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the Staggered Origins of
Vertebrate Fossils in
PDF Copy of this Lesson
with Standards met in lesson
|NOTICE: If a student ever challenges you with criticisms or doubt for the reliability or validity of geological age-dating methods, CLICK HERE|
Students gradually build a realistic sense of deep, geological time from familiar linear analogs, e.g., calendars, millimeters and football fields, relative to their short lifetimes. They learn that if we equate 10 years of their life to 1 mm, a million years will equal a football field, and 500 million years will equal 30 miles - all distances with which they are familiar.
They also learn to associate the earliest member of each group of vertebrates with the geologic time of its emergence, on their "familiar scale" of relative distances from their school. The stair-step pattern of emergence revealed by this activity leads naturally to an inquiry for an explanation, with the hypothesis that each group (class) originated from a preceding group. In order to test this idea, students are guided to seek further clues, e.g., the possession of common features, with a few new features added with each new class, and some of the many transitional fossils showing gradual changes of features. And they find them.
See article describing this lesson in the NSTA's journal for middle school teachers, Science Scope for February, 2011, pp. 40-45 (or click here for pdf copy of the article)
|The fossil record shows a pattern of increasing diversity and large-scale gradual changes through time.|
|1. The vastness of deep geological time can be
understood on a recognizable scale of familiar dimensions.
2. There are vast periods of time (tens of millions of years) that separate the gradual emergence of each major vertebrate group. Vertebrate groups did not appear suddenly or over any short period of time.
3. Each successive vertebrate group emerges with the characteristics of the previous group, plus a few key modifications unique to the new group.
4. There are many transitional fossils showing gradual changes over time.
|Pre/Post Quiz for lesson (short, w/
key; version showed ~90% improvement in 8th grade LS classes)
Real fossils and/or models and/or pictures of fossils, from a variety of organisms, including different classes of vertebrates.
Pictures of modern fishes, amphibians, reptiles, mammals and birds.
(Check our collection of pictures of living and earliest vertebrates.).
Do Web search for additional pictures if needed (or have students do this).
Animals of the Past: Patterns in the Fossil Record (for overhead or PowerPoint) - and/or enlarge for wall.
Animals of the Past: Showing likely phylogenetic connections
Calendar, with squares for each day of the week. Calendar with 1" wide days provided (makes for easy scaling - see PP 10, 11)
Football field picture - awkward scale
Football field picture - useful scale
Register tape (strip of at least 10 yards). Mark off 1 inch, 7 inches, and 30'4" (about 10 yards).
Meter stick (and enough metric rulers for students to observe in pairs), and
Big Map of your area in a 40 mile radius of your school -
with scale (try GoogleMaps or MapQuest)
Big Map of your region or state (within about 280 miles of your school) -
with scale (ditto)
Large Circle Compass, or length of string (for finding point of interest at
particular distance from school)
Geologic Time Scale Chart (spreadsheet)
Demo TimeMarker Scale strip on Map
Sample "Time Map" of your area (or another area, as an example, e.g.,...)
Sample "Time Map" of San Francisco Bay Area
Sample "Time Map" of MIddle California
Teacher Guide for using TimeMarker and Preparing Scaled Map
Teacher Guide for Students Calculating Scale Dimensions
Vertebrates Over Time Key: Vertical Bars from Labled Tics
Stack of 10 $1-bills, and a stack of 100 $1-bills (optional)
"Jumbo" size paper clip (wire = 1mm thick)
|One 45 minute period for the time concept and map layout. Building the Vertebrates Over Time chart, and using inquiry to show how this chart suggests the evolutionary connectedness of the groups, will require an additional period (or two).|
Accumulating Traits in the Vertebrate Fossil Record (chart)
TimeMarker Scale strip (1 per team)
Scaled Map of your area (1 per team)
Vertebrate Patterns (information and Practice Procedures) (1 per team)
Vertebrates Over Time - Grid (Bare Time Scale Grid)... OR...
Vertebrates Over Time - Tics (Tics for key group beginnings)...OR...
Vertebrates Over Time - Labeled Tics (easiest/quickest)
Pre-Post Test: Consider giving this to measure effectiveness
of the lesson. (see teachers materials above).
Skipping Parts? Whether you walk your students step-by-step through the scaled measurements, or just jump to the essential scale (thickness of dollar bill = one year, so football field = one million years) depends partly on the age and experiences of your students, and the amount of time you can devote to this. Don't feel bad if you decide to skip the gradual development of the scale, but be prepared to help students confused by the scale-up - maybe offer to go over it with a small group after school or during lunch break.
ENGAGE: Fossils over time
Ask: "If you found these fossils in some rocks, what
questions would you ask?
As part of this, show the class an enlarged version of the
of the Past: Patterns in the Fossil Record," point
out how the different major groups of vertebrates did not
all appear at once, but separately, over several 100s of millions
of years. Emphasize that there are NO fossils of
mammals prior to about 220 mya (millions of years ago), NO reptiles
prior to about 310 mya, NO fishes prior to about 500 mya.
Ask "how long is 1 million years? Any idea? What about
a billion years? A thousand years?
Let's see if we can develop a better understanding of those
big numbers, and some major events that happened so long ago,
and to see if there are any interesting patterns in those events.
EXPLORE: Time and Distance
Presentation: Ask probing questions to get students
thinking about time and distance:
[The inch is used here for unity because it is more appropriately
larger than a cm. If the days on your calendar are more than
1", tell class "let's assume that each day-square is
1 inch across."]
How many fbf for 100 years? [10 fbf].... 1000 years? [100
fbf], etc. Can you visualize this very well? How far do you think
that would be (say in miles)?
EXPLAIN: A DIFFERENT - BETTER
Have them find 1 mm on their metric rulers, and look at the
wire of a large paper clip]. Ask how many mm in a meter? [show
meter stick.] If they don't know, have them count mm in 1 cm
, and cm in the meter , so 10x100 = 1000 mm in a meter].
How many years would that be? [10 x 1000 = 10,000 years].
Write down (or show) this scale equivalence so the whole class
can see it as you proceed "[show that thickness of wire
in a "Jumbo" paper clip = 1mm]:
ELABORATE: APPLICATION: In order for students to build a familiarity with the time/distances used in this scale, they should actually plot those distances on a scale map of their area. You may want to demonstrate this first, as follows, then have students do the assignment. And the Student assignment can be fairly simple, with no calculations, or a bit more challenging, requiring students to calculate scale dimensions. For getting a properly scaled map of your area, see TimeMarker and Preparing Scaled Map in the Materials section.
TEACHER DEMO: Notice that we are now talking about 10s and 100s of millions of years, so we'll want to translate football fields into miles on a map of your area to give students some idea of the vastness of time involved. You will find that all the major fossils, on this scale will be less than about 40 miles away, a distance that your students have probably traveled. [You may want to have a large map of your area and a large circle-drawing compass or two, e.g., a standard pencil-compass and probably an old chalkboard compass for longer distances, or use a string.] Be prepared to mark off circles with radii that represent key "distances" in time, so the kids can find landmarks (towns, special places, buildings, etc.) that they may have visited, and therefore have some sense of their distances. A Geologic Time Scale chart with such distances for key events in the geological past, based on the football field = 1 mya scale, is provided for you with this lesson. Note especially the vertical "Miles" columns (colored) that you - or, even better, the students) can mark out on the map of your area (using the map scale for distances). Miles are used here, rather than kilometers, because most people in our country have resisted moving to metric, and are therefore unfamiliar with it.
STUDENT ASSIGNMENT: Using a properly scaled map of your area, showing a series of towns or other landmarks more-or-less aligned for about 40 miles in one direction from your school, students position a TimeMarker Scale, with its several key events in geological time, so that they can find familiar towns or other landmarks whose distances coincide approximately with those key events (mostly the earliest fossils for each major vertebrate group). The scale is based on 10 years = 1 mm (or 1 million years = a football field). Students then record the name of each town (or landmark) on their Scale Events Worksheet tables, and answer the Discussion Questions there.
If you would like students to work more closely with the simple math of scaling, and finding the map distances for whatever scaled map you can provide, then CLICK HERE.
Detailed Teacher Preparation & Instructions for
two approaches (Click on your preference here):
In either case, the object is to find a familiar "Special Place" located at the distance from school associated with each Time Distance. For nearby distances (recent times), this could be their house, or a friend's or relative's house, a school, a familiar store, or park, etc. For larger distances, it could be a town, amusement park, theater, stadium, etc. These landmarks don't need to be precise - just reasonably close to each Time Distance from school.
See example of "Time Map" done for the SF Bay Area,
with San Jose as the focus, and also the Time Map done using
the TimeMarker strip (for a school in the San Jose area).
And here's an example of "Time Map" done for the SF Bay Area,
with San Jose as the focus, using a compass to scribe the different
If time allows, or students are interested, it would be instructive
to plot the "distance" to the beginning our solar system
(4.6 bya). Here is a Time
Map of southern California showing that distance relative
to the 1/2 billion (500 mya) year circle marking the earliest
(jawless) fishes in the early Cambrian.
BACK TO THE FOSSILS: The History of Life on Earth
TO THE TEACHER: Students should know that most of the familiar animals they know about are vertebrates, and can be divided into five main classes: fishes, amphibians, reptiles, birds, and mammals. If not, it would be good to review those groups, what they have in common [vertebrate traits], and what makes them different. Show pictures and models or living examples of each group, and either provide the two-page "Vertebrate Patterns" handout for them to read (homework), or walk them through the "What Are They?" and "Accumulating Traits" material on that handout, based on the abundant fossil record. Those two pages can be printed back-to-back on a single sheet to hand out.
BUILDING A "VERTEBRATES OVER TIME" DIAGRAM
Next, students label each of those "firsts" with the name of that group. For example, the 500 mya mark would be labeled "1st Jawless Fish" - the 440 mya mark would be "1st Jawed Fish" - and so on. Use the "Accumulating Traits" table for this. In addition, if you like, students could add a few of the key new traits associated with each group. And have them notice how many millions of years passed between each new emergence.
To show that each group (except one) continues to exist to the present, have students draw vertical lines from each tic mark up to the most recent members of that group (top line). All but one will meet the "NOW" line at the top. Label each vertical line with the name of that class. For an example of this process, show your students slides 33, 34, and 35 in the PowerPoint presentation for this lesson.
On the other hand, ask what they would predict if the hypothesis is not correct. Their responses may include: 1) no transitional fossils would be found; 2) no evidence of gradual changes in features of the fossils; 3) no examples of mixtures of old and new features in single fossils. If students are not forthcoming, drop some hints towards these ideas.
TESTING the PREDICTIONS:
Different groups of students could be assigned different sites to study (good homework assignment), but be sure to provide a few specific points to look for and think about, e.g., 1) Find 2-3 good examples of series of fossils that apparently show transition from one class to another. Record the source of the information, the names of the two classes in each case, and list the particular features that show step-wise change. 2) Be critical: Can you think of any reasons why those features might not actually be transitional features? 3) Be prepared - as a team - to discuss your findings and conclusions with the class, It would be helpful to have a large diagram or two to illustrate your brief presentation (always makes it more interesting). Perhaps team members could prepare a large drawing or two based on the most impressive examples found.
Here are some useful sites to suggest:
There are also a few examples showing series of transitional vertebrate fossils near the end of the PowerPoint presentation with this lesson.
Evidence of the gradual accumulation of traits: Give students a chance to study the handout sheet: "Accumulating Traits" to see how each new class simply adds a few new traits.
FAMILY TREE: PHYLOGENY - A Graphic Display of the Conclusion
QUESTIONS ABOUT the RELIABILITY of GEOLOGICAL TIME
Use the Assessable Objectives as a basis for formative and summative assessments. Create test questions that require students to recognize particular sequences of a few key vertebrate groups, and relative periods of time, using a few of the most notable key events in geological time that were studied. They should identify such "time spans" as linear dimensions on the scale used in class (10 years = 1 mm, and 1 football field = 1 million years), applied to a familiar map of the area. They should also recognize that the major vertebrate groups emerged over 100s of millions of years, with each successive group modifying some features possessed by the previous group. Perhaps most important is that students get a clear picture of the vastness of geological time, the confidence that scientists have in those numerical time spans, and the fact that the major vertebrate groups did not appear at the same time or even over a short period of time.
Precise times (in millions of years ago) are not so important. It would be helpful to learn approximations of a few of the key reference points in time, e.g., the earliest fish - about 500 mya, earliest mammals about 220 mya, and most other vertebrate groups emerged roughly 40-60 million years apart, staggered over about 300 million years. It's also important to know that each successive group is defined by a few new features, modified from previously existing features found in their predecessors, and that there are "transitional fossils" that document those gradual modifications over time. These are examples of the "Patterns in Time" that tell us that life has evolved over time.
1. If you feel that your students are sufficiently computer competent, let them search for the "first mammals," first amphibians," etc. Remind them the Wikipedia site is a good place to start, but that results should be compared to information on other sites. They should try to use university or professional society sites as much as possible. An excellent source for "first xxx" in each vertebrate class is the list of "Transitional Vertebrates" on TalkOrigins.com. They will find a fair amount of variation (note comments above on the cause of this), but differences in ages of first members of a major group shouldn't be huge. Earlier sources (20+ years ago) or non-academic / non-professional sources, could be way off the mark, for various reasons. You and/or your students can prepare a table for them to post their findings, or let them create their own tables. Be sure that you let each team share their findings with the class, and come up with a class consensus to serve as basis for building the scale to be used for plotting out the time spans (to scale) on the map.
2. For ongoing reinforcement, consider installing a large horizontal time scale chart in your classroom, either around the room (perimeter = age of solar system), or along one side or across the front of the room. Having this handy throughout the year allows convenient reference to geological or biological events in time that you can point to when discussing them. It's a memory aid that will stay with students for a long time. See The Time Machine lesson on the ENSI site for details and suggestions for making this room-size time scale AND taking your class on a dramatic voyage back in time.
3. You might also consider making a big enlargement of the Animals of the Past figure that you could post permanently on the wall for ongoing reinforcement and reference. You could do this on a large scale enlarging copier at Kinko's or similar copy place, or have an artistically talented student do it for you (for extra credit).
4. An interesting extension would be to ask students to figure out how far away (in miles) it would be to a scale distance representing the age of our planet (and our solar system) - about 4.6 bya, or 276 miles in our scale, or the age of the known universe (13.7 bya), about 822 miles with our scale. Have them find a spot on a larger scale map that shows those distances from their school/city. [For example, Los Angeles is about 280 miles from San Jose, CA, and Tucson, AZ is about 823 miles by road from San Jose, CA].
5. GEOLOGICAL TIME SCALE - VARIATIONS
When you or your students look for the ages of specific fossils, or the earliest members of a particular group, the time is sometimes given in the name of a geological period and/or epoch. The numerical ages of those named time periods may be slightly different in different resources. This could be confusing, until you realize that those ages are periodically revised by an international organization to reflect the latest research and improved dating techniques (see Resources below). Most of the adjustments (since 1982) have been relatively minor in geological terms (varying no more than about 5-10 million years up or down in most cases). Charts showing this can be found in the PowerPoint presentation on slides 48-50. Each age value used in this lesson is the closest multiple of 5 to the latest numerical age to make time differences and scale calculations easier.
6. GEOLOGICAL TIME - RELIABILITY: Furthermore, the numerical ages used are based on a variety of radiometric dating methods, all based on the regular and reliable time it takes for particular isotopes of certain elements to decay to new isotopes. The physics of this process are well-known and the techniques are extremely reliable, giving fairly consistent results when all sources of possible error are critically accounted for. There is even a technique known as the "Isochron" method, where ratios of different isotope pairs are compared in the same crystals that formed in the molten rock when it cooled. This technique automatically provides a form of "proofreading" that virtually eliminates significant errors. For a fascinating tutorial on radiometric dating, especially the isochron method, you (or your students) can go to the interactive tutorial: Virtual Age Dating (linked to from the ENSI site) where simulations of the dating process are run, and formative assessment questions are asked along the way. A certificate of completion is printed out for each person who completes the tutorial successfully.
7. Billions of Years and Billions of Dollars
A useful application of this scale for personalizing deep geological time, into millions and billions of years, is to relate it to money. Instead of equating a $1 bill with a year, just keep it in dollars! A million dollars would stack about a football field's length; a billion bills would stack about 60 miles high!
In these times of trillion dollar deficits - or costs of dealing
with global warming - it would be interesting to have your students
figure out how far away a trillion dollars would stack. That's
1000 x 1 billion [so on our scale, that would be 60,000 miles].
Then have them find something that is that far away (from the
Earth, or around the Earth). [They may discover that the Earth's
circumference at the equator is about 24,900 miles, so ONE trillion
dollars would stack 60 / 24.9 = ~2.4 times around the world!
Or, with about 2564 miles between San Francisco and New York,
ONE trillion dollars would stack 60 / 2.564 = ~ 23.4 times across
8. See the other lessons on this site that deal with geological and paleontological patterns (INDEX - click on "Synopses" there).
An excellent source for the latest geological time
scale charts is:
The International Commission on Stratigraphy: http://www.stratigraphy.org/
Also, (same site): Time Scale Chart and Timescale comparison charts (to scale - 1937-2004) - These are useful to show changes in the Time Scale Charts over the past 50 years. These are also shown in the PowerPoint presentation for this lesson, slides 48-50.
|There are several excellent articles on transitional fossil series and the proper use of phylogenetic trees and cladograms, all in the June 2009 issue of Evolution Education & Outreach Online. They are written by professional scientists, but in relatively non-technical language for use by teachers and students. They are freely accessible and downloadable. For reviews and access information, CLICK HERE.|
For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our review of an article in the American Biology Teacher.
For a great series of jaws, with color-coded bones and and names and the periods they represent, clearly showing gradual change over time, see:
29+ Evidences for Macroevolution at http://www.talkorigins.org/faqs/comdesc/section1.html
Scroll down to see the beautiful sequence of skulls and jaws, in color, 8 species, from pelycosaurs to mammals, from the Carboniferous to the Jurassic. This would make a great visual to show students on overhead or PowerPoint. Or have an artistically talented student make an enlarged copy of this for the wall (for extra credit).
A simpler version (3 skulls) is shown further up, but this doesn't carry the strong impression of gradual change over time that the larger illustration does.
See http://www.palaeos.com/Vertebrates/Units/Unit390/000.html for an excellent phylogenetic tree of the synapsids (pre-mammals) over time
See http://www.gcssepm.org/special/cuffey_05.htm for jaws showing teeth, especially the increasing variety of teeth that gradually characterize pre-mammals and is so typical of true mammals.
If you would like to have a nice sharp (8.5 x 11) jpg version of any of the illustrations mentioned here, let me know. I'd be happy to send it to you. Please be specific. Contact the webmaster.
SCIENCE STANDARDS MET WITH THIS LESSON
Meets these National Science Education Standards (1995):
Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.
1. Original Source: Created and developed by Larry Flammer,
posted on the ENSI site April 2008
3. Major revision February 2010