Important words and concepts
from Chapter 25, Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to
access text’s website Vocabulary
words
are found below |
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(1) Chapter title: Tracing Phylogeny (in 2002
edition of text called “Phylogeny and Systematics”)
(a)
This chapter deals with a number of subjects, all of which revolve
around the concept of macroevolution
(b)
[tracing phylogeny (Google Search)]
(a)
Macroevolution is evolution that occurs above the level of the species
(b)
By contrast, microevolution is
evolution that occurs below the level of species
(c)
At the very least, macroevolution and microevolution communicate via speciation events
(d)
That is, microevolutionary processes can result in speciation events,
and speciation events serve as the foundation for macroevolution
(e)
"Macroevolution is the origin of taxonomic groups
higher than the species level. . . macroevolutionary
change is substantial enough that we view its products as new genera, new
families, or even new phyla."
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Macroevolution vs.
Microevolution |
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Any time you
consider… ·
the likelihood of births of new species (speciation events) ·
the likelihood of the death of species (extinction) ·
the adaptive radiation of lineages (birth of many species) ·
mass extinction (death of many species) ·
evolutionary relationships between species ·
the evolutionary history of a lineage ·
biogeography, or ·
shared derived characters …you
are considering macroevolutionary processes. |
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Any time you
consider… ·
natural selection ·
genetic drift (within species) ·
mutation ·
gene flow between populations, or ·
the randomness of mating within populations ·
all up to and just about including the act of speciation itself …you
are considering microevolutionary processes. |
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Note
that the adaptation of a species to its natural environment (microevolution)
will not necessarily have a positive impact on the ability of that species to
give rise to descendant species (macroevolution)… that is, microevolution and
macroevolution are not identical processes even though certainly microevolutionary
processes impact on macroevolutionary processes. |
(f)
[macroevolution (Google Search)]
[paleontological collection
catalogs and related resources (The Museum of Paleontology – University of California,
Berkeley)] [macroevolution (Talk.Origins)] [index]
LOOKING AT OLD THINGS IN
ROCKS
(a)
Paleontology is the study of the biological past via a study of the
remnants of organisms, fossils
(b)
Paleontology, systematics, and the study of macroevolution go
hand in hand because a paleontologist attempts to
characterize, identify, and classify fossils, thus working out an understanding
of what species of organisms lived when and where
(c)
To understand the strengths and limitations of paleontology, and
therefore the strengths and limitations of our understanding of extinct life
forms, it is important to understand the strengths and limitations of the
fossil record
(d)
[paleontology (Google Search)]
[index]
(a)
"A fossil is a preserved remnant or impression left by an organism
that lived in the past."
(b)
See Figure 25.1, A gallery
of fossils
(c)
Remnants may consist of the actual molecules which were found in the
organism or, more likely, represent micro or macro casts of the organism [images of fossils]
(d)
Petrifaction, for example, involves the gradual replacement of the
molecules making up a dead organism with minerals found in ground water flowing
around the fossil; great detail of the dead organism can be preserved by this
process to the extent petrifaction replaces the organism molecule by molecule
(e)
More typically, the minerals will fill up a mold created by the dead
organism, but fill up that mold after the soft parts of an organism have
already rotted away
(f)
Footprints and other traces of organisms can fossilize, thus
fossilizing (especially) animal behavior
(g)
To understand the strengths and limitations of the fossil record, it is
important to understand the processes of fossilization
(h)
[fossils (Google Search)]
[how fossils form (ZoomDinosaurs.Com)]
[fossil formation (Kansas Geological Survey)] [fossil links (Access Indiana)] [fossil formation
(Sherry Tutt)] [index]
(a)
Fossilization is the mechanism by which a dead organism becomes a fossil
(b)
Fossilization can occur by many means but common to all processes is
some kind of sealing of the dead organism away from the atmosphere
(c)
Typically sealing is accomplished via burying (either in sediment or by
volcanic ash) but can also be accomplished by such things as plant resins,
water in peat bogs, or tar pits
(d)
By far and away, the most common form of burying occurs within the
sediments deposited at the bottom of a body of water; this is one reason why
the fossil record of shallow water marine organisms is so complete (the other
reason is that many such organisms have hard, durable shells)
(e)
For a terrestrial (land) organism, fossilization occurs most typically
should they either fall into water or are buried where they lie; large numbers
of fossils can accumulate in places where rivers deposit large amounts of
sediment
(f)
Note that very often dead organisms are predated upon, scavenged, or
partially decomposed prior to their being buried; thus the fossilized remains
of these organisms, even their skeletons, are rarely found complete
(g)
Following burial, for a fossil to yield its clues to modern humans,
that fossil must remain buried, must be found in rock that does not become too
distorted by geological processes, and then must find its way back to the
surface in a location accessible to humans, in a form recognizable as a fossil
(h)
"The discovery of a fossil is the culmination of a sequence of
improbable coincidences. First, the organism had to die in the right place at
the right time for burial conditions to favor fossilization. Then the rock
layer containing the fossil had to escape geological processes that destroy or
severely distort rocks, such as erosion, pressure from superimposed strata, or
the melting of rocks that occurs at some locations. If the fossil was preserved, there is only a slight
chance that a river carving a canyon or some other process will expose the rock
containing the fossil. There is an even more remote chance that someone will
find the fossil, although discovery is more probable for people who are
purposefully looking for fossils. No wonder the fossil record is incomplete. A
substantial fraction of the species that
have lived probably left no fossils, most fossils that formed have been
destroyed, and only a fraction of the existing fossils have been discovered.
The fossil record, far from being a complete sampling of organisms of the past,
is slanted in favor of species that existed for a long time, were abundant and
widespread, and had shells or hard skeletons [i.e., things that easily
fossilize]. Paleontologists, like all
historians, must reconstruct the past from incomplete records. Even with its
limitations, however, the fossil record is a remarkably detailed document of macroevolution
over the vast scale of
geological time."
(p. 455.
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Fossilization |
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Fossilization |
Fossilization unlikely |
Start with dead organism
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Loss
of organism parts due to scavenging, predation, rotting; typically at best
only hard parts remain for reasonable duration |
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Protect organism from air, e.g., by burying in
sediments, by volcanic ash, in peat bogs, in tar pits, in tree sap |
Organisms
that live in forests tend not to fossilize due to a lack of burying
mechanisms |
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Lack of erosion prior to
mineralization |
Old
strata that is being built up over time will retain fossils; gotta have the
rock to have the fossil |
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Lack of geological
distortion |
Melting,
twisting, bending, etc. of rock is not good for fossil preservation |
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Reexposure to air |
Presumably
the vast majority of fossils have not yet been unburied |
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Discovery by trained
person |
Once
a fossil is no longer buried, it deteriorates rapidly and likely will be
known to science only if discovered by a trained individual during a brief
period before its loss |
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Conclusion: Things with hard parts,
that live in environments in which burying soon after death is likely, and
are represented by large, long-lived populations will likely fossilize. |
Conclusion: Things with no hard
parts, that live in environments in which burying soon after death is
unlikely, and are represented by small, short-lived populations will likely
not fossilize |
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Fossilization (supplemental discussion from www.sciam.com) |
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What are the odds of a
dead dinosaur becoming fossilized? M. Paleontologist Gregory
M. Erickson of It
is often stated in the paleontological literature that the chance an animal
will become fossilized is "one in a million." This number is meant
to be taken figuratively, the point being that the odds of surviving the
rigors of deep time are extremely remote. Nevertheless, all field
paleontologists know that the earth is biased when it comes to giving up its
dead--the odds of an animal being preserved and consequently exhumed are much
greater in some settings than others. Studies
by taphonomists (paleontologists who study the transition of animals from the
biosphere to the lithosphere; taphonomy literally means "burial
laws") have shown that organisms that die on land in lush jungle locales
are rarely fossilized. In these settings, there is little chance of being
buried, scavenging vertebrates and insects are prevalent, bacteria that break
down flesh and bones are abundant, and the soils are extremely acidic and
tend to dissolve bones. As a result, remains of dinosaurs from such former
surroundings are practically nonexistent. Conversely, dinosaurs are commonly
found in areas that were once fluvial settings and in regions of extreme
aridity. In the former case, it is clear that dinosaur remains were rapidly
buried before substantial scavenging could take place. Remains of dinosaurs
that were washed into the fluvial systems are found buried in actual river
channels, whereas others are found out on the former floodplains at the
location where they fell and were covered by sediments from floodwaters that
breached river banks. Because river currents tend to scatter and break up
bones, remains from river channels are often biased toward certain bones
depending on the strength of the current. (Such aggregations are called
Voorhies groups after one of the first paleontologists to study the
phenomenon by which certain bones, such as ribs and vertebrae, tend to
readily tumble downstream, leaving behind only partial skeletons.) Dinosaur
fossils found on former floodplains also often show bias toward elements such
as pelvises and larger long bones that were difficult for scavenging or
predaceous theropod dinosaurs to consume. In
any event, once bones were entombed in fluvial sediments, not only were they
protected from scavengers and many types of bioorganisms, but they could also
begin a process known as permineralization. Water percolating through the
sands or muds was often rich in silica (natural glass) and other minerals,
which could infill the pores of the bones and make them physically resistant
to crushing by the overlying sediment. At least some minor replacement of the
actual bone matrix usually occurred as well, typically by iron-rich minerals,
but it should be noted that most dinosaur bones actually retain much of the
original calcium and phosphatic minerals they possessed in life. As such, the
phrase "turned to stone"--often used to describe fossil bone--is
misleading. Dinosaurs
dying in arid regions also stood a reasonable chance of becoming fossilized.
Aridity tends to desiccate a carcass, making it less attractive to
scavengers. And unlike jungle or forest settings, deserts have considerably
fewer organisms suited for the breakdown of animal tissues. Windblown sands,
as well as drifting and collapsing sand dunes, were agents of burial for such
animals. Subsequent rainfall during the wet seasons carried minerals into the
buried bones. If
dinosaur remains entombed in the ways described above did not later become
metamorphosed (modified by upheavals of the earth) there is a good chance
they are still around today, thus enabling the details of their burial to be
pondered by taphonomists, either professional or amateur. Answer posted on September 16, 2002 http://www.sciam.com/askexpert_directory.cfm |
(i)
["Why don't we have a
fossil record for gorillas or chimps? …The answer is almost certainly habitat.
If, as seems likely, they lived in forests like they do now, well, that's a
horrible place to be if you want to end up fossilized. ;-) Problem is you rot,
and little bugs and whatnot eat you, and you don't get covered up by sediment
or volcanic ash, which are topnotch ways to get fossilized. Animals which spend
a great deal of time in, for instance, mud flats or shallow water get
fossilized at one hell of a
rate. That's why there's so many fossil pigs in Africa that they can be used to
check dating processes…"]
(j)
[fossilization (Google Search)]
[fossilization and adaptation: activities
in paleontology (Brent H. Breithaupt—
GEOLOGIC TIME
(a)
The first thing to realize about the dating of fossils is that the
first professionals to care were not biologists but instead geologists
(b)
This is because geologists used fossils to relative date rocks of geological
interest
(c)
Thus, much of the classical descriptions of geological time scales were accomplished based on a detailed
characterization of the fossils that they contained
(d)
What was discovered, which proved most useful, is that certain fossil
types (species of extinct organisms) tend to be found
together while other types are never found together, and that these groupings
appear to be consistent around the world (those fossils of most use to
geologists were termed index fossils)
(e)
Thus, a geologist could infer the relative date of a stratum of rock as
being the same as another stratum found elsewhere in the world on the basis of
both strata displaying similar fossils
(f)
Using this information, as well as knowledge of abrupt and significant
changes in the types of fossils found, the entire history of the earth was
divided into intervals: Eras, Periods, and Epochs
(g)
[dating fossils (Google Search)]
[index]
(a)
See Table 25.1, The
Geological Time Scale
(b)
The Eras making up the history of the Earth include (in order, going
from oldest to newest, with the approximate date, in millions of years before
present, of their ends)
(i)
Precambrian (~550)
(ii)
Paleozoic (~250)
(iii)
Mesozoic (65)
(iv)
Cenozoic (present)
(c)
[If you are into memorization, then Table 25.1 may be learned in part
by using this mnemonic—not that I’m suggesting that you learn that table: Pregnant camels ordinarily sit down carefully. Perhaps their joints creak. Perhaps early oiling might prevent permanent hobbling or rhematism. My personal favorite for the
Mesozoic era only is Can Our Soldiers Drink Carbonated
Pepsi?]
(d)
Note that
(i)
The Earth began approximately 4600 million years ago
(ii)
Life began (or began fossilizing) approximately 3500 million years ago
(iii)
The fossilization of multicellular animals began in
earnest 550 million years ago
(iv)
The “age of the dinosaurs” began ~250 million years ago
(v)
The “age of the mammals” began 65 million years ago
(e)
Most of the history of the planet as well as most of the history of
life on this planet occurred during the Precambrian era
(f)
"Each era represents a distinct age in the history of the Earth
and its life; the boundaries are marked in the fossil record by explosive
radiations of many new forms of life following mass extinctions."
|
Era |
Began
(mya) |
Ended (mya) |
Details |
|
Precambrian
era |
~4600 |
550 |
Starts
at beginning of Earth; fossilization of bacteria starts about 3500 mya |
Paleozoic era
|
~550 |
~250 |
Starts
with animal fossilization in earnest |
|
Mesozoic
era |
~250 |
65 |
Age
of the dinosaurs (on land) |
|
Cenozoic
era |
65 |
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Age
of the mammals |
(g)
[geological time scales,
precambrian era, paleozoic era, mesozoic era, cenozoic era (Google Search)]
[geologic ages of Earth history (Dinosauria On-Line)] [Dr. Bob’s geologic time page
(features geologic time pnemonics) (Dr. Bob)] [index]
(a)
Typically, rocks are laid down such that the oldest rocks are found
farther down than are newer rocks
(b)
This is the case in sedimentary rock
(c)
Fossils found in lower strata therefore are considered to be
older (i.e., have died earlier) than fossils found in higher strata
(d)
This idea of relative age being reflected in relative depth is the idea
behind relative dating
(e)
Older fossils are deeper unless geological forces have flipped a
deposit upside down (not unheard of, but also not exactly a common occurrence)
(f)
[relative dating (Google Search)]
[relative dating
(lots of nice images) (Geology for Engineers—University of Saskatchewan)] [index]
(a) Relative dating gives information on relative ages but does not allow one to assign an actual date