EXTENSIONS
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NEW FOLLOWUP LESSON:
WHALE ANKLES AND DNA
Take a look at this; uses new data that students analyze, revealing
the closest living relative of whales.
In this lesson, students search for the nearest mammal
cousins of whales by studying and comparing the ankles of early
whales, mesonychids, early perissodactyls and early artiodactyls,
and discover the striking similarities to the artiodactyls. Narrowing
down the search, a portion of DNA from the gene for making beta
casein (milk protein) is compared in a number of mammals, including
whales and several artiodactyls, and discover the striking similarity
to the DNA of hippos!
UPDATE...
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NEW DISCOVERY: 12.20.07 Nature: Hans Thewissen reports on a likely 48
million year old artiodactyl "little deer-like" ancestor
to the whale line. If time, hand out 5-page information packet (with questions)
about this little creature, found in Kashmir and named Indohyus.
This assignment packet is slightly modified from one prepared
by teacher Jennifer Wright. After students read the article and
answer the questions, discuss this in class, and relate to the
"Becoming Whales" lesson (maybe prepare a strip of Indohyus
to be added to the time line)
and conclusions from the whale ankles and DNA experience. Be
sure to take a look at the Oxygen
isotope ratios associated with osmoregulation in different early whale fossils.
AN EFFECTIVE AND ENGAGING INTRO TO THE "BECOMING WHALES"
LESSON:
The following suggestions would be very helpful, especially with
younger students in middle school settings. See the PDF listings
(materials), try the Teaching Outline, whch choreographs
many of these ideas.
1. Obtain and place large pictures of modern whales
near the top of the classroom timescale, along with their skeletons.
Point out that the earliest odontocete and mysticete fossils
are only about 34 my old (upper Eocene).
2. Next, demonstrate the actual sizes of some modern
whales AND the fossil whales to be discovered. An easy way to
do that is to prepare strips of adding machine tape cut to the
appropriate lengths, each clearly labeled with the name of the
whale represented, and its actual (average or maximum) length
(in meters). This could be a fairly easy assignment for your
students to do: each team could be assigned one or two of the
whales, and cut off the needed length of paper strip to do this.
[Teacher can provide a measuring strip of tape, marked off in
cm, along a counter top to facilitate this.] Students can hold
up their whale strips as they are discussed, or they can all
be mounted on a wall in the room. Display or hand out the Whale
Sizes data table with these lengths (pdf file in Materials
section.)
A more convenient variation is to use corrugated border strips
(which come in 50 foot lengths of various colors, available for
a few dollars in educator's or office supply stores). These are
pre-measured, and much more durable for re-use each period.
3. GOOD INTRODUCTION: Establish or confirm that whales
are mammals, and why we assume that they must have evolved
from a particular group of four-legged land mammals millions
of years ago. You can use the "What Kind of Creature
is a Whale?" outline on your overhead (see pdf
index in the Materials section). The comparison of various
features between whales and a fish or a cat is taken directly
from the delightful online interactive experience: the "Whale Evolution Kiosk"
(described at the end of the Extensions and Variations section).
You could also display the picture of a dolphin embryo with a hind limb bud!
(with kind permission of Hans Thewissen). You could also
show the picture of a nursing whale, and share information
about whale hair, the most widely recognized
traits of mammals.
DISCUSSION EXTENSIONS AND FOLLOWUP:
4. Growing out of discussion question #3, you might find it useful
to show pictures of the ancient Tethys Sea which existed
prior to around 55 mya between the landmass we now call India
and the Asian mainland. The Mediterranean represents the westward
extension of that sea, but the continental drift pushed
India into Asia, pushing up the land mass to form the Himalayan
Mountains (and Mt. Everest), and eliminating this eastern portion
of the Tethys Sea. If there is an animation in your department
showing plate tectonics (on a laser disk, CD, or online),
show it to your class, using stop action to step through the
stages showing were India moves into Asia. The timing of this
event coincides nicely with the Eocene, during which many long-isolated
mammals on the rafting India were able to move across to the
Asian mainland (and vice versa), introducing a major increase
in new competitions and resulting in active selection episodes
and increasing diversity. Whale evolution seems to have emerged
from that geological event and the resulting biological upheavals.
[See PaleoWorld video described below.]
5. During discussion question #5, ask for other possibilities
one might expect for the body form of Pakicetus. Then,
show the diagram of "Pakicetus 2", with
one reconstruction found on a Greek (?) museum website, (also
in the PaleoWorld video described below in #8). If possible.
show the latest version on Thewissen's site (see below), based
on the new post-cranial fossils. Discuss what clues might
suggest the features shown here (remember, we only had skull
fossils when this lesson was created, no post-cranial parts of
the skeleton). Hopefully, students will point out the early whale-like
teeth and ears of Pakicetus, so without any post-cranial
bones, an artist might easily assume tail flukes. Pakicetus
1, shown on the strip, was found in Zimmer's book, page 203.
[Pay particular attention to the whale flukes on Pakicetus
2; would they be there that early, especially since Ambulocetus
probably had none?]
6. After class discussion of question #9, display the
Family Tree of Whales diagram on the overhead (found on
Hans Thewissen's web site, but available in Materials).
Note how the several archaeocetes are shown as colateral branches
from the direct line of descent to modern whales. A further extension
of this could be to show the Provisional Phylogenetic Tree
of Whale Relatives (a type of cladogram) showing how whales
appear to relate to hippos and other artiodactyls, based on recent
DNA analyses (Nikaido, et al, 1999). The earliest mesonychids
existed before the earliest artiodactyls, and cetaceans are deeply
nested within the artiodactyl tree, as a sister family to the
hippopotamids (suggesting that the cetaceans be re-classified
as an artiodactyl family rather than their classical status as
a separate order), so any connection between mesonychids and
cetaceans now appears to be more remote. This close affinity
to the hippo family is reinforced by the work of Gatesy, et al
(1999) in which numerous DNA sequences were simultaneously analysed
in several different species of cetaceans and artiodactyls, producing
their "WHIPPO" data sets. See the excellent discussion
of these developments in Evolutionary Analysis by Freeman
and Herron (chapter 13). This is a chance to point out how ideas
in science can change with new information and perspectives.
[NOTE: This change is still not settled. Some whale scientists
have suggested that the DNA data are subject to different interpretaions.]
7. A very nice example of another independent line of evidence
which reinforces the paleontological evidence indicates habitat
changes associated with early whale evolution. This can be seen
in the Osmoregulation Diagram showing the relative percentage
of the Oxygen-18 isotope (significantly higher in the teeth and
bones of marine cetaceans than in those of freshwater cetaceans).
This is due to their incorporation of the particular ratio of
oxygen isotopes in fresh vs. salt water ingested. The
earliest archaeocetes (e.g. Pakicetus and other Pakicetids)
have lower O-18 ratios, associated with a freshwater habitat,
while Indocetus (and Rodhocetus), and Zygorhiza
(Gaviacetus), very similar to Prozeuglodon and
Dorudon, all have higher ratios, indicating a fully marine
habitat. Ambulocetus data show a wide range of O-18 levels,
suggesting they lived in a wide range of salinities, as one might
expect for a clearly transitional form. The original work on
this was published by Thewissen, Roe, and others in 1996.
8. If you can get a good video of whale evolution,
it might provide further reinforcement and perhaps raise further
questions for discussion. There is a useful 15 minute segment
in the WGBH-PBS-Evolution series (first part of show #2).
An older (1994) but interesting half-hour tape in the "PaleoWorld"
series was entitled "Return to the Seas", possibly
still available in a collection of their tapes, through Carolina
Biological Supply. The major caution is that this video gives
the impression that each of the "transitional whales"
evolved into the next more recent species directly, even using
"morphing" animation to show each species gradually
changing form to become the next species in time, as a series
of "links in a continuous chain of life", a long outmoded
idea now replaced with the far more likely picture of "cousin"
relationships. On the other hand, there are nice references to
how the movement of India into the Asian continent caused the
Tethys Sea to become shallow and saltier, creating a rich food
supply for any creature able to take advantage of it, and providing
a long term selective pressure favoring adaptations to specialize
in such feeding opportunities in the marine environment. The
result: whale evolution.
9. If you can, prepare and mount a scaled linear Earth
Timeline around your room (for the past 4.5 billion years),
with the last 540 million years somewhat detailed into the 3
major eras, and showing the main life forms characterizing those
eras. You can nicely show where whale evolution fits into the
total scheme of time, in relation to the age of dinosaurs, human
evolution, and any of the many other events and features of geological
time. The constant presence throughout the year of this timeline
helps to reinforce the deep time concept, the spaced-out sequence
of events, and provide a convenient focus from time to time to
point out when various biological events occurred. For a few
approaches to help with this, see the "Time Machine" lesson on this
site. As part of your introduction to geological time, be sure
to consider the short lesson on Deep
Time on the site, which explains how scientists actually
measure time on that scale, and why they are so confident of
its accuracy, providing a critical challenge to anyone claiming
a Young Earth age of only several thousand years.
10. A question which may arise when students see that the
archaeocetes seem to occupy the Eocene, and modern type whales
are not found below the Miocene (on the classroom timeline of
the Cenozoic), is "Why no whale fossils in the Oligocene?"
You can find the answer to this in the abbreviated version of
Kathleen Hunt's "Transitional
Vertebrate Fossils" on this site. Read especially
parts B-1 and B-3. Actually, there ARE some archaeocete fossils
in the Oligocene, but they're fairly fragmentary. There is also
a fair number of archaeocete fossils spread through the middle-to-upper
Eocene, but they are clearly whales, very similar to Dorudon,
so they weren't included in the lesson, and this seems to leave
an apparent "gap" which doesn't really exist.
11. If your class has ready access to the internet, (especially
for advanced classes), an excellent extension of this lesson
is the tutorial on this site: "Using Online Molecular Databases to Examine
Evolutionary Questions." This lesson takes the student
through the process of gathering amino acid sequences of beta-hemoglobin
in several different species from an online database, using an
online tool to compare the differences in those sequences, then
discussing what this indicates in terms of relationships. Comparing
whale hemoglobin with that of other animals is part of this exercise.
Be sure to take a look at our WHALE ANKLES AND DNA.
It uses new data that students analyze, revealing the closest
living relative of whales. In this lesson, students
search for the nearest mammal cousins of whales by studying and
comparing the ankles of early whales, mesonychids, early perissodactyls
and early artiodactyls, and discover the striking similarities
to the artiodactyls. Narrowing down the search, a portion of
DNA from the gene for making beta casein (milk protein) is compared
in a number of mammals, including whales and several artiodactyls,
and discover the striking similarity to the DNA of hippos!
12. The latest chapter in whale evolution was added
with the simulataneous publication in late 2001 of two reports
which concur that, based on the analyses of newly found ankle
and heel bones of early archaeocetes (in Pakistan), whale origins
are strongly associated with the origin of artiodactyls (even-toed
hooved animals). This is consistent with recent molecular studies
which also suggest this close tie. Neither study specifies a
closer hippopotamus connection necessarily. Both studies put
the mesonychid connection as more remote than once thought. See
the four articles listed below for 2001, in Nature
and Science for details. The Nature article
(by Thewissen et al) also has excellent graphics of the post-cranial
skeleton of Pakicetus, along with a very nice reconstruction
by Carl Buell, who created the beautiful action picture of Ambulocetus
shown at the beginning of this lesson. To see (and download)
these images (available in high resolution versions), click here,
or go to Thewissen's site. Also. see the new
addition to our "Great
Fossil Hunt" lesson, a page with those Pakicetus
fossils which are cut apart for students to "find"
and reconstruct as they are found, then discover that it is an
early WHALE!
13. VISIT THE
WHALE EVOLUTION KIOSK. This is a new, very clever interactive
online experience for your students, created by Lara Sox-Harris
at San Jose State University, who has kindly consented to this
link. When you click on the title (Whale Evolution Kiosk) above,
it will take you into a self-guided tutorial on the necessary
elements of whale anatomy, fossils, DNA, and classification.
These will all provide the mutually reinforcing evidence for
whale evolution, all in delightful animations and interactions.
Help your students with a guided tour of the kiosk, providing
more focus, and a way for you to confirm that they probably did
indeed visit the site, give them the Whale Evolution Kiosk Worksheet. This
was developed and kindly shared with us by Gail Bromiley
of DeBakey H.S. in Houston, TX. Gail also provides a key to facilitate
your discussion of the site and worksheet.
14. Another optional extension: Assign different parts of
the 11 page article "Origin of Whales..." (by
Ray Sutera) to different students or student teams. Article is
available from the PDF materials page. You could even cut it
into sections and give each of the nine sections to a different
team. Each team totally immerses in its assigned portion and
gathers whatever details it can find (internet) to gain full
understanding. Teams report back to class, so that everyone realizes
that there are multiple independent lines of evidence all pointing
to the evolution of whales from certain terrestrial mammals.
15. If time allows, consider distributing the Whale Evolution
Data Table, (available from the PDF materials page) and making
numerous resources available (websites, articles, etc.) from
which students (or teams) can gather information to complete
the table. For a key to the table, contact the webmaster.
16. SPECIAL NOTE: If students challenge the idea of macroevolution
(origin of a major group from a different major group), Click here to help them explore many of
the different lines of evidence pointing to speciation and macroevolution.
For a very useful diagram to help students see how macroevolution
relates to microevolution, see the Macroevolution Diagram below.
17. How ancient whales lost their
legs, got sleek and conquered the oceans: an Evo-Devo solution.
(Posted 1 June 2006)
Read this beautiful blending of paleontology, developmental morphology
and the blossoming field of evolutionary developmental biology,
and find an excellent example of MILEs: multiple independent
lines of evidence, confirming the tetrapod origin of whales.
A recent study, using porpoise embryos, has revealed how a mutation
in the gene for "sonic hedgehog" (shh), a developmental
signaling protein necessary for normal limb development, resulted
in the loss of the hind limbs of early whales about 35 million
years ago. Fossils have shown the gradual reduction in hind limbs
prior to that time, over a 15 million year period, but the shh
mutation appears to be the final step bringing the full sleekness
that we see in cetaceans today. Very clever science.
This 2006 PNAS report, by whale evolution veteran JGM Thewissen,
et al., is nicely summarized (with full citation to the original)
by PZ Myers on the Pharyngula site at: http://scienceblogs.com/pharyngula/2006/05/no_genes_were_lost_in_the_maki.php
It includes an excellent illustrated cladogram (from the original)
that shows the gradual hind limb reduction in ancestral whales,
and the corresponding changes in regulatory genes.
My thanks to John Pastor, University of Florida for his help
in gathering this information.
18. Another teacher's experience,
and suggested modification:
I've used the fossil hunt for a
few years in my courses and modified it so that it is a little
more student centered --I cut the reading part up into segments
and place them into separate envelopes so that each student in
a group of four has to read one or two of the scenarios and then
the group follows the directions. Allows the college students
to work at their own pace more and delve into some areas further
without constant interuption from the teacher--may be less effective
for younger kids. My pre-service teachers like the lesson and
a few have taken it into their own classrooms and used it also.
Dr. Christine Lotter
Assistant Professor, Secondary Science Education
Instruction and Teacher Education, SC
19. Still another approach, from another
teacher, is to provide each student or team of students with
a WORKSHEET (see the pdf handouts page). This more structured
approach allows each student/team to progress independently,
following the printed narrative and placing the fossils stips
as they go. Includes discussion questions. Could be a problem
with some teams/students finishing ahead of others (harder to
keep class in stiep).
MACROEVOLUTION DIAGRAM: See the Macroevolution
Diagram and a page of directions for using that diagram on
an overhead projector. This nicely shows how accumulated speciations
can eventually form all the groups and subgroups of organisms.
It also shows how classification is related to evolution. A very
nice colorful version of this can be found on
page 32 of that most useful resource: Teaching About Evolution
and the Nature of Science, by the National Academy of Sciences
(1998) (see our Resources section). A particularly interesting
alternative diagram is the one Darwin included in The Origin
of Species (chapter IV), the only diagram in that book! His
discussion there of that diagram should be required reading for
any biology teacher. Darwin's
Tree makes a great overhead transparency for discussing his
concept of evolution by natural selection, as well as how classification
reflects that evolution.
For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our
review of an article in the American Biology Teacher.
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RESOURCES
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Books:
Freeman, Scott & Jon C. Herron. 2001. Evolutionary Analysis.
Prentice Hall.
Zimmer, Carl. 1998. At the Water's Edge.
The Free Press. An excellent, recent treatment of the search
for evidence of whale evolution, macroevolution in general, and
some of the "behind the scenes" stories of the scientists
involved. Highly recommended, for teacher and interested students.
Articles:
Thewissen, J.G.M., et al. 2001. "Skeletons of terrestrial
cetaceans and the relationship of whales to artiodactyls."
Nature, 413:217-281 (20 Sep 2001). This report hinges
largely on new postcranial fossils of Pakicetus. To see excellent
figures and brief descriptions, click here. (thanks to David
N. Brown for this link).
de Muizen, Christian. 2001. "Walking
with whales." Nature, 413:259-260 (20 Sep 2001).
A summary discussion of Thewissen's report.
Gingerich, P.D. et al. 2001. "Origin
of Whales from Early Artiodactyls: Hands and Feet of Eocene Protocetidae
from Pakistan." Science, 293:2239-2242 (21 Sep).
This report hinges largely on new fossils of Rodhocetus.
Rose, Kenneth. 2001. "The Ancestry of
Whales." Science, 293:2216-2217. This is a summary
of Gingerich's report, and includes a cladogram showing the proposed
ancestry.
Sutera, Raymond. 2000. "The Origin of
Whales and the Power of Independent Evidence". In Reports
of the National Center for Science Education, vol.20, no.5
(Sep/Oct 2000), pp. 33-41. An excellent overview of cetacean
evolution, and pointing to several different independent lines
of evidence in support of the process. (Mildly critical of creationist
veiws). [Copy available at end of lesson]
Gatesy, J.M. et al 1999. "Stability of
cladistic relationships between Cetacea an higher-level artiodactyl
taxa." Systematic Biology 48(1):6-20.
Nikaido, Masato, et al. 1999. "Phylogenetic
relationships among cetartiodactyls based on [DNA] insertions
of short and long interspersed elements: Hippopotamuses are the
closest extant relatives of whales." Proc. Natl. Acad.
Sci. USA, vol.96, pp. 10261-10266.
Thewissen, J.G.M., L. J. Roe, et al. 1996.
"Evolution of cetacean osmoregulation." Nature,
vol.381, 30 May 1996, pp. 379 380. Study showing oxygen isotope
ratios associated with freshwater ingestion vs. seawater ingestion,
and whale evolution. [Also see "Osmoregulation" on
Thewissen's website]
Blackburn, Daniel G. 1995. "Paleontology
Meets the Creationist Challenge". Creation/Evolution
Issue 36 (July 1995), pp. 30-31 on whale evolution. [Available
from NCSE; see website listings below].
Zimmer, Carl. 1995. "Back to the Sea"
January 1995 Discover Magazine, pp. 82-84.
Wells, Neil. 1994. Review of Darwinism: Science or Philosophy,.
In Creation/Evolution Issue 38 (July 1996), pp. 20-21
on whale evolution, rebuttals to views of Johnson, Behe and Gish.
[from NCSE].
Wilford, John N. 1994. "How the Whale
Lost Its Legs And Returned to the Sea." In The Science
Times Book of Fossils and Evolution, ed. by Nicholas Wade,
1998, The New York Times, pp 143-148.
Gould, Stephen Jay. 1994. "Hooking Leviathan
by Its Past". May 1994 Natural History Magazine.
Gingerich, Philip D. 1994. "The Whales
of Tehthys". April 1994 Natural History Magazine.
Berta, Annalisa. 1994. "What is a Whale?"
Science 14 Jan. 1994 (vol.263, pp. 180-181).
Novacek, Michael. 1993 "Genes tell a
new whale tale." 28 January 1993 Nature (vol. 361,
pp 298-299.
Landau, Matthew. 1982. "Whales: Can Evolution
Account for Them?" Creation/Evolution, Issue X (Fall
1982)., pp. 14-19. [Available from NCSE; see website listings
below].
Conrad, Ernest C. 1982. "True Vestigial
Structures in Whales and Dolphins." Creation/Evolution,
Issue X (Fall 1982), pp. 8-13. [Available from NCSE]. Ref. to
hind limb buds in whale embryos, etc.
Web Links:
(if a listed site is not working, please let us know, and
try a Google search):
WHALE EVOLUTION
Whale Evolution: Short video clip (6') in
Video #3 of the PBS Evolution Series: with Phil Gingerich and
Pakicetus (play online, or purchase this great series of single-concept
videos:
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Thewissen: Whale evolution <http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/index.html>
Transitional Whales <http://www.talkorigins.org/faqs/faq-transitional/part2b.html>
Cetacean Evolution <http://www.ucmp.berkeley.edu/mammal/cetacea/cetacean.html>
Ambulocetus
as Transitional Fossil <http://members.home.net/fsteiger/whales.htm>
A Whale of a Tale <http://detnews.com/1997/discover/9707/10/07070019.htm>
Primitive Whales <http://www.enchantedlearning.com/subjects/whales/allabout/Evol.shtml>
Whale embryo hind limb bud picture: <http://imiloa.wcc.hawaii.edu/krupp/BIOL101/present/lcture15/sld034.htm>
Whale nursing: <http://www.seaworld.org/infobooks/KillerWhale/birthkw.html>
Whale hair info: <http://whale.wheelock.edu/archives/ask97/0252.html>
Whale hair info 2: <http://whale.wheelock.edu/archives/ask99/0336.html>
Whale
hair picture: <http://www.coreresearch.org/what.htm>
GENERAL EVOLUTION
Evolution
on line (WGBH/PBS Evolution Web Site) <http://www.pbs.org/evolution>
NAS (Nat'l Acad. of Sciences): Teaching About Evol. and Nat. of Science.
<http://www.nap.edu/readingroom/books/evolution98/evol2.html>
NCSE (National
Center for Science Education): <http://www.ncseweb.org>
e-mail:
ncse@ncseweb.org
GEOLOGIC TIME SCALES (CURRENT)
Geological Society of America <http://www.geosociety.org/science/timescale/timescl.htm>
USGS short version <http://geology.er.usgs.gov/paleo/geotime.shtml>
USGS w/ details <http://vulcan.wr.usgs.gov/Glossary/geo_time_scale.html>
Time Machine (ENSI) <http://www.indiana.edu/~ensiweb/lessons/time.mac.html>
(Extensions, Other Resources.)
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