Phylogenises & History of life Chapter 27, Flashcards Preview

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Flashcards in Phylogenises & History of life Chapter 27, Deck (45):


Correctly interpret phylogenetic trees and understand how they depict evolutionary relatedness.



Describe how fossils provide evidence of organisms that lived in the past.

[*] The fossil record provides the only direct evidence about what organisms that lived in the past looked like, where they lived, and when they existed.



Identify the eras of the past 542 million years of Earth history and the major evolutionary events.



Describe why adaptive radiations occur.



Identify the five major mass extinction events.


Distinguish between ancestral and derived traits.  Provide an example that demonstrates the relative nature of ancestral and derived.

•An ancestral trait is a characteristic that existed in an ancestor.

•A derived trait is one that is a modified form of the ancestral trait, found in a descendant.



What are synapomorphies and how are they used?

Synapomorphies Identify Monophyletic Groups.

  • synapomorphies are changes in a DNA sequence.


Differentiate between homology and homoplasy.

•Homology occurs when traits are similar due to shared ancestry.

•Homoplasy occurs when traits are similar for reasons other than common ancestry.

–For example, ichthyosaurs (extinct aquatic reptiles) and dolphins (extant mammals) are very similar, but these similarities are not due to common ancestry.


Discuss the idea of convergent evolution using dolphins and ichthyosaurs

Homoplasy: Traits Are Similar but Not Inherited from a Common Ancestor. Dolphins and ichthyosaurs look similar but are not closely related—dolphins are mammals; ichthyosaurs are reptiles.


Whale evolution: a case history.

Where does the phylogeny based on morphological data place whales with reference to artiodactyls?

•Artiodactyls, including hippos, cows, deer, and pigs, are mammals that have hooves, an even number of toes, and an unusual pulley-shaped ankle bone (astragalus).

•Traditionally, phylogenetic trees based on morphological data place whales as the outgroup—that is, a species or group that is closely related to the monophyletic group but not part of it.


Whale evolution: a case history.

Where does the phylogeny based on DNA sequence data place whales with reference to the artiodactyls?

DNA sequence data, however, suggest a close relationship between whales and hippos. This tree would require two changes to the astragalus trait.
•Recent data on gene sequences called short interspersed nuclear elements (SINEs) show that whales and hippos share several SINE genes that are absent in other artiodactyl groups.
•These SINEs are shared derived traits (synapomorphies) and support the hypothesis that whales and hippos are indeed closely related.


Whale evolution: a case history.

How did the phylogeny based on transposable elements resolve this issue?


From the phylogenetic tree in Figure 27.3 determine if Mollusks are more closely related to Echinoderms or Arthropods.  What is the reasoning?


From Figure 27.5 b) determine if pigs are more closely related to camels or cows.


What are fossils?  Provide a summary of how a fossil might form.

•There are four main types of fossils:
1.Intact fossils form when decomposition does not occur.
2.Compression fossils form when sediments accumulate on top of the material and compress it into a thin film.
3.Cast fossils form when the remains decompose after burial and dissolved minerals create a cast in the remaining hole.
4.Permineralized fossils form when the remains rot extremely slowly and dissolved minerals infiltrate the interior of the cells and harden into stone.


Discuss the limitations (biases) of the fossil record.

  1. Habitat bias occurs because organisms that live in areas where sediments are actively being deposited are more likely to fossilize than are organisms that live in other habitats.
  2. Taxonomic bias is due to the fact that some organisms (e.g., those with bones) are more likely to decay slowly and leave fossil evidence.
  3. Temporal bias occurs because more recent fossils are more common than ancient fossils.
  4. Abundance bias occurs because organisms that are abundant, widespread, and present on Earth for a long time leave evidence much more often than do species that are rare, local, or ephemeral.


Life’s Time Line.

Approximately how old is planet Earth?

•The Precambrian encompasses the Hadean, Archaean, and Proterozoic eons. This period spans from the formation of the Earth to the appearance of most animal groups about 542 million years ago (mya).


Life’s Time Line.

List two important things to note regarding the Precambrian era.

•In the Precambrian era, almost all life was unicellular and hardly any oxygen was present for almost two billion years after the origin of life.


Life’s Time Line.

What is the time frame for the Phanerozoic eon?

•The Phanerozoic eon spans the interval between 542 mya and the present.  It is divided into three eras—the Paleozoic, the Mesozoic, and the Cenozoic—that are further divided into periods.


Life’s Time Line.

List the three eras of the Phanerozoic eon and their time frames.


  1. Paleozoic era covers the interval from 542 to 251 mya - Many animal groups—including fungi, land plants, and land animals—appeared in the Paleozoic era. This era ends with the obliteration of almost all multicellular life-forms at the end of the Permian period.
  2. Mesozoic era (Age of Reptiles) covers the interval from 251 to 65.5 mya. –This era saw the rise and dominance of the dinosaurs and ended with their extinction.

3. •Cenozoic era (Age of Mammals) includes the interval from 65.5 mya to the present. –During this time the mammals diversified after the disappearance of the dinosaurs. –Events that occur today are considered to be part of the Cenozoic era.



Life`s time line

Provide a very brief summary of how the oceans and continents have varied over the past 542 million years.

•Earth’s crust is broken into enormous plates that are in constant motion, driven by heat rising from the planet’s core.

•Movement of these plates has dramatically shifted the extent and position of the continents over time.

•There have been major changes in climate as well.


What is adaptive radiation?  Discuss the example of Hawaiian silverswords.


Discuss another example of how ecological opportunity resulted in adaptive radiation.

•adaptive radiation is when rapid speciation in a single lineage is followed by divergence into many different adaptive forms.
•The Hawaiian silverswords fulfill the three hallmarks of an adaptive radiation:
–They are a monophyletic group.
–They speciated rapidly.
–They diversified ecologically.
•Biologists use the term niche to describe the range of resources that a species can use and the range of conditions that it can tolerate. Silverswords occupy a wide array of niches.


Discuss two examples of morphological innovations that resulted in adaptive radiations.

[*] Two general mechanisms can trigger adaptive radiations:  new resources, and new ways to exploit resources.

•One of the most consistent triggers of adaptive radiations is ecological opportunity—the availability of new types of resources and new ways to exploit resources.

•Biologists have documented adaptive radiations of the Anolis lizards of the Caribbean islands.

•On the two islands studied, the same four ecological types eventually evolved, because the islands had similar varieties of habitats.
•Therefore, similar adaptive radiations took place independently on the two islands, triggered by the available environment and lack of competition.

•Morphological innovation can also be a trigger for adaptive radiation, as was seen in the Cambrian explosion.•Many of the other important diversification events in the history of life started off with the evolution of a key morphological trait that allowed descendants to live in new areas, exploit new food sources, or move in new ways.


What is the significance of the Cambrian explosion?

•The first animals—sponges, jellyfish, and simple worms—appear in the fossil record around 565 mya, at the end of the Proterozoic eon.
•Soon after that in geologic time, by about 50 million years later, animals had diversified into almost all the major groups living today.
•This diversification is known as the Cambrian explosion.
•This period saw what was arguably the most evolutionary change in the history of life.


Briefly discuss four hypotheses that may have triggered the Cambrian explosion.

•There are four non-mutually-exclusive hypotheses:
1.Higher oxygen levels made aerobic respiration more efficient.

2.The evolution of predation exerted selection pressure for prey defense strategies, driving morphological divergence.

3.New niches beget more new niches.  The ability to exploit new niches created new niches for predators, driving speciation and ecological diversification.

4.New genes, new bodies.  Mutations increased the number of Hox genes in animals and made it possible for larger, more complex bodies to evolve.


How do mass extinctions differ from background extinctions?

•A mass extinction is the rapid extinction of a large number of lineages scattered throughout the tree of life. A mass extinction occurs when at least 60 percent of the species present are wiped out within 1 million years.
•Mass extinctions are caused by catastrophic events.
•Paleontologists traditionally recognize five mass extinctions ("The Big Five").
Background extinction is the lower, average rate of extinction, representing the relatively constant, normal loss of some species.


Five mass extinction events have occurred since multicellular life evolved.  Discuss the End-Permian extinction.

•The largest mass extinction was the end-Permian extinction, which resulted in the disappearance of 90 percent of all species.
•There are four hypotheses about the cause of this event:
1.Flood basalts called the Siberian traps added enormous quantities of heat, CO2, and sulfur dioxide to the atmosphere.  This led to intense global warming and the formation of toxic sulfuric acid.
2.Oceans became completely or largely anoxic—meaning that they lacked oxygen. These conditions are fatal to organisms that rely on aerobic respiration.

3.Sea level dropped dramatically during the extinction event, reducing the amount of habitat available for marine organisms.

4.Low oxygen concentrations and high CO2 levels in the atmosphere may have restricted terrestrial animals to small patches of low-elevation habitats.

The cause of the end-Permian extinction may be the most important unsolved question in research on the history of life. In contrast, the cause of the dinosaur’s demise is settled


The End-Cretaceous Extinction: What killed the Dinosaurs? In your discussion be sure to mention the K-P boundary, iridium, shocked quartz, microtektites and global consequences of the K-P asteroid strike.

•The impact hypothesis for the extinction of dinosaurs proposes that an asteroid struck Earth 65 mya, resulting in the extinction of an estimated 60–80% of the multicellular species alive.

•Conclusive evidence—including iridium, shocked quartz, and microtektites found in rock layers dated to 65 mya, as well as a huge crater off Mexico’s Yucatán peninsula—has led researchers to accept the impact hypothesis.


Consider the following six organisms.







What traits are shared by all these animals?


What traits do the mammals and chicken have in common but not the fish?


What traits do the primates share but not the dog?


  1. What traits do the orangutan and gorilla share, but not the human?


Differentiate between shared traits and derived traits.


Draw a phylogentic tree for these organisms.


•The evolutionary history of a group of organisms is called ________.

a phylogeny


a ______________________ which shows ancestor-descendant relationships among populations or species

phylogenetic tree,



___________________occurs when natural selection favors similar solutions to the problems posed by a similar way of life.

•Convergent evolution



define phylogeny

The evolutionary history of a group of organisms



________ is the physical trace left by an organism that lived in the past.

• fossil


•The _____________ is the total collection of fossils that have been found throughout the world.

fossil record