and evolved—over time.
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