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
|
|
Course-external links are
in brackets Click [index] to access site index Click here to
access text’s website Vocabulary
words
are found below |
|
(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."
|
Macroevolution vs.
Microevolution |
|
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. |
|
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. |
|
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.
|
Fossilization |
|
|
Fossilization |
Fossilization unlikely |
Start with dead organism
|
Loss
of organism parts due to scavenging, predation, rotting; typically at best
only hard parts remain for reasonable duration |
|
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 |
|
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 |
|
Lack of geological
distortion |
Melting,
twisting, bending, etc. of rock is not good for fossil preservation |
|
Reexposure to air |
Presumably
the vast majority of fossils have not yet been unburied |
|
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 |
|
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 |
|
Fossilization (supplemental discussion from www.sciam.com) |
|
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 |
|
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 to a deposit
(b)
To do so one must employ absolute dating, i.e., a determination of an
actual date of a deposit (actual in the sense of a date plus or minus some
amount of error)
(c)
With an absolute date of a deposit in hand, one can then infer, through
relative dating, that the date of lower sediments is older than that absolute
date while the date of a higher deposit is younger
(d)
To absolute date a sediment, one needs both a clock and a way in which
the clock is started
(e)
Clocks typically involve the radioactive decay of radioactive elements
as well as the accumulation of their products (radiometric dating)
(f)
"An isotope's half-life, the number of years it takes for 50% of
the original sample to decay, is unaffected by temperature, pressure, and other
environmental variables." Plus is determinable in the laboratory
(g)
See figure 25.2, Radiometric
dating
(h)
Clocks are started in a variety of ways
(i)
Carbon-14 accumulates in the atmosphere at reasonably similar rates
(from cosmic-ray bombardment of the upper atmosphere) resulting in Carbon-14
making up a similar proportion of the carbon in carbon
dioxide found in the atmosphere; producers (plants) incorporate Carbon-14 and
Carbon-12 in this ratio during photosynthesis; animals incorporate the
carbon of plants also in this ratio; when either dies the clock starts because the
organism is essentially cut off from the atmospheric supply of Carbon-14
(j)
In potassium-argon dating the radioactive potassium decays into argon;
the amount of argon, a gas, is set to zero when a rock is melted; strata made
up of volcanic ash typically can be readily absolute dated (via the
potassium-argon method), thus allowing a more precise relative dating of
strata found above and below the ash layer; it is especially helpful when a
stratum of interest is found sandwiched between two datable layers of ash
(k)
[absolute dating, carbon dating, potassium-argon dating
(Google Search)]
[absolute dating (Geology for Engineers—University of Saskatchewan)] [index]
ERA, PERIOD, AND
EPOCH-DEFINING EVENTS
(10) Mass
extinction and adaptive radiation
(a)
(b)
See Figure 25.5, Diversity
of life and periods of mass extinction
(c)
That is, by sudden changes in the types of species commonly found in the fossil record (macroevolution)
(d)
A mass extinction is a correlated die off of species well above the
normal background level of extinction typically observed, e.g.,
(i)
the Permian extinction 250 million years ago which defined the end of
the Paleozoic era and the beginning of the Mesozoic era
(ii)
The Cretaceous extinction 65 million years ago which defined the end of
the Mesozoic era and the beginning of the Cenozoic era
(iii)
Our own personal mass extinction which began coincident with man and
which ultimately may define the end of the Cenozoic era, the age of the
mammals, not to forget to mention our killing off of the reptiles, the fish,
the amphibians, the plants, the fungi, etc., etc., etc.
(e)
Mass extinctions open up ecological niches
by killing off the organisms previously filling those niches
(f)
Adaptive radiations represent the filling of opened up niches by new
organisms
(g)
[mass extinction, adaptive radiation,
Permian extinction,
cretaceous extinction
(Google Search)] [index]
(11)
Adaptive zone (supplemental discussion)
(a)
An adaptive zone represents a potential adaptive radiation
that occurs as a consequence of the opening up of previously unexplored niches
due to an "invention" of a new way of exploiting the world
(b)
"Many taxonomic groups have diversified
prolifically early in their history after the evolution of some novel
characteristic that opened a new adaptive zone, a term for a new way of life
that presents many previously unexploited opportunities."
(c)
For example, the invention of teeth in a world of otherwise
unprotected, soft things; and the subsequent invention of hard parts to protect
otherwise soft things from teeth
(d)
"An evolutionary novelty cannot enable organisms to take advantage
of adaptive zones that do not exist or are already occupied."
(e)
[adaptive zone (Google Search)]
[index]
CLASSIFYING ORGANISMS
(12)
Higher taxa (domain,
kingdom, phyla, phylum,
class, order, family, genera, genus, taxa, taxon)
(a)
A taxon (pl. taxa) is a unit of classification of organisms
(b)
So far in this course we have concentrated on the taxonomic category
known as species
(c)
Higher taxonomic categories (taxa) group species together, ideally
according to what evolutionary (blood) relationships exist between species
(just as human individuals group themselves into families, etc.)
(d)
Taxonomic categories, going from larger (most inclusive) to smaller
include
(i)
Domains
(ii)
Kingdoms
(iii)
Phyla (phylum)
(iv)
Class
(v)
Order
(vi)
Family
(vii)
Genera (genus)
(viii)
Species
(e)
See Figure 25.7,
Hierarchical classification
(f)
As an aid in memorizing these, try using one of these pnemonics:
(i)
Darn Kids Picking Cacti On Fridays Get Stuck
(ii)
Dumb Kids Playing Catch On Freeways Get Squished
(iii)
Did King Phillip Come Over For Great Sex?
(iv)
Do Kiss Pigs Carefully Or Face Grimy Smiles
(v)
Do Kings Play Chess On Fine Grained Sand
(vi)
Did King Phillip Came Over From
(vii)
Did King Peter Came Over From
(viii)
Do Kindly Produce Credit Or Furnish Good Security
(ix)
Do Keep Peeling Cold Onions For Good Smells
(x)
Do Keep Putting Coal On the Fire Grate Slowly
(xi)
Did King Phillip Cry, "Oh, For Goodness Sake!"?
(xii)
Do Keep Putting Cheese On Five Green Spoons
(xiii)
Did Karen's Pups Chew On Furry Grey Squirrels?
(xiv)
Did King Phillip Come Over For Good Spaghetti?
(xv)
Did King Phillip Court Ophelia For Good Sex?
(xvi)
Did Karl Push Cliff Over Football Grand Stand?
(xvii)
Did King Peter Come Over From
(xviii)
Do Kings Play Chess On Fat Girl's Stomach
(xix)
Do Keep Privates Clean Or Forget Getting Sex
(g)
[higher taxa (Google Search)]
[index]
(13) Systematics (taxonomy, identification,
classification)
(a)
Our concern with the rest of the material presented in this chapter
will focus on our understanding macroevolutionary processes; the study of such
processes ultimately converges on the science of systematics
(b)
Systematics consists of three sub-disciplines
(i)
Taxonomy (not Taxodermy!)
(ii)
Identification
(iii)
Classification
(c)
Taxonomy is the naming of species
(d)
Identification is the assigning of new specimens to known taxonomic
categories
(e)
Classification is an attempt to organize living things meaningfully
such that the names assigned by taxonomy reflect real relationships between
species
(f)
Ultimately, classification attempts to organize living things in terms
of their evolutionary relationships
(g)
“As a component of systematics, taxonomy has two main objectives. The
first is to sort out closely related organisms and assign them to species,
describing the diagnostic characteristics that distinguish one species from
another. The second major objective of taxonomy is classification, the
arranging of species into the broader taxonomic categories, from genera
to domains.”
p. 475, Campbell et al.,
1999
(h)
[systematics, taxonomy (Google Search)]
[index]
DEFINING EVOLUTIONARY RELATEDNESS
(a)
A typical goal of systematics (and paleontology) is the construction of phylogonies
(b)
A phylogeny of a description of the genealogical (i.e., blood, i.e.,
evolutionary) relationships between groups of organisms
(c)
A phylogeny thus can be a description of the macroevolutionary
history of a species or of more than one species
(d)
[phylogenies (Google Search)]
[index]
(a)
A cladogram is a graphical representation of a phylogeny
(b)
See Figure 25.8, The
connection between classification and phylogeny
(c)
Cladograms come in a variety of types; typical among all is an attempt
to properly sort nodes, i.e., speciation events,
such that descendant species are
properly connected to their ancestral species, and species are grouped more
closely to related species than they are to less-well related species
(d)
As with the phylogeny it represents, the goal of a cladogram is to
properly represent correct evolutionary relationships
(e)
[cladogram (Google Search)]
[index]
(16)
Monophyletic taxon (clade)
(a)
The goal of systematics is to define monophyletic taxa
(a.k.a., clades)
(b)
A monophyletic taxon is one that includes the common ancestor species as
well as all descendant species
(c)
See Figure 25.9a,
Monophyletic versus paraphyletic and polyphyletic groups
(d)
"The ideal in systematics is for each taxon to be a
monophyletic grouping, creating a classification that
reflects the evolutionary history of organisms. . . achieving this ideal is
often easier said than done."
(e)
[monophyletic, clades (Google Search)]
[index]
(a)
A polyphyletic taxon
represents a mistake in classification
(b)
Essentially, a polyphyletic taxon is one that contains at least two
descendant species but
not all ancestor species
(c)
Such things happen when a species is inadvertently included in a clade
that it doesn't belong in
(d)
See Figure 25.9b, Monophyletic
versus paraphyletic and polyphyletic groups
(e)
[origin of species (Google Search)]
[index]
(18)
Convergent evolution (analogy)
(a)
Polyphyletic taxa occur as a consequence of
mistaking analogies for homologies
(b)
Analogies are two structures that superficially resemble each other,
i.e., which appear (at the very least at first glance) to be homologous but are
not
(c)
Analogies result from convergent evolution: the two species do similar
things in similar environments so consequently evolve similar structures to
perform these similar functions
(d)
The key difference between an analogy and a homology are two-fold:
(i)
The common ancestor between the two species will have lacked the common
structure
(ii)
The development of the structure will differ—more generally, homologies predict
other homologies between two species whereas
anaologies give rise to much less predictive power about the existence of
additional homologies between
two species
(e)
See Figure 25.16, Parsiomony
and the analogy-versus-homology pitfall
(f)
[convergent evolution,
polyphyletic (Google Search)]
[index]
(a)
A paraphyletic taxon is also a mistake, but a legitimately
made one (unlike a polyphyletic taxon)
(b)
Like a polyphyletic taxon, a paraphyletic taxon does
not represent a clade
(c)
However, paraphyletic taxa are not clades for a reason and that reason
has to do with evolutionary innovation
(d)
Typically, paraphyletic taxa are ones which include phenotypically
similar descendant taxa, but exclude phenotypically
dissimilar taxa
(e)
For example,
(i)
reptiles form a paraphyletic taxon if mammals and birds are not
included among the reptiles
(ii)
Lizards are paraphyletic if you don’t include snakes (which are derived
from lizards)
(iii)
Similarly, the apes form a
paraphyletic taxon if humans are not
included among the apes
(f)
See Figure 25.9c, Monophyletic
versus paraphyletic and polyphyletic groups
(g)
See Figure 25.18, Modern
systematics is shaking some phylogenetic trees
(h)
Note that Taxon 1 in Figure 25.9 would represent the mammals or birds
or humans in the above examples, while taxon 3 would represent the reptiles or
apes
(i)
[polyphyletic (Google Search)]
[index]
(a)
Cladistics is a technique by which organisms are assigned to different
(monophyletic) taxa
(b)
Cladistics works by identifying homologies
and grouping together organisms such that within taxa individuals share more
homologies than they do with individuals found in different taxa
(c)
Cladistics also rejects the inclusion of similarities
(i)
That are the result convergent evolution (i.e., analogies)
(ii)
That are homologies but that are shared with other taxa
(d)
Note, that this is not to say that it is necessarily easy to
distinguish analogies from homologies
(e)
See Figure 25.11, Constructing
a cladogram
(f)
Cladistic techniques are not able to judge evolutionary divergence in
terms of the time between nodes (speciation events);
time information instead is derived from the fossil record
(g)
“Cladistic analysis has become synonymous with phylogenetic analysis. A
clade (Gr. Clados, “branch”) is an evolutionary branch. Cladistic
analysis classifies organisms according to the order in time that branches
arose along a dichotomous phylogenetic tree. Each branch point in a tree is
defined by novel homologies unique to various species on that branch. Because
it views the extent of divergence among organisms as uninformative in assessing
evolutionary relationships, cladistic analysis considers only homologies
in developing hypotheses about classification and phylogony.” p. 482, Campbell et al.,
1999
(h)
See Figure 25.12, Cladistics
and taxonomy
(i)
[cladistics (Google Search)]
[plant cladistics controversy (MicroDude)]
[index]
(21) Shared derived characters
(a)
A cladist derives phylogonies from shared
derived characters (a.k.a.,
synapomorphies), those homologies that are unique to individual taxa
(possessed by all members of a given clade)
(b)
For example, in cladistics the fact that bats have wings
would not include bats in a taxa including birds on the basis of both
having wings (birds and bats both have wings as a consequence of convergent
evolution, and a bat-bird taxon, were such a taxon to exist, would be a good
example of a polyphyletic
taxon since it would
exclude the non-winged common ancestor to both the birds and the bats)
(c)
In general, the existence of homologies predicts the existence of
additional homologies, and cladistics uses these correlations to define taxa
(d)
[shared derived characters,
shared derived character
(Google Search)][index]
(22)
Shared primitive characters
(a)
Not all shared characters are shared derived characters
(b)
For example, a cladist would not use the fact that both dogs and bears
have hair as a means of classifying both dogs and bears as carnivores, since
the ancestor of the ancestral carnivore, a mammal, also had hair
(c)
However, a cladist would use the fact that dogs and bears both have
hair to include both among the mammals
(d)
That is, hair cannot be employed to distinguish mammals because hair is
a shared by all mammals, i.e., it is a shared primitive character when
comparing among mammals, but a shared derived character when grouping mammals
as distinct from other lineages
(e)
See Figure 25.12, Cladistics
and taxonomy
(f)
[shared primitive characters,
shared primitive character
(Google Search)]
[index]
(a)
In the past two decades molecular systematics has come to dominate the
study of evolutionary relations (which is not to say that molecular systematics
has supplanted other approaches, it instead serves as an increasingly important
tool)
(b)
Molecular systematics seeks out homologies, like cladistics, though it is more difficult to distinguish
analogies from homologies (that is, two nucleotides in a gene sequence could be
identical because they have always been identical, i.e., since common ancestry,
or due to divergence followed by mutation back to the same nucleotide)
(c)
"One advantage of this molecular tool of systematics is that it is
objective and quantitative. A second advantage is that it can be used to assess
relationships between groups of organisms that are so physiologically distant
that they share very few morphological similarities…[Third] molecular
comparisons go right to the heart of evolutionary relationships."
(d)
Molecular techniques include
(i)
Protein comparison
(iii)
Restriction mapping
(iv)
DNA sequencing
(e)
See Figure 25.13, Aligning
segments of DNA
(f)
See Figure 25.19, When did
most major mammalian orders originate?
(g)
[molecular systematics
(Google Search)]
[index]
VOCABULARY
(24)
Vocabulary [index]
(a)
Absolute dating
(b)
Analogy
(c)
Clade
(d)
Cladistics
(e)
Cladogram
(f)
Class
(g)
Classification
(i)
Dating fossils
(j)
Domain
(k)
Family
(l)
Fossilization
(m)
Fossils
(n)
Genera
(o)
Genus
(q)
Higher taxa
(r)
Identification
(s)
Kingdom
(t)
Macroevolution
(u)
Mass extinction
and adaptive radiation
(x)
Order
(y)
Paleontology
(aa)
Phyla
(bb)
Phylogenies
(cc)
Phylum
(dd)
Polyphyletic
taxa
(ee)
Relative dating
(ff)
Shared derived characters
(gg)
Shared primitive characters
(hh)
Systematics
(ii)
Taxa
(jj)
Taxon
(kk)
Taxonomy